]> Telchemy Incorporated

2905 Premiere Parkway, Suite 280 Duluth GA 30097 USA alan.d.clark@telchemy.com

Aalto University

School of Electrical Engineering Otakaari 5 A Espoo FIN 02150 Finland varun@comnet.tkk.fi

Huawei

101 Software Avenue, Yuhua District Nanjing Jiangsu 210012 China sunseawq@huawei.com

Real-time Applications and Infrastructure Area Audio/Video Transport Working Group RFC Request for Comments I-D Internet-Draft Real Time Control Protocol This document defines an RTP Control Protocol (RTCP) Extended Report (XR) Block that allows the reporting of Jitter Buffer metrics for a range of RTP applications.

This document defines a new block type to augment those defined in , for use in a range of RTP applications. The new block type provides information on jitter buffer configuration and performance. The metric belongs to the class of transport-related end system metrics defined in . Instances of this Metrics Block refer by Synchronization source (SSRC) to the separate auxiliary Measurement Information block which contains information such as the SSRC of the measured stream, and RTP sequence numbers and time intervals indicating the span of the report.

The use of RTCP for reporting is defined in . defines an extensible structure for reporting using an RTCP Extended Report (XR). This document defines a new Extended Report block for use with and .

The Performance Metrics Framework provides guidance on the definition and specification of performance metrics. The RTP Monitoring Architectures provides guideline for reporting block format using RTCP XR. Metrics described in this draft are in accordance with the guidelines in and .

Real-time applications employ a jitter buffer to absorb jitter introduced on the path from source to destination. These metrics are used to report how the jitter buffer at the receiving end of RTP stream behaves as a result of jitter in the network and are applicable to a range of RTP applications. These metrics reflect how terminal-related factors affect real-time application quality and are useful to provide better end-user quality of experience (QoE).

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 RFC 2119.

A jitter buffer is required to absorb delay variation in network delivery of media packets. A jitter buffer works by holding media data for a period of time after it is received and before it is played out. Packets that arrive early are held in the jitter buffer longer. If packets arrive too early they may be discarded if there is no available jitter buffer space. If packets are delayed excessively by the network they may be discarded if they miss their playout time. Overall user perceived delay = network round trip delay + local (jitter buffer (nominal) delay + encoder serialization delay) + remote (jitter buffer (nominal) delay + encoder serialization delay) The jitter buffer can be considered as a time window with early edge aligned with the delay corresponding to the earliest arriving packet and late edge representing the maximum permissible delay before a late arriving packet would be discarded. The delay applied to packets that arrive at their expected time is known as the Nominal Delay and this is equivalent to the late edge. The reference for the expected arrival time may, for example, be the first packet in the session or the running average delay. If all packets arrived at their expected arrival time then then every packet would be held in the jitter buffer exactly the Nominal Delay. The Jitter Buffer maximum delay is the delay that is applied to an earliest arriving packet that is not discarded and corresponds to the early edge of the jitter buffer time window.

In practice jitter buffer implementations vary considerably however should behave in a manner conceptually consistent with an idealized jitter buffer described as follows: (i). Receive the first packet and delay playout by D ms. Keep the RTP timestamp and receive time as a reference.RTP TS[1]receive time[1]Assume that both are normalized in ticks. (ii). Receive the next packet (iii). Calculate r = RTP TS[n] - RTP TS[1] and t = receive time[n] - receive time[1]. If r = t then the packet arrived on time. If r < t then the packet arrived late and if r > t then the packet arrived early. (iv). Delay playout of packet by D + (r -t) (v). Go back to (ii) Note that this idealized implementation assumes that the sender's RTP clock is synchronized to the clock in the receiver which is used to timestamp packet arrivals. If there is no such inherent synchronization, the system may need to use an adaptive jitter buffer or other techniques to ensure reliable reception.

The fixed jitter buffers have a fixed size and the packets leaving the jitter buffer have a constant delay.

An adaptive jitter buffer have variable size and variable delay. It allows the nominal delay to be set to a low value initially, to minimize user perceived delay, however can automatically extend the late edge (and possibly also retract the early edge) of buffer window if a significant proportion of packets are arriving late (and hence being discarded).

This block describes the configuration and operating parameters of the jitter buffer in the receiver of the RTP end system or RTP mixer which sends the report. Instances of this Metrics Block refer by SSRC to the separate auxiliary Measurement Information block which describes the measurement interval in use. This Metrics Block relies on the measurement interval in the Measurement Information block indicating the span of the report and should be sent in the same compound RTCP packet as the measurement information block. If the measurement interval is not received in the same compound RTCP packet as this Metrics Block, this Metrics Block should be discarded.

JB Metrics Block

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BT=NJB | I |C| Rsvd. | block length=3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC of Source | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | JB nominal | JB maximum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | JB high water mark | JB low water mark | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A Jitter Buffer Metrics Report Block is identified by the constant NJB. [Note to RFC Editor: please replace NJB with the IANA provided RTCP XR block type for this block.] This field is used to indicate whether the Jitter Buffer metrics are Sampled, Interval or Cumulative metrics: I=01: Sampled Value - the reported value is a sampled instantaneous value. I=10: Interval Duration - the reported value applies to the most recent measurement interval duration between successive metrics reports. I=11: Cumulative Duration - the reported value applies to the accumulation period characteristic of cumulative measurements. This field is used to identify the jitter buffer method in use at the receiver, according to the following code: 0 = Fixed jitter buffer 1 = Adaptive jitter buffer These bits are reserved. They MUST be set to zero by senders ignored by receivers (See section 4.2). The length of this report block in 32-bit words, minus one, in accordance with the definition in . This field MUST be set to 3 to match the fixed length of the report block. This is the current nominal jitter buffer delay in milliseconds, which corresponds to the nominal jitter buffer delay for packets that arrive exactly on time. It is calculated based on the time spend in the jitter buffer for the packet that arrives exactly on time. This parameter MUST be provided for both fixed and adaptive jitter buffer implementations. If the measured value exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF MUST be reported. This is the current maximum jitter buffer delay in milliseconds which corresponds to the earliest arriving packet that would not be discarded. It is calculated based on the time spent in the jitter buffer for the earliest arriving packet In simple queue implementations this may correspond to the size of the jitter buffer. In adaptive jitter buffer implementations, this value may vary dynamically. This parameter MUST be provided for both fixed and adaptive jitter buffer implementations. If the measured value exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF MUST be reported. This is the highest value of the jitter buffer nominal delay in milliseconds which occurred at any time during the reporting interval. This parameter MUST be provided for adaptive jitter buffer implementations and its value MUST be set to JB maximum for fixed jitter buffer implementations. If the measured value exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF MUST be reported. This is the lowest value of the jitter buffer nominal delay in milliseconds which occurred at any time during the reporting interval. This parameter MUST be provided for adaptive jitter buffer implementations and its value MUST be set to JB maximum for fixed jitter buffer implementations. If the measured value exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF MUST be reported.

[RFC3611] defines the use of SDP (Session Description Protocol) for signaling the use of XR blocks. However XR blocks MAY be used without prior signaling (see section 5 of RFC3611).

This section augments the SDP attribute "rtcp-xr" defined in by providing an additional value of "xr-format" to signal the use of the report block defined in this document.

xr-format =/ xr-jb-block xr-jb-block = "jitter-bfr"

When SDP is used in offer-answer context, the SDP Offer/Answer usage defined in for unilateral "rtcp-xr" attribute parameters applies. For detailed usage of Offer/Answer for unilateral parameter, refer to section 5.2 of .

New block types for RTCP XR are subject to IANA registration. For general guidelines on IANA considerations for RTCP XR, refer to .

This document assigns the block type value NJB in the IANA "RTCP XR Block Type Registry" to the "JB Metrics Block". [Note to RFC Editor: please replace NJB with the IANA provided RTCP XR block type for this block.]

This document also registers a new parameter "jitter-bfr" in the "RTCP XR SDP Parameters Registry".

The contact information for the registrations is: Qin Wu (sunseawq@huawei.com) 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China

It is believed that this proposed RTCP XR report block introduces no new security considerations beyond those described in . This block does not provide per-packet statistics so the risk to confidentiality documented in Section 7, paragraph 3 of does not apply.

Geoff Hunt wrote the initial draft of this document.

The authors gratefully acknowledge reviews and feedback provided by Bruce Adams, Philip Arden, Amit Arora, Bob Biskner, Kevin Connor, Claus Dahm, Randy Ethier, Roni Even, Jim Frauenthal, Albert Higashi, Tom Hock, Shane Holthaus, Paul Jones, Rajesh Kumar, Keith Lantz, Mohamed Mostafa, Amy Pendleton, Colin Perkins, Mike Ramalho, Ravi Raviraj, Albrecht Schwarz, Tom Taylor, Hideaki Yamada,Claire Bi,Colin Perkin, Dan Romascanu, Kevin Gross and Glen Zorn.

Harvard University

1350 Mass. Ave. Cambridge MA 02138 - +1 617 495 3864 sob@harvard.edu

General keyword In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. Authors who follow these guidelines should incorporate this phrase near the beginning of their document: 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 RFC 2119. Note that the force of these words is modified by the requirement level of the document in which they are used. This document defines the Extended Report (XR) packet type for the RTP Control Protocol (RTCP), and defines how the use of XR packets can be signaled by an application if it employs the Session Description Protocol (SDP). XR packets are composed of report blocks, and seven block types are defined here. The purpose of the extended reporting format is to convey information that supplements the six statistics that are contained in the report blocks used by RTCP's Sender Report (SR) and Receiver Report (RR) packets. Some applications, such as multicast inference of network characteristics (MINC) or voice over IP (VoIP) monitoring, require other and more detailed statistics. In addition to the block types defined here, additional block types may be defined in the future by adhering to the framework that this document provides. This memo defines the Session Description Protocol (SDP). SDP is intended for describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation. [STANDARDS-TRACK] Columbia University

jitter buffer nominal delay Metric Metric Name: jitter buffer nominal delay Metric Description: The "expected arrival time" is the time that a RTP packet would arrive if there was no delay variation. The delay applied to packets that arrive at their expected time is known as the Nominal Delay. Method of Measurement or Calculation: See section 4.2, jitter buffer nominal delay definition for measurement or calculation method. Units of Measurement: See section 4.2, jitter buffer nominal delay definition for units of measurement. Measurement Point(s) with Potential Measurement Domain: See section 4, 1st paragraph for measurement point. Measurement Timing: See section 4, 1st paragraph for measurement timing and section 4.2 paragraph for Interval Metric flag. Use and applications: See section 1.4 for use and applications. Reporting model: See RFC3611 for reporting model. jitter buffer maximum delay Metric Metric Name: jitter buffer maximum delay Metric Description: It is the current maximum jitter buffer delay for RTP traffic which corresponds to the earliest arriving packet that would not be discarded. Method of Measurement or Calculation: See section 4.2, jitter buffer maximum delay definition and section 3, the last paragraph for measurement or calculation method. Units of Measurement: See section 4.2, jitter buffer maximum delay definition for units of measurement. Measurement Point(s) with Potential Measurement Domain: See section 4, 1st paragraph for measurement point. Measurement Timing: See section 4, 1st paragraph for measurement timing and section 4.2 paragraph for Interval Metric flag. Use and applications: See section 1.4 for use and applications. Reporting model: See RFC3611 for reporting model. jitter buffer high water mark Metric Metric Name: jitter buffer high water mark Metric Description: It is the highest value of the jitter buffer nominal delay for RTP traffic which occurred at any time during the reporting interval. Method of Measurement or Calculation: See section 4.2, jitter buffer high water mark definition for measurement or calculation method. Units of Measurement: See section 4.2, jitter buffer nominal delay definition for units of measurement. Measurement Point(s) with Potential Measurement Domain: See section 4, 1st paragraph for measurement point. Measurement Timing: See section 4, 1st paragraph for measurement timing and section 4.2 paragraph for Interval Metric flag. Use and applications: See section 1.4 for use and applications. Reporting model: See RFC3611 for reporting model. jitter buffer low water mark Metric Metric Name: jitter buffer low water mark Metric Description: It is the lowest value of the jitter buffer nominal delay for RTP traffic which occurred at any time during the reporting interval. Method of Measurement or Calculation: See section 4.2, jitter buffer low water mark definition for measurement or calculation method. Units of Measurement: See section 4.2, jitter buffer low water mark definition for units of measurement. Measurement Point(s) with Potential Measurement Domain: See section 4, 1st paragraph for measurement point. Measurement Timing: See section 4, 1st paragraph for measurement timing and section 4.2 paragraph for Interval Metric flag. Use and applications: See section 1.4 for use and applications. Reporting model: See RFC3611 for reporting model.

Note to the RFC-Editor: please remove this section prior to publication as an RFC.

The following are the major changes to previous version : Incorporate proposed changes by Kevin and proposed text by Alan to address interoperability report issue. Add new appendix to format metrics using RFC6390 template.

The following are the major changes to previous version : Rewrote descriptive text and definitions for clarification.

The following are the major changes to previous version : Add one new section to discuss jitter buffer operation.

The following are the major changes to previous version : Some editorial change changes based on the discussion with Glen and Kevin on the list.

The following are the major changes to previous version : Reduce the "jb cfg" to 1-bit based on discussion in the WGLC. Other editorial change changes aligning with PDV,Delay draft.

The following are the major changes to previous version : Add some explanation text in the SDP offer/answer section. Add some text in applicability section to explain the use to report jitter buffer metrics. Other editorial change changes aligning with PDV,Delay draft.

The following are the major changes to previous version : Outdated reference update Add one Editor notes to ask clarification on the use of reporting jitter buffer metrics. Other Editorial changes.

The following are the major changes to previous version : Boilerplate updates. references updates allocate 32 bit field in report block for SSRC Other editorial changes to get alignment with MONARCH draft.