    Internet Engineering Task Force (IETF)                  E. Grossman, Ed.
    Request for Comments: 8578                                         DOLBY
    Category: Informational                                         May 2019
    ISSN: 2070-1721

                       Deterministic Networking Use Cases

    Abstract

       This document presents use cases for diverse industries that have in
       common a need for "deterministic flows".  "Deterministic" in this
       context means that such flows provide guaranteed bandwidth, bounded
       latency, and other properties germane to the transport of time-
       sensitive data.  These use cases differ notably in their network
       topologies and specific desired behavior, providing as a group broad
       industry context for Deterministic Networking (DetNet).  For each use
       case, this document will identify the use case, identify
       representative solutions used today, and describe potential
       improvements that DetNet can enable.

    Status of This Memo

       This document is not an Internet Standards Track specification; it is
       published for informational purposes.

       This document is a product of the Internet Engineering Task Force
       (IETF).  It represents the consensus of the IETF community.  It has
       received public review and has been approved for publication by the
       Internet Engineering Steering Group (IESG).  Not all documents
       approved by the IESG are candidates for any level of Internet
       Standard; see Section 2 of RFC 7841.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       https://www.rfc-editor.org/info/rfc8578.

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    Copyright Notice

       Copyright (c) 2019 IETF Trust and the persons identified as the
       document authors.  All rights reserved.

       This document is subject to BCP 78 and the IETF Trust's Legal
       Provisions Relating to IETF Documents
       (https://trustee.ietf.org/license-info) in effect on the date of
       publication of this document.  Please review these documents
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       include Simplified BSD License text as described in Section 4.e of
       the Trust Legal Provisions and are provided without warranty as
       described in the Simplified BSD License.

    Table of Contents

       1. Introduction ....................................................6
       2. Pro Audio and Video .............................................7
          2.1. Use Case Description .......................................7
               2.1.1. Uninterrupted Stream Playback .......................8
               2.1.2. Synchronized Stream Playback ........................9
               2.1.3. Sound Reinforcement .................................9
               2.1.4. Secure Transmission ................................10
                      2.1.4.1. Safety ....................................10
          2.2. Pro Audio Today ...........................................10
          2.3. Pro Audio in the Future ...................................10
               2.3.1. Layer 3 Interconnecting Layer 2 Islands ............10
               2.3.2. High-Reliability Stream Paths ......................11
               2.3.3. Integration of Reserved Streams into IT Networks ...11
               2.3.4. Use of Unused Reservations by Best-Effort Traffic ..11
               2.3.5. Traffic Segregation ................................11
                      2.3.5.1. Packet-Forwarding Rules, VLANs,
                               and Subnets ...............................12
                      2.3.5.2. Multicast Addressing (IPv4 and IPv6) ......12
               2.3.6. Latency Optimization by a Central Controller .......12
               2.3.7. Reduced Device Costs due to Reduced Buffer Memory ..13
          2.4. Pro Audio Requests to the IETF ............................13
       3. Electrical Utilities ...........................................14
          3.1. Use Case Description ......................................14
               3.1.1. Transmission Use Cases .............................14
                      3.1.1.1. Protection ................................14
                      3.1.1.2. Intra-substation Process Bus
                               Communications ............................21
                      3.1.1.3. Wide-Area Monitoring and Control Systems ..23
                      3.1.1.4. WAN Engineering Guidelines
                               Requirement Classification ................25

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               3.1.2. Generation Use Case ................................26
                      3.1.2.1. Control of the Generated Power ............26
                      3.1.2.2. Control of the Generation Infrastructure ..27
               3.1.3. Distribution Use Case ..............................32
                      3.1.3.1. Fault Location, Isolation, and
                               Service Restoration (FLISR) ...............32
          3.2. Electrical Utilities Today ................................33
               3.2.1. Current Security Practices and Their Limitations ...34
          3.3. Electrical Utilities in the Future ........................35
               3.3.1. Migration to Packet-Switched Networks ..............36
               3.3.2. Telecommunications Trends ..........................37
                      3.3.2.1. General Telecommunications Requirements ...37
                      3.3.2.2. Specific Network Topologies of
                               Smart-Grid Applications ...................38
                      3.3.2.3. Precision Time Protocol ...................38
               3.3.3. Security Trends in Utility Networks ................39
          3.4. Electrical Utilities Requests to the IETF .................41
       4. Building Automation Systems (BASs) .............................41
          4.1. Use Case Description ......................................41
          4.2. BASs Today ................................................42
               4.2.1. BAS Architecture ...................................42
               4.2.2. BAS Deployment Model ...............................44
               4.2.3. Use Cases for Field Networks .......................45
                      4.2.3.1. Environmental Monitoring ..................45
                      4.2.3.2. Fire Detection ............................46
                      4.2.3.3. Feedback Control ..........................46
               4.2.4. BAS Security Considerations ........................46
          4.3. BASs in the Future ........................................46
          4.4. BAS Requests to the IETF ..................................47
       5. Wireless for Industrial Applications ...........................47
          5.1. Use Case Description ......................................47
               5.1.1. Network Convergence Using 6TiSCH ...................48
               5.1.2. Common Protocol Development for 6TiSCH .............48
          5.2. Wireless Industrial Today .................................49
          5.3. Wireless Industrial in the Future .........................49
               5.3.1. Unified Wireless Networks and Management ...........49
                      5.3.1.1. PCE and 6TiSCH ARQ Retries ................51
               5.3.2. Schedule Management by a PCE .......................52
                      5.3.2.1. PCE Commands and 6TiSCH CoAP Requests .....52
                      5.3.2.2. 6TiSCH IP Interface .......................54
               5.3.3. 6TiSCH Security Considerations .....................54
          5.4. Wireless Industrial Requests to the IETF ..................54

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       6. Cellular Radio .................................................54
          6.1. Use Case Description ......................................54
               6.1.1. Network Architecture ...............................54
               6.1.2. Delay Constraints ..................................55
               6.1.3. Time-Synchronization Constraints ...................57
               6.1.4. Transport-Loss Constraints .........................59
               6.1.5. Cellular Radio Network Security Considerations .....60
          6.2. Cellular Radio Networks Today .............................60
               6.2.1. Fronthaul ..........................................60
               6.2.2. Midhaul and Backhaul ...............................60
          6.3. Cellular Radio Networks in the Future .....................61
          6.4. Cellular Radio Networks Requests to the IETF ..............64
       7. Industrial Machine to Machine (M2M) ............................64
          7.1. Use Case Description ......................................64
          7.2. Industrial M2M Communications Today .......................66
               7.2.1. Transport Parameters ...............................66
               7.2.2. Stream Creation and Destruction ....................67
          7.3. Industrial M2M in the Future ..............................67
          7.4. Industrial M2M Requests to the IETF .......................67
       8. Mining Industry ................................................68
          8.1. Use Case Description ......................................68
          8.2. Mining Industry Today .....................................68
          8.3. Mining Industry in the Future .............................69
          8.4. Mining Industry Requests to the IETF ......................70
       9. Private Blockchain .............................................70
          9.1. Use Case Description ......................................70
               9.1.1. Blockchain Operation ...............................71
               9.1.2. Blockchain Network Architecture ....................71
               9.1.3. Blockchain Security Considerations .................72
          9.2. Private Blockchain Today ..................................72
          9.3. Private Blockchain in the Future ..........................72
          9.4. Private Blockchain Requests to the IETF ...................72
       10. Network Slicing ...............................................73
          10.1. Use Case Description .....................................73
          10.2. DetNet Applied to Network Slicing ........................73
               10.2.1. Resource Isolation across Slices ..................73
               10.2.2. Deterministic Services within Slices ..............74
          10.3. A Network Slicing Use Case Example - 5G Bearer Network ...74
          10.4. Non-5G Applications of Network Slicing ...................75
          10.5. Limitations of DetNet in Network Slicing .................75
          10.6. Network Slicing Today and in the Future ..................75
          10.7. Network Slicing Requests to the IETF .....................75
       11. Use Case Common Themes ........................................76
          11.1. Unified, Standards-Based Networks ........................76
               11.1.1. Extensions to Ethernet ............................76
               11.1.2. Centrally Administered Networks ...................76
               11.1.3. Standardized Data-Flow Information Models .........76

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               11.1.4. Layer 2 and Layer 3 Integration ...................76
               11.1.5. IPv4 Considerations ...............................76
               11.1.6. Guaranteed End-to-End Delivery ....................77
               11.1.7. Replacement for Multiple Proprietary
                       Deterministic Networks ............................77
               11.1.8. Mix of Deterministic and Best-Effort Traffic ......77
               11.1.9. Unused Reserved Bandwidth to Be Available
                       to Best-Effort Traffic ............................77
               11.1.10. Lower-Cost, Multi-Vendor Solutions ...............77
          11.2. Scalable Size ............................................78
               11.2.1. Scalable Number of Flows ..........................78
          11.3. Scalable Timing Parameters and Accuracy ..................78
               11.3.1. Bounded Latency ...................................78
               11.3.2. Low Latency .......................................78
               11.3.3. Bounded Jitter (Latency Variation) ................79
               11.3.4. Symmetrical Path Delays ...........................79
          11.4. High Reliability and Availability ........................79
          11.5. Security .................................................79
          11.6. Deterministic Flows ......................................79
       12. Security Considerations .......................................80
       13. IANA Considerations ...........................................80
       14. Informative References ........................................80
       Appendix A. Use Cases Explicitly Out of Scope for DetNet ..........90
         A.1. DetNet Scope Limitations ...................................90
         A.2. Internet-Based Applications ................................90
           A.2.1. Use Case Description ...................................91
             A.2.1.1. Media Content Delivery .............................91
             A.2.1.2. Online Gaming ......................................91
             A.2.1.3. Virtual Reality ....................................91
           A.2.2. Internet-Based Applications Today ......................91
           A.2.3. Internet-Based Applications in the Future ..............91
           A.2.4. Internet-Based Applications Requests to the IETF .......92
         A.3. Pro Audio and Video - Digital Rights Management (DRM) ......92
         A.4. Pro Audio and Video - Link Aggregation .....................92
         A.5. Pro Audio and Video - Deterministic Time to Establish
              Streaming ..................................................93
       Acknowledgments ...................................................93
       Contributors ......................................................95
       Author's Address ..................................................97

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    1.  Introduction

       This memo documents use cases for diverse industries that require
       deterministic flows over multi-hop paths.  Deterministic Networking
       (DetNet) flows can be established from either a Layer 2 or Layer 3
       (IP) interface, and such flows can coexist on an IP network with
       best-effort traffic.  DetNet also provides for highly reliable flows
       through provision for redundant paths.

       The DetNet use cases explicitly do not suggest any specific design
       for DetNet architecture or protocols; these are topics for other
       DetNet documents.

       The DetNet use cases, as originally submitted, explicitly were not
       considered by the DetNet Working Group (WG) to be concrete
       requirements.  The DetNet WG and Design Team considered these use
       cases, identifying which of their elements could be feasibly
       implemented within the charter of DetNet; as a result, certain
       originally submitted use cases (or elements thereof) were moved to
       Appendix A ("Use Cases Explicitly Out of Scope for DetNet") of this
       document.

       This document provides context regarding DetNet design decisions.  It
       also serves a long-lived purpose of helping those learning (or new
       to) DetNet understand the types of applications that can be supported
       by DetNet.  It also allows those WG contributors who are users to
       ensure that their concerns are addressed by the WG; for them, this
       document (1) covers their contributions and (2) provides a long-term
       reference regarding the problems that they expect will be served by
       the technology, in terms of the short-term deliverables and also as
       the technology evolves in the future.

       This document has served as a "yardstick" against which proposed
       DetNet designs can be measured, answering the question "To what
       extent does a proposed design satisfy these various use cases?"

       The industries covered by the use cases in this document are

       o  professional audio and video (Section 2)

       o  electrical utilities (Section 3)

       o  building automation systems (BASs) (Section 4)

       o  wireless for industrial applications (Section 5)

       o  cellular radio (Section 6)

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       o  industrial machine to machine (M2M) (Section 7)

       o  mining (Section 8)

       o  private blockchain (Section 9)

       o  network slicing (Section 10)

       For each use case, the following questions are answered:

       o  What is the use case?

       o  How is it addressed today?

       o  How should it be addressed in the future?

       o  What should the IETF deliver to enable this use case?

       The level of detail in each use case is intended to be sufficient to
       express the relevant elements of the use case but no more than that.

       DetNet does not directly address clock distribution or time
       synchronization; these are considered to be part of the overall
       design and implementation of a time-sensitive network, using existing
       (or future) time-specific protocols (such as [IEEE-8021AS] and/or
       [RFC5905]).

       Section 11 enumerates the set of common properties implied by these
       use cases.

    2.  Pro Audio and Video

    2.1.  Use Case Description

       The professional audio and video industry ("ProAV") includes:

       o  Music and film content creation

       o  Broadcast

       o  Cinema

       o  Live sound

       o  Public address, media, and emergency systems at large venues
          (e.g., airports, stadiums, churches, theme parks)

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       These industries have already transitioned audio and video signals
       from analog to digital.  However, the digital interconnect systems
       remain primarily point to point, with a single signal or a small
       number of signals per link, interconnected with purpose-built
       hardware.

       These industries are now transitioning to packet-based
       infrastructures to reduce cost, increase routing flexibility, and
       integrate with existing IT infrastructures.

       Today, ProAV applications have no way to establish deterministic
       flows from a standards-based Layer 3 (IP) interface; this is a
       fundamental limitation of the use cases described here.  Today,
       deterministic flows can be created within standards-based Layer 2
       LANs (e.g., using IEEE 802.1 TSN ("TSN" stands for "Time-Sensitive
       Networking")); however, these flows are not routable via IP and thus
       are not effective for distribution over wider areas (for example,
       broadcast events that span wide geographical areas).

       It would be highly desirable if such flows could be routed over the
       open Internet; however, solutions of more-limited scope (e.g.,
       enterprise networks) would still provide substantial improvements.

       The following sections describe specific ProAV use cases.

    2.1.1.  Uninterrupted Stream Playback

       Transmitting audio and video streams for live playback is unlike
       common file transfer in that uninterrupted stream playback in the
       presence of network errors cannot be achieved by retrying the
       transmission; by the time the missing or corrupt packet has been
       identified, it is too late to execute a retry operation.  Buffering
       can be used to provide enough delay to allow time for one or more
       retries; however, this is not an effective solution in applications
       where large delays (latencies) are not acceptable (as discussed
       below).

       Streams with guaranteed bandwidth can eliminate congestion on the
       network as a cause of transmission errors that would lead to playback
       interruption.  The use of redundant paths can further mitigate
       transmission errors and thereby provide greater stream reliability.

       Additional techniques, such as Forward Error Correction (FEC), can
       also be used to improve stream reliability.

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    2.1.2.  Synchronized Stream Playback

       Latency in this context is the time between when a signal is
       initially sent over a stream and when it is received.  A common
       example in ProAV is time-synchronizing audio and video when they take
       separate paths through the playback system.  In this case, the
       latency of both the audio stream and the video stream must be bounded
       and consistent if the sound is to remain matched to the movement in
       the video.  A common tolerance for audio/video synchronization is one
       National Television System Committee (NTSC) video frame (about
       33 ms); to maintain the audience's perception of correct lip-sync,
       the latency needs to be consistent within some reasonable tolerance
       -- for example, 10%.

       A common architecture for synchronizing multiple streams that have
       different paths through the network (and thus potentially different
       latencies) enables measurement of the latency of each path and has
       the data sinks (for example, speakers) delay (buffer) all packets on
       all but the slowest path.  Each packet of each stream is assigned a
       presentation time that is based on the longest required delay.  This
       implies that all sinks must maintain a common time reference of
       sufficient accuracy, which can be achieved by various techniques.

       This type of architecture is commonly implemented using a central
       controller that determines path delays and arbitrates buffering
       delays.

    2.1.3.  Sound Reinforcement

       Consider the latency (delay) between the time when a person speaks
       into a microphone and when their voice emerges from the speaker.  If
       this delay is longer than about 10-15 ms, it is noticeable and can
       make a sound-reinforcement system unusable (see slide 6 of
       [SRP_LATENCY]).  (If you have ever tried to speak in the presence of
       a delayed echo of your voice, you might be familiar with this
       experience.)

       Note that the 15 ms latency bound includes all parts of the signal
       path -- not just the network -- so the network latency must be
       significantly less than 15 ms.

       In some cases, local performers must perform in synchrony with a
       remote broadcast.  In such cases, the latencies of the broadcast
       stream and the local performer must be adjusted to match each other,
       with a worst case of one video frame (33 ms for NTSC video).

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       In cases where audio phase is a consideration -- for example,
       beam-forming using multiple speakers -- latency can be in the 10 us
       range (one audio sample at 96 kHz).

    2.1.4.  Secure Transmission

    2.1.4.1.  Safety

       Professional audio systems can include amplifiers that are capable of
       generating hundreds or thousands of watts of audio power.  If used
       incorrectly, such amplifiers can cause hearing damage to those in the
       vicinity.  Apart from the usual care required by the systems
       operators to prevent such incidents, the network traffic that
       controls these devices must be secured (as with any sensitive
       application traffic).

    2.2.  Pro Audio Today

       Some proprietary systems have been created that enable deterministic
       streams at Layer 3; however, they are "engineered networks" that
       require careful configuration to operate and often require that the
       system be over-provisioned.  Also, it is implied that all devices on
       the network voluntarily play by the rules of that network.  To enable
       these industries to successfully transition to an interoperable
       multi-vendor packet-based infrastructure requires effective open
       standards.  Establishing relevant IETF standards is a crucial factor.

    2.3.  Pro Audio in the Future

    2.3.1.  Layer 3 Interconnecting Layer 2 Islands

       It would be valuable to enable IP to connect multiple Layer 2 LANs.

       As an example, ESPN constructed a state-of-the-art 194,000 sq. ft.,
       $125-million broadcast studio called "Digital Center 2" (DC2).  The
       DC2 network is capable of handling 46 Tbps of throughput with 60,000
       simultaneous signals.  Inside the facility are 1,100 miles of fiber
       feeding four audio control rooms (see [ESPN_DC2]).

       In designing DC2, they replaced as much point-to-point technology as
       they could with packet-based technology.  They constructed seven
       individual studios using Layer 2 LANs (using IEEE 802.1 TSN) that
       were entirely effective at routing audio within the LANs.  However,
       to interconnect these Layer 2 LAN islands together, they ended up
       using dedicated paths in a custom SDN (Software-Defined Networking)
       router because there is no standards-based routing solution
       available.

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    2.3.2.  High-Reliability Stream Paths

       On-air and other live media streams are often backed up with
       redundant links that seamlessly act to deliver the content when the
       primary link fails for any reason.  In point-to-point systems, this
       redundancy is provided by an additional point-to-point link; the
       analogous requirement in a packet-based system is to provide an
       alternate path through the network such that no individual link can
       bring down the system.

    2.3.3.  Integration of Reserved Streams into IT Networks

       A commonly cited goal of moving to a packet-based media
       infrastructure is that costs can be reduced by using off-the-shelf,
       commodity-network hardware.  In addition, economy of scale can be
       realized by combining media infrastructure with IT infrastructure.
       In keeping with these goals, stream-reservation technology should be
       compatible with existing protocols and should not compromise the use
       of the network for best-effort (non-time-sensitive) traffic.

    2.3.4.  Use of Unused Reservations by Best-Effort Traffic

       In cases where stream bandwidth is reserved but not currently used
       (or is underutilized), that bandwidth must be available to
       best-effort (i.e., non-time-sensitive) traffic.  For example, a
       single stream may be "nailed up" (reserved) for specific media
       content that needs to be presented at different times of the day,
       ensuring timely delivery of that content, yet in between those times
       the full bandwidth of the network can be utilized for best-effort
       tasks such as file transfers.

       This also addresses a concern of IT network administrators that are
       considering adding reserved-bandwidth traffic to their networks that
       "users will reserve large quantities of bandwidth and then never
       unreserve it even though they are not using it, and soon the network
       will have no bandwidth left."

    2.3.5.  Traffic Segregation

       Sink devices may be low-cost devices with limited processing power.
       In order to not overwhelm the CPUs in these devices, it is important
       to limit the amount of traffic that these devices must process.

       As an example, consider the use of individual seat speakers in a
       cinema.  These speakers are typically required to be cost reduced,
       since the quantities in a single theater can reach hundreds of seats.
       Discovery protocols alone in a 1,000-seat theater can generate enough
       broadcast traffic to overwhelm a low-powered CPU.  Thus, an

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       installation like this will benefit greatly from some type of traffic
       segregation that can define groups of seats to reduce traffic within
       each group.  All seats in the theater must still be able to
       communicate with a central controller.

       There are many techniques that can be used to support this feature,
       including (but not limited to) the following examples.

    2.3.5.1.  Packet-Forwarding Rules, VLANs, and Subnets

       Packet-forwarding rules can be used to eliminate some extraneous
       streaming traffic from reaching potentially low-powered sink devices;
       however, there may be other types of broadcast traffic that should be
       eliminated via other means -- for example, VLANs or IP subnets.

    2.3.5.2.  Multicast Addressing (IPv4 and IPv6)

       Multicast addressing is commonly used to keep bandwidth utilization
       of shared links to a minimum.

       Because Layer 2 bridges by design forward Media Access Control (MAC)
       addresses, it is important that a multicast MAC address only be
       associated with one stream.  This will prevent reservations from
       forwarding packets from one stream down a path that has no interested
       sinks simply because there is another stream on that same path that
       shares the same multicast MAC address.

       In other words, since each multicast MAC address can represent 32
       different IPv4 multicast addresses, there must be a process in place
       to make sure that any given multicast MAC address is only associated
       with exactly one IPv4 multicast address.  Requiring the use of IPv6
       addresses could help in this regard, due to the much larger address
       range of IPv6; however, due to the continued prevalence of IPv4
       installations, solutions that are effective for IPv4 installations
       would be practical in many more use cases.

    2.3.6.  Latency Optimization by a Central Controller

       A central network controller might also perform optimizations based
       on the individual path delays; for example, sinks that are closer to
       the source can inform the controller that they can accept greater
       latency, since they will be buffering packets to match presentation
       times of sinks that are farther away.  The controller might then move
       a stream reservation on a short path to a longer path in order to
       free up bandwidth for other critical streams on that short path.  See
       slides 3-5 of [SRP_LATENCY].

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       Additional optimization can be achieved in cases where sinks have
       differing latency requirements; for example, at a live outdoor
       concert, the speaker sinks have stricter latency requirements than
       the recording-hardware sinks.  See slide 7 of [SRP_LATENCY].

    2.3.7.  Reduced Device Costs due to Reduced Buffer Memory

       Device costs can be reduced in a system with guaranteed reservations
       with a small bounded latency due to the reduced requirements for
       buffering (i.e., memory) on sink devices.  For example, a theme park
       might broadcast a live event across the globe via a Layer 3 protocol.
       In such cases, the size of the buffers required is defined by the
       worst-case latency and jitter values of the worst-case segment of the
       end-to-end network path.  For example, on today's open Internet, the
       latency is typically unacceptable for audio and video streaming
       without many seconds of buffering.  In such scenarios, a single
       gateway device at the local network that receives the feed from the
       remote site would provide the expensive buffering required to mask
       the latency and jitter issues associated with long-distance delivery.
       Sink devices in the local location would have no additional buffering
       requirements, and thus no additional costs, beyond those required for
       delivery of local content.  The sink device would be receiving
       packets identical to those sent by the source and would be unaware of
       any latency or jitter issues along the path.

    2.4.  Pro Audio Requests to the IETF

       o  Layer 3 routing on top of Audio Video Bridging (AVB) (and/or other
          high-QoS (Quality of Service) networks)

       o  Content delivery with bounded, lowest possible latency

       o  IntServ and DiffServ integration with AVB (where practical)

       o  Single network for A/V and IT traffic

       o  Standards-based, interoperable, multi-vendor solutions

       o  IT-department-friendly networks

       o  Enterprise-wide networks (e.g., the size of San Francisco but not
          the whole Internet (yet...))

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    3.  Electrical Utilities

    3.1.  Use Case Description

       Many systems that an electrical utility deploys today rely on high
       availability and deterministic behavior of the underlying networks.
       Presented here are use cases for transmission, generation, and
       distribution, including key timing and reliability metrics.  In
       addition, security issues and industry trends that affect the
       architecture of next-generation utility networks are discussed.

    3.1.1.  Transmission Use Cases

    3.1.1.1.  Protection

       "Protection" means not only the protection of human operators but
       also the protection of the electrical equipment and the preservation
       of the stability and frequency of the grid.  If a fault occurs in the
       transmission or distribution of electricity, then severe damage can
       occur to human operators, electrical equipment, and the grid itself,
       leading to blackouts.

       Communication links, in conjunction with protection relays, are used
       to selectively isolate faults on high-voltage lines, transformers,
       reactors, and other important electrical equipment.  The role of the
       teleprotection system is to selectively disconnect a faulty part by
       transferring command signals within the shortest possible time.

    3.1.1.1.1.  Key Criteria

       The key criteria for measuring teleprotection performance are command
       transmission time, dependability, and security.  These criteria are
       defined by International Electrotechnical Commission (IEC)
       Standard 60834 [IEC-60834] as follows:

       o  Transmission time (speed): The time between the moment when a
          state change occurs at the transmitter input and the moment of the
          corresponding change at the receiver output, including propagation
          delay.  The overall operating time for a teleprotection system is
          the sum of (1) the time required to initiate the command at the
          transmitting end, (2) the propagation delay over the network
          (including equipment), and (3) the time required to make the
          necessary selections and decisions at the receiving end, including
          any additional delay due to a noisy environment.

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       o  Dependability: The ability to issue and receive valid commands in
          the presence of interference and/or noise, by minimizing the
          Probability of Missing Commands (PMC).  Dependability targets are
          typically set for a specific Bit Error Rate (BER) level.

       o  Security: The ability to prevent false tripping due to a noisy
          environment, by minimizing the Probability of Unwanted Commands
          (PUC).  Security targets are also set for a specific BER level.

       Additional elements of the teleprotection system that impact its
       performance include:

       o  Network bandwidth

       o  Failure recovery capacity (aka resiliency)

    3.1.1.1.2.  Fault Detection and Clearance Timing

       Most power-line equipment can tolerate short circuits or faults for
       up to approximately five power cycles before sustaining irreversible
       damage or affecting other segments in the network.  This translates
       to a total fault clearance time of 100 ms.  As a safety precaution,
       however, the actual operation time of protection systems is limited
       to 70-80% of this period, including fault recognition time, command
       transmission time, and line breaker switching time.

       Some system components, such as large electromechanical switches,
       require a particularly long time to operate and take up the majority
       of the total clearance time, leaving only a 10 ms window for the
       telecommunications part of the protection scheme, independent of the
       distance of travel.  Given the sensitivity of the issue, new
       networks impose requirements that are even more stringent: IEC
       Standard 61850-5:2013 [IEC-61850-5:2013] limits the transfer time for
       protection messages to 1/4-1/2 cycle or 4-8 ms (for 60 Hz lines) for
       messages considered the most critical.

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    3.1.1.1.3.  Symmetric Channel Delay

       Teleprotection channels that are differential must be synchronous;
       this means that any delays on the transmit and receive paths must
       match each other.  Ideally, teleprotection systems support zero
       asymmetric delay; typical legacy relays can tolerate delay
       discrepancies of up to 750 us.

       Some tools available for lowering delay variation below this
       threshold are as follows:

       o  For legacy systems using Time-Division Multiplexing (TDM), jitter
          buffers at the multiplexers on each end of the line can be used to
          offset delay variation by queuing sent and received packets.  The
          length of the queues must balance the need to regulate the rate of
          transmission with the need to limit overall delay, as larger
          buffers result in increased latency.

       o  For jitter-prone IP networks, traffic management tools can ensure
          that the teleprotection signals receive the highest transmission
          priority to minimize jitter.

       o  Standard packet-based synchronization technologies, such as the
          IEEE 1588-2008 Precision Time Protocol (PTP) [IEEE-1588] and
          synchronous Ethernet (syncE) [syncE], can help keep networks
          stable by maintaining a highly accurate clock source on the
          various network devices.

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    3.1.1.1.4.  Teleprotection Network Requirements

       Table 1 captures the main network metrics.  (These metrics are based
       on IEC Standard 61850-5:2013 [IEC-61850-5:2013].)

       +---------------------------------+---------------------------------+
       |    Teleprotection Requirement   |            Attribute            |
       +---------------------------------+---------------------------------+
       |      One-way maximum delay      |             4-10 ms             |
       |                                 |                                 |
       |    Asymmetric delay required    |               Yes               |
       |                                 |                                 |
       |          Maximum jitter         |   Less than 250 us (750 us for  |
       |                                 |           legacy IEDs)          |
       |                                 |                                 |
       |             Topology            |     Point to point, point to    |
       |                                 |            multipoint           |
       |                                 |                                 |
       |           Availability          |             99.9999%            |
       |                                 |                                 |
       |     Precise timing required     |               Yes               |
       |                                 |                                 |
       |  Recovery time on node failure  |    Less than 50 ms - hitless    |
       |                                 |                                 |
       |      Performance management     |          Yes; mandatory         |
       |                                 |                                 |
       |            Redundancy           |               Yes               |
       |                                 |                                 |
       |           Packet loss           |            0.1% to 1%           |
       +---------------------------------+---------------------------------+

                   Table 1: Teleprotection Network Requirements

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    3.1.1.1.5.  Inter-trip Protection Scheme

       "Inter-tripping" is the signal-controlled tripping of a circuit
       breaker to complete the isolation of a circuit or piece of apparatus
       in concert with the tripping of other circuit breakers.

       +---------------------------------+---------------------------------+
       |      Inter-trip Protection      |            Attribute            |
       |           Requirement           |                                 |
       +---------------------------------+---------------------------------+
       |      One-way maximum delay      |               5 ms              |
       |                                 |                                 |
       |    Asymmetric delay required    |                No               |
       |                                 |                                 |
       |          Maximum jitter         |           Not critical          |
       |                                 |                                 |
       |             Topology            |     Point to point, point to    |
       |                                 |            multipoint           |
       |                                 |                                 |
       |            Bandwidth            |             64 kbps             |
       |                                 |                                 |
       |           Availability          |             99.9999%            |
       |                                 |                                 |
       |     Precise timing required     |               Yes               |
       |                                 |                                 |
       |  Recovery time on node failure  |    Less than 50 ms - hitless    |
       |                                 |                                 |
       |      Performance management     |          Yes; mandatory         |
       |                                 |                                 |
       |            Redundancy           |               Yes               |
       |                                 |                                 |
       |           Packet loss           |               0.1%              |
       +---------------------------------+---------------------------------+

                Table 2: Inter-trip Protection Network Requirements

    3.1.1.1.6.  Current Differential Protection Scheme

       Current differential protection is commonly used for line protection
       and is typically used to protect parallel circuits.  At both ends of
       the lines, the current is measured by the differential relays; both
       relays will trip the circuit breaker if the current going into the
       line does not equal the current going out of the line.  This type of
       protection scheme assumes that some form of communication is present
       between the relays at both ends of the line, to allow both relays to
       compare measured current values.  Line differential protection
       schemes assume that the telecommunications delay between both relays
       is very low -- often as low as 5 ms.  Moreover, as those systems are

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       often not time-synchronized, they also assume that the delay over
       symmetric telecommunications paths is constant; this allows the
       comparison of current measurement values taken at exactly the
       same time.

       +---------------------------------+---------------------------------+
       | Current Differential Protection |            Attribute            |
       |           Requirement           |                                 |
       +---------------------------------+---------------------------------+
       |      One-way maximum delay      |               5 ms              |
       |                                 |                                 |
       |    Asymmetric delay required    |               Yes               |
       |                                 |                                 |
       |          Maximum jitter         |   Less than 250 us (750 us for  |
       |                                 |           legacy IEDs)          |
       |                                 |                                 |
       |             Topology            |     Point to point, point to    |
       |                                 |            multipoint           |
       |                                 |                                 |
       |            Bandwidth            |             64 kbps             |
       |                                 |                                 |
       |           Availability          |             99.9999%            |
       |                                 |                                 |
       |     Precise timing required     |               Yes               |
       |                                 |                                 |
       |  Recovery time on node failure  |    Less than 50 ms - hitless    |
       |                                 |                                 |
       |      Performance management     |          Yes; mandatory         |
       |                                 |                                 |
       |            Redundancy           |               Yes               |
       |                                 |                                 |
       |           Packet loss           |               0.1%              |
       +---------------------------------+---------------------------------+

                 Table 3: Current Differential Protection Metrics

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    3.1.1.1.7.  Distance Protection Scheme

       The distance (impedance relay) protection scheme is based on voltage
       and current measurements.  The network metrics are similar (but not
       identical) to the metrics for current differential protection.

       +---------------------------------+---------------------------------+
       | Distance Protection Requirement |            Attribute            |
       +---------------------------------+---------------------------------+
       |      One-way maximum delay      |               5 ms              |
       |                                 |                                 |
       |    Asymmetric delay required    |                No               |
       |                                 |                                 |
       |          Maximum jitter         |           Not critical          |
       |                                 |                                 |
       |             Topology            |     Point to point, point to    |
       |                                 |            multipoint           |
       |                                 |                                 |
       |            Bandwidth            |             64 kbps             |
       |                                 |                                 |
       |           Availability          |             99.9999%            |
       |                                 |                                 |
       |     Precise timing required     |               Yes               |
       |                                 |                                 |
       |  Recovery time on node failure  |    Less than 50 ms - hitless    |
       |                                 |                                 |
       |      Performance management     |          Yes; mandatory         |
       |                                 |                                 |
       |            Redundancy           |               Yes               |
       |                                 |                                 |
       |           Packet loss           |               0.1%              |
       +---------------------------------+---------------------------------+

                     Table 4: Distance Protection Requirements

    3.1.1.1.8.  Inter-substation Protection Signaling

       This use case describes the exchange of sampled values and/or GOOSE
       (Generic Object Oriented Substation Events) messages between
       Intelligent Electronic Devices (IEDs) in two substations for
       protection and tripping coordination.  The two IEDs are in
       master-slave mode.

       The Current Transformer or Voltage Transformer (CT/VT) in one
       substation sends the sampled analog voltage or current value to the
       Merging Unit (MU) over hard wire.  The MU sends the time-synchronized
       sampled values (as specified by IEC 61850-9-2:2011
       [IEC-61850-9-2:2011]) to the slave IED.  The slave IED forwards the

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       information to the master IED in the other substation.  The master
       IED makes the determination (for example, based on sampled value
       differentials) to send a trip command to the originating IED.  Once
       the slave IED/relay receives the GOOSE message containing the command
       to trip the breaker, it opens the breaker.  It then sends a
       confirmation message back to the master.  All data exchanges between
       IEDs are through sampled values and/or GOOSE messages.

       +---------------------------------+---------------------------------+
       |   Inter-substation Protection   |            Attribute            |
       |           Requirement           |                                 |
       +---------------------------------+---------------------------------+
       |      One-way maximum delay      |               5 ms              |
       |                                 |                                 |
       |    Asymmetric delay required    |                No               |
       |                                 |                                 |
       |          Maximum jitter         |           Not critical          |
       |                                 |                                 |
       |             Topology            |     Point to point, point to    |
       |                                 |            multipoint           |
       |                                 |                                 |
       |            Bandwidth            |             64 kbps             |
       |                                 |                                 |
       |           Availability          |             99.9999%            |
       |                                 |                                 |
       |     Precise timing required     |               Yes               |
       |                                 |                                 |
       |  Recovery time on node failure  |    Less than 50 ms - hitless    |
       |                                 |                                 |
       |      Performance management     |          Yes; mandatory         |
       |                                 |                                 |
       |            Redundancy           |               Yes               |
       |                                 |                                 |
       |           Packet loss           |                1%               |
       +---------------------------------+---------------------------------+

                 Table 5: Inter-substation Protection Requirements

    3.1.1.2.  Intra-substation Process Bus Communications

       This use case describes the data flow from the CT/VT to the IEDs in
       the substation via the MU.  The CT/VT in the substation sends the
       analog voltage or current values to the MU over hard wire.  The MU
       converts the analog values into digital format (typically
       time-synchronized sampled values as specified by IEC 61850-9-2:2011
       [IEC-61850-9-2:2011]) and sends them to the IEDs in the substation.
       The Global Positioning System (GPS) Master Clock can send 1PPS or
       IRIG-B format to the MU through a serial port or IEEE 1588 protocol

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       via a network.  1PPS (One Pulse Per Second) is an electrical signal
       that has a width of less than 1 second and a sharply rising or
       abruptly falling edge that accurately repeats once per second.  1PPS
       signals are output by radio beacons, frequency standards, other types
       of precision oscillators, and some GPS receivers.  IRIG (Inter-Range
       Instrumentation Group) time codes are standard formats for
       transferring timing information.  Atomic frequency standards and GPS
       receivers designed for precision timing are often equipped with an
       IRIG output.  Process bus communication using IEC 61850-9-2:2011
       [IEC-61850-9-2:2011] simplifies connectivity within the substation,
       removes the requirement for multiple serial connections, and removes
       the slow serial-bus architectures that are typically used.  This also
       ensures increased flexibility and increased speed with the use of
       multicast messaging between multiple devices.

       +---------------------------------+---------------------------------+
       |   Intra-substation Protection   |            Attribute            |
       |           Requirement           |                                 |
       +---------------------------------+---------------------------------+
       |      One-way maximum delay      |               5 ms              |
       |                                 |                                 |
       |    Asymmetric delay required    |                No               |
       |                                 |                                 |
       |          Maximum jitter         |           Not critical          |
       |                                 |                                 |
       |             Topology            |     Point to point, point to    |
       |                                 |            multipoint           |
       |                                 |                                 |
       |            Bandwidth            |             64 kbps             |
       |                                 |                                 |
       |           Availability          |             99.9999%            |
       |                                 |                                 |
       |     Precise timing required     |               Yes               |
       |                                 |                                 |
       |  Recovery time on node failure  |    Less than 50 ms - hitless    |
       |                                 |                                 |
       |      Performance management     |          Yes; mandatory         |
       |                                 |                                 |
       |            Redundancy           |            Yes or No            |
       |                                 |                                 |
       |           Packet loss           |               0.1%              |
       +---------------------------------+---------------------------------+

                 Table 6: Intra-substation Protection Requirements

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    3.1.1.3.  Wide-Area Monitoring and Control Systems

       The application of synchrophasor measurement data from Phasor
       Measurement Units (PMUs) to wide-area monitoring and control systems
       promises to provide important new capabilities for improving system
       stability.  Access to PMU data enables more-timely situational
       awareness over larger portions of the grid than what has been
       possible historically with normal SCADA (Supervisory Control and Data
       Acquisition) data.  Handling the volume and the real-time nature of
       synchrophasor data presents unique challenges for existing
       application architectures.  The Wide-Area Management System (WAMS)
       makes it possible for the condition of the bulk power system to be
       observed and understood in real time so that protective,
       preventative, or corrective action can be taken.  Because of the very
       high sampling rate of measurements and the strict requirement for
       time synchronization of the samples, the WAMS has stringent
       telecommunications requirements in an IP network, as captured in
       Table 7:

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       +---------------------------------+---------------------------------+
       |         WAMS Requirement        |            Attribute            |
       +---------------------------------+---------------------------------+
       |      One-way maximum delay      |              50 ms              |
       |                                 |                                 |
       |    Asymmetric delay required    |                No               |
       |                                 |                                 |
       |          Maximum jitter         |           Not critical          |
       |                                 |                                 |
       |             Topology            |     Point to point, point to    |
       |                                 |    multipoint, multipoint to    |
       |                                 |            multipoint           |
       |                                 |                                 |
       |            Bandwidth            |             100 kbps            |
       |                                 |                                 |
       |           Availability          |             99.9999%            |
       |                                 |                                 |
       |     Precise timing required     |               Yes               |
       |                                 |                                 |
       |  Recovery time on node failure  |    Less than 50 ms - hitless    |
       |                                 |                                 |
       |      Performance management     |          Yes; mandatory         |
       |                                 |                                 |
       |            Redundancy           |               Yes               |
       |                                 |                                 |
       |           Packet loss           |                1%               |
       |                                 |                                 |
       |     Consecutive packet loss     |     At least one packet per     |
       |                                 |    application cycle must be    |
       |                                 |            received.            |
       +---------------------------------+---------------------------------+

                 Table 7: WAMS Special Communication Requirements

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    3.1.1.4.  WAN Engineering Guidelines Requirement Classification

       The IEC has published a technical report (TR) that offers guidelines
       on how to define and deploy Wide-Area Networks (WANs) for the
       interconnection of electric substations, generation plants, and SCADA
       operation centers.  IEC TR 61850-90-12:2015 [IEC-61850-90-12:2015]
       provides four classes of WAN communication requirements, as
       summarized in Table 8:

       +----------------+-----------+----------+----------+----------------+
       |      WAN       |  Class WA | Class WB | Class WC |    Class WD    |
       |  Requirement   |           |          |          |                |
       +----------------+-----------+----------+----------+----------------+
       |  Application   |    EHV    | HV (High |    MV    |    General-    |
       |     field      |  (Extra-  | Voltage) | (Medium  |    purpose     |
       |                |    High   |          | Voltage) |                |
       |                |  Voltage) |          |          |                |
       |                |           |          |          |                |
       |    Latency     |    5 ms   |  10 ms   |  100 ms  |    >100 ms     |
       |                |           |          |          |                |
       |     Jitter     |   10 us   |  100 us  |   1 ms   |     10 ms      |
       |                |           |          |          |                |
       |    Latency     |   100 us  |   1 ms   |  10 ms   |     100 ms     |
       |   asymmetry    |           |          |          |                |
       |                |           |          |          |                |
       | Time accuracy  |    1 us   |  10 us   |  100 us  |  10 to 100 ms  |
       |                |           |          |          |                |
       |      BER       |  10^-7 to | 10^-5 to |  10^-3   |                |
       |                |   10^-6   |  10^-4   |          |                |
       |                |           |          |          |                |
       | Unavailability |  10^-7 to | 10^-5 to |  10^-3   |                |
       |                |   10^-6   |  10^-4   |          |                |
       |                |           |          |          |                |
       | Recovery delay |    Zero   |  50 ms   |   5 s    |      50 s      |
       |                |           |          |          |                |
       | Cybersecurity  | Extremely |   High   |  Medium  |     Medium     |
       |                |    high   |          |          |                |
       +----------------+-----------+----------+----------+----------------+

                 Table 8: Communication Requirements (Courtesy of
                             IEC TR 61850-90-12:2015)

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    3.1.2.  Generation Use Case

       Energy generation systems are complex infrastructures that require
       control of both the generated power and the generation
       infrastructure.

    3.1.2.1.  Control of the Generated Power

       The electrical power generation frequency must be maintained within a
       very narrow band.  Deviations from the acceptable frequency range are
       detected, and the required signals are sent to the power plants for
       frequency regulation.

       Automatic Generation Control (AGC) is a system for adjusting the
       power output of generators at different power plants, in response to
       changes in the load.

       +---------------------------------+---------------------------------+
       |     FCAG (Frequency Control     |            Attribute            |
       |      Automatic Generation)      |                                 |
       |           Requirement           |                                 |
       +---------------------------------+---------------------------------+
       |      One-way maximum delay      |              500 ms             |
       |                                 |                                 |
       |    Asymmetric delay required    |                No               |
       |                                 |                                 |
       |          Maximum jitter         |           Not critical          |
       |                                 |                                 |
       |             Topology            |          Point to point         |
       |                                 |                                 |
       |            Bandwidth            |             20 kbps             |
       |                                 |                                 |
       |           Availability          |             99.999%             |
       |                                 |                                 |
       |     Precise timing required     |               Yes               |
       |                                 |                                 |
       |  Recovery time on node failure  |               N/A               |
       |                                 |                                 |
       |      Performance management     |          Yes; mandatory         |
       |                                 |                                 |
       |            Redundancy           |               Yes               |
       |                                 |                                 |
       |           Packet loss           |                1%               |
       +---------------------------------+---------------------------------+

                     Table 9: FCAG Communication Requirements

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    3.1.2.2.  Control of the Generation Infrastructure

       The control of the generation infrastructure combines requirements
       from industrial automation systems and energy generation systems.
       This section describes the use case for control of the generation
       infrastructure of a wind turbine.

       Figure 1 presents the subsystems that operate a wind turbine.

                           |
                           |
                           |  +-----------------+
                           |  |   +----+        |
                           |  |   |WTRM| WGEN   |
                      WROT x==|===|    |        |
                           |  |   +----+    WCNV|
                           |  |WNAC             |
                           |  +---+---WYAW---+--+
                           |      |          |
                           |      |          |        +----+
                                  |WTRF      |        |WMET|
                                  |          |        |    |
                           Wind Turbine      |        +--+-+
                           Controller        |           |
                             WTUR |          |           |
                             WREP |          |           |
                             WSLG |          |           |
                             WALG |     WTOW |           |

                      Figure 1: Wind Turbine Control Network

       The subsystems shown in Figure 1 include the following:

       o  WROT (rotor control)

       o  WNAC (nacelle control) (nacelle: housing containing the generator)

       o  WTRM (transmission control)

       o  WGEN (generator)

       o  WYAW (yaw controller) (of the tower head)

       o  WCNV (in-turbine power converter)

       o  WTRF (wind turbine transformer information)

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       o  WMET (external meteorological station providing real-time
          information to the tower's controllers)

       o  WTUR (wind turbine general information)

       o  WREP (wind turbine report information)

       o  WSLG (wind turbine state log information)

       o  WALG (wind turbine analog log information)

       o  WTOW (wind turbine tower information)

       Traffic characteristics relevant to the network planning and
       dimensioning process in a wind turbine scenario are listed below.
       The values in this section are based mainly on the relevant
       references [Ahm14] and [Spe09].  Each logical node (Figure 1) is a
       part of the metering network and produces analog measurements and
       status information that must comply with their respective data-rate
       constraints.

       +-----------+--------+----------+-----------+-----------+-----------+
       | Subsystem | Sensor |  Analog  | Data Rate |   Status  | Data Rate |
       |           | Count  |  Sample  | (bytes/s) |   Sample  | (bytes/s) |
       |           |        |  Count   |           |   Count   |           |
       +-----------+--------+----------+-----------+-----------+-----------+
       |    WROT   |   14   |    9     |    642    |     5     |     10    |
       |           |        |          |           |           |           |
       |    WTRM   |   18   |    10    |    2828   |     8     |     16    |
       |           |        |          |           |           |           |
       |    WGEN   |   14   |    12    |   73764   |     2     |     4     |
       |           |        |          |           |           |           |
       |    WCNV   |   14   |    12    |   74060   |     2     |     4     |
       |           |        |          |           |           |           |
       |    WTRF   |   12   |    5     |   73740   |     2     |     4     |
       |           |        |          |           |           |           |
       |    WNAC   |   12   |    9     |    112    |     3     |     6     |
       |           |        |          |           |           |           |
       |    WYAW   |   7    |    8     |    220    |     4     |     8     |
       |           |        |          |           |           |           |
       |    WTOW   |   4    |    1     |     8     |     3     |     6     |
       |           |        |          |           |           |           |
       |    WMET   |   7    |    7     |    228    |     -     |     -     |
       +-----------+--------+----------+-----------+-----------+-----------+

                   Table 10: Wind Turbine Data-Rate Constraints

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       QoS constraints for different services are presented in Table 11.
       These constraints are defined by IEEE Standard 1646 [IEEE-1646] and
       IEC Standard 61400 Part 25 [IEC-61400-25].

       +---------------------+---------+-------------+---------------------+
       |       Service       | Latency | Reliability |   Packet Loss Rate  |
       +---------------------+---------+-------------+---------------------+
       |  Analog measurement |  16 ms  |    99.99%   |        <10^-6       |
       |                     |         |             |                     |
       |  Status information |  16 ms  |    99.99%   |        <10^-6       |
       |                     |         |             |                     |
       |  Protection traffic |   4 ms  |   100.00%   |        <10^-9       |
       |                     |         |             |                     |
       |    Reporting and    |   1 s   |    99.99%   |        <10^-6       |
       |       logging       |         |             |                     |
       |                     |         |             |                     |
       |  Video surveillance |   1 s   |    99.00%   |     No specific     |
       |                     |         |             |     requirement     |
       |                     |         |             |                     |
       | Internet connection |  60 min |    99.00%   |     No specific     |
       |                     |         |             |     requirement     |
       |                     |         |             |                     |
       |   Control traffic   |  16 ms  |   100.00%   |        <10^-9       |
       |                     |         |             |                     |
       |     Data polling    |  16 ms  |    99.99%   |        <10^-6       |
       +---------------------+---------+-------------+---------------------+

            Table 11: Wind Turbine Reliability and Latency Constraints

    3.1.2.2.1.  Intra-domain Network Considerations

       A wind turbine is composed of a large set of subsystems, including
       sensors and actuators that require time-critical operation.  The
       reliability and latency constraints of these different subsystems are
       shown in Table 11.  These subsystems are connected to an intra-domain
       network that is used to monitor and control the operation of the
       turbine and connect it to the SCADA subsystems.  The different
       components are interconnected using fiber optics, industrial buses,
       industrial Ethernet, EtherCAT [EtherCAT], or a combination thereof.
       Industrial signaling and control protocols such as Modbus [MODBUS],
       PROFIBUS [PROFIBUS], PROFINET [PROFINET], and EtherCAT are used
       directly on top of the Layer 2 transport or encapsulated over TCP/IP.

       The data collected from the sensors and condition-monitoring systems
       is multiplexed onto fiber cables for transmission to the base of the
       tower and to remote control centers.  The turbine controller
       continuously monitors the condition of the wind turbine and collects

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       statistics on its operation.  This controller also manages a large
       number of switches, hydraulic pumps, valves, and motors within the
       wind turbine.

       There is usually a controller at the bottom of the tower and also in
       the nacelle.  The communication between these two controllers usually
       takes place using fiber optics instead of copper links.  Sometimes, a
       third controller is installed in the hub of the rotor and manages the
       pitch of the blades.  That unit usually communicates with the nacelle
       unit using serial communications.

    3.1.2.2.2.  Inter-domain Network Considerations

       A remote control center belonging to a grid operator regulates the
       power output, enables remote actuation, and monitors the health of
       one or more wind parks in tandem.  It connects to the local control
       center in a wind park over the Internet (Figure 2) via firewalls at
       both ends.  The Autonomous System (AS) path between the local control
       center and the wind park typically involves several ISPs at different
       tiers.  For example, a remote control center in Denmark can regulate
       a wind park in Greece over the normal public AS path between the two
       locations.

       +--------------+
       |              |
       |              |
       | Wind Park #1 +----+
       |              |    |      XXXXXX
       |              |    |      X    XXXXXXXX           +----------------+
       +--------------+    |   XXXX    X      XXXXX       |                |
                           +---+                XXX       | Remote Control |
                               XXX    Internet       +----+     Center     |
                           +----+X                XXX     |                |
       +--------------+    |    XXXXXXX             XX    |                |
       |              |    |          XX     XXXXXXX      +----------------+
       |              |    |            XXXXX
       | Wind Park #2 +----+
       |              |
       |              |
       +--------------+

                    Figure 2: Wind Turbine Control via Internet

       The remote control center is part of the SCADA system, setting the
       desired power output to the wind park and reading back the result
       once the new power output level has been set.  Traffic between the
       remote control center and the wind park typically consists of
       protocols like IEC 60870-5-104 [IEC-60870-5-104], OPC XML-Data Access

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       (XML-DA) [OPCXML], Modbus [MODBUS], and SNMP [RFC3411].  At the time
       of this writing, traffic flows between the remote control center and
       the wind park are best effort.  QoS requirements are not strict, so
       no Service Level Agreements (SLAs) or service-provisioning mechanisms
       (e.g., VPNs) are employed.  In the case of such events as equipment
       failure, tolerance for alarm delay is on the order of minutes, due to
       redundant systems already in place.

       Future use cases will require bounded latency, bounded jitter, and
       extraordinarily low packet loss for inter-domain traffic flows due to
       the softwarization and virtualization of core wind-park equipment
       (e.g., switches, firewalls, and SCADA server components).  These
       factors will create opportunities for service providers to install
       new services and dynamically manage them from remote locations.  For
       example, to enable failover of a local SCADA server, a SCADA server
       in another wind-park site (under the administrative control of the
       same operator) could be utilized temporarily (Figure 3).  In that
       case, local traffic would be forwarded to the remote SCADA server,
       and existing intra-domain QoS and timing parameters would have to be
       met for inter-domain traffic flows.

       +--------------+
       |              |
       |              |
       | Wind Park #1 +----+
       |              |    |      XXXXXX
       |              |    |      X    XXXXXXXX           +----------------+
       +--------------+    |   XXXX           XXXXX       |                |
                           +---+      Operator-   XXX     | Remote Control |
                               XXX    Administered   +----+     Center     |
                           +----+X    WAN         XXX     |                |
       +--------------+    |    XXXXXXX             XX    |                |
       |              |    |          XX     XXXXXXX      +----------------+
       |              |    |            XXXXX
       | Wind Park #2 +----+
       |              |
       |              |
       +--------------+

           Figure 3: Wind Turbine Control via Operator-Administered WAN

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    3.1.3.  Distribution Use Case

    3.1.3.1.  Fault Location, Isolation, and Service Restoration (FLISR)

       "Fault Location, Isolation, and Service Restoration (FLISR)" refers
       to the ability to automatically locate the fault, isolate the fault,
       and restore service in the distribution network.  This will likely
       be the first widespread application of distributed intelligence in
       the grid.

       The static power-switch status (open/closed) in the network dictates
       the power flow to secondary substations.  Reconfiguring the network
       in the event of a fault is typically done manually on site to
       energize/de-energize alternate paths.  Automating the operation of
       substation switchgear allows the flow of power to be altered
       automatically under fault conditions.

       FLISR can be managed centrally from a Distribution Management System
       (DMS) or executed locally through distributed control via intelligent
       switches and fault sensors.

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       +---------------------------------+---------------------------------+
       |        FLISR Requirement        |            Attribute            |
       +---------------------------------+---------------------------------+
       |      One-way maximum delay      |              80 ms              |
       |                                 |                                 |
       |    Asymmetric delay required    |                No               |
       |                                 |                                 |
       |          Maximum jitter         |              40 ms              |
       |                                 |                                 |
       |             Topology            |     Point to point, point to    |
       |                                 |    multipoint, multipoint to    |
       |                                 |            multipoint           |
       |                                 |                                 |
       |            Bandwidth            |             64 kbps             |
       |                                 |                                 |
       |           Availability          |             99.9999%            |
       |                                 |                                 |
       |     Precise timing required     |               Yes               |
       |                                 |                                 |
       |  Recovery time on node failure  |    Depends on customer impact   |
       |                                 |                                 |
       |      Performance management     |          Yes; mandatory         |
       |                                 |                                 |
       |            Redundancy           |               Yes               |
       |                                 |                                 |
       |           Packet loss           |               0.1%              |
       +---------------------------------+---------------------------------+

                    Table 12: FLISR Communication Requirements

    3.2.  Electrical Utilities Today

       Many utilities still rely on complex environments consisting of
       multiple application-specific proprietary networks, including TDM
       networks.

       In this kind of environment, there is no mixing of Operation
       Technology (OT) and IT applications on the same network, and
       information is siloed between operational areas.

       Specific calibration of the full chain is required; this is costly.

       This kind of environment prevents utility operations from realizing
       operational efficiency benefits, visibility, and functional
       integration of operational information across grid applications and
       data networks.

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       In addition, there are many security-related issues, as discussed in
       the following section.

    3.2.1.  Current Security Practices and Their Limitations

       Grid-monitoring and control devices are already targets for cyber
       attacks, and legacy telecommunications protocols have many intrinsic
       network-related vulnerabilities.  For example, the Distributed
       Network Protocol (DNP3) [IEEE-1815], Modbus, PROFIBUS/PROFINET, and
       other protocols are designed around a common paradigm of "request and
       respond".  Each protocol is designed for a master device such as an
       HMI (Human-Machine Interface) system to send commands to subordinate
       slave devices to perform data retrieval (reading inputs) or control
       functions (writing to outputs).  Because many of these protocols lack
       authentication, encryption, or other basic security measures, they
       are prone to network-based attacks, allowing a malicious actor or
       attacker to utilize the request-and-respond system as a mechanism for
       functionality similar to command and control.  Specific security
       concerns common to most industrial-control protocols (including
       utility telecommunications protocols) include the following:

       o  Network or transport errors (e.g., malformed packets or excessive
          latency) can cause protocol failure.

       o  Protocol commands may be available that are capable of forcing
          slave devices into inoperable states, including powering devices
          off, forcing them into a listen-only state, or disabling alarming.

       o  Protocol commands may be available that are capable of
          interrupting processes (e.g., restarting communications).

       o  Protocol commands may be available that are capable of clearing,
          erasing, or resetting diagnostic information such as counters and
          diagnostic registers.

       o  Protocol commands may be available that are capable of requesting
          sensitive information about the controllers, their configurations,
          or other need-to-know information.

       o  Most protocols are application-layer protocols transported over
          TCP; it is therefore easy to transport commands over non-standard
          ports or inject commands into authorized traffic flows.

       o  Protocol commands may be available that are capable of
          broadcasting messages to many devices at once (i.e., a
          potential DoS).

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       o  Protocol commands may be available that will query the device
          network to obtain defined points and their values (i.e., perform a
          configuration scan).

       o  Protocol commands may be available that will list all available
          function codes (i.e., perform a function scan).

       These inherent vulnerabilities, along with increasing connectivity
       between IT and OT networks, make network-based attacks very feasible.
       By injecting malicious protocol commands, an attacker could take
       control over the target process.  Altering legitimate protocol
       traffic can also alter information about a process and disrupt the
       legitimate controls that are in place over that process.  A
       man-in-the-middle attack could result in (1) improper control over a
       process and (2) misrepresentation of data that is sent back to
       operator consoles.

    3.3.  Electrical Utilities in the Future

       The business and technology trends that are sweeping the utility
       industry will drastically transform the utility business from the way
       it has been for many decades.  At the core of many of these changes
       is a drive to modernize the electrical grid with an integrated
       telecommunications infrastructure.  However, interoperability
       concerns, legacy networks, disparate tools, and stringent security
       requirements all add complexity to the grid's transformation.  Given
       the range and diversity of the requirements that should be addressed
       by the next-generation telecommunications infrastructure, utilities
       need to adopt a holistic architectural approach to integrate the
       electrical grid with digital telecommunications across the entire
       power delivery chain.

       The key to modernizing grid telecommunications is to provide a
       common, adaptable, multi-service network infrastructure for the
       entire utility organization.  Such a network serves as the platform
       for current capabilities while enabling future expansion of the
       network to accommodate new applications and services.

       To meet this diverse set of requirements both today and in the
       future, the next-generation utility telecommunications network will
       be based on an open-standards-based IP architecture.  An end-to-end
       IP architecture takes advantage of nearly three decades of IP
       technology development, facilitating interoperability and device
       management across disparate networks and devices, as has already been
       demonstrated in many mission-critical and highly secure networks.

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       IPv6 is seen as a future telecommunications technology for the smart
       grid; the IEC and different national committees have mandated a
       specific ad hoc group (AHG8) to define the strategy for migration to
       IPv6 for all the IEC Technical Committee 57 (TC 57) power automation
       standards.  The AHG8 has finalized its work on the migration
       strategy, and IEC TR 62357-200:2015 [IEC-62357-200:2015] has been
       issued.

       Cloud-based SCADA systems will control and monitor the critical and
       non-critical subsystems of generation systems -- for example, wind
       parks.

    3.3.1.  Migration to Packet-Switched Networks

       Throughout the world, utilities are increasingly planning for a
       future based on smart-grid applications requiring advanced
       telecommunications systems.  Many of these applications utilize
       packet connectivity for communicating information and control signals
       across the utility's WAN, made possible by technologies such as
       Multiprotocol Label Switching (MPLS).  The data that traverses the
       utility WAN includes:

       o  Grid monitoring, control, and protection data

       o  Non-control grid data (e.g., asset data for condition monitoring)

       o  Data (e.g., voice and video) related to physical safety and
          security

       o  Remote worker access to corporate applications (voice, maps,
          schematics, etc.)

       o  Field area network Backhaul for smart metering

       o  Distribution-grid management

       o  Enterprise traffic (email, collaboration tools, business
          applications)

       WANs support this wide variety of traffic to and from substations,
       the transmission and distribution grid, and generation sites; between
       control centers; and between work locations and data centers.  To
       maintain this rapidly expanding set of applications, many utilities
       are taking steps to evolve present TDM-based and frame relay
       infrastructures to packet systems.  Packet-based networks are
       designed to provide greater functionalities and higher levels of
       service for applications, while continuing to deliver reliability and
       deterministic (real-time) traffic support.

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    3.3.2.  Telecommunications Trends

       These general telecommunications topics are provided in addition to
       the use cases that have been addressed so far.  These include both
       current and future telecommunications-related topics that should be
       factored into the network architecture and design.

    3.3.2.1.  General Telecommunications Requirements

       o  IP connectivity everywhere

       o  Monitoring services everywhere, and from different remote centers

       o  Moving services to a virtual data center

       o  Unified access to applications/information from the corporate
          network

       o  Unified services

       o  Unified communications solutions

       o  Mix of fiber and microwave technologies - obsolescence of the
          Synchronous Optical Network / Synchronous Digital Hierarchy
          (SONET/SDH) or TDM

       o  Standardizing grid telecommunications protocols to open standards,
          to ensure interoperability

       o  Reliable telecommunications for transmission and distribution
          substations

       o  IEEE 1588 time-synchronization client/server capabilities

       o  Integration of multicast design

       o  Mapping of QoS requirements

       o  Enabling future network expansion

       o  Substation network resilience

       o  Fast convergence design

       o  Scalable headend design

       o  Defining SLAs and enabling SLA monitoring

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       o  Integration of 3G/4G technologies and future technologies

       o  Ethernet connectivity for station bus architecture

       o  Ethernet connectivity for process bus architecture

       o  Protection, teleprotection, and PMUs on IP

    3.3.2.2.  Specific Network Topologies of Smart-Grid Applications

       Utilities often have very large private telecommunications networks
       that can cover an entire territory/country.  Until now, the main
       purposes of these networks have been to (1) support transmission
       network monitoring, control, and automation, (2) support remote
       control of generation sites, and (3) provide FCAPS (Fault,
       Configuration, Accounting, Performance, and Security) services from
       centralized network operation centers.

       Going forward, one network will support the operation and maintenance
       of electrical networks (generation, transmission, and distribution),
       voice and data services for tens of thousands of employees and for
       exchanges with neighboring interconnections, and administrative
       services.  To meet those requirements, a utility may deploy several
       physical networks leveraging different technologies across the
       country -- for instance, an optical network and a microwave network.
       Each protection and automation system between two points has two
       telecommunications circuits, one on each network.  Path diversity
       between two substations is key.  Regardless of the event type
       (hurricane, ice storm, etc.), one path needs to stay available so the
       system can still operate.

       In the optical network, signals are transmitted over more than tens
       of thousands of circuits using fiber optic links, microwave links,
       and telephone cables.  This network is the nervous system of the
       utility's power transmission operations.  The optical network
       represents tens of thousands of kilometers of cable deployed along
       the power lines, with individual runs as long as 280 km.

    3.3.2.3.  Precision Time Protocol

       Some utilities do not use GPS clocks in generation substations.  One
       of the main reasons is that some of the generation plants are 30 to
       50 meters deep underground and the GPS signal can be weak and
       unreliable.  Instead, atomic clocks are used.  Clocks are
       synchronized amongst each other.  Rubidium clocks provide clock and
       1 ms timestamps for IRIG-B.

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       Some companies plan to transition to PTP [IEEE-1588], distributing
       the synchronization signal over the IP/MPLS network.  PTP provides a
       mechanism for synchronizing the clocks of participating nodes to a
       high degree of accuracy and precision.

       PTP operates based on the following assumptions:

       o  The network eliminates cyclic forwarding of PTP messages within
          each communication path (e.g., by using a spanning tree protocol).

       o  PTP is tolerant of an occasional missed message, duplicated
          message, or message that arrived out of order.  However, PTP
          assumes that such impairments are relatively rare.

       o  As designed, PTP expects a multicast communication model; however,
          PTP also supports a unicast communication model as long as the
          behavior of the protocol is preserved.

       o  Like all message-based time transfer protocols, PTP time accuracy
          is degraded by delay asymmetry in the paths taken by event
          messages.  PTP cannot detect asymmetry, but if such delays are
          known a priori, time values can be adjusted to correct for
          asymmetry.

       The use of PTP for power automation is defined in
       IEC/IEEE 61850-9-3:2016 [IEC-IEEE-61850-9-3:2016].  It is based on
       Annex B of IEC 62439-3:2016 [IEC-62439-3:2016], which offers the
       support of redundant attachment of clocks to Parallel Redundancy
       Protocol (PRP) and High-availability Seamless Redundancy (HSR)
       networks.

    3.3.3.  Security Trends in Utility Networks

       Although advanced telecommunications networks can assist in
       transforming the energy industry by playing a critical role in
       maintaining high levels of reliability, performance, and
       manageability, they also introduce the need for an integrated
       security infrastructure.  Many of the technologies being deployed to
       support smart-grid projects such as smart meters and sensors can
       increase the vulnerability of the grid to attack.  Top security
       concerns for utilities migrating to an intelligent smart-grid
       telecommunications platform center on the following trends:

       o  Integration of distributed energy resources

       o  Proliferation of digital devices to enable management, automation,
          protection, and control

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       o  Regulatory mandates to comply with standards for critical
          infrastructure protection

       o  Migration to new systems for outage management, distribution
          automation, condition-based maintenance, load forecasting, and
          smart metering

       o  Demand for new levels of customer service and energy management

       This development of a diverse set of networks to support the
       integration of microgrids, open-access energy competition, and the
       use of network-controlled devices is driving the need for a converged
       security infrastructure for all participants in the smart grid,
       including utilities, energy service providers, large commercial and
       industrial customers, and residential customers.  Securing the assets
       of electric power delivery systems (from the control center to the
       substation, to the feeders and down to customer meters) requires an
       end-to-end security infrastructure that protects the myriad of
       telecommunications assets used to operate, monitor, and control power
       flow and measurement.

       "Cybersecurity" refers to all the security issues in automation and
       telecommunications that affect any functions related to the operation
       of the electric power systems.  Specifically, it involves the
       concepts of:

       o  Integrity: data cannot be altered undetectably

       o  Authenticity (data origin authentication): the telecommunications
          parties involved must be validated as genuine

       o  Authorization: only requests and commands from authorized users
          can be accepted by the system

       o  Confidentiality: data must not be accessible to any
          unauthenticated users

       When designing and deploying new smart-grid devices and
       telecommunications systems, it is imperative to understand the
       various impacts of these new components under a variety of attack
       situations on the power grid.  The consequences of a cyber attack on
       the grid telecommunications network can be catastrophic.  This is why
       security for the smart grid is not just an ad hoc feature or product;
       it's a complete framework integrating both physical and cybersecurity
       requirements and covering the entire smart-grid networks from
       generation to distribution.  Security has therefore become one of the
       main foundations of the utility telecom network architecture and must
       be considered at every layer with a defense-in-depth approach.

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       Migrating to IP-based protocols is key to addressing these challenges
       for two reasons:

       o  IP enables a rich set of features and capabilities to enhance the
          security posture.

       o  IP is based on open standards; this allows interoperability
          between different vendors and products, driving down the costs
          associated with implementing security solutions in OT networks.

       Securing OT telecommunications over packet-switched IP networks
       follows the same principles that are foundational for securing the IT
       infrastructure, i.e., consideration must be given to (1) enforcing
       electronic access control for both person-to-machine and machine-to-
       machine communications and (2) providing the appropriate levels of
       data privacy, device and platform integrity, and threat detection and
       mitigation.

    3.4.  Electrical Utilities Requests to the IETF

       o  Mixed Layer 2 and Layer 3 topologies

       o  Deterministic behavior

       o  Bounded latency and jitter

       o  Tight feedback intervals

       o  High availability, low recovery time

       o  Redundancy, low packet loss

       o  Precise timing

       o  Centralized computing of deterministic paths

       o  Distributed configuration (may also be useful)

    4.  Building Automation Systems (BASs)

    4.1.  Use Case Description

       A BAS manages equipment and sensors in a building for improving
       residents' comfort, reducing energy consumption, and responding to
       failures and emergencies.  For example, the BAS measures the
       temperature of a room using sensors and then controls the HVAC
       (heating, ventilating, and air conditioning) to maintain a set
       temperature and minimize energy consumption.

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       A BAS primarily performs the following functions:

       o  Periodically measures states of devices -- for example, humidity
          and illuminance of rooms, open/close state of doors, fan speed.

       o  Stores the measured data.

       o  Provides the measured data to BAS operators.

       o  Generates alarms for abnormal state of devices.

       o  Controls devices (e.g., turns room lights off at 10:00 PM).

    4.2.  BASs Today

    4.2.1.  BAS Architecture

       A typical present-day BAS architecture is shown in Figure 4.

                              +----------------------------+
                              |                            |
                              |       BMS        HMI       |
                              |        |          |        |
                              |  +----------------------+  |
                              |  |  Management Network  |  |
                              |  +----------------------+  |
                              |        |          |        |
                              |        LC         LC       |
                              |        |          |        |
                              |  +----------------------+  |
                              |  |     Field Network    |  |
                              |  +----------------------+  |
                              |     |     |     |     |    |
                              |    Dev   Dev   Dev   Dev   |
                              |                            |
                              +----------------------------+

                              BMS: Building Management Server
                              HMI: Human-Machine Interface
                              LC: Local Controller

                            Figure 4: BAS Architecture

       There are typically two layers of a network in a BAS.  The upper
       layer is called the management network, and the lower layer is called
       the field network.  In management networks, an IP-based communication
       protocol is used, while in field networks, non-IP-based communication

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       protocols ("field protocols") are mainly used.  Field networks have
       specific timing requirements, whereas management networks can be best
       effort.

       An HMI is typically a desktop PC used by operators to monitor and
       display device states, send device control commands to Local
       Controllers (LCs), and configure building schedules (for example,
       "turn off all room lights in the building at 10:00 PM").

       A building management server (BMS) performs the following operations.

       o  Collects and stores device states from LCs at regular intervals.

       o  Sends control values to LCs according to a building schedule.

       o  Sends an alarm signal to operators if it detects abnormal device
          states.

       The BMS and HMI communicate with LCs via IP-based "management
       protocols" (see standards [BACnet-IP] and [KNX]).

       An LC is typically a Programmable Logic Controller (PLC) that is
       connected to several tens or hundreds of devices using "field
       protocols".  An LC performs the following kinds of operations:

       o  Measures device states and provides the information to a BMS
          or HMI.

       o  Sends control values to devices, unilaterally or as part of a
          feedback control loop.

       At the time of this writing, many field protocols are in use; some
       are standards-based protocols, and others are proprietary (see
       standards [LonTalk], [MODBUS], [PROFIBUS], and [FL-net]).  The result
       is that BASs have multiple MAC/PHY modules and interfaces.  This
       makes BASs more expensive and slower to develop and can result in
       "vendor lock-in" with multiple types of management applications.

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    4.2.2.  BAS Deployment Model

       An example BAS for medium or large buildings is shown in Figure 5.
       The physical layout spans multiple floors and includes a monitoring
       room where the BAS management entities are located.  Each floor will
       have one or more LCs, depending on the number of devices connected to
       the field network.

                   +--------------------------------------------------+
                   |                                          Floor 3 |
                   |     +----LC~~~~+~~~~~+~~~~~+                     |
                   |     |          |     |     |                     |
                   |     |         Dev   Dev   Dev                    |
                   |     |                                            |
                   |---  |  ------------------------------------------|
                   |     |                                    Floor 2 |
                   |     +----LC~~~~+~~~~~+~~~~~+  Field Network      |
                   |     |          |     |     |                     |
                   |     |         Dev   Dev   Dev                    |
                   |     |                                            |
                   |---  |  ------------------------------------------|
                   |     |                                    Floor 1 |
                   |     +----LC~~~~+~~~~~+~~~~~+   +-----------------|
                   |     |          |     |     |   | Monitoring Room |
                   |     |         Dev   Dev   Dev  |                 |
                   |     |                          |    BMS   HMI    |
                   |     |   Management Network     |     |     |     |
                   |     +--------------------------------+-----+     |
                   |                                |                 |
                   +--------------------------------------------------+

             Figure 5: BAS Deployment Model for Medium/Large Buildings

       Each LC is connected to the monitoring room via the management
       network, and the management functions are performed within the
       building.  In most cases, Fast Ethernet (e.g., 100BASE-T) is used for
       the management network.  Since the management network is not a
       real-time network, the use of Ethernet without QoS is sufficient for
       today's deployments.

       Many physical interfaces used in field networks have specific timing
       requirements -- for example, RS232C and RS485.  Thus, if a field
       network is to be replaced with an Ethernet or wireless network, such
       networks must support time-critical deterministic flows.

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       Figure 6 shows another deployment model, in which the management
       system is hosted remotely.  This model is becoming popular for small
       offices and residential buildings, in which a standalone monitoring
       system is not cost effective.

                                                         +---------------+
                                                         | Remote Center |
                                                         |               |
                                                         |  BMS     HMI  |
                +------------------------------------+   |   |       |   |
                |                            Floor 2 |   |   +---+---+   |
                |    +----LC~~~~+~~~~~+ Field Network|   |       |       |
                |    |          |     |              |   |     Router    |
                |    |         Dev   Dev             |   +-------|-------+
                |    |                               |           |
                |--- | ------------------------------|           |
                |    |                       Floor 1 |           |
                |    +----LC~~~~+~~~~~+              |           |
                |    |          |     |              |           |
                |    |         Dev   Dev             |           |
                |    |                               |           |
                |    |   Management Network          |     WAN   |
                |    +------------------------Router-------------+
                |                                    |
                +------------------------------------+

                  Figure 6: Deployment Model for Small Buildings

       Some interoperability is possible in today's management networks but
       is not possible in today's field networks due to their non-IP-based
       design.

    4.2.3.  Use Cases for Field Networks

       Below are use cases for environmental monitoring, fire detection, and
       feedback control, and their implications for field network
       performance.

    4.2.3.1.  Environmental Monitoring

       The BMS polls each LC at a maximum measurement interval of 100 ms
       (for example, to draw a historical chart of 1-second granularity with
       a 10x sampling interval) and then performs the operations as
       specified by the operator.  Each LC needs to measure each of its
       several hundred sensors once per measurement interval.  Latency is
       not critical in this scenario as long as all sensor value
       measurements are completed within the measurement interval.
       Availability is expected to be 99.999%.

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    4.2.3.2.  Fire Detection

       On detection of a fire, the BMS must stop the HVAC, close the fire
       shutters, turn on the fire sprinklers, send an alarm, etc.  There are
       typically tens of fire sensors per LC that the BMS needs to manage.
       In this scenario, the measurement interval is 10-50 ms, the
       communication delay is 10 ms, and the availability must be 99.9999%.

    4.2.3.3.  Feedback Control

       BASs utilize feedback control in various ways; the most time-critical
       is control of DC motors, which require a short feedback interval
       (1-5 ms) with low communication delay (10 ms) and jitter (1 ms).  The
       feedback interval depends on the characteristics of the device and on
       the requirements for the control values.  There are typically tens of
       feedback sensors per LC.

       Communication delay is expected to be less than 10 ms and jitter less
       than 1 ms, while the availability must be 99.9999%.

    4.2.4.  BAS Security Considerations

       When BAS field networks were developed, it was assumed that the field
       networks would always be physically isolated from external networks;
       therefore, security was not a concern.  In today's world, many BASs
       are managed remotely and are thus connected to shared IP networks;
       therefore, security is a definite concern.  Note, however, that
       security features are not currently available in the majority of BAS
       field network deployments.

       The management network, being an IP-based network, has the protocols
       available to enable network security, but in practice many BASs do
       not implement even such available security features as device
       authentication or encryption for data in transit.

    4.3.  BASs in the Future

       In the future, lower energy consumption and environmental monitoring
       that is more fine-grained will emerge; these will require more
       sensors and devices, thus requiring larger and more-complex building
       networks.

       Building networks will be connected to or converged with other
       networks (enterprise networks, home networks, and the Internet).

       Therefore, better facilities for network management, control,
       reliability, and security are critical in order to improve resident
       and operator convenience and comfort.  For example, the ability to

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       monitor and control building devices via the Internet would enable
       (for example) control of room lights or HVAC from a resident's
       desktop PC or phone application.

    4.4.  BAS Requests to the IETF

       The community would like to see an interoperable protocol
       specification that can satisfy the timing, security, availability,
       and QoS constraints described above, such that the resulting
       converged network can replace the disparate field networks.  Ideally,
       this connectivity could extend to the open Internet.

       This would imply an architecture that can guarantee

       o  Low communication delays (from <10 ms to 100 ms in a network of
          several hundred devices)

       o  Low jitter (<1 ms)

       o  Tight feedback intervals (1-10 ms)

       o  High network availability (up to 99.9999%)

       o  Availability of network data in disaster scenarios

       o  Authentication between management devices and field devices (both
          local and remote)

       o  Integrity and data origin authentication of communication data
          between management devices and field devices

       o  Confidentiality of data when communicated to a remote device

    5.  Wireless for Industrial Applications

    5.1.  Use Case Description

       Wireless networks are useful for industrial applications -- for
       example, (1) when portable, fast-moving, or rotating objects are
       involved and (2) for the resource-constrained devices found in the
       Internet of Things (IoT).

       Such network-connected sensors, actuators, control loops, etc.
       typically require that the underlying network support real-time QoS,
       as well as such specific network properties as reliability,
       redundancy, and security.

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       These networks may also contain very large numbers of devices -- for
       example, for factories, "big data" acquisition, and the IoT.  Given
       the large numbers of devices installed and the potential
       pervasiveness of the IoT, this is a huge and very cost-sensitive
       market such that small cost reductions can save large amounts of
       money.

    5.1.1.  Network Convergence Using 6TiSCH

       Some wireless network technologies support real-time QoS and are thus
       useful for these kinds of networks, but others do not.

       This use case focuses on one specific wireless network technology
       that provides the required deterministic QoS: "IPv6 over the TSCH
       mode of IEEE 802.15.4e" (6TiSCH, where "TSCH" stands for
       "Time-Slotted Channel Hopping"; see [Arch-for-6TiSCH], [IEEE-802154],
       and [RFC7554]).

       There are other deterministic wireless buses and networks available
       today; however, they are incompatible with each other and with IP
       traffic (for example, see [ISA100] and [WirelessHART]).

       Thus, the primary goal of this use case is to apply 6TiSCH as a
       converged IP-based and standards-based wireless network for
       industrial applications, i.e., to replace multiple proprietary and/or
       incompatible wireless networking and wireless network management
       standards.

    5.1.2.  Common Protocol Development for 6TiSCH

       Today, there are a number of protocols required by 6TiSCH that are
       still in development.  Another goal of this use case is to highlight
       the ways in which these "missing" protocols share goals in common
       with DetNet.  Thus, it is possible that some of the protocol
       technology developed for DetNet will also be applicable to 6TiSCH.

       These protocol goals are identified here, along with their
       relationship to DetNet.  It is likely that ultimately the resulting
       protocols will not be identical but will share design principles that
       contribute to the efficiency of enabling both DetNet and 6TiSCH.

       One such commonality is that -- although on a different time scale --
       in both TSN [IEEE-8021TSNTG] and TSCH, a packet that crosses the
       network from node to node follows a precise schedule, as does a train
       that leaves intermediate stations at precise times along its path.
       This kind of operation reduces collisions, saves energy, and enables
       engineering of the network for deterministic properties.

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       Another commonality is remote monitoring and scheduling management of
       a TSCH network by a Path Computation Element (PCE) and Network
       Management Entity (NME).  The PCE and NME manage timeslots and device
       resources in a manner that minimizes the interaction with, and the
       load placed on, resource-constrained devices.  For example, a tiny
       IoT device may have just enough buffers to store one or a few IPv6
       packets; it will have limited bandwidth between peers such that it
       can maintain only a small amount of peer information, and it will not
       be able to store many packets waiting to be forwarded.  It is
       advantageous, then, for the IoT device to only be required to carry
       out the specific behavior assigned to it by the PCE and NME (as
       opposed to maintaining its own IP stack, for example).

       It is possible that there will be some peer-to-peer communication;
       for example, the PCE may communicate only indirectly with some
       devices in order to enable hierarchical configuration of the system.

       6TiSCH depends on [PCE] and [DetNet-Arch].

       6TiSCH also depends on the fact that DetNet will maintain consistency
       with [IEEE-8021TSNTG].

    5.2.  Wireless Industrial Today

       Today, industrial wireless technology ("wireless industrial") is
       accomplished using multiple deterministic wireless networks that are
       incompatible with each other and with IP traffic.

       6TiSCH is not yet fully specified, so it cannot be used in today's
       applications.

    5.3.  Wireless Industrial in the Future

    5.3.1.  Unified Wireless Networks and Management

       DetNet and 6TiSCH together can enable converged transport of
       deterministic and best-effort traffic flows between real-time
       industrial devices and WANs via IP routing.  A high-level view of
       this type of basic network is shown in Figure 7.

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                   ---+-------- ............ ------------
                      |      External Network       |
                      |                          +-----+
                   +-----+                       | NME |
                   |     | LLN Border            |     |
                   |     | Router                +-----+
                   +-----+
                 o    o   o
          o     o   o     o
             o   o LLN   o    o     o
                o   o   o       o
                        o

          LLN: Low-Power and Lossy Network

                          Figure 7: Basic 6TiSCH Network

       Figure 8 shows a backbone router federating multiple synchronized
       6TiSCH subnets into a single subnet connected to the external
       network.

                      ---+-------- ............ ------------
                         |      External Network       |
                         |                          +-----+
                         |             +-----+      | NME |
                      +-----+          |  +-----+   |     |
                      |     | Router   |  | PCE |   +-----+
                      |     |          +--|     |
                      +-----+             +-----+
                         |                   |
                         | Subnet Backbone   |
                   +--------------------+------------------+
                   |                    |                  |
                +-----+             +-----+             +-----+
                |     | Backbone    |     | Backbone    |     | Backbone
           o    |     | Router      |     | Router      |     | Router
                +-----+             +-----+             +-----+
           o                  o                   o                 o   o
               o    o   o         o   o  o   o         o  o   o    o
          o             o        o  LLN      o      o         o      o
             o   o    o      o      o o     o  o   o    o    o     o

                         Figure 8: Extended 6TiSCH Network

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       The backbone router must ensure end-to-end deterministic behavior
       between the LLN and the backbone.  This should be accomplished in
       conformance with the work done in [DetNet-Arch] with respect to
       Layer 3 aspects of deterministic networks that span multiple Layer 2
       domains.

       The PCE must compute a deterministic path end to end across the TSCH
       network and IEEE 802.1 TSN Ethernet backbone, and DetNet protocols
       are expected to enable end-to-end deterministic forwarding.

    5.3.1.1.  PCE and 6TiSCH ARQ Retries

       6TiSCH uses the Automatic Repeat reQuest (ARQ) mechanism
       [IEEE-802154] to provide higher reliability of packet delivery.  ARQ
       is related to Packet Replication and Elimination (PRE) because there
       are two independent paths for packets to arrive at the destination.
       If an expected packet does not arrive on one path, then it checks for
       the packet on the second path.

       Although to date this mechanism is only used by wireless networks,
       this technique might be appropriate for DetNet, and aspects of the
       enabling protocol could therefore be co-developed.

       For example, in Figure 9, a track is laid out from a field device in
       a 6TiSCH network to an IoT gateway that is located on an IEEE 802.1
       TSN backbone.

                         +-----+
                         | IoT |
                         | G/W |
                         +-----+
                            ^  <---- Elimination
                           | |
            Track Branch   | |
                   +-------+ +--------+ Subnet Backbone
                   |                  |
                +--|--+            +--|--+
                |  |  | Backbone   |  |  | Backbone
           o    |  |  | Router     |  |  | Router
                +--/--+            +--|--+
           o     /    o     o---o----/       o
               o    o---o--/   o      o   o  o   o
          o     \  /     o               o   LLN    o
             o   v  <---- Replication
                 o

                         Figure 9: 6TiSCH Network with PRE

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       In ARQ, the replication function in the field device sends a copy of
       each packet over two different branches, and the PCE schedules each
       hop of both branches so that the two copies arrive in due time at the
       gateway.  In the case of a loss on one branch, one hopes that the
       other copy of the packet will still arrive within the allocated time.
       If two copies make it to the IoT gateway, the elimination function in
       the gateway ignores the extra packet and presents only one copy to
       upper layers.

       At each 6TiSCH hop along the track, the PCE may schedule more than
       one timeslot for a packet, so as to support Layer 2 retries (ARQ).

       At the time of this writing, a deployment's TSCH track does not
       necessarily support PRE but is systematically multipath.  This means
       that a track is scheduled so as to ensure that each hop has at least
       two forwarding solutions.  The forwarding decision will be to try the
       preferred solution and use the other solution in the case of Layer 2
       transmission failure as detected by ARQ.

    5.3.2.  Schedule Management by a PCE

       A common feature of 6TiSCH and DetNet is actions taken by a PCE when
       configuring paths through the network.  Specifically, what is needed
       is a protocol and data model that the PCE will use to get/set the
       relevant configuration from/to the devices, as well as perform
       operations on the devices.  Specifically, both DetNet and 6TiSCH need
       to develop a protocol (and associated data model) that the PCE can
       use to (1) get/set the relevant configuration from/to the devices and
       (2) perform operations on the devices.  These could be initially
       developed by DetNet, with consideration for their reuse by 6TiSCH.
       The remainder of this section provides a bit more context from the
       6TiSCH side.

    5.3.2.1.  PCE Commands and 6TiSCH CoAP Requests

       The 6TiSCH device does not expect to place the request for bandwidth
       between itself and another device in the network.  Rather, an
       operation control system invoked through a human interface specifies
       the traffic requirements and the end nodes (in terms of latency and
       reliability).  Based on this information, the PCE must compute a path
       between the end nodes and provision the network with per-flow state
       that describes the per-hop operation for a given packet, the
       corresponding timeslots, the flow identification that enables
       recognizing that a certain packet belongs to a certain path, etc.

       For a static configuration that serves a certain purpose for a long
       period of time, it is expected that a node will be provisioned in one
       shot with a full schedule, i.e., a schedule that defines the behavior

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       of the node with respect to all data flows through that node. 6TiSCH
       expects that the programming of the schedule will be done over the
       Constrained Application Protocol (CoAP) as discussed in
       [CoAP-6TiSCH].

       6TiSCH expects that the PCE commands will be mapped back and forth
       into CoAP by a gateway function at the edge of the 6TiSCH network.
       For instance, it is possible that a mapping entity on the backbone
       transforms a non-CoAP protocol such as the Path Computation Element
       Communication Protocol (PCEP) into the RESTful interfaces that the
       6TiSCH devices support.  This architecture will be refined to comply
       with DetNet [DetNet-Arch] when the work is formalized.  Related
       information about 6TiSCH can be found in [Interface-6TiSCH-6top] and
       [RFC6550] ("RPL: IPv6 Routing Protocol for Low-Power and Lossy
       Networks").

       A protocol may be used to update the state in the devices during
       runtime -- for example, if it appears that a path through the network
       has ceased to perform as expected, but in 6TiSCH that flow was not
       designed and no protocol was selected.  DetNet should define the
       appropriate end-to-end protocols to be used in that case.  The
       implication is that these state updates take place once the system is
       configured and running, i.e., they are not limited to the initial
       communication of the configuration of the system.

       A "slotFrame" is the base object that a PCE would manipulate to
       program a schedule into an LLN node [Arch-for-6TiSCH].

       The PCE should read energy data from devices and compute paths that
       will implement policies on how energy in devices is consumed -- for
       instance, to ensure that the spent energy does not exceed the
       available energy over a period of time.  Note that this statement
       implies that an extensible protocol for communicating device
       information to the PCE and enabling the PCE to act on it will be part
       of the DetNet architecture; however, for subnets with specific
       protocols (e.g., CoAP), a gateway may be required.

       6TiSCH devices can discover their neighbors over the radio using a
       mechanism such as beacons, but even though the neighbor information
       is available in the 6TiSCH interface data model, 6TiSCH does not
       describe a protocol to proactively push the neighbor information to a
       PCE.  DetNet should define such a protocol; one possible design
       alternative is that it could operate over CoAP.  Alternatively, it
       could be converted to/from CoAP by a gateway.  Such a protocol could
       carry multiple metrics -- for example, metrics similar to those used
       for RPL operations [RFC6551].

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    5.3.2.2.  6TiSCH IP Interface

       Protocol translation between the TSCH MAC layer and IP is
       accomplished via the "6top" sublayer [Sublayer-6TiSCH-6top].  The
       6top data model and management interfaces are further discussed in
       [Interface-6TiSCH-6top] and [CoAP-6TiSCH].

       An IP packet that is sent along a 6TiSCH path uses a differentiated
       services Per-Hop Behavior Group (PHB) called "deterministic
       forwarding", as described in [Det-Fwd-PHB].

    5.3.3.  6TiSCH Security Considerations

       In addition to the classical requirements for protection of control
       signaling, it must be noted that 6TiSCH networks operate on limited
       resources that can be depleted rapidly in a DoS attack on the system
       -- for instance, by placing a rogue device in the network or by
       obtaining management control and setting up unexpected additional
       paths.

    5.4.  Wireless Industrial Requests to the IETF

       6TiSCH depends on DetNet to define:

       o  Configuration (state) and operations for deterministic paths

       o  End-to-end protocols for deterministic forwarding (tagging, IP)

       o  A protocol for PRE

    6.  Cellular Radio

    6.1.  Use Case Description

       This use case describes the application of deterministic networking
       in the context of cellular telecom transport networks.  Important
       elements include time synchronization, clock distribution, and ways
       to establish time-sensitive streams for both Layer 2 and Layer 3
       user-plane traffic.

    6.1.1.  Network Architecture

       Figure 10 illustrates a 3GPP-defined cellular network architecture
       typical at the time of this writing.  The architecture includes
       "Fronthaul", "Midhaul", and "Backhaul" network segments.  The
       "Fronthaul" is the network connecting base stations (Baseband Units
       (BBUs)) to the Remote Radio Heads (RRHs) (also referred to here as
       "antennas").  The "Midhaul" is the network that interconnects base

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       stations (or small-cell sites).  The "Backhaul" is the network or
       links connecting the radio base station sites to the network
       controller/gateway sites (i.e., the core of the 3GPP cellular
       network).

                  Y (RRHs (antennas))
                   \
               Y__  \.--.                   .--.         +------+
                  \_(    `.     +---+     _(    `.       | 3GPP |
           Y------( Front- )----|eNB|----( Back-  )------| core |
                 ( `  .haul )   +---+   ( ` .haul) )     | netw |
                 /`--(___.-'      \      `--(___.-'      +------+
              Y_/     /            \.--.       \
                   Y_/            _(Mid-`.      \
                                 (   haul )      \
                                ( `  .  )  )      \
                                 `--(___.-'\_____+---+    (small-cell sites)
                                       \         |SCe|__Y
                                      +---+      +---+
                                   Y__|eNB|__Y
                                      +---+
                                    Y_/   \_Y ("local" radios)

            Figure 10: Generic 3GPP-Based Cellular Network Architecture

       In Figure 10, "eNB" ("E-UTRAN Node B") is the hardware that is
       connected to the mobile phone network and enables the mobile phone
       network to communicate with mobile handsets [TS36300].  ("E-UTRAN"
       stands for "Evolved Universal Terrestrial Radio Access Network".)

    6.1.2.  Delay Constraints

       The available processing time for Fronthaul networking overhead is
       limited to the available time after the baseband processing of the
       radio frame has completed.  For example, in Long Term Evolution (LTE)
       radio, 3 ms is allocated for the processing of a radio frame, but
       typically the baseband processing uses most of it, allowing only a
       small fraction to be used by the Fronthaul network.  In this example,
       out of 3 ms, the maximum time allocated to the Fronthaul network for
       one-way delay is 250 us, and the existing specification [NGMN-Fronth]
       specifies a maximum delay of only 100 us.  This ultimately determines
       the distance the RRHs can be located from the base stations (e.g.,
       100 us equals roughly 20 km of optical fiber-based transport).
       Allocation options regarding the available time budget between
       processing and transport are currently undergoing heavy discussion in
       the mobile industry.

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       For packet-based transport, the allocated transport time between the
       RRH and the BBU is consumed by node processing, buffering, and
       distance-incurred delay.  An example of the allocated transport time
       is 100 us (from the Common Public Radio Interface [CPRI]).

       The baseband processing time and the available "delay budget" for the
       Fronthaul is likely to change in the forthcoming "5G" due to reduced
       radio round-trip times and other architectural and service
       requirements [NGMN].

       The transport time budget, as noted above, places limitations on the
       distance that RRHs can be located from base stations (i.e., the link
       length).  In the above analysis, it is assumed that the entire
       transport time budget is available for link propagation delay.
       However, the transport time budget can be broken down into three
       components: scheduling/queuing delay, transmission delay, and link
       propagation delay.  Using today's Fronthaul networking technology,
       the queuing, scheduling, and transmission components might become the
       dominant factors in the total transport time, rather than the link
       propagation delay.  This is especially true in cases where the
       Fronthaul link is relatively short and is shared among multiple
       Fronthaul flows -- for example, in indoor and small-cell networks,
       massive Multiple Input Multiple Output (MIMO) antenna networks, and
       split Fronthaul architectures.

       DetNet technology can improve Fronthaul networks by controlling and
       reducing the time required for the queuing, scheduling, and
       transmission operations by properly assigning network resources, thus
       (1) leaving more of the transport time budget available for link
       propagation and (2) enabling longer link lengths.  However, link
       length is usually a predetermined parameter and is not a controllable
       network parameter, since RRH and BBU sites are usually located in
       predetermined locations.  However, the number of antennas in an RRH
       site might increase -- for example, by adding more antennas,
       increasing the MIMO capability of the network, or adding support for
       massive MIMO.  This means increasing the number of Fronthaul flows
       sharing the same Fronthaul link.  DetNet can now control the
       bandwidth assignment of the Fronthaul link and the scheduling of
       Fronthaul packets over this link and can provide adequate buffer
       provisioning for each flow to reduce the packet loss rate.

       Another way in which DetNet technology can aid Fronthaul networks is
       by providing effective isolation between flows -- for example,
       between flows originating in different slices within a network-sliced
       5G network.  Note, however, that this isolation applies to DetNet
       flows for which resources have been preallocated, i.e., it does not
       apply to best-effort flows within a DetNet.  DetNet technology can
       also dynamically control the bandwidth-assignment, scheduling, and

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       packet-forwarding decisions, as well as the buffer provisioning of
       the Fronthaul flows to guarantee the end-to-end delay of the
       Fronthaul packets and minimize the packet loss rate.

       [METIS] documents the fundamental challenges as well as overall
       technical goals of the future 5G mobile and wireless systems as the
       starting point.  These future systems should support much higher data
       volumes and rates and significantly lower end-to-end latency for 100x
       more connected devices (at cost and energy-consumption levels similar
       to today's systems).

       For Midhaul connections, delay constraints are driven by inter-site
       radio functions such as Coordinated Multi-Point (CoMP) processing
       (see [CoMP]).  CoMP reception and transmission constitute a framework
       in which multiple geographically distributed antenna nodes cooperate
       to improve performance for the users served in the common cooperation
       area.  The design principle of CoMP is to extend single-cell-to-
       multi-UE (User Equipment) transmission to a multi-cell-to-multi-UE
       transmission via cooperation among base stations.

       CoMP has delay-sensitive performance parameters: "Midhaul latency"
       and "CSI (Channel State Information) reporting and accuracy".  The
       essential feature of CoMP is signaling between eNBs, so Midhaul
       latency is the dominating limitation of CoMP performance.  Generally,
       CoMP can benefit from coordinated scheduling (either distributed or
       centralized) of different cells if the signaling delay between eNBs
       is within 1-10 ms.  This delay requirement is both rigid and
       absolute, because any uncertainty in delay will degrade performance
       significantly.

       Inter-site CoMP is one of the key requirements for 5G and is also a
       goal for 4.5G network architectures.

    6.1.3.  Time-Synchronization Constraints

       Fronthaul time-synchronization requirements are given by [TS25104],
       [TS36104], [TS36211], and [TS36133].  These can be summarized for the
       3GPP LTE-based networks as:

       Delay accuracy:
          +-8 ns (i.e., +-1/32 Tc, where Tc is the Universal Mobile
          Telecommunications System (UMTS) Chip time of 1/3.84 MHz),
          resulting in a round-trip accuracy of +-16 ns.  The value is this
          low in order to meet the 3GPP Timing Alignment Error (TAE)
          measurement requirements.  Note that performance guarantees of
          low-nanosecond values such as these are considered to be below the
          DetNet layer -- it is assumed that the underlying implementation
          (e.g., the hardware) will provide sufficient support (e.g.,

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          buffering) to enable this level of accuracy.  These values are
          maintained in the use case to give an indication of the overall
          application.

       TAE:
          TAE is problematic for Fronthaul networks and must be minimized.
          If the transport network cannot guarantee TAE levels that are low
          enough, then additional buffering has to be introduced at the
          edges of the network to buffer out the jitter.  Buffering is not
          desirable, as it reduces the total available delay budget.

          Packet Delay Variation (PDV) requirements can be derived from TAE
          measurements for packet-based Fronthaul networks.

          *  For MIMO or TX diversity transmissions, at each carrier
             frequency, TAE measurements shall not exceed 65 ns (i.e.,
             1/4 Tc).

          *  For intra-band contiguous carrier aggregation, with or without
             MIMO or TX diversity, TAE measurements shall not exceed 130 ns
             (i.e., 1/2 Tc).

          *  For intra-band non-contiguous carrier aggregation, with or
             without MIMO or TX diversity, TAE measurements shall not exceed
             260 ns (i.e., 1 Tc).

          *  For inter-band carrier aggregation, with or without MIMO or TX
             diversity, TAE measurements shall not exceed 260 ns.

       Transport link contribution to radio frequency errors:
          +-2 PPB.  This value is considered to be "available" for the
          Fronthaul link out of the total 50 PPB budget reserved for the
          radio interface.  Note that the transport link contributes to
          radio frequency errors for the following reason: at the time of
          this writing, Fronthaul communication is direct communication from
          the radio unit to the RRH.  The RRH is essentially a passive
          device (e.g., without buffering).  The transport drives the
          antenna directly by feeding it with samples, and everything the
          transport adds will be introduced to the radio "as is".  So, if
          the transport causes any additional frequency errors, the errors
          will show up immediately on the radio as well.  Note that
          performance guarantees of low-nanosecond values such as these are
          considered to be below the DetNet layer -- it is assumed that the
          underlying implementation (e.g., the hardware) will provide
          sufficient support to enable this level of performance.  These
          values are maintained in the use case to give an indication of the
          overall application.

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       The above-listed time-synchronization requirements are difficult to
       meet with point-to-point connected networks and are more difficult to
       meet when the network includes multiple hops.  It is expected that
       networks must include buffering at the ends of the connections as
       imposed by the jitter requirements, since trying to meet the jitter
       requirements in every intermediate node is likely to be too costly.
       However, every measure to reduce jitter and delay on the path makes
       it easier to meet the end-to-end requirements.

       In order to meet the timing requirements, both senders and receivers
       must remain time synchronized, demanding very accurate clock
       distribution -- for example, support for IEEE 1588 transparent clocks
       or boundary clocks in every intermediate node.

       In cellular networks from the LTE radio era onward, phase
       synchronization is needed in addition to frequency synchronization
       [TS36300] [TS23401].  Time constraints are also important due to
       their impact on packet loss.  If a packet is delivered too late, then
       the packet may be dropped by the host.

    6.1.4.  Transport-Loss Constraints

       Fronthaul and Midhaul networks assume that transport is almost
       error free.  Errors can cause a reset of the radio interfaces, in
       turn causing reduced throughput or broken radio connectivity for
       mobile customers.

       For packetized Fronthaul and Midhaul connections, packet loss may be
       caused by BER, congestion, or network failure scenarios.  Different
       Fronthaul "functional splits" are being considered by 3GPP, requiring
       strict Frame Loss Ratio (FLR) guarantees.  As one example (referring
       to the legacy CPRI split, which is option 8 in 3GPP), lower-layer
       splits may imply an FLR of less than 10^-7 for data traffic and less
       than 10^-6 for control and management traffic.

       Many of the tools available for eliminating packet loss for Fronthaul
       and Midhaul networks have serious challenges; for example,
       retransmitting lost packets or using FEC to circumvent bit errors (or
       both) is practically impossible, due to the additional delay
       incurred.  Using redundant streams for better guarantees of delivery
       is also practically impossible in many cases, due to high bandwidth
       requirements for Fronthaul and Midhaul networks.  Protection
       switching is also a candidate, but at the time of this writing,
       available technologies for the path switch are too slow to avoid a
       reset of mobile interfaces.

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       It is assumed that Fronthaul links are symmetric.  All Fronthaul
       streams (i.e., those carrying radio data) have equal priority and
       cannot delay or preempt each other.

       All of this implies that it is up to the network to guarantee that
       each time-sensitive flow meets its schedule.

    6.1.5.  Cellular Radio Network Security Considerations

       Establishing time-sensitive streams in the network entails reserving
       networking resources for long periods of time.  It is important that
       these reservation requests be authenticated to prevent malicious
       reservation attempts from hostile nodes (or accidental
       misconfiguration).  This is particularly important in the case where
       the reservation requests span administrative domains.  Furthermore,
       the reservation information itself should be digitally signed to
       reduce the risk of a legitimate node pushing a stale or hostile
       configuration into another networking node.

       Note: This is considered important for the security policy of the
       network but does not affect the core DetNet architecture and design.

    6.2.  Cellular Radio Networks Today

    6.2.1.  Fronthaul

       Today's Fronthaul networks typically consist of:

       o  Dedicated point-to-point fiber connection (common)

       o  Proprietary protocols and framings

       o  Custom equipment and no real networking

       At the time of this writing, solutions for Fronthaul are direct
       optical cables or Wavelength-Division Multiplexing (WDM) connections.

    6.2.2.  Midhaul and Backhaul

       Today's Midhaul and Backhaul networks typically consist of:

       o  Mostly normal IP networks, MPLS-TP, etc.

       o  Clock distribution and synchronization using IEEE 1588 and syncE

       Telecommunications networks in the Midhaul and Backhaul are already
       heading towards transport networks where precise time-synchronization
       support is one of the basic building blocks.  In order to meet

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       bandwidth and cost requirements, most transport networks have already
       transitioned to all-IP packet-based networks; however, highly
       accurate clock distribution has become a challenge.

       In the past, Midhaul and Backhaul connections were typically based on
       TDM and provided frequency-synchronization capabilities as a part of
       the transport media.  More recently, other technologies such as GPS
       or syncE [syncE] have been used.

       Ethernet, IP/MPLS [RFC3031], and pseudowires (as described in
       [RFC3985] ("Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture")
       for legacy transport support)) have become popular tools for building
       and managing new all-IP Radio Access Networks (RANs)
       [SR-IP-RAN-Use-Case].  Although various timing and synchronization
       optimizations have already been proposed and implemented, including
       PTP enhancements [IEEE-1588] (see also [Timing-over-MPLS] and
       [RFC8169]), these solutions are not necessarily sufficient for the
       forthcoming RAN architectures, nor do they guarantee the more
       stringent time-synchronization requirements such as [CPRI].

       Existing solutions for TDM over IP include those discussed in
       [RFC4553], [RFC5086], and [RFC5087]; [MEF8] addresses TDM over
       Ethernet transports.

    6.3.  Cellular Radio Networks in the Future

       Future cellular radio networks will be based on a mix of different
       xHaul networks (xHaul = Fronthaul, Midhaul, and Backhaul), and future
       transport networks should be able to support all of them
       simultaneously.  It is already envisioned today that:

       o  Not all "cellular radio network" traffic will be IP; for example,
          some will remain at Layer 2 (e.g., Ethernet based).  DetNet
          solutions must address all traffic types (Layer 2 and Layer 3)
          with the same tools and allow their transport simultaneously.

       o  All types of xHaul networks will need some types of DetNet
          solutions.  For example, with the advent of 5G, some Backhaul
          traffic will also have DetNet requirements (for example, traffic
          belonging to time-critical 5G applications).

       o  Different functional splits between the base stations and the
          on-site units could coexist on the same Fronthaul and Backhaul
          network.

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       Future cellular radio networks should contain the following:

       o  Unified standards-based transport protocols and standard
          networking equipment that can make use of underlying deterministic
          link-layer services

       o  Unified and standards-based network management systems and
          protocols in all parts of the network (including Fronthaul)

       New RAN deployment models and architectures may require TSN services
       with strict requirements on other parts of the network that
       previously were not considered to be packetized at all.  Time and
       synchronization support are already topical for Backhaul and Midhaul
       packet networks [MEF22.1.1] and are also becoming a real issue for
       Fronthaul networks.  Specifically, in Fronthaul networks, the timing
       and synchronization requirements can be extreme for packet-based
       technologies -- for example, on the order of a PDV of +-20 ns or less
       and frequency accuracy of +-0.002 PPM [Fronthaul].

       The actual transport protocols and/or solutions for establishing
       required transport "circuits" (pinned-down paths) for Fronthaul
       traffic are still undefined.  Those protocols are likely to include
       (but are not limited to) solutions directly over Ethernet, over IP,
       and using MPLS/pseudowire transport.

       Interesting and important work for TSN has been done for Ethernet
       [IEEE-8021TSNTG]; this work specifies the use of PTP [IEEE-1588] in
       the context of IEEE 802.1D and IEEE 802.1Q.  [IEEE-8021AS] specifies
       a Layer 2 time-synchronizing service, and other specifications such
       as IEEE 1722 [IEEE-1722] specify Ethernet-based Layer 2 transport for
       time-sensitive streams.

       However, even these Ethernet TSN features may not be sufficient for
       Fronthaul traffic.  Therefore, having specific profiles that take
       Fronthaul requirements into account is desirable [IEEE-8021CM].

       New promising work seeks to enable the transport of time-sensitive
       Fronthaul streams in Ethernet bridged networks [IEEE-8021CM].
       Analogous to IEEE 1722, standardization efforts in the IEEE 1914.3
       Task Force [IEEE-19143] to define the Layer 2 transport encapsulation
       format for transporting Radio over Ethernet (RoE) are ongoing.

       As mentioned in Section 6.1.2, 5G communications will provide one of
       the most challenging cases for delay-sensitive networking.  In order
       to meet the challenges of ultra-low latency and ultra-high
       throughput, 3GPP has studied various functional splits for 5G, i.e.,
       physical decomposition of the 5G "gNodeB" base station and deployment
       of its functional blocks in different locations [TR38801].

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       These splits are numbered from split option 1 (dual connectivity, a
       split in which the radio resource control is centralized and other
       radio stack layers are in distributed units) to split option 8 (a
       PHY-RF split in which RF functionality is in a distributed unit and
       the rest of the radio stack is in the centralized unit), with each
       intermediate split having its own data-rate and delay requirements.
       Packetized versions of different splits have been proposed, including
       enhanced CPRI (eCPRI) [eCPRI] and RoE (as previously noted).  Both
       provide Ethernet encapsulations, and eCPRI is also capable of IP
       encapsulation.

       All-IP RANs and xHaul networks would benefit from time
       synchronization and time-sensitive transport services.  Although
       Ethernet appears to be the unifying technology for the transport,
       there is still a disconnect when it comes to providing Layer 3
       services.  The protocol stack typically has a number of layers below
       Ethernet Layer 2 that might be "visible" to Layer 3.  In a fairly
       common scenario, on top of the lowest-layer (optical) transport is
       the first (lowest) Ethernet layer, then one or more layers of MPLS,
       pseudowires, and/or other tunneling protocols, and finally one or
       more Ethernet layers that are visible to Layer 3.

       Although there exist technologies for establishing circuits through
       the routed and switched networks (especially in the MPLS/PWE space),
       there is still no way to signal the time-synchronization and
       time-sensitive stream requirements/reservations for Layer 3 flows in
       a way that addresses the entire transport stack, including the
       Ethernet layers that need to be configured.

       Furthermore, not all "user-plane" traffic will be IP.  Therefore, the
       solution in question also must address the use cases where the
       user-plane traffic is on a different layer (for example, Ethernet
       frames).

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    6.4.  Cellular Radio Networks Requests to the IETF

       A standard for data-plane transport specifications that is:

       o  Unified among all xHauls (meaning that different flows with
          diverse DetNet requirements can coexist in the same network and
          traverse the same nodes without interfering with each other)

       o  Deployed in a highly deterministic network environment

       o  Capable of supporting multiple functional splits simultaneously,
          including existing Backhaul and CPRI Fronthaul, and (potentially)
          new modes as defined, for example, in 3GPP; these goals can be
          supported by the existing DetNet use case "common themes"
          (Section 11); of special note are Sections 11.1.8 ("Mix of
          Deterministic and Best-Effort Traffic"), 11.3.1 ("Bounded
          Latency"), 11.3.2 ("Low Latency"), 11.3.4 ("Symmetrical Path
          Delays"), and 11.6 ("Deterministic Flows")

       o  Capable of supporting network slicing and multi-tenancy; these
          goals can be supported by the same DetNet themes noted above

       o  Capable of transporting both in-band and out-of-band control
          traffic (e.g., Operations, Administration, and Maintenance (OAM)
          information)

       o  Deployable over multiple data-link technologies (e.g., IEEE 802.3,
          mmWave)

       A standard for data-flow information models that is:

       o  Aware of the time sensitivity and constraints of the target
          networking environment

       o  Aware of underlying deterministic networking services (e.g., on
          the Ethernet layer)

    7.  Industrial Machine to Machine (M2M)

    7.1.  Use Case Description

       "Industrial automation" in general refers to automation of
       manufacturing, quality control, and material processing.  This M2M
       use case focuses on machine units on a plant floor that periodically
       exchange data with upstream or downstream machine modules and/or a
       supervisory controller within a LAN.

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       PLCs are the "actors" in M2M communications.  Communication between
       PLCs, and between PLCs and the supervisory PLC (S-PLC), is achieved
       via critical control/data streams (Figure 11).

                  S (Sensor)
                   \                                  +-----+
             PLC__  \.--.                   .--.   ---| MES |
                  \_(    `.               _(    `./   +-----+
           A------( Local  )-------------(  L2    )
                 (      Net )           (      Net )    +-------+
                 /`--(___.-'             `--(___.-' ----| S-PLC |
              S_/     /       PLC   .--. /              +-------+
                   A_/           \_(    `.
                (Actuator)       (  Local )
                                (       Net )
                                 /`--(___.-'\
                                /       \    A
                               S         A

          Figure 11: Current Generic Industrial M2M Network Architecture

       This use case focuses on PLC-related communications; communication to
       Manufacturing Execution Systems (MESs) are not addressed.

       This use case covers only critical control/data streams; non-critical
       traffic between industrial automation applications (such as
       communication of state, configuration, setup, and database
       communication) is adequately served by prioritizing techniques
       available at the time of this writing.  Such traffic can use up to
       80% of the total bandwidth required.  There is also a subset of
       non-time-critical traffic that must be reliable even though it is not
       time sensitive.

       In this use case, deterministic networking is primarily needed to
       provide end-to-end delivery of M2M messages within specific timing
       constraints -- for example, in closed-loop automation control.
       Today, this level of determinism is provided by proprietary
       networking technologies.  In addition, standard networking
       technologies are used to connect the local network to remote
       industrial automation sites, e.g., over an enterprise or metro
       network that also carries other types of traffic.  Therefore, flows
       that should be forwarded with deterministic guarantees need to be
       sustained, regardless of the amount of other flows in those networks.

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    7.2.  Industrial M2M Communications Today

       Today, proprietary networks fulfill the needed timing and
       availability for M2M networks.

       The network topologies used today by industrial automation are
       similar to those used by telecom networks: daisy chain, ring,
       hub-and-spoke, and "comb" (a subset of daisy chain).

       PLC-related control/data streams are transmitted periodically and
       carry either a preconfigured payload or a payload configured during
       runtime.

       Some industrial applications require time synchronization at the end
       nodes.  For such time-coordinated PLCs, accuracy of 1 us is required.
       Even in the case of "non-time-coordinated" PLCs, time synchronization
       may be needed, e.g., for timestamping of sensor data.

       Industrial-network scenarios require advanced security solutions.  At
       the time of this writing, many industrial production networks are
       physically separated.  Filtering policies that are typically enforced
       in firewalls are used to prevent critical flows from being leaked
       outside a domain.

    7.2.1.  Transport Parameters

       The cycle time defines the frequency of message(s) between industrial
       actors.  The cycle time is application dependent, in the range of
       1-100 ms for critical control/data streams.

       Because industrial applications assume that deterministic transport
       will be used for critical control-data-stream parameters (instead of
       having to define latency and delay-variation parameters), it is
       sufficient to fulfill requirements regarding the upper bound of
       latency (maximum latency).  The underlying networking infrastructure
       must ensure a maximum end-to-end message delivery time in the range
       of 100 us to 50 ms, depending on the control-loop application.

       The bandwidth requirements of control/data streams are usually
       calculated directly from the bytes-per-cycle parameter of the control
       loop.  For PLC-to-PLC communication, one can expect 2-32 streams with
       packet sizes in the range of 100-700 bytes.  For S-PLC-to-PLC
       communication, the number of streams is higher -- up to 256 streams.
       Usually, no more than 20% of available bandwidth is used for
       critical control/data streams.  In today's networks, 1 Gbps links
       are commonly used.

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       Most PLC control loops are rather tolerant of packet loss; however,
       critical control/data streams accept a loss of no more than one
       packet per consecutive communication cycle (i.e., if a packet gets
       lost in cycle "n", then the next cycle ("n+1") must be lossless).
       After the loss of two or more consecutive packets, the network may be
       considered to be "down" by the application.

       As network downtime may impact the whole production system, the
       required network availability is rather high (99.999%).

       Based on the above parameters, some form of redundancy will be
       required for M2M communications; however, any individual solution
       depends on several parameters, including cycle time and
       delivery time.

    7.2.2.  Stream Creation and Destruction

       In an industrial environment, critical control/data streams are
       created rather infrequently, on the order of ~10 times per
       day/week/month.  Most of these critical control/data streams get
       created at machine startup; however, flexibility is also needed
       during runtime -- for example, when adding or removing a machine.  As
       production systems become more flexible going forward, there will be
       a significant increase in the rate at which streams are created,
       changed, and destroyed.

    7.3.  Industrial M2M in the Future

       We foresee a converged IP-standards-based network with deterministic
       properties that can satisfy the timing, security, and reliability
       constraints described above.  Today's proprietary networks could then
       be interfaced to such a network via gateways; alternatively, in the
       case of new installations, devices could be connected directly to the
       converged network.

       For this use case, time-synchronization accuracy on the order of 1 us
       is expected.

    7.4.  Industrial M2M Requests to the IETF

       o  Converged IP-based network

       o  Deterministic behavior (bounded latency and jitter)

       o  High availability (presumably through redundancy) (99.999%)

       o  Low message delivery time (100 us to 50 ms)

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       o  Low packet loss (with a bounded number of consecutive lost
          packets)

       o  Security (e.g., preventing critical flows from being leaked
          between physically separated networks)

    8.  Mining Industry

    8.1.  Use Case Description

       The mining industry is highly dependent on networks to monitor and
       control their systems, in both open-pit and underground extraction as
       well as in transport and refining processes.  In order to reduce
       risks and increase operational efficiency in mining operations, the
       location of operators has been relocated (as much as possible) from
       the extraction site to remote control and monitoring sites.

       In the case of open-pit mining, autonomous trucks are used to
       transport the raw materials from the open pit to the refining factory
       where the final product (e.g., copper) is obtained.  Although the
       operation is autonomous, the tracks are remotely monitored from a
       central facility.

       In pit mines, the monitoring of the tailings or mine dumps is
       critical in order to minimize environmental pollution.  In the past,
       monitoring was conducted through manual inspection of preinstalled
       dataloggers.  Cabling is not typically used in such scenarios, due to
       its high cost and complex deployment requirements.  At the time of
       this writing, wireless technologies are being employed to monitor
       these cases permanently.  Slopes are also monitored in order to
       anticipate possible mine collapse.  Due to the unstable terrain,
       cable maintenance is costly and complex; hence, wireless technologies
       are employed.

       In the case of underground monitoring, autonomous vehicles with
       extraction tools travel independently through the tunnels, but their
       operational tasks (such as excavation, stone-breaking, and transport)
       are controlled remotely from a central facility.  This generates
       upstream video and feedback traffic plus downstream actuator-control
       traffic.

    8.2.  Mining Industry Today

       At the time of this writing, the mining industry uses a
       packet-switched architecture supported by high-speed Ethernet.
       However, in order to comply with requirements regarding delay and
       packet loss, the network bandwidth is overestimated.  This results in
       very low efficiency in terms of resource usage.

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       QoS is implemented at the routers to separate video, management,
       monitoring, and process-control traffic for each stream.

       Since mobility is involved in this process, the connections between
       the backbone and the mobile devices (e.g., trucks, trains, and
       excavators) are implemented using a wireless link.  These links are
       based on IEEE 802.11 [IEEE-80211] for open-pit mining and "leaky
       feeder" communications for underground mining.  (A "leaky feeder"
       communication system consists of a coaxial cable, run along tunnels,
       that emits and receives radio waves, functioning as an extended
       antenna.  The cable is "leaky" in that it has gaps or slots in its
       outer conductor to allow the radio signal to leak into or out of the
       cable along its entire length.)

       Lately, in pit mines the use of Low-Power WAN (LPWAN) technologies
       has been extended: tailings, slopes, and mine dumps are monitored by
       battery-powered dataloggers that make use of robust long-range radio
       technologies.  Reliability is usually ensured through retransmissions
       at Layer 2.  Gateways or concentrators act as bridges, forwarding the
       data to the backbone Ethernet network.  Deterministic requirements
       are biased towards reliability rather than latency, as events are
       triggered slowly or can be anticipated in advance.

       At the mineral-processing stage, conveyor belts and refining
       processes are controlled by a SCADA system that provides an
       in-factory delay-constrained networking environment.

       At the time of this writing, voice communications are served by a
       redundant trunking infrastructure, independent from data networks.

    8.3.  Mining Industry in the Future

       Mining operations and management are converging towards a combination
       of autonomous operation and teleoperation of transport and extraction
       machines.  This means that video, audio, monitoring, and process-
       control traffic will increase dramatically.  Ideally, all activities
       at the mine will rely on network infrastructure.

       Wireless for open-pit mining is already a reality with LPWAN
       technologies; it is expected to evolve to more-advanced LPWAN
       technologies, such as those based on LTE, to increase last-hop
       reliability or novel LPWAN flavors with deterministic access.

       One area in which DetNet can improve this use case is in the wired
       networks that make up the "backbone network" of the system.  These
       networks connect many wireless Access Points (APs) together.  The
       mobile machines (which are connected to the network via wireless)

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       transition from one AP to the next as they move about.  A
       deterministic, reliable, low-latency backbone can enable these
       transitions to be more reliable.

       Connections that extend all the way from the base stations to the
       machinery via a mix of wired and wireless hops would also be
       beneficial -- for example, to improve the responsiveness of digging
       machines to remote control.  However, to guarantee deterministic
       performance of a DetNet, the end-to-end underlying network must be
       deterministic.  Thus, for this use case, if a deterministic wireless
       transport is integrated with a wire-based DetNet network, it could
       create the desired wired plus wireless end-to-end deterministic
       network.

    8.4.  Mining Industry Requests to the IETF

       o  Improved bandwidth efficiency

       o  Very low delay, to enable machine teleoperation

       o  Dedicated bandwidth usage for high-resolution video streams

       o  Predictable delay, to enable real-time monitoring

       o  Potential for constructing a unified DetNet network over a
          combination of wired and deterministic wireless links

    9.  Private Blockchain

    9.1.  Use Case Description

       Blockchain was created with Bitcoin as a "public" blockchain on the
       open Internet; however, blockchain has also spread far beyond its
       original host into various industries, such as smart manufacturing,
       logistics, security, legal rights, and others.  In these industries,
       blockchain runs in designated and carefully managed networks in which
       deterministic networking requirements could be addressed by DetNet.
       Such implementations are referred to as "private" blockchain.

       The sole distinction between public and private blockchain is defined
       by who is allowed to participate in the network, execute the
       consensus protocol, and maintain the shared ledger.

       Today's networks manage the traffic from blockchain on a best-effort
       basis, but blockchain operation could be made much more efficient if
       deterministic networking services were available to minimize latency
       and packet loss in the network.

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    9.1.1.  Blockchain Operation

       A "block" runs as a container of a batch of primary items (e.g.,
       transactions, property records).  The blocks are chained in such a
       way that the hash of the previous block works as the pointer to the
       header of the new block.  Confirmation of each block requires a
       consensus mechanism.  When an item arrives at a blockchain node, the
       latter broadcasts this item to the rest of the nodes, which receive
       it, verify it, and put it in the ongoing block.  The block
       confirmation process begins as the number of items reaches the
       predefined block capacity, at which time the node broadcasts its
       proved block to the rest of the nodes, to be verified and chained.
       The result is that block N+1 of each chain transitively vouches for
       blocks N and previous of that chain.

    9.1.2.  Blockchain Network Architecture

       Blockchain node communication and coordination are achieved mainly
       through frequent point-to-multipoint communication; however,
       persistent point-to-point connections are used to transport both the
       items and the blocks to the other nodes.  For example, consider the
       following implementation.

       When a node is initiated, it first requests the other nodes'
       addresses from a specific entity, such as DNS.  The node then creates
       persistent connections with each of the other nodes.  If a node
       confirms an item, it sends the item to the other nodes via these
       persistent connections.

       As a new block in a node is completed and is proven by the
       surrounding nodes, it propagates towards its neighbor nodes.  When
       node A receives a block, it verifies it and then sends an invite
       message to its neighbor B.  Neighbor B checks to see if the
       designated block is available and responds to A if it is unavailable;
       A then sends the complete block to B.  B repeats the process (as was
       done by A) to start the next round of block propagation.

       The challenge of blockchain network operation is not overall data
       rates, since the volume from both the block and the item stays
       between hundreds of bytes and a couple of megabytes per second;
       rather, the challenge is in transporting the blocks with minimum
       latency to maximize the efficiency of the blockchain consensus
       process.  The efficiency of differing implementations of the
       consensus process may be affected to a differing degree by the
       latency (and variation of latency) of the network.

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    9.1.3.  Blockchain Security Considerations

       Security is crucial to blockchain applications; at the time of this
       writing, blockchain systems address security issues mainly at the
       application level, where cryptography as well as hash-based consensus
       play a leading role in preventing both double-spending and malicious
       service attacks.  However, there is concern that in the proposed use
       case for a private blockchain network that is dependent on
       deterministic properties the network could be vulnerable to delays
       and other specific attacks against determinism, as these delays and
       attacks could interrupt service.

    9.2.  Private Blockchain Today

       Today, private blockchain runs in Layer 2 or Layer 3 VPNs, generally
       without guaranteed determinism.  The industry players are starting to
       realize that improving determinism in their blockchain networks could
       improve the performance of their service, but at present these goals
       are not being met.

    9.3.  Private Blockchain in the Future

       Blockchain system performance can be greatly improved through
       deterministic networking services, primarily because low latency
       would accelerate the consensus process.  It would be valuable to be
       able to design a private blockchain network with the following
       properties:

       o  Transport of point-to-multipoint traffic in a coordinated network
          architecture rather than at the application layer (which typically
          uses point-to-point connections)

       o  Guaranteed transport latency

       o  Reduced packet loss (to the point where delay incurred by packet
          retransmissions would be negligible)

    9.4.  Private Blockchain Requests to the IETF

       o  Layer 2 and Layer 3 multicast of blockchain traffic

       o  Item and block delivery with bounded, low latency and negligible
          packet loss

       o  Coexistence of blockchain and IT traffic in a single network

       o  Ability to scale the network by distributing the centralized
          control of the network across multiple control entities

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    10.  Network Slicing

    10.1.  Use Case Description

       Network slicing divides one physical network infrastructure into
       multiple logical networks.  Each slice, which corresponds to a
       logical network, uses resources and network functions independently
       from each other.  Network slicing provides flexibility of resource
       allocation and service quality customization.

       Future services will demand network performance with a wide variety
       of characteristics such as high data rate, low latency, low loss
       rate, security, and many other parameters.  Ideally, every service
       would have its own physical network satisfying its particular
       performance requirements; however, that would be prohibitively
       expensive.  Network slicing can provide a customized slice for a
       single service, and multiple slices can share the same physical
       network.  This method can optimize performance for the service at
       lower cost, and the flexibility of setting up and releasing the
       slices also allows the user to allocate network resources
       dynamically.

       Unlike the other use cases presented here, network slicing is not a
       specific application that depends on specific deterministic
       properties; rather, it is introduced as an area of networking to
       which DetNet might be applicable.

    10.2.  DetNet Applied to Network Slicing

    10.2.1.  Resource Isolation across Slices

       One of the requirements discussed for network slicing is the "hard"
       separation of various users' deterministic performance.  That is, it
       should be impossible for activity, lack of activity, or changes in
       activity of one or more users to have any appreciable effect on the
       deterministic performance parameters of any other slices.  Typical
       techniques used today, which share a physical network among users, do
       not offer this level of isolation.  DetNet can supply point-to-point
       or point-to-multipoint paths that offer a user bandwidth and latency
       guarantees that cannot be affected by other users' data traffic.
       Thus, DetNet is a powerful tool when reliability and low latency are
       required in network slicing.

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    10.2.2.  Deterministic Services within Slices

       Slices may need to provide services with DetNet-type performance
       guarantees; note, however, that a system can be implemented to
       provide such services in more than one way.  For example, the slice
       itself might be implemented using DetNet, and thus the slice can
       provide service guarantees and isolation to its users without any
       particular DetNet awareness on the part of the users' applications.
       Alternatively, a "non-DetNet-aware" slice may host an application
       that itself implements DetNet services and thus can enjoy similar
       service guarantees.

    10.3.  A Network Slicing Use Case Example - 5G Bearer Network

       Network slicing is a core feature of 5G as defined in 3GPP.  The
       system architecture for 5G is under development at the time of this
       writing [TS23501].  A network slice in a mobile network is a complete
       logical network, including RANs and Core Networks (CNs).  It provides
       telecommunications services and network capabilities, which may vary
       from slice to slice.  A 5G bearer network is a typical use case for
       network slicing; for example, consider three 5G service scenarios:
       eMBB, URLLC, and mMTC.

       o  eMBB (Enhanced Mobile Broadband) focuses on services characterized
          by high data rates, such as high-definition video, Virtual Reality
          (VR), augmented reality, and fixed mobile convergence.

       o  URLLC (Ultra-Reliable and Low Latency Communications) focuses on
          latency-sensitive services, such as self-driving vehicles, remote
          surgery, or drone control.

       o  mMTC (massive Machine Type Communications) focuses on services
          that have high connection-density requirements, such as those
          typically used in smart-city and smart-agriculture scenarios.

       A 5G bearer network could use DetNet to provide hard resource
       isolation across slices and within a given slice.  For example,
       consider Slice-A and Slice-B, with DetNet used to transit services
       URLLC-A and URLLC-B over them.  Without DetNet, URLLC-A and URLLC-B
       would compete for bandwidth resources, and latency and reliability
       requirements would not be guaranteed.  With DetNet, URLLC-A and
       URLLC-B have separate bandwidth reservations; there is no resource
       conflict between them, as though they were in different physical
       networks.

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    10.4.  Non-5G Applications of Network Slicing

       Although the operation of services not related to 5G is not part of
       the 5G network slicing definition and scope, network slicing is
       likely to become a preferred approach for providing various services
       across a shared physical infrastructure.  Examples include providing
       services for electrical utilities and pro audio via slices.  Use
       cases like these could become more common once the work for the 5G CN
       evolves to include wired as well as wireless access.

    10.5.  Limitations of DetNet in Network Slicing

       DetNet cannot cover every network slicing use case.  One issue is
       that DetNet is a point-to-point or point-to-multipoint technology;
       however, network slicing ultimately needs multipoint-to-multipoint
       guarantees.  Another issue is that the number of flows that can be
       carried by DetNet is limited by DetNet scalability; flow aggregation
       and queuing management modification may help address this issue.
       Additional work and discussion are needed to address these topics.

    10.6.  Network Slicing Today and in the Future

       Network slicing has promise in terms of satisfying many requirements
       of future network deployment scenarios, but it is still a collection
       of ideas and analyses without a specific technical solution.  DetNet
       is one of various technologies that could potentially be used in
       network slicing, along with, for example, Flex-E and segment routing.
       For more information, please see the IETF 99 Network Slicing BoF
       session agenda and materials as provided in [IETF99-netslicing-BoF].

    10.7.  Network Slicing Requests to the IETF

       o  Isolation from other flows through queuing management

       o  Service quality customization and guarantees

       o  Security

    Grossman                      Informational                    [Page 75]

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    11.  Use Case Common Themes

       This section summarizes the expected properties of a DetNet network,
       based on the use cases as described in this document.

    11.1.  Unified, Standards-Based Networks

    11.1.1.  Extensions to Ethernet

       A DetNet network is not "a new kind of network" -- it is based on
       extensions to existing Ethernet standards, including elements of
       IEEE 802.1 TSN and related standards.  Presumably, it will be
       possible to run DetNet over other underlying transports besides
       Ethernet, but Ethernet is explicitly supported.

    11.1.2.  Centrally Administered Networks

       In general, a DetNet network is not expected to be "plug and play";
       rather, some type of centralized network configuration and control
       system is expected.  Such a system may be in a single central
       location, or it may be distributed across multiple control entities
       that function together as a unified control system for the network.
       However, the ability to "hot swap" components (e.g., due to
       malfunction) is similar enough to "plug and play" that this kind of
       behavior may be expected in DetNet networks, depending on the
       implementation.

    11.1.3.  Standardized Data-Flow Information Models

       Data-flow information models to be used with DetNet networks are to
       be specified by DetNet.

    11.1.4.  Layer 2 and Layer 3 Integration

       A DetNet network is intended to integrate between Layer 2 (bridged)
       network(s) (e.g., an AVB/TSN LAN) and Layer 3 (routed) network(s)
       (e.g., using IP-based protocols).  One example of this is making
       AVB/TSN-type deterministic performance available from Layer 3
       applications, e.g., using RTP.  Another example is connecting two
       AVB/TSN LANs ("islands") together through a standard router.

    11.1.5.  IPv4 Considerations

       This document explicitly does not specify any particular
       implementation or protocol; however, it has been observed that
       various use cases (and their associated industries) described herein
       are explicitly based on IPv4 (as opposed to IPv6), and it is not
       considered practical to expect such implementations to migrate to

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       IPv6 in order to use DetNet.  Thus, the expectation is that even if
       not every feature of DetNet is available in an IPv4 context, at least
       some of the significant benefits (such as guaranteed end-to-end
       delivery and low latency) will be available.

    11.1.6.  Guaranteed End-to-End Delivery

       Packets in a DetNet flow are guaranteed not to be dropped by the
       network due to congestion.  However, the network may drop packets for
       intended reasons, e.g., per security measures.  Similarly,
       best-effort traffic on a DetNet is subject to being dropped (as on a
       non-DetNet IP network).  Also note that this guarantee applies to
       actions taken by DetNet protocol software and does not provide any
       guarantee against lower-level errors such as media errors or checksum
       errors.

    11.1.7.  Replacement for Multiple Proprietary Deterministic Networks

       There are many proprietary non-interoperable deterministic Ethernet-
       based networks available; DetNet is intended to provide an
       open-standards-based alternative to such networks.

    11.1.8.  Mix of Deterministic and Best-Effort Traffic

       DetNet is intended to support the coexistence of time-sensitive
       operational (OT) traffic and informational (IT) traffic on the same
       ("unified") network.

    11.1.9.  Unused Reserved Bandwidth to Be Available to Best-Effort
             Traffic

       If bandwidth reservations are made for a stream but the associated
       bandwidth is not used at any point in time, that bandwidth is made
       available on the network for best-effort traffic.  If the owner of
       the reserved stream then starts transmitting again, the bandwidth is
       no longer available for best-effort traffic; this occurs on a
       moment-to-moment basis.  Note that such "temporarily available"
       bandwidth is not available for time-sensitive traffic, which must
       have its own reservation.

    11.1.10.  Lower-Cost, Multi-Vendor Solutions

       The DetNet network specifications are intended to enable an ecosystem
       in which multiple vendors can create interoperable products, thus
       promoting device diversity and potentially higher numbers of each
       device manufactured, promoting cost reduction and cost competition

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       among vendors.  In other words, vendors should be able to create
       DetNet networks at lower cost and with greater diversity of available
       devices than existing proprietary networks.

    11.2.  Scalable Size

       DetNet networks range in size from very small (e.g., inside a single
       industrial machine) to very large (e.g., a utility-grid network
       spanning a whole country and involving many "hops" over various kinds
       of links -- for example, radio repeaters, microwave links, or fiber
       optic links).  However, recall that the scope of DetNet is confined
       to networks that are centrally administered and thereby explicitly
       excludes unbounded decentralized networks such as the Internet.

    11.2.1.  Scalable Number of Flows

       The number of flows in a given network application can potentially be
       large and can potentially grow faster than the number of nodes and
       hops, so the network should provide a sufficient (perhaps
       configurable) maximum number of flows for any given application.

    11.3.  Scalable Timing Parameters and Accuracy

    11.3.1.  Bounded Latency

       DetNet data-flow information models are expected to provide means to
       configure the network that include parameters for querying network
       path latency, requesting bounded latency for a given stream,
       requesting worst-case maximum and/or minimum latency for a given path
       or stream, and so on.  It is expected that the network may not be
       able to provide a given requested service level; if this is indeed
       the case, the network control system should reply that the requested
       services are not available (as opposed to accepting the parameter but
       then not delivering the desired behavior).

    11.3.2.  Low Latency

       Various applications may state that they require "extremely low
       latency"; however, depending on the application, "extremely low" may
       imply very different latency bounds.  For example, "low latency"
       across a utility-grid network is a different order of magnitude of
       latency values compared to "low latency" in a motor control loop in a
       small machine.  It is intended that the mechanisms for specifying
       desired latency include wide ranges and that architecturally there is
       nothing to prevent arbitrarily low latencies from being implemented
       in a given network.

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    11.3.3.  Bounded Jitter (Latency Variation)

       As with the other latency-related elements noted above, parameters
       that can determine or request permitted variations in latency should
       be available.

    11.3.4.  Symmetrical Path Delays

       Some applications would like to specify that the transit delay time
       values be equal for both the transmit path and the return path.

    11.4.  High Reliability and Availability

       Reliability is of critical importance to many DetNet applications,
       because the consequences of failure can be extraordinarily high in
       terms of cost and even human life.  DetNet-based systems are expected
       to be implemented with essentially arbitrarily high availability --
       for example, 99.9999% uptime (where 99.9999 means "six nines") or
       even 12 nines.  DetNet designs should not make any assumptions about
       the level of reliability and availability that may be required of a
       given system and should define parameters for communicating these
       kinds of metrics within the network.

       A strategy used by DetNet for providing such extraordinarily high
       levels of reliability is to provide redundant paths so that a system
       can seamlessly switch between the paths while maintaining its
       required level of performance.

    11.5.  Security

       Security is of critical importance to many DetNet applications.  A
       DetNet network must have the ability to be made secure against device
       failures, attackers, misbehaving devices, and so on.  In a DetNet
       network, the data traffic is expected to be time sensitive; thus, in
       addition to arriving with the data content as intended, the data must
       also arrive at the expected time.  This may present "new" security
       challenges to implementers and must be addressed accordingly.  There
       are other security implications, including (but not limited to) the
       change in attack surface presented by PRE.

    11.6.  Deterministic Flows

       Reserved-bandwidth data flows must be isolated from each other and
       from best-effort traffic, so that even if the network is saturated
       with best-effort (and/or reserved-bandwidth) traffic, the configured
       flows are not adversely affected.

    Grossman                      Informational                    [Page 79]

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    12.  Security Considerations

       This document covers a number of representative applications and
       network scenarios that are expected to make use of DetNet
       technologies.  Each of the potential DetNet use cases will have
       security considerations from both the use-specific perspective and
       the DetNet technology perspective.  While some use-specific security
       considerations are discussed above, a more comprehensive discussion
       of such considerations is captured in [DetNet-Security]
       ("Deterministic Networking (DetNet) Security Considerations").
       Readers are encouraged to review [DetNet-Security] to gain a more
       complete understanding of DetNet-related security considerations.

    13.  IANA Considerations

       This document has no IANA actions.

    14.  Informative References

       [Ahm14]    Ahmed, M. and R. Kim, "Communication Network Architectures
                  for Smart-Wind Power Farms", Energies 2014, pp. 3900-3921,
                  DOI 10.3390/en7063900, June 2014.

       [Arch-for-6TiSCH]
                  Thubert, P., Ed., "An Architecture for IPv6 over the TSCH
                  mode of IEEE 802.15.4", Work in Progress,
                  draft-ietf-6tisch-architecture-20, March 2019.

       [BACnet-IP]
                  ASHRAE, "Annex J to ANSI/ASHRAE 135-1995 - BACnet/IP",
                  January 1999, <http://www.bacnet.org/Addenda/
                  Add-1995-135a.pdf>.

       [BAS-DetNet]
                  Kaneko, Y. and S. Das, "Building Automation Use Cases and
                  Requirements for Deterministic Networking", Work in
                  Progress, draft-bas-usecase-detnet-00, October 2015.

       [CoAP-6TiSCH]
                  Sudhaakar, R., Ed. and P. Zand, "6TiSCH Resource
                  Management and Interaction using CoAP", Work in Progress,
                  draft-ietf-6tisch-coap-03, March 2015.

       [CoMP]     NGMN Alliance, "RAN EVOLUTION PROJECT COMP EVALUATION AND
                  ENHANCEMENT", VERSION 2.0, NGMN Alliance, March 2015,
                  <https://www.ngmn.org/fileadmin/user_upload/
                  NGMN_RANEV_D3_CoMP_Evaluation_and_Enhancement_v2.0.pdf>.

    Grossman                      Informational                    [Page 80]

    RFC 8578                    DetNet Use Cases                    May 2019

       [Content_Protection]
                  Olsen, D., "1722a Content Protection", April 2012,
                  <http://grouper.ieee.org/groups/1722/contributions/2012/
                  avtp_dolsen_1722a_content_protection.pdf>.

       [CPRI]     CPRI Cooperation, "Common Public Radio Interface (CPRI);
                  Interface Specification", CPRI Specification V6.1,
                  July 2014, <http://www.cpri.info/downloads/
                  CPRI_v_6_1_2014-07-01.pdf>.

       [DCI]      Digital Cinema Initiatives, LLC, "DCI Specification,
                  Version 1.3", June 2018, <https://www.dcimovies.com/>.

       [Det-Fwd-PHB]
                  Shah, S. and P. Thubert, "Deterministic Forwarding PHB",
                  Work in Progress,
                  draft-svshah-tsvwg-deterministic-forwarding-04,
                  August 2015.

       [DetNet-6TiSCH]
                  Thubert, P., Ed., "6TiSCH requirements for DetNet", Work
                  in Progress, draft-thubert-6tisch-4detnet-01, June 2015.

       [DetNet-Arch]
                  Finn, N., Thubert, P., Varga, B., and J. Farkas,
                  "Deterministic Networking Architecture", Work in Progress,
                  draft-ietf-detnet-architecture-13, May 2019.

       [DetNet-Audio-Reqs]
                  Gunther, C., Ed. and E. Grossman, Ed., "Deterministic
                  Networking Professional Audio Requirements", Work in
                  Progress, draft-gunther-detnet-proaudio-req-01,
                  March 2015.

       [DetNet-Mobile]
                  Zha, Y., "Deterministic Networking Use Case in Mobile
                  Network", Work in Progress, draft-zha-detnet-use-case-00,
                  July 2015.

       [DetNet-RAN]
                  Korhonen, J., "Deterministic networking for radio
                  access networks", Work in Progress,
                  draft-korhonen-detnet-telreq-00, May 2015.

    Grossman                      Informational                    [Page 81]

    RFC 8578                    DetNet Use Cases                    May 2019

       [DetNet-Security]
                  Mizrahi, T., Grossman, E., Ed., Hacker, A., Das, S.,
                  Dowdell, J., Austad, H., Stanton, K., and N. Finn,
                  "Deterministic Networking (DetNet) Security
                  Considerations", Work in Progress,
                  draft-ietf-detnet-security-04, March 2019.

       [DetNet-Util-Reqs]
                  Wetterwald, P. and J. Raymond, "Deterministic Networking
                  Uitilities requirements", Work in Progress,
                  draft-wetterwald-detnet-utilities-reqs-02, June 2015.

       [eCPRI]    IEEE Standards Association, "Common Public Radio
                  Interface: eCPRI Interface Specification V1.2", June 2018,
                  <http://www.cpri.info/>.

       [ESPN_DC2] Daley, D., "ESPN's DC2 Scales AVB Large", SVG News,
                  June 2014, <https://sportsvideo.org/main/blog/2014/06/
                  espns-dc2-scales-avb-large>.

       [EtherCAT] "EtherCAT Technology Group",
                  <https://www.ethercat.org/default.htm>.

       [FL-net]   Japan Electrical Manufacturers Association, "JEMA 1479 -
                  English Edition", September 2012,
                  <https://www.jema-net.or.jp/Japanese/standard/opcn/pdf/
                  JEM_1479e(20120927).pdf>.

       [Fronthaul]
                  Chen, D. and T. Mustala, "Ethernet Fronthaul
                  Considerations", IEEE 1904.3, February 2015,
                  <http://www.ieee1904.org/3/meeting_archive/2015/02/
                  tf3_1502_chen_1.pdf>.

       [IEC-60834]
                  International Electrotechnical Commission, "Teleprotection
                  equipment of power systems - Performance and testing",
                  IEC 60834, October 1999.

       [IEC-60870-5-104]
                  International Electrotechnical Commission, "Telecontrol
                  equipment and systems - Part 5-104: Transmission protocols
                  - Network access for IEC 60870-5-101 using standard
                  transport profiles", IEC 60870-5-104, June 2006.

    Grossman                      Informational                    [Page 82]

    RFC 8578                    DetNet Use Cases                    May 2019

       [IEC-61400-25]
                  International Electrotechnical Commission, "Communications
                  for monitoring and control of wind power plants",
                  IEC 61400-25, June 2013.

       [IEC-61850-5:2013]
                  International Electrotechnical Commission, "Communication
                  networks and systems for power utility automation -
                  Part 5: Communication requirements for functions and
                  device models", IEC 61850-5, January 2013.

       [IEC-61850-9-2:2011]
                  International Electrotechnical Commission, "Communication
                  networks and systems for power utility automation -
                  Part 9-2: Specific communication service mapping (SCSM) -
                  Sampled values over ISO/IEC 8802-3", IEC 61850-9-2,
                  September 2011.

       [IEC-61850-90-12:2015]
                  International Electrotechnical Commission, "Communication
                  networks and systems for power utility automation -
                  Part 90-12: Wide area network engineering guidelines",
                  IEC TR 61850-90-12, July 2015.

       [IEC-62357-200:2015]
                  International Electrotechnical Commission, "Power systems
                  management and associated information exchange - Part 200:
                  Guidelines for migration from Internet Protocol version 4
                  (IPv4) to Internet Protocol version 6 (IPv6)",
                  IEC 62357-200:2015, July 2015.

       [IEC-62439-3:2016]
                  International Electrotechnical Commission, "Industrial
                  communication networks - High availability automation
                  networks - Part 3: Parallel Redundancy Protocol (PRP) and
                  High-availability Seamless Redundancy (HSR)", March 2016.

       [IEC-IEEE-61850-9-3:2016]
                  International Electrotechnical Commission, "Communication
                  networks and systems for power utility automation -
                  Part 9-3: Precision time protocol profile for power
                  utility automation", IEC 61850-9-3, May 2016.

       [IEEE-1588]
                  IEEE, "IEEE Standard for a Precision Clock Synchronization
                  Protocol for Networked Measurement and Control Systems",
                  IEEE Standard 1588, <https://standards.ieee.org/findstds/
                  standard/1588-2008.html>.

    Grossman                      Informational                    [Page 83]

    RFC 8578                    DetNet Use Cases                    May 2019

       [IEEE-1646]
                  IEEE, "IEEE Standard Communication Delivery Time
                  Performance Requirements for Electric Power Substation
                  Automation", IEEE Standard 1646,
                  <https://standards.ieee.org/standard/1646-2004.html>.

       [IEEE-1722]
                  IEEE, "IEEE Standard for a Transport Protocol for
                  Time-Sensitive Applications in Bridged Local Area
                  Networks", IEEE Standard 1722,
                  <https://standards.ieee.org/findstds/
                  standard/1722-2016.html>.

       [IEEE-1815]
                  IEEE Standards Association, "IEEE Standard for Electric
                  Power Systems Communications-Distributed Network Protocol
                  (DNP3)", IEEE Standard 1815, <https://ieeexplore.ieee.org/
                  servlet/opac?punumber=6327576>.

       [IEEE-19143]
                  IEEE Standards Association, "IEEE Standard for Radio over
                  Ethernet Encapsulations and Mappings", IEEE 1914.3,
                  <https://standards.ieee.org/develop/project/1914.3.html>.

       [IEEE-80211]
                  IEEE Standard for Information technology, "IEEE Std.
                  802.11, Telecommunications and information exchange
                  between systems--Local and metropolitan area networks--
                  Specific requirements - Part 11: Wireless LAN Medium
                  Access Control (MAC) and Physical Layer (PHY)
                  Specifications",
                  <https://standards.ieee.org/standard/802_11-2016.html>.

       [IEEE-802154]
                  IEEE Standard for Information technology, "IEEE Std.
                  802.15.4, Part 15.4: Wireless Medium Access Control (MAC)
                  and Physical Layer (PHY) Specifications for Low Rate
                  Wireless Personal Area Networks (WPANs)",
                  <https://standards.ieee.org/standard/802_15_4-2015.html>.

       [IEEE-8021AS]
                  IEEE, "IEEE Standard for Local and Metropolitan Area
                  Networks - Timing and Synchronization for Time-Sensitive
                  Applications in Bridged Local Area Networks",
                  IEEE 802.1AS,
                  <http://www.ieee802.org/1/pages/802.1as.html>.

    Grossman                      Informational                    [Page 84]

    RFC 8578                    DetNet Use Cases                    May 2019

       [IEEE-8021CM]
                  "IEEE Standard for Local and metropolitan area networks -
                  Time-Sensitive Networking for Fronthaul", IEEE
                  Standard 802.1CM,
                  <https://standards.ieee.org/standard/802_1CM-2018.html>.

       [IEEE-8021TSNTG]
                  IEEE Standards Association, "IEEE 802.1 Time-Sensitive
                  Networking Task Group",
                  <http://www.ieee802.org/1/pages/avbridges.html>.

       [IETF99-netslicing-BoF]
                  "Network Slicing (netslicing) BoF", IETF 99, Prague,
                  July 2017, <https://datatracker.ietf.org/meeting/99/
                  materials/slides-99-netslicing-chairs-netslicing-bof-04>.

       [Interface-6TiSCH-6top]
                  Wang, Q., Ed. and X. Vilajosana, "6TiSCH Operation
                  Sublayer (6top) Interface", Work in Progress,
                  draft-ietf-6tisch-6top-interface-04, July 2015.

       [ISA100]   ISA/ANSI, "ISA100, Wireless Systems for Automation",
                  <https://www.isa.org/isa100/>.

       [KNX]      KNX Association, "ISO/IEC 14543-3 - KNX", November 2006.

       [LonTalk]  Echelon Corp., "LonTalk(R) Protocol Specification
                  Version 3.0", 1994, <http://www.enerlon.com/JobAids/
                  Lontalk%20Protocol%20Spec.pdf>.

       [MailingList-6TiSCH]
                  IETF, "6TiSCH Mailing List",
                  <https://mailarchive.ietf.org/arch/browse/6tisch/>.

       [MEF22.1.1]
                  Metro Ethernet Forum, "Mobile Backhaul Phase 2 Amendment 1
                  -- Small Cells", MEF 22.1.1, July 2014,
                  <http://www.mef.net/Assets/Technical_Specifications/PDF/
                  MEF_22.1.1.pdf>.

       [MEF8]     Metro Ethernet Forum, "Implementation Agreement for the
                  Emulation of PDH Circuits over Metro Ethernet Networks",
                  MEF 8, October 2004, <https://www.mef.net/
                  Assets/Technical_Specifications/PDF/MEF_8.pdf>.

    Grossman                      Informational                    [Page 85]

    RFC 8578                    DetNet Use Cases                    May 2019

       [METIS]    METIS, "Scenarios, requirements and KPIs for 5G mobile and
                  wireless system", Document Number ICT-317669-METIS/D1.1,
                  April 2013, <https://metis2020.com/wp-content/
                  uploads/deliverables/METIS_D1.1_v1.pdf>.

       [MODBUS]   Modbus Organization, Inc., "MODBUS Application Protocol
                  Specification", April 2012,
                  <http://www.modbus.org/specs.php>.

       [NGMN]     NGMN Alliance, "5G White Paper", NGMN 5G White Paper v1.0,
                  February 2015, <https://www.ngmn.org/fileadmin/ngmn/
                  content/downloads/Technical/2015/
                  NGMN_5G_White_Paper_V1_0.pdf>.

       [NGMN-Fronth]
                  NGMN Alliance, "Fronthaul Requirements for C-RAN",
                  March 2015, <https://www.ngmn.org/fileadmin/user_upload/
                  NGMN_RANEV_D1_C-RAN_Fronthaul_Requirements_v1.0.pdf>.

       [OPCXML]   OPC Foundation, "OPC Data Access (OPC DA) Specification",
                  <http://www.opcti.com/opc-da-specification.aspx>.

       [PCE]      IETF, "Path Computation Element",
                  <https://datatracker.ietf.org/doc/charter-ietf-pce/>.

       [PROFIBUS] IEC, "PROFIBUS Standard - DP Specification (IEC 61158
                  Type 3)", <https://www.profibus.com/>.

       [PROFINET] "PROFINET Technology",
                  <https://us.profinet.com/technology/profinet/>.

       [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
                  Label Switching Architecture", RFC 3031,
                  DOI 10.17487/RFC3031, January 2001,
                  <https://www.rfc-editor.org/info/rfc3031>.

       [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
                  Architecture for Describing Simple Network Management
                  Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
                  DOI 10.17487/RFC3411, December 2002,
                  <https://www.rfc-editor.org/info/rfc3411>.

       [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
                  Edge-to-Edge (PWE3) Architecture", RFC 3985,
                  DOI 10.17487/RFC3985, March 2005,
                  <https://www.rfc-editor.org/info/rfc3985>.

    Grossman                      Informational                    [Page 86]

    RFC 8578                    DetNet Use Cases                    May 2019

       [RFC4553]  Vainshtein, A., Ed. and YJ. Stein, Ed., "Structure-
                  Agnostic Time Division Multiplexing (TDM) over Packet
                  (SAToP)", RFC 4553, DOI 10.17487/RFC4553, June 2006,
                  <https://www.rfc-editor.org/info/rfc4553>.

       [RFC5086]  Vainshtein, A., Ed., Sasson, I., Metz, E., Frost, T., and
                  P. Pate, "Structure-Aware Time Division Multiplexed (TDM)
                  Circuit Emulation Service over Packet Switched Network
                  (CESoPSN)", RFC 5086, DOI 10.17487/RFC5086, December 2007,
                  <https://www.rfc-editor.org/info/rfc5086>.

       [RFC5087]  Stein, Y(J)., Shashoua, R., Insler, R., and M. Anavi,
                  "Time Division Multiplexing over IP (TDMoIP)", RFC 5087,
                  DOI 10.17487/RFC5087, December 2007,
                  <https://www.rfc-editor.org/info/rfc5087>.

       [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
                  "Network Time Protocol Version 4: Protocol and Algorithms
                  Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
                  <https://www.rfc-editor.org/info/rfc5905>.

       [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
                  Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
                  JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
                  Low-Power and Lossy Networks", RFC 6550,
                  DOI 10.17487/RFC6550, March 2012,
                  <https://www.rfc-editor.org/info/rfc6550>.

       [RFC6551]  Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
                  and D. Barthel, "Routing Metrics Used for Path Calculation
                  in Low-Power and Lossy Networks", RFC 6551,
                  DOI 10.17487/RFC6551, March 2012,
                  <https://www.rfc-editor.org/info/rfc6551>.

       [RFC7554]  Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
                  IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
                  Internet of Things (IoT): Problem Statement", RFC 7554,
                  DOI 10.17487/RFC7554, May 2015,
                  <https://www.rfc-editor.org/info/rfc7554>.

       [RFC8169]  Mirsky, G., Ruffini, S., Gray, E., Drake, J., Bryant, S.,
                  and A. Vainshtein, "Residence Time Measurement in MPLS
                  Networks", RFC 8169, DOI 10.17487/RFC8169, May 2017,
                  <https://www.rfc-editor.org/info/rfc8169>.

    Grossman                      Informational                    [Page 87]

    RFC 8578                    DetNet Use Cases                    May 2019

       [Spe09]    Barbosa, R., Sadre, R., and A. Pras, "A First Look into
                  SCADA Network Traffic", IP Network Operations and
                  Management Symposium, DOI 10.1109/NOMS.2012.6211945,
                  June 2012, <https://ieeexplore.ieee.org/document/6211945>.

       [SR-IP-RAN-Use-Case]
                  Khasnabish, B., Hu, F., and L. Contreras, "Segment
                  Routing in IP RAN use case", Work in Progress,
                  draft-kh-spring-ip-ran-use-case-02, November 2014.

       [SRP_LATENCY]
                  Gunther, C., "Specifying SRP Acceptable Latency",
                  March 2014, <http://www.ieee802.org/1/files/public/
                  docs2014/cc-cgunther-acceptable-latency-0314-v01.pdf>.

       [Sublayer-6TiSCH-6top]
                  Wang, Q., Ed. and X. Vilajosana, "6TiSCH Operation
                  Sublayer (6top)", Work in Progress,
                  draft-wang-6tisch-6top-sublayer-04, November 2015.

       [syncE]    International Telecommunication Union, "Timing and
                  synchronization aspects in packet networks", ITU-T
                  Recommendation G.8261, August 2013,
                  <https://www.itu.int/rec/T-REC-G.8261>.

       [Timing-over-MPLS]
                  Davari, S., Oren, A., Bhatia, M., Roberts, P., and L.
                  Montini, "Transporting Timing messages over MPLS
                  Networks", Work in Progress,
                  draft-ietf-tictoc-1588overmpls-07, October 2015.

       [TR38801]  3GPP, "Study on new radio access technology: Radio access
                  architecture and interfaces (Release 14)", 3GPP TR 38.801,
                  April 2017,
                  <https://portal.3gpp.org/desktopmodules/Specifications/
                  SpecificationDetails.aspx?specificationId=3056>.

       [TS23401]  3GPP, "General Packet Radio Service (GPRS) enhancements
                  for Evolved Universal Terrestrial Radio Access Network
                  (E-UTRAN) access (Release 16)", 3GPP TS 23.401,
                  March 2019, <https://portal.3gpp.org/
                  desktopmodules/ Specifications/
                  SpecificationDetails.aspx?specificationId=849>.

       [TS23501]  3GPP, "System architecture for the 5G System (5GS)
                  (Release 15)", 3GPP TS 23.501, March 2019,
                  <https://portal.3gpp.org/desktopmodules/Specifications/
                  SpecificationDetails.aspx?specificationId=3144>.

    Grossman                      Informational                    [Page 88]

    RFC 8578                    DetNet Use Cases                    May 2019

       [TS25104]  3GPP, "Base Station (BS) radio transmission and reception
                  (FDD) (Release 16)", 3GPP TS 25.104, January 2019,
                  <https://portal.3gpp.org/desktopmodules/Specifications/
                  SpecificationDetails.aspx?specificationId=1154>.

       [TS36104]  3GPP, "Evolved Universal Terrestrial Radio Access
                  (E-UTRA); Base Station (BS) radio transmission and
                  reception (Release 16)", 3GPP TS 36.104, January 2019,
                  <https://portal.3gpp.org/desktopmodules/Specifications/
                  SpecificationDetails.aspx?specificationId=2412>.

       [TS36133]  3GPP, "Evolved Universal Terrestrial Radio Access
                  (E-UTRA); Requirements for support of radio resource
                  management (Release 16)", 3GPP TS 36.133, January 2019,
                  <https://portal.3gpp.org/desktopmodules/Specifications/
                  SpecificationDetails.aspx?specificationId=2420>.

       [TS36211]  3GPP, "Evolved Universal Terrestrial Radio Access
                  (E-UTRA); Physical channels and modulation (Release 15)",
                  3GPP TS 36.211, January 2019,
                  <https://portal.3gpp.org/desktopmodules/Specifications/
                  SpecificationDetails.aspx?specificationId=2425>.

       [TS36300]  3GPP, "Evolved Universal Terrestrial Radio Access (E-UTRA)
                  and Evolved Universal Terrestrial Radio Access Network
                  (E-UTRAN); Overall description; Stage 2 (Release 15)",
                  3GPP TS 36.300, January 2019,
                  <https://portal.3gpp.org/desktopmodules/Specifications/
                  SpecificationDetails.aspx?specificationId=2430>.

       [WirelessHART]
                  International Electrotechnical Commission, "Industrial
                  networks - Wireless communication network and
                  communication profiles - WirelessHART(TM)",
                  IEC 62591:2016, March 2016.

    Grossman                      Informational                    [Page 89]

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    Appendix A.  Use Cases Explicitly Out of Scope for DetNet

       This appendix contains text regarding use cases that have been
       determined to be outside the scope of the present DetNet work.

    A.1.  DetNet Scope Limitations

       The scope of DetNet is deliberately limited to specific use cases
       that are consistent with the WG charter, subject to the
       interpretation of the WG.  At the time that the DetNet use cases were
       solicited and provided by the authors, the scope of DetNet was not
       clearly defined.  As the scope has been clarified, certain use cases
       have been determined to be outside the scope of the present DetNet
       work.  Text regarding these use cases was moved to this appendix to
       clarify that they will not be supported by the DetNet work.

       The text was moved to this appendix based on the following
       "exclusion" principles.  Please note that as an alternative to moving
       all such text to this appendix some text has been modified in situ to
       reflect these same principles.

       The following principles have been established to clarify the scope
       of the present DetNet work.

       o  The scope of networks addressed by DetNet is limited to networks
          that can be centrally controlled, i.e., an "enterprise" (aka
          "corporate") network.  This explicitly excludes "the open
          Internet".

       o  Maintaining time synchronization across a DetNet network is
          crucial to its operation; however, DetNet assumes that time is to
          be maintained using other means.  One example would be PTP
          [IEEE-1588].  A use case may state the accuracy and reliability
          that it expects from the DetNet network as part of a whole system;
          however, it is understood that such timing properties are not
          guaranteed by DetNet itself.  At the time of this writing, two
          open questions remain: (1) whether DetNet protocols will include a
          way for an application to communicate expectations regarding such
          timing properties to the network and (2) if so, whether those
          properties would likely have a material effect on network
          performance as a result.

    A.2.  Internet-Based Applications

       There are many applications that communicate over the open Internet
       that could benefit from guaranteed delivery and bounded latency.
       However, as noted above, all such applications, when run over the
       open Internet, are out of scope for DetNet.  These same applications

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       may be in scope when run in constrained environments, i.e., within a
       centrally controlled DetNet network.  The following are some examples
       of such applications.

    A.2.1.  Use Case Description

    A.2.1.1.  Media Content Delivery

       Media content delivery continues to be an important use of the
       Internet, yet users often experience poor-quality audio and video due
       to the delay and jitter inherent in today's Internet.

    A.2.1.2.  Online Gaming

       Online gaming is a significant part of the gaming market; however,
       latency can degrade the end user's experience.  For example, "First
       Person Shooter" (FPS) games are highly delay sensitive.

    A.2.1.3.  Virtual Reality

       VR has many commercial applications, including real estate
       presentations, remote medical procedures, and so on.  Low latency is
       critical to interacting with the virtual world, because perceptual
       delays can cause motion sickness.

    A.2.2.  Internet-Based Applications Today

       Internet service today is by definition "best effort", with no
       guarantees regarding delivery or bandwidth.

    A.2.3.  Internet-Based Applications in the Future

       One should be able to play Internet videos without glitches and play
       Internet games without lag.

       For online gaming, the desired maximum allowance for round-trip delay
       is typically 100 ms.  However, it may be less for specific types of
       games; for example, for FPS games, the maximum delay should be 50 ms.
       Transport delay is the dominant part, with a budget of 5-20 ms.

       For VR, a maximum delay of 1-10 ms is needed; if doing remote VR, the
       total network delay budget is 1-5 ms.

       Flow identification can be used for gaming and VR, i.e., it can
       recognize a critical flow and provide appropriate latency bounds.

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    A.2.4.  Internet-Based Applications Requests to the IETF

       o  Unified control and management protocols that handle time-critical
          data flows

       o  An application-aware flow-filtering mechanism that recognizes
          time-critical flows without doing 5-tuple matching

       o  A unified control plane that provides low-latency service on
          Layer 3 without changing the data plane

       o  An OAM system and protocols that can help provide service
          provisioning that is sensitive to end-to-end delays

    A.3.  Pro Audio and Video - Digital Rights Management (DRM)

       The following text was moved to this appendix because this
       information is considered a link-layer topic for which DetNet is not
       directly responsible.

       Digital Rights Management (DRM) is very important to the audio and
       video industries.  Whenever protected content is introduced into a
       network, there are DRM concerns that must be taken into account (see
       [Content_Protection]).  Many aspects of DRM are outside the scope of
       network technology; however, there are cases when a secure link
       supporting authentication and encryption is required by content
       owners to carry their audio or video content when it is outside their
       own secure environment (for example, see [DCI]).

       As an example, two such techniques are Digital Transmission Content
       Protection (DTCP) and High-bandwidth Digital Content Protection
       (HDCP).  HDCP content is not approved for retransmission within any
       other type of DRM, while DTCP content may be retransmitted under
       HDCP.  Therefore, if the source of a stream is outside of the network
       and it uses HDCP, it is only allowed to be placed on the network with
       that same type of protection (i.e., HDCP).

    A.4.  Pro Audio and Video - Link Aggregation

       Note: The term "link aggregation" is used here as defined by the text
       in the following paragraph, i.e., not following a more common
       network-industry definition.

       For transmitting streams that require more bandwidth than a single
       link in the target network can support, link aggregation is a
       technique for combining (aggregating) the bandwidth available on
       multiple physical links to create a single logical link that provides

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    RFC 8578                    DetNet Use Cases                    May 2019

       the required bandwidth.  However, if aggregation is to be used, the
       network controller (or equivalent) must be able to determine the
       maximum latency of any path through the aggregate link.

    A.5.  Pro Audio and Video - Deterministic Time to Establish Streaming

       The DetNet WG decided that guidelines for establishing a
       deterministic time to establish stream startup are not within the
       scope of DetNet.  If the bounded timing for establishing or
       re-establishing streams is required in a given use case, it is up to
       the application/system to achieve it.

    Acknowledgments

       Pro audio (Section 2)

          As also acknowledged in [DetNet-Audio-Reqs], the editor would like
          to acknowledge the help of the following individuals and the
          companies they represent.

             Jeff Koftinoff, Meyer Sound
             Jouni Korhonen, Associate Technical Director, Broadcom
             Pascal Thubert, CTAO, Cisco
             Kieran Tyrrell, Sienda New Media Technologies GmbH

       Utility telecom (Section 3)

          Information regarding utility telecom was derived from
          [DetNet-Util-Reqs].  As in that document, the following
          individuals are acknowledged here.

             Faramarz Maghsoodlou, Ph.D., IoT Connected Industries
                and Energy Practice, Cisco
             Pascal Thubert, CTAO, Cisco

          The wind power generation use case has been extracted from the
          study of wind parks conducted within the 5GPPP VirtuWind Project.
          The project is funded by the European Union's Horizon 2020
          research and innovation programme under grant agreement No. 671648
          (VirtuWind).

       Building automation systems (Section 4)

          Please see [BAS-DetNet].

    Grossman                      Informational                    [Page 93]

    RFC 8578                    DetNet Use Cases                    May 2019

       Wireless for industrial applications (Section 5)

          See [DetNet-6TiSCH].

          [DetNet-6TiSCH] derives from the 6TiSCH architecture, which is the
          result of multiple interactions -- in particular, during the
          6TiSCH (bi)weekly interim call, relayed through the 6TiSCH mailing
          list at the IETF [MailingList-6TiSCH].

          As also acknowledged in [DetNet-6TiSCH], the editor wishes to
          thank Kris Pister, Thomas Watteyne, Xavier Vilajosana, Qin Wang,
          Tom Phinney, Robert Assimiti, Michael Richardson, Zhuo Chen,
          Malisa Vucinic, Alfredo Grieco, Martin Turon, Dominique Barthel,
          Elvis Vogli, Guillaume Gaillard, Herman Storey, Maria Rita
          Palattella, Nicola Accettura, Patrick Wetterwald, Pouria Zand,
          Raghuram Sudhaakar, and Shitanshu Shah for their participation and
          various contributions.

       Cellular radio (Section 6)

          See [DetNet-RAN].

       Internet applications and CoMP (Section 6)

          As also acknowledged in [DetNet-Mobile], authored by Yiyong Zha,
          the editor would like to thank the following people for their
          reviews, suggestions, comments, and proposed text: Jing Huang,
          Junru Lin, Lehong Niu, and Oliver Huang.

       Industrial Machine to Machine (M2M) (Section 7)

          The editor would like to thank Feng Chen and Marcel Kiessling for
          their comments and suggestions.

       Mining industry (Section 8)

          This text was written by Diego Dujovne, who worked in conjunction
          with Xavier Vilajosana.

       Private blockchain (Section 9)

          This text was written by Daniel Huang.

       Network slicing (Section 10)

          This text was written by Xuesong Geng, who would like to
          acknowledge Norm Finn and Mach Chen for their useful comments.

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    Contributors

       RFC 7322 ("RFC Style Guide") generally limits the number of authors
       listed on the front page of a document to five individuals -- far
       fewer than the 19 individuals listed below, who also made important
       contributions to this document.  The editor wishes to thank and
       acknowledge each of the following authors for contributing text to
       this document.  See also the Acknowledgments section.

          Craig Gunther (Harman International)
          10653 South River Front Parkway
          South Jordan, UT  84095
          United States of America
          Phone: +1 801 568 7675
          Email: craig.gunther@harman.com

          Pascal Thubert (Cisco Systems, Inc.)
          Building D, 45 Allee des Ormes - BP1200
          Mougins - Sophia Antipolis  06254
          France
          Phone: +33 4 97 23 26 34
          Email: pthubert@cisco.com

          Patrick Wetterwald (Cisco Systems)
          45 Allee des Ormes
          Mougins  06250
          France
          Phone: +33 4 97 23 26 36
          Email: pwetterw@cisco.com

          Jean Raymond (Hydro-Quebec)
          1500 University
          Montreal, Quebec  H3A 3S7
          Canada
          Phone: +1 514 840 3000
          Email: raymond.jean@hydro.qc.ca

          Jouni Korhonen (Broadcom Corporation)
          3151 Zanker Road
          San Jose, CA  95134
          United States of America
          Email: jouni.nospam@gmail.com

          Yu Kaneko (Toshiba)
          1 Komukai-Toshiba-cho
          Saiwai-ku, Kasasaki-shi, Kanagawa
          Japan
          Email: yu1.kaneko@toshiba.co.jp

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    RFC 8578                    DetNet Use Cases                    May 2019

          Subir Das (Vencore Labs)
          150 Mount Airy Road
          Basking Ridge, NJ  07920
          United States of America
          Email: sdas@appcomsci.com

          Balazs Varga (Ericsson)
          Konyves Kalman krt. 11/B
          Budapest  1097
          Hungary
          Email: balazs.a.varga@ericsson.com

          Janos Farkas (Ericsson)
          Konyves Kalman krt. 11/B
          Budapest  1097
          Hungary
          Email: janos.farkas@ericsson.com

          Franz-Josef Goetz (Siemens)
          Gleiwitzerstr. 555
          Nurnberg  90475
          Germany
          Email: franz-josef.goetz@siemens.com

          Juergen Schmitt (Siemens)
          Gleiwitzerstr. 555
          Nurnberg  90475
          Germany
          Email: juergen.jues.schmitt@siemens.com

          Xavier Vilajosana (Worldsensing)
          483 Arago
          Barcelona, Catalonia  08013
          Spain
          Email: xvilajosana@worldsensing.com

          Toktam Mahmoodi (King's College London)
          Strand, London  WC2R 2LS
          United Kingdom
          Email: toktam.mahmoodi@kcl.ac.uk

          Spiros Spirou (Intracom Telecom)
          19.7 km Markopoulou Ave.
          Peania, Attiki  19002
          Greece
          Email: spiros.spirou@gmail.com

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    RFC 8578                    DetNet Use Cases                    May 2019

          Petra Vizarreta (Technical University of Munich)
          Maxvorstadt, Arcisstrasse 21
          Munich  80333
          Germany
          Email: petra.stojsavljevic@tum.de

          Daniel Huang (ZTE Corporation, Inc.)
          No. 50 Software Avenue
          Nanjing, Jiangsu  210012
          China
          Email: huang.guangping@zte.com.cn

          Xuesong Geng (Huawei Technologies)
          Email: gengxuesong@huawei.com

          Diego Dujovne (Universidad Diego Portales)
          Email: diego.dujovne@mail.udp.cl

          Maik Seewald (Cisco Systems)
          Email: maseewal@cisco.com

    Author's Address

       Ethan Grossman (editor)
       Dolby Laboratories, Inc.
       1275 Market Street
       San Francisco, CA  94103
       United States of America

       Phone: +1 415 645 4726
       Email: ethan.grossman@dolby.com
       URI:   http://www.dolby.com

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