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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 a simple discard count metric for use in 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 supports the reporting of the number of packets which are received correctly but are never played out, typically because they arrive too late to be played out (buffer underflow) or too early (buffer overflow). The metric is applicable both to systems which use packet loss repair techniques (such as forward error correction or retransmission ) and to those which do not. This metric is useful for identifying the existence, and characterizing the severity, of a packet transport problem which may affect users' perception of a service delivered over RTP. This block may be used in conjunction with which provides additional information on the pattern of discarded packets. However the metric in may be used independently of the metrics in this block. In case of Discard count Metrics Block sent together with Burst gap discard Metrics Block defined in to the media sender or RTP based network management system, information carried in the discard count Metrics Block and Burst gap discard Metrics Block allows them calculate the some bust gap summary statistics, e.g., gap discard rate. The metric belongs to the class of transport-related end system metrics defined in .

The use of RTCP for reporting is defined in . defined 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. The Metrics Block described in this document are in accordance with the guidelines in and .

This metric is believed to be applicable to a large class of RTP applications which use a jitter buffer. Discards due to late or early arriving packets affects user experience. The reporting of discards alerts senders and other receivers to the need to adjust their transmission or reception strategies. The reports allow network managers to diagnose these user experience problems. The ability to detect duplicate packets can be used by managers to detect network layer or sender behavior which may indicate network or device issues. Based on the reports, these issues may be addressed prior to any impact on user experience.

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. In addition, the following terms are defined: A packet shall be regarded as lost if it fails to arrive within an implementation-specific time window. A packet that arrives within this time window but is too early or late to be played out or thrown away before playout due to packet duplication or redundancy shall be regarded as discarded. A packet shall be classified as one of received (or OK), discarded or lost. The Discard Count Metric counts only discarded packets. The metric "cumulative number of packets lost" defined in reports a count of packets lost from the media stream (single SSRC within single RTP session). Similarly the metric "number of packets discarded" reports a count of packets discarded from the media stream (single SSRC within single RTP session) arriving at the receiver. Another metric defined in is available to report on packets which are not recovered by any repair techniques which may be in use.

Metrics in this block report on the number of packets discarded in the stream arriving at the RTP end system. The measurement of these metrics is made at the receiving end of the RTP stream. Instances of this Metrics Block refer by SSRC to the separate auxiliary Measurement Information block which describes measurement Intervals in use. This Metrics Block relies on the measurement interval in the Measurement Information block indicating the span of the report and MUST 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 MUST be discarded.

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=PDC | I |DT | resv.| block length = 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC of Source | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | number of packets discarded | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A Discard Count Metric Report Block is identified by the constant PDC. [Note to RFC Editor: please replace PDC with the IANA provided RTCP XR block type for this block.] This field indicates whether the reported metric is an interval, cumulative, or sampled metric . The Discard Count Metric can only be measured over definite intervals, and cannot be sampled. Accordingly, the value I=01, indicating a sampled value, MUST NOT be sent, and MUST be discarded when received. In addition, the value I=00 is reserved and also MUST NOT be sent, and MUST be discarded when received. This field is used to identify the discard type used in this report block. The discard type is defined as follows: 00: Report packet discarded or being thrown away before playout due to packets duplication. 01: Report packet discarded due to too early to be played out. 10: Report packet discarded due to too late to be played out. The value DT=11 is reserved for future definition and MUST NOT be Sent,and MUST be discarded when received.An endpoint MAY report any combination of discard types in each reporting interval by including several Discard Count Metric Report Blocks in a single RTCP XR packet.Some systems send duplicate RTP packets for robustness or error resilience. This is NOT RECOMMENDED since it breaks RTCP packet statistics. If duplication is desired for error resilience, the mechanism described in can be used, since this will not cause breakage of RTP streams or RTCP statistics. These bits are reserved. They MUST be set to zero by senders and ignored by receivers (See RFC6709 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 2 to match the fixed length of the report block. The block MUST be discarded if the block length is set to a different value. As defined in Section 4.1 of . Number of packets discarded over the period (Interval or Cumulative) covered by this report. The measured value is unsigned value. If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFFFF MUST be reported. Note that the number of packets expected in the period associated with this metric (whether interval or cumulative) is available from the difference between a pair of extended sequence numbers in the Measurement Information block , so need not be repeated in this block.

[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-pdc-block xr-pdc-block = "pkt-discard-count"

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 PDC in the IANA " RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry " to the "Discard Count Metrics Block". [Note to RFC Editor: please replace PDC with the IANA provided RTCP XR block type for this block.]

This document also registers a new parameter "pkt-discard-count" in the " RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters Registry ".

The following contact information is provided for all registrations in this document: 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, and Hideaki Yamada, Kevin Gross, Varun Singh, Claire Bi, Roni Even, Dan Romascanu and Jonathan Lennox.

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

RFC EDITOR NOTE: please change XXXX in [RFCXXXX] by the new RFC number, when assigned. Number of packets discarded Metric Metric Name: Number of RTP packets discarded Metric Metric Description: Number of RTP packets discarded over the period covered by this report. Method of Measurement or Calculation: See section 3.2, number of packets discarded definition [RFCXXXX]. Units of Measurement: See section 3.2, number of packets discarded definition [RFCXXXX]. Measurement Point(s) with Potential Measurement Domain: See section 3, 1st paragraph [RFCXXXX]. Measurement Timing: See section 3, 1st paragraph [RFCXXXX] for measurement timing and section 3.2 [RFCXXXX] for Interval Metric flag. Use and applications: See section 1.4 [RFCXXXX]. Reporting model: See RFC3611.

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

The following are the major changes compared to previous version: Incorporate some changes to burst gap draft that applies to this document. Use RFC6390 template to the metrics in the appendix.

The following are the major changes compared to previous version: Editorial change t based on SDP Directorate and Colin's Review.

The following are the major changes compared to previous version: Editorial change to get in line with recently discussed drafts. Remove DT=3 based on the discussion to summary statistics draft.

The following are the major changes compared to previous version: SDP Duplicated Parameter Deleting.

The following are the major changes compared to previous version: Outdated reference update. Editorial changes based on comments that applied to PDV and Delay drafts.