    Internet Engineering Task Force (IETF)                  J. Martocci, Ed.
    Request for Comments: 5867                         Johnson Controls Inc.
    Category: Informational                                        P. De Mil
    ISSN: 2070-1721                                  Ghent University - IBCN
                                                                     N. Riou
                                                          Schneider Electric
                                                                W. Vermeylen
                                                         Arts Centre Vooruit
                                                                   June 2010

                    Building Automation Routing Requirements
                        in Low-Power and Lossy Networks

    Abstract

       The Routing Over Low-Power and Lossy (ROLL) networks Working Group
       has been chartered to work on routing solutions for Low-Power and
       Lossy Networks (LLNs) in various markets: industrial, commercial
       (building), home, and urban networks.  Pursuant to this effort, this
       document defines the IPv6 routing requirements for building
       automation.

    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 a candidate for any level of Internet
       Standard; see Section 2 of RFC 5741.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       http://www.rfc-editor.org/info/rfc5867.

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    RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

    Copyright Notice

       Copyright (c) 2010 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
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       described in the Simplified BSD License.

       This document may contain material from IETF Documents or IETF
       Contributions published or made publicly available before November
       10, 2008.  The person(s) controlling the copyright in some of this
       material may not have granted the IETF Trust the right to allow
       modifications of such material outside the IETF Standards Process.
       Without obtaining an adequate license from the person(s) controlling
       the copyright in such materials, this document may not be modified
       outside the IETF Standards Process, and derivative works of it may
       not be created outside the IETF Standards Process, except to format
       it for publication as an RFC or to translate it into languages other
       than English.

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    RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

    Table of Contents

       1. Introduction ....................................................4
       2. Terminology .....................................................6
          2.1. Requirements Language ......................................6
       3. Overview of Building Automation Networks ........................6
          3.1. Introduction ...............................................6
          3.2. Building Systems Equipment .................................7
               3.2.1. Sensors/Actuators ...................................7
               3.2.2. Area Controllers ....................................7
               3.2.3. Zone Controllers ....................................8
          3.3. Equipment Installation Methods .............................8
          3.4. Device Density .............................................9
               3.4.1. HVAC Device Density .................................9
               3.4.2. Fire Device Density .................................9
               3.4.3. Lighting Device Density ............................10
               3.4.4. Physical Security Device Density ...................10
       4. Traffic Pattern ................................................10
       5. Building Automation Routing Requirements .......................12
          5.1. Device and Network Commissioning ..........................12
               5.1.1. Zero-Configuration Installation ....................12
               5.1.2. Local Testing ......................................12
               5.1.3. Device Replacement .................................13
          5.2. Scalability ...............................................13
               5.2.1. Network Domain .....................................13
               5.2.2. Peer-to-Peer Communication .........................13
          5.3. Mobility ..................................................13
               5.3.1. Mobile Device Requirements .........................14
          5.4. Resource Constrained Devices ..............................15
               5.4.1. Limited Memory Footprint on Host Devices ...........15
               5.4.2. Limited Processing Power for Routers ...............15
               5.4.3. Sleeping Devices ...................................15
          5.5. Addressing ................................................16
          5.6. Manageability .............................................16
               5.6.1. Diagnostics ........................................17
               5.6.2. Route Tracking .....................................17
          5.7. Route Selection ...........................................17
               5.7.1. Route Cost .........................................17
               5.7.2. Route Adaptation ...................................18
               5.7.3. Route Redundancy ...................................18
               5.7.4. Route Discovery Time ...............................18
               5.7.5. Route Preference ...................................18
               5.7.6. Real-Time Performance Measures .....................18
               5.7.7. Prioritized Routing ................................18

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          5.8. Security Requirements .....................................19
               5.8.1. Building Security Use Case .........................19
               5.8.2. Authentication .....................................20
               5.8.3. Encryption .........................................20
               5.8.4. Disparate Security Policies ........................21
               5.8.5. Routing Security Policies to Sleeping Devices ......21
       6. Security Considerations ........................................21
       7. Acknowledgments ................................................22
       8. References .....................................................22
          8.1. Normative References ......................................22
          8.2. Informative References ....................................22
       Appendix A. Additional Building Requirements ......................23
          A.1. Additional Commercial Product Requirements ................23
               A.1.1. Wired and Wireless Implementations .................23
               A.1.2. World-Wide Applicability ...........................23
          A.2. Additional Installation and Commissioning Requirements ....23
               A.2.1. Unavailability of an IP Network ....................23
          A.3. Additional Network Requirements ...........................23
               A.3.1. TCP/UDP ............................................23
               A.3.2. Interference Mitigation ............................23
               A.3.3. Packet Reliability .................................24
               A.3.4. Merging Commissioned Islands .......................24
               A.3.5. Adjustable Routing Table Sizes .....................24
               A.3.6. Automatic Gain Control .............................24
               A.3.7. Device and Network Integrity .......................24
          A.4. Additional Performance Requirements .......................24
               A.4.1. Data Rate Performance ..............................24
               A.4.2. Firmware Upgrades ..................................25
               A.4.3. Route Persistence ..................................25

    1.  Introduction

       The Routing Over Low-Power and Lossy (ROLL) networks Working Group
       has been chartered to work on routing solutions for Low-Power and
       Lossy Networks (LLNs) in various markets: industrial, commercial
       (building), home, and urban networks.  Pursuant to this effort, this
       document defines the IPv6 routing requirements for building
       automation.

       Commercial buildings have been fitted with pneumatic, and
       subsequently electronic, communication routes connecting sensors to
       their controllers for over one hundred years.  Recent economic and
       technical advances in wireless communication allow facilities to
       increasingly utilize a wireless solution in lieu of a wired solution,
       thereby reducing installation costs while maintaining highly reliant
       communication.

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       The cost benefits and ease of installation of wireless sensors allow
       customers to further instrument their facilities with additional
       sensors, providing tighter control while yielding increased energy
       savings.

       Wireless solutions will be adapted from their existing wired
       counterparts in many of the building applications including, but not
       limited to, heating, ventilation, and air conditioning (HVAC);
       lighting; physical security; fire; and elevator/lift systems.  These
       devices will be developed to reduce installation costs while
       increasing installation and retrofit flexibility, as well as
       increasing the sensing fidelity to improve efficiency and building
       service quality.

       Sensing devices may be battery-less, battery-powered, or mains-
       powered.  Actuators and area controllers will be mains-powered.  Due
       to building code and/or device density (e.g., equipment room), it is
       envisioned that a mix of wired and wireless sensors and actuators
       will be deployed within a building.

       Building management systems (BMSs) are deployed in a large set of
       vertical markets including universities, hospitals, government
       facilities, kindergarten through high school (K-12), pharmaceutical
       manufacturing facilities, and single-tenant or multi-tenant office
       buildings.  These buildings range in size from 100K-sq.-ft.
       structures (5-story office buildings), to 1M-sq.-ft. skyscrapers
       (100-story skyscrapers), to complex government facilities such as the
       Pentagon.  The described topology is meant to be the model to be used
       in all of these types of environments but clearly must be tailored to
       the building class, building tenant, and vertical market being
       served.

       Section 3 describes the necessary background to understand the
       context of building automation including the sensor, actuator, area
       controller, and zone controller layers of the topology; typical
       device density; and installation practices.

       Section 4 defines the traffic flow of the aforementioned sensors,
       actuators, and controllers in commercial buildings.

       Section 5 defines the full set of IPv6 routing requirements for
       commercial buildings.

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       Appendix A documents important commercial building requirements that
       are out of scope for routing yet will be essential to the final
       acceptance of the protocols used within the building.

       Section 3 and Appendix A are mainly included for educational
       purposes.

       The expressed aim of this document is to provide the set of IPv6
       routing requirements for LLNs in buildings, as described in
       Section 5.

    2.  Terminology

       For a description of the terminology used in this specification,
       please see [ROLL-TERM].

    2.1.  Requirements Language

       The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
       "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
       document are to be interpreted as described in [RFC2119].

    3.  Overview of Building Automation Networks

    3.1.  Introduction

       To understand the network systems requirements of a building
       management system in a commercial building, this document uses a
       framework to describe the basic functions and composition of the
       system.  A BMS is a hierarchical system of sensors, actuators,
       controllers, and user interface devices that interoperate to provide
       a safe and comfortable environment while constraining energy costs.

       A BMS is divided functionally across different but interrelated
       building subsystems such as heating, ventilation, and air
       conditioning (HVAC); fire; security; lighting; shutters; and
       elevator/lift control systems, as denoted in Figure 1.

       Much of the makeup of a BMS is optional and installed at the behest
       of the customer.  Sensors and actuators have no standalone
       functionality.  All other devices support partial or complete
       standalone functionality.  These devices can optionally be tethered
       to form a more cohesive system.  The customer requirements dictate
       the level of integration within the facility.  This architecture
       provides excellent fault tolerance since each node is designed to
       operate in an independent mode if the higher layers are unavailable.

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                     +------+ +-----+ +------+ +------+ +------+ +------+

       Bldg App'ns   |      | |     | |      | |      | |      | |      |

                     |      | |     | |      | |      | |      | |      |

       Building Cntl |      | |     | |   S  | |   L  | |   S  | |  E   |

                     |      | |     | |   E  | |   I  | |   H  | |  L   |

       Area Control  |  H   | |  F  | |   C  | |   G  | |   U  | |  E   |

                     |  V   | |  I  | |   U  | |   H  | |   T  | |  V   |

       Zone Control  |  A   | |  R  | |   R  | |   T  | |   T  | |  A   |

                     |  C   | |  E  | |   I  | |   I  | |   E  | |  T   |

       Actuators     |      | |     | |   T  | |   N  | |   R  | |  O   |

                     |      | |     | |   Y  | |   G  | |   S  | |  R   |

       Sensors       |      | |     | |      | |      | |      | |      |

                     +------+ +-----+ +------+ +------+ +------+ +------+

                      Figure 1: Building Systems and Devices

    3.2.  Building Systems Equipment

    3.2.1.  Sensors/Actuators

       As Figure 1 indicates, a BMS may be composed of many functional
       stacks or silos that are interoperably woven together via building
       applications.  Each silo has an array of sensors that monitor the
       environment and actuators that modify the environment, as determined
       by the upper layers of the BMS topology.  The sensors typically are
       at the edge of the network structure, providing environmental data
       for the system.  The actuators are the sensors' counterparts,
       modifying the characteristics of the system, based on the sensor data
       and the applications deployed.

    3.2.2.  Area Controllers

       An area describes a small physical locale within a building,
       typically a room.  HVAC (temperature and humidity) and lighting (room
       lighting, shades, solar loads) vendors oftentimes deploy area
       controllers.  Area controllers are fed by sensor inputs that monitor

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       the environmental conditions within the room.  Common sensors found
       in many rooms that feed the area controllers include temperature,
       occupancy, lighting load, solar load, and relative humidity.  Sensors
       found in specialized rooms (such as chemistry labs) might include air
       flow, pressure, and CO2 and CO particle sensors.  Room actuation
       includes temperature setpoint, lights, and blinds/curtains.

    3.2.3.  Zone Controllers

       Zone controllers support a similar set of characteristics to area
       controllers, albeit for an extended space.  A zone is normally a
       logical grouping or functional division of a commercial building.  A
       zone may also coincidentally map to a physical locale such as a
       floor.

       Zone controllers may have direct sensor inputs (smoke detectors for
       fire), controller inputs (room controllers for air handlers in HVAC),
       or both (door controllers and tamper sensors for security).  Like
       area/room controllers, zone controllers are standalone devices that
       operate independently or may be attached to the larger network for
       more synergistic control.

    3.3.  Equipment Installation Methods

       A BMS is installed very differently from most other IT networks.  IT
       networks are typically installed as an overlay onto the existing
       environment and are installed from the inside out.  That is, the
       network wiring infrastructure is installed; the switches, routers,
       and servers are connected and made operational; and finally, the
       endpoints (e.g., PCs, VoIP phones) are added.

       BMSs, on the other hand, are installed from the outside in.  That is,
       the endpoints (thermostats, lights, smoke detectors) are installed in
       the spaces first; local control is established in each room and
       tested for proper operation.  The individual rooms are later lashed
       together into a subsystem (e.g., lighting).  The individual
       subsystems (e.g., lighting, HVAC) then coalesce.  Later, the entire
       system may be merged onto the enterprise network.

       The rationale for this is partly due to the different construction
       trades having access to a building under construction at different
       times.  The sheer size of a building often dictates that even a
       single trade may have multiple independent teams working
       simultaneously.  Furthermore, the HVAC, lighting, and fire systems
       must be fully operational before the building can obtain its
       occupancy permit.  Hence, the BMS must be in place and configured
       well before any of the IT servers (DHCP; Authentication,
       Authorization, and Accounting (AAA); DNS; etc.) are operational.

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       This implies that the BMS cannot rely on the availability of the IT
       network infrastructure or application servers.  Rather, the BMS
       installation should be planned to dovetail into the IT system once
       the IT system is available for easy migration onto the IT network.
       Front-end planning of available switch ports, cable runs, access
       point (AP) placement, firewalls, and security policies will
       facilitate this adoption.

    3.4.  Device Density

       Device density differs, depending on the application and as dictated
       by the local building code requirements.  The following subsections
       detail typical installation densities for different applications.

    3.4.1.  HVAC Device Density

       HVAC room applications typically have sensors/actuators and
       controllers spaced about 50 ft. apart.  In most cases, there is a 3:1
       ratio of sensors/actuators to controllers.  That is, for each room
       there is an installed temperature sensor, flow sensor, and damper
       actuator for the associated room controller.

       HVAC equipment room applications are quite different.  An air handler
       system may have a single controller with up to 25 sensors and
       actuators within 50 ft. of the air handler.  A chiller or boiler is
       also controlled with a single equipment controller instrumented with
       25 sensors and actuators.  Each of these devices would be
       individually addressed since the devices are mandated or optional as
       defined by the specified HVAC application.  Air handlers typically
       serve one or two floors of the building.  Chillers and boilers may be
       installed per floor, but many times they service a wing, building, or
       the entire complex via a central plant.

       These numbers are typical.  In special cases, such as clean rooms,
       operating rooms, pharmaceutical facilities, and labs, the ratio of
       sensors to controllers can increase by a factor of three.  Tenant
       installations such as malls would opt for packaged units where much
       of the sensing and actuation is integrated into the unit; here, a
       single device address would serve the entire unit.

    3.4.2.  Fire Device Density

       Fire systems are much more uniformly installed, with smoke detectors
       installed about every 50 ft.  This is dictated by local building
       codes.  Fire pull boxes are installed uniformly about every 150 ft.
       A fire controller will service a floor or wing.  The fireman's fire
       panel will service the entire building and typically is installed in
       the atrium.

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    3.4.3.  Lighting Device Density

       Lighting is also very uniformly installed, with ballasts installed
       approximately every 10 ft.  A lighting panel typically serves 48 to
       64 zones.  Wired systems tether many lights together into a single
       zone.  Wireless systems configure each fixture independently to
       increase flexibility and reduce installation costs.

    3.4.4.  Physical Security Device Density

       Security systems are non-uniformly oriented, with heavy density near
       doors and windows and lighter density in the building's interior
       space.

       The recent influx of interior and perimeter camera systems is
       increasing the security footprint.  These cameras are atypical
       endpoints requiring up to 1 megabit/second (Mbit/s) data rates per
       camera, as contrasted by the few kbit/s needed by most other BMS
       sensing equipment.  Previously, camera systems had been deployed on
       proprietary wired high-speed networks.  More recent implementations
       utilize wired or wireless IP cameras integrated into the enterprise
       LAN.

    4.  Traffic Pattern

       The independent nature of the automation subsystems within a building
       can significantly affect network traffic patterns.  Much of the real-
       time sensor environmental data and actuator control stays within the
       local LLN environment, while alarms and other event data will
       percolate to higher layers.

       Each sensor in the LLN unicasts point to point (P2P) about 200 bytes
       of sensor data to its associated controller each minute and expects
       an application acknowledgment unicast returned from the destination.
       Each controller unicasts messages at a nominal rate of 6 kbit/minute
       to peer or supervisory controllers.  Thirty percent of each node's
       packets are destined for other nodes within the LLN.  Seventy percent
       of each node's packets are destined for an aggregation device
       (multipoint to point (MP2P)) and routed off the LLN.  These messages
       also require a unicast acknowledgment from the destination.  The
       above values assume direct node-to-node communication; meshing and
       error retransmissions are not considered.

       Multicasts (point to multipoint (P2MP)) to all nodes in the LLN occur
       for node and object discovery when the network is first commissioned.
       This data is typically a one-time bind that is henceforth persisted.
       Lighting systems will also readily use multicasting during normal
       operations to turn banks of lights "on" and "off" simultaneously.

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       BMSs may be either polled or event-based.  Polled data systems will
       generate a uniform and constant packet load on the network.  Polled
       architectures, however, have proven not to be scalable.  Today, most
       vendors have developed event-based systems that pass data on event.
       These systems are highly scalable and generate low data on the
       network at quiescence.  Unfortunately, the systems will generate a
       heavy load on startup since all initial sensor data must migrate to
       the controller level.  They also will generate a temporary but heavy
       load during firmware upgrades.  This latter load can normally be
       mitigated by performing these downloads during off-peak hours.

       Devices will also need to reference peers periodically for sensor
       data or to coordinate operation across systems.  Normally, though,
       data will migrate from the sensor level upwards through the local and
       area levels, and then to the supervisory level.  Traffic bottlenecks
       will typically form at the funnel point from the area controllers to
       the supervisory controllers.

       Initial system startup after a controlled outage or unexpected power
       failure puts tremendous stress on the network and on the routing
       algorithms.  A BMS is comprised of a myriad of control algorithms at
       the room, area, zone, and enterprise layers.  When these control
       algorithms are at quiescence, the real-time data rate is small, and
       the network will not saturate.  An overall network traffic load of 6
       kbit/s is typical at quiescence.  However, upon any power loss, the
       control loops and real-time data quickly atrophy.  A short power
       disruption of only 10 minutes may have a long-term deleterious impact
       on the building control systems, taking many hours to regain proper
       control.  Control applications that cannot handle this level of
       disruption (e.g., hospital operating rooms) must be fitted with a
       secondary power source.

       Power disruptions are unexpected and in most cases will immediately
       impact lines-powered devices.  Power disruptions, however, are
       transparent to battery-powered devices.  These devices will continue
       to attempt to access the LLN during the outage.  Battery-powered
       devices designed to buffer data that has not been delivered will
       further stress network operations when power returns.

       Upon restart, lines-powered devices will naturally dither due to
       primary equipment delays or variance in the device self-tests.
       However, most lines-powered devices will be ready to access the LLN
       network within 10 seconds of power-up.  Empirical testing indicates
       that routes acquired during startup will tend to be very oblique
       since the available neighbor lists are incomplete.  This demands an
       adaptive routing protocol to allow for route optimization as the
       network stabilizes.

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    5.  Building Automation Routing Requirements

       Following are the building automation routing requirements for
       networks used to integrate building sensor, actuator, and control
       products.  These requirements are written not presuming any
       preordained network topology, physical media (wired), or radio
       technology (wireless).

    5.1.  Device and Network Commissioning

       Building control systems typically are installed and tested by
       electricians having little computer knowledge and no network
       communication knowledge whatsoever.  These systems are often
       installed during the building construction phase, before the drywall
       and ceilings are in place.  For new construction projects, the
       building enterprise IP network is not in place during installation of
       the building control system.  For retrofit applications, the
       installer will still operate independently from the IP network so as
       not to affect network operations during the installation phase.

       In traditional wired systems, correct operation of a light
       switch/ballast pair was as simple as flipping on the light switch.
       In wireless applications, the tradesperson has to assure the same
       operation, yet be sure the operation of the light switch is
       associated with the proper ballast.

       System-level commissioning will later be deployed using a more
       computer savvy person with access to a commissioning device (e.g., a
       laptop computer).  The completely installed and commissioned
       enterprise IP network may or may not be in place at this time.
       Following are the installation routing requirements.

    5.1.1.  Zero-Configuration Installation

       It MUST be possible to fully commission network devices without
       requiring any additional commissioning device (e.g., a laptop).  From
       the ROLL perspective, "zero configuration" means that a node can
       obtain an address and join the network on its own, without human
       intervention.

    5.1.2.  Local Testing

       During installation, the room sensors, actuators, and controllers
       SHOULD be able to route packets amongst themselves and to any other
       device within the LLN, without requiring any additional routing
       infrastructure or routing configuration.

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    5.1.3.  Device Replacement

       To eliminate the need to reconfigure the application upon replacing a
       failed device in the LLN, the replaced device must be able to
       advertise the old IP address of the failed device in addition to its
       new IP address.  The routing protocols MUST support hosts and routers
       that advertise multiple IPv6 addresses.

    5.2.  Scalability

       Building control systems are designed for facilities from 50,000 sq.
       ft. to 1M+ sq. ft.  The networks that support these systems must
       cost-effectively scale accordingly.  In larger facilities,
       installation may occur simultaneously on various wings or floors, yet
       the end system must seamlessly merge.  Following are the scalability
       requirements.

    5.2.1.  Network Domain

       The routing protocol MUST be able to support networks with at least
       2,000 nodes, where 1,000 nodes would act as routers and the other
       1,000 nodes would be hosts.  Subnetworks (e.g., rooms, primary
       equipment) within the network must support up to 255 sensors and/or
       actuators.

    5.2.2.  Peer-to-Peer Communication

       The data domain for commercial BMSs may sprawl across a vast portion
       of the physical domain.  For example, a chiller may reside in the
       facility's basement due to its size, yet the associated cooling
       towers will reside on the roof.  The cold-water supply and return
       pipes snake through all of the intervening floors.  The feedback
       control loops for these systems require data from across the
       facility.

       A network device MUST be able to communicate in an end-to-end manner
       with any other device on the network.  Thus, the routing protocol
       MUST provide routes between arbitrary hosts within the appropriate
       administrative domain.

    5.3.  Mobility

       Most devices are affixed to walls or installed on ceilings within
       buildings.  Hence, the mobility requirements for commercial buildings
       are few.  However, in wireless environments, location tracking of
       occupants and assets is gaining favor.  Asset-tracking applications,
       such as tracking capital equipment (e.g., wheelchairs) in medical

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       facilities, require monitoring movement with granularity of a minute;
       however, tracking babies in a pediatric ward would require latencies
       less than a few seconds.

       The following subsections document the mobility requirements in the
       routing layer for mobile devices.  Note, however, that mobility can
       be implemented at various layers of the system, and the specific
       requirements depend on the chosen layer.  For instance, some devices
       may not depend on a static IP address and are capable of re-
       establishing application-level communications when given a new IP
       address.  Alternatively, mobile IP may be used, or the set of routers
       in a building may give an impression of a building-wide network and
       allow devices to retain their addresses regardless of where they are,
       handling routing between the devices in the background.

    5.3.1.  Mobile Device Requirements

       To minimize network dynamics, mobile devices while in motion should
       not be allowed to act as forwarding devices (routers) for other
       devices in the LLN.  Network configuration should allow devices to be
       configured as routers or hosts.

    5.3.1.1.  Device Mobility within the LLN

       An LLN typically spans a single floor in a commercial building.
       Mobile devices may move within this LLN.  For example, a wheelchair
       may be moved from one room on the floor to another room on the same
       floor.

       A mobile LLN device that moves within the confines of the same LLN
       SHOULD re-establish end-to-end communication with a fixed device also
       in the LLN within 5 seconds after it ceases movement.  The LLN
       network convergence time should be less than 10 seconds once the
       mobile device stops moving.

    5.3.1.2.  Device Mobility across LLNs

       A mobile device may move across LLNs, such as a wheelchair being
       moved to a different floor.

       A mobile device that moves outside of its original LLN SHOULD re-
       establish end-to-end communication with a fixed device also in the
       new LLN within 10 seconds after the mobile device ceases movement.
       The network convergence time should be less than 20 seconds once the
       mobile device stops moving.

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    5.4.  Resource Constrained Devices

       Sensing and actuator device processing power and memory may be 4
       orders of magnitude less (i.e., 10,000x) than many more traditional
       client devices on an IP network.  The routing mechanisms must
       therefore be tailored to fit these resource constrained devices.

    5.4.1.  Limited Memory Footprint on Host Devices

       The software size requirement for non-routing devices (e.g., sleeping
       sensors and actuators) SHOULD be implementable in 8-bit devices with
       no more than 128 KB of memory.

    5.4.2.  Limited Processing Power for Routers

       The software size requirements for routing devices (e.g., room
       controllers) SHOULD be implementable in 8-bit devices with no more
       than 256 KB of flash memory.

    5.4.3.  Sleeping Devices

       Sensing devices will, in some cases, utilize battery power or energy
       harvesting techniques for power and will operate mostly in a sleep
       mode to maintain power consumption within a modest budget.  The
       routing protocol MUST take into account device characteristics such
       as power budget.

       Typically, sensor battery life (2,000 mAh) needs to extend for at
       least 5 years when the device is transmitting its data (200 octets)
       once per minute over a low-power transceiver (25 mA) and expecting an
       application acknowledgment.  In this case, the transmitting device
       must leave its receiver in a high-powered state, awaiting the return
       of the application ACK.  To minimize this latency, a highly efficient
       routing protocol that minimizes hops, and hence end-to-end
       communication, is required.  The routing protocol MUST take into
       account node properties, such as "low-powered node", that produce
       efficient low-latency routes that minimize radio "on" time for these
       devices.

       Sleeping devices MUST be able to receive inbound data.  Messages sent
       to battery-powered nodes MUST be buffered by the last-hop router for
       a period of at least 20 seconds when the destination node is
       currently in its sleep cycle.

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    5.5.  Addressing

       Building management systems require different communication schemes
       to solicit or post network information.  Multicasts or anycasts need
       to be used to decipher unresolved references within a device when the
       device first joins the network.

       As with any network communication, multicasting should be minimized.
       This is especially a problem for small embedded devices with limited
       network bandwidth.  Multicasts are typically used for network joins
       and application binding in embedded systems.  Routing MUST support
       anycast, unicast, and multicast.

    5.6.  Manageability

       As previously noted in Section 3.3, installation of LLN devices
       within a BMS follows an "outside-in" work flow.  Edge devices are
       installed first and tested for communication and application
       integrity.  These devices are then aggregated into islands, then
       LLNs, and later affixed onto the enterprise network.

       The need for diagnostics most often occurs during the installation
       and commissioning phase, although at times diagnostic information may
       be requested during normal operation.  Battery-powered wireless
       devices typically will have a self-diagnostic mode that can be
       initiated via a button press on the device.  The device will display
       its link status and/or end-to-end connectivity when the button is
       pressed.  Lines-powered devices will continuously display
       communication status via a bank of LEDs, possibly denoting signal
       strength and end-to-end application connectivity.

       The local diagnostics noted above oftentimes are suitable for
       defining room-level networks.  However, as these devices aggregate,
       system-level diagnostics may need to be executed to ameliorate route
       vacillation, excessive hops, communication retries, and/or network
       bottlenecks.

       In operational networks, due to the mission-critical nature of the
       application, the LLN devices will be temporally monitored by the
       higher layers to assure that communication integrity is maintained.
       Failure to maintain this communication will result in an alarm being
       forwarded to the enterprise network from the monitoring node for
       analysis and remediation.

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       In addition to the initial installation and commissioning of the
       system, it is equally important for the ongoing maintenance of the
       system to be simple and inexpensive.  This implies a straightforward
       device swap when a failed device is replaced, as noted in Section
       5.1.3.

    5.6.1.  Diagnostics

       To improve diagnostics, the routing protocol SHOULD be able to be
       placed in and out of "verbose" mode.  Verbose mode is a temporary
       debugging mode that provides additional communication information
       including, at least, the total number of routed packets sent and
       received, the number of routing failures (no route available),
       neighbor table members, and routing table entries.  The data provided
       in verbose mode should be sufficient that a network connection graph
       could be constructed and maintained by the monitoring node.

       Diagnostic data should be kept by the routers continuously and be
       available for solicitation at any time by any other node on the
       internetwork.  Verbose mode will be activated/deactivated via
       unicast, multicast, or other means.  Devices having available
       resources may elect to support verbose mode continuously.

    5.6.2.  Route Tracking

       Route diagnostics SHOULD be supported, providing information such as
       route quality, number of hops, and available alternate active routes
       with associated costs.  Route quality is the relative measure of
       "goodness" of the selected source to destination route as compared to
       alternate routes.  This composite value may be measured as a function
       of hop count, signal strength, available power, existing active
       routes, or any other criteria deemed by ROLL as the route cost
       differentiator.

    5.7.  Route Selection

       Route selection determines reliability and quality of the
       communication among the devices by optimizing routes over time and
       resolving any nuances developed at system startup when nodes are
       asynchronously adding themselves to the network.

    5.7.1.  Route Cost

       The routing protocol MUST support a metric of route quality and
       optimize selection according to such metrics within constraints
       established for links along the routes.  These metrics SHOULD reflect
       metrics such as signal strength, available bandwidth, hop count,
       energy availability, and communication error rates.

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    5.7.2.  Route Adaptation

       Communication routes MUST be adaptive and converge toward optimality
       of the chosen metric (e.g., signal quality, hop count) in time.

    5.7.3.  Route Redundancy

       The routing layer SHOULD be configurable to allow secondary and
       tertiary routes to be established and used upon failure of the
       primary route.

    5.7.4.  Route Discovery Time

       Mission-critical commercial applications (e.g., fire, security)
       require reliable communication and guaranteed end-to-end delivery of
       all messages in a timely fashion.  Application-layer time-outs must
       be selected judiciously to cover anomalous conditions such as lost
       packets and/or route discoveries, yet not be set too large to over-
       damp the network response.  If route discovery occurs during packet
       transmission time (reactive routing), it SHOULD NOT add more than 120
       ms of latency to the packet delivery time.

    5.7.5.  Route Preference

       The routing protocol SHOULD allow for the support of manually
       configured static preferred routes.

    5.7.6.  Real-Time Performance Measures

       A node transmitting a "request with expected reply" to another node
       must send the message to the destination and receive the response in
       not more than 120 ms.  This response time should be achievable with 5
       or less hops in each direction.  This requirement assumes network
       quiescence and a negligible turnaround time at the destination node.

    5.7.7.  Prioritized Routing

       Network and application packet routing prioritization must be
       supported to assure that mission-critical applications (e.g., fire
       detection) cannot be deferred while less critical applications access
       the network.  The routing protocol MUST be able to provide routes
       with different characteristics, also referred to as Quality of
       Service (QoS) routing.

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    5.8.  Security Requirements

       This section sets forth specific requirements that are placed on any
       protocols developed or used in the ROLL building environment, in
       order to ensure adequate security and retain suitable flexibility of
       use and function of the protocol.

       Due to the variety of buildings and tenants, the BMSs must be
       completely configurable on-site.

       Due to the quantity of the BMS devices (thousands) and their
       inaccessibility (oftentimes above ceilings), security configuration
       over the network is preferred over local configuration.

       Wireless encryption and device authentication security policies need
       to be considered in commercial buildings, while keeping in mind the
       impact on the limited processing capabilities and additional latency
       incurred on the sensors, actuators, and controllers.

       BMSs are typically highly configurable in the field, and hence the
       security policy is most often dictated by the type of building to
       which the BMS is being installed.  Single-tenant owner-occupied
       office buildings installing lighting or HVAC control are candidates
       for implementing a low level of security on the LLN, especially when
       the LLN is not connected to an external network.  Antithetically,
       military or pharmaceutical facilities require strong security
       policies.  As noted in the installation procedures described in
       Sections 3.3 and 5.2, security policies MUST support dynamic
       configuration to allow for a low level of security during the
       installation phase (prior to building occupancy, when it may be
       appropriate to use only diagnostic levels of security), yet to make
       it possible to easily raise the security level network-wide during
       the commissioning phase of the system.

    5.8.1.  Building Security Use Case

       LLNs for commercial building applications should always implement and
       use encrypted packets.  However, depending on the state of the LLN,
       the security keys may either be:

       1) a key obtained from a trust center already operable on the LLN;

       2) a pre-shared static key as defined by the general contractor or
          its designee; or

       3) a well-known default static key.

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       Unless a node entering the network had previously received its
       credentials from the trust center, the entering node will try to
       solicit the trust center for the network key.  If the trust center is
       accessible, the trust center will MAC-authenticate the entering node
       and return the security keys.  If the trust center is not available,
       the entering node will check to determine if it has been given a
       network key by an off-band means and use it to access the network.
       If no network key has been configured in the device, it will revert
       to the default network key and enter the network.  If neither of
       these keys were valid, the device would signal via a fault LED.

       This approach would allow for independent simplified commissioning,
       yet centralized authentication.  The building owner or building type
       would then dictate when the trust center would be deployed.  In many
       cases, the trust center need not be deployed until all of the local
       room commissioning is complete.  Yet, at the province of the owner,
       the trust center may be deployed from the onset, thereby trading
       installation and commissioning flexibility for tighter security.

    5.8.2.  Authentication

       Authentication SHOULD be optional on the LLN.  Authentication SHOULD
       be fully configurable on-site.  Authentication policy and updates
       MUST be routable over-the-air.  Authentication SHOULD occur upon
       joining or rejoining a network.  However, once authenticated, devices
       SHOULD NOT need to reauthenticate with any other devices in the LLN.
       Packets may need authentication at the source and destination nodes;
       however, packets routed through intermediate hops should not need
       reauthentication at each hop.

       These requirements mean that at least one LLN routing protocol
       solution specification MUST include support for authentication.

    5.8.3.  Encryption

    5.8.3.1.  Encryption Types

       Data encryption of packets MUST be supported by all protocol solution
       specifications.  Support can be provided by use of a network-wide key
       and/or an application key.  The network key would apply to all
       devices in the LLN.  The application key would apply to a subset of
       devices in the LLN.

       The network key and application key would be mutually exclusive.  The
       routing protocol MUST allow routing a packet encrypted with an
       application key through forwarding devices without requiring each
       node in the route to have the application key.

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    5.8.3.2.  Packet Encryption

       The encryption policy MUST support either encryption of the payload
       only or of the entire packet.  Payload-only encryption would
       eliminate the decryption/re-encryption overhead at every hop,
       providing more real-time performance.

    5.8.4.  Disparate Security Policies

       Due to the limited resources of an LLN, the security policy defined
       within the LLN MUST be able to differ from that of the rest of the IP
       network within the facility, yet packets MUST still be able to route
       to or through the LLN from/to these networks.

    5.8.5.  Routing Security Policies to Sleeping Devices

       The routing protocol MUST gracefully handle routing temporal security
       updates (e.g., dynamic keys) to sleeping devices on their "awake"
       cycle to assure that sleeping devices can readily and efficiently
       access the network.

    6.  Security Considerations

       The requirements placed on the LLN routing protocol in order to
       provide the correct level of security support are presented in
       Section 5.8.

       LLNs deployed in a building environment may be entirely isolated from
       other networks, attached to normal IP networks within the building
       yet physically disjoint from the wider Internet, or connected either
       directly or through other IP networks to the Internet.  Additionally,
       even where no wired connectivity exists outside of the building, the
       use of wireless infrastructure within the building means that
       physical connectivity to the LLN is possible for an attacker.

       Therefore, it is important that any routing protocol solution
       designed to meet the requirements included in this document addresses
       the security features requirements described in Section 5.8.
       Implementations of these protocols will be required in the protocol
       specifications to provide the level of support indicated in Section
       5.8, and will be encouraged to make the support flexibly configurable
       to enable an operator to make a judgment of the level of security
       that they want to deploy at any time.

       As noted in Section 5.8, use/deployment of the different security
       features is intended to be optional.  This means that, although the
       protocols developed must conform to the requirements specified, the
       operator is free to determine the level of risk and the trade-offs

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       against performance.  An implementation must not make those choices
       on behalf of the operator by avoiding implementing any mandatory-to-
       implement security features.

       This informational requirements specification introduces no new
       security concerns.

    7.  Acknowledgments

       In addition to the authors, JP. Vasseur, David Culler, Ted Humpal,
       and Zach Shelby are gratefully acknowledged for their contributions
       to this document.

    8.  References

    8.1.  Normative References

       [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
                   Requirement Levels", BCP 14, RFC 2119, March 1997.

    8.2.  Informative References

       [ROLL-TERM] Vasseur, JP., "Terminology in Low power And Lossy
                   Networks", Work in Progress, March 2010.

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    Appendix A.  Additional Building Requirements

       Appendix A contains additional building requirements that were deemed
       out of scope for ROLL, yet provided ancillary substance for the
       reader.

    A.1.  Additional Commercial Product Requirements

    A.1.1.  Wired and Wireless Implementations

       Vendors will likely not develop a separate product line for both
       wired and wireless networks.  Hence, the solutions set forth must
       support both wired and wireless implementations.

    A.1.2.  World-Wide Applicability

       Wireless devices must be supportable unlicensed bands.

    A.2.  Additional Installation and Commissioning Requirements

    A.2.1.  Unavailability of an IP Network

       Product commissioning must be performed by an application engineer
       prior to the installation of the IP network (e.g., switches, routers,
       DHCP, DNS).

    A.3.  Additional Network Requirements

    A.3.1.  TCP/UDP

       Connection-based and connectionless services must be supported.

    A.3.2.  Interference Mitigation

       The network must automatically detect interference and seamlessly
       switch the channel to improve communication.  Channel changes, and
       the nodes' responses to a given channel change, must occur within 60
       seconds.

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    A.3.3.  Packet Reliability

       In building automation, it is required that the network meet the
       following minimum criteria:

       <1% MAC-layer errors on all messages, after no more than three
       retries;

       <0.1% network-layer errors on all messages, after no more than three
       additional retries;

       <0.01% application-layer errors on all messages.

       Therefore, application-layer messages will fail no more than once
       every 100,000 messages.

    A.3.4.  Merging Commissioned Islands

       Subsystems are commissioned by various vendors at various times
       during building construction.  These subnetworks must seamlessly
       merge into networks and networks must seamlessly merge into
       internetworks since the end user wants a holistic view of the system.

    A.3.5.  Adjustable Routing Table Sizes

       The routing protocol must allow constrained nodes to hold an
       abbreviated set of routes.  That is, the protocol should not mandate
       that the node routing tables be exhaustive.

    A.3.6.  Automatic Gain Control

       For wireless implementations, the device radios should incorporate
       automatic transmit power regulation to maximize packet transfer and
       minimize network interference, regardless of network size or density.

    A.3.7.  Device and Network Integrity

       Commercial-building devices must all be periodically scanned to
       assure that each device is viable and can communicate data and alarm
       information as needed.  Routers should maintain previous packet flow
       information temporally to minimize overall network overhead.

    A.4.  Additional Performance Requirements

    A.4.1.  Data Rate Performance

       An effective data rate of 20 kbit/s is the lowest acceptable
       operational data rate on the network.

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    A.4.2.  Firmware Upgrades

       To support high-speed code downloads, routing should support
       transports that provide parallel downloads to targeted devices, yet
       guarantee packet delivery.  In cases where the spatial position of
       the devices requires multiple hops, the algorithm should recurse
       through the network until all targeted devices have been serviced.
       Devices receiving a download may cease normal operation, but upon
       completion of the download must automatically resume normal
       operation.

    A.4.3.  Route Persistence

       To eliminate high network traffic in power-fail or brown-out
       conditions, previously established routes should be remembered and
       invoked prior to establishing new routes for those devices re-
       entering the network.

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    Authors' Addresses

       Jerry Martocci
       Johnson Controls Inc.
       507 E. Michigan Street
       Milwaukee, WI  53202
       USA
       Phone: +1 414 524 4010
       EMail: jerald.p.martocci@jci.com

       Pieter De Mil
       Ghent University - IBCN
       G. Crommenlaan 8 bus 201
       Ghent  9050
       Belgium
       Phone: +32 9331 4981
       Fax:   +32 9331 4899
       EMail: pieter.demil@intec.ugent.be

       Nicolas Riou
       Schneider Electric
       Technopole 38TEC T3
       37 quai Paul Louis Merlin
       38050 Grenoble Cedex 9
       France
       Phone: +33 4 76 57 66 15
       EMail: nicolas.riou@fr.schneider-electric.com

       Wouter Vermeylen
       Arts Centre Vooruit
       Ghent  9000
       Belgium
       EMail: wouter@vooruit.be

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