Audio/Video Transport Working G. Hunt Group BT Internet-Draft A. Clark Intended status: Standards Track Telchemy Expires: April 28, 2009 October 25, 2008 RTCP XR Report Block for Discard metric Reporting draft-ietf-avt-rtcp-xr-discard-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 28, 2009. Hunt & Clark Expires April 28, 2009 [Page 1] Internet-Draft RTCP XR Discard October 2008 Abstract This document defines an RTCP XR Report Block that allows the reporting of a simple discard count metric for use in a range of RTP applications. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Discard Report Block . . . . . . . . . . . . . . . . . . . 3 1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3 1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3 1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Discard Metric Report Block . . . . . . . . . . . . . . . . . 6 3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 6 3.2. Definition of Fields in Discard Metric Report Block . . . 6 4. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . . 12 8.2. Informative References . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 Intellectual Property and Copyright Statements . . . . . . . . . . 14 Hunt & Clark Expires April 28, 2009 [Page 2] Internet-Draft RTCP XR Discard October 2008 1. Introduction 1.1. Discard Report Block This draft defines a new block type to augment those defined in [RFC3611] 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 [RFC5109] or retransmission [RFC4588]) and to those which do not. This metric is useful for identifying the existence, and characterising the severity, of a packet transport problem which may affect users' perception of a service delivered over RTP. The metric belongs to the class of transport-related terminal metrics defined in [MONARCH] (work in progress). Instances of this Metrics Block refer by tag to the separate auxiliary Measurement Identity block [MEASIDENT] 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 Measurement Identity block provides extended sequence numbers for the beginning and end of both Interval and Cumulative reporting periods. This allows systems receiving the report to calculate the number of packets expected. 1.2. RTCP and RTCP XR Reports The use of RTCP for reporting is defined in [RFC3550]. [RFC3611] defined an extensible structure for reporting using an RTCP Extended Report (XR). This draft defines a new Extended Report block that MUST be used as defined in [RFC3550] and [RFC3611]. 1.3. Performance Metrics Framework The Performance Metrics Framework [PMOLFRAME] provides guidance on the definition and specification of performance metrics. Metrics described in this draft either reference external definitions or define metrics generally in accordance with the guidelines in [PMOLFRAME]. Hunt & Clark Expires April 28, 2009 [Page 3] Internet-Draft RTCP XR Discard October 2008 1.4. Applicability This metric is believed to be applicable to a large class of RTP applications which use a jitter buffer. Hunt & Clark Expires April 28, 2009 [Page 4] Internet-Draft RTCP XR Discard October 2008 2. Definitions Received, Lost and Discarded 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 shall be regarded as discarded. A packet shall be classified as one of received (or OK), discarded or lost. The Discard Metric counts only discarded packets. The metric "cumulative number of packets lost" defined in [RFC3550] reports a count of lost packets in the primary media stream. Another metric defined in [POSTREPAIRLOSS] is available to report on packets which are not recovered by any repair techniques which may be in use. If Voice Activity Detection is used then the proportion of packets lost and discarded shall be determined based on transmitted packets, i.e. packets that contained silence and were not transmitted shall not be considered, because they do not form part of the RTP sequence. Hunt & Clark Expires April 28, 2009 [Page 5] Internet-Draft RTCP XR Discard October 2008 3. Discard Metric Report Block 3.1. Report Block Structure 0 1 2 3 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | BT=ND |I| tag | resv | block length=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | number of packets discarded | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Report Block Structure 3.2. Definition of Fields in Discard Metric Report Block block type (BT): 8 bits A Discard Metric Report Block is identified by the constant ND. [Note to RFC Editor: please replace ND with the IANA provided RTCP XR block type for this block.] Interval Metric flag (I): 1 bit This field is used to indicate whether the Discard metric is an Interval or a Cumulative metric, that is, whether the reported value applies to the most recent measurement interval duration between successive metrics reports (I=1) (the Interval Duration) or to the accumulation period characteristic of cumulative measurements (I=0) (the Cumulative Duration). Numerical values for both these intervals are provided in the Measurement Identifier block referenced by the tag field below. Measurement Identifier association (tag): 3 bits This field is used to identify the Measurement Identifier block [MEASIDENT] which describes this measurement. The relevant Measurement Identifier block has the same tag value as the Discard Metric block. Note that there may be more than one Measurement Identifier block per RTCP packet. Reserved (resv): 4 bits These bits are reserved. They SHOULD be set to zero by senders and MUST be ignored by receivers. block length: 16 bits Hunt & Clark Expires April 28, 2009 [Page 6] Internet-Draft RTCP XR Discard October 2008 The length of this report block in 32-bit words minus one. For the Discard Metric block, the block length is equal to 1. Number of packets lost: 32 bits Number of packets discarded over the period (Interval or Cumulative) covered by this report. If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFFFF SHOULD be reported. Note that the number of packets expected in the period covered by the metric (whether interval or cumulative) is available from the difference between a pair of extended sequence numbers in the Measurement Identity block, so need not be repeated in this block. Hunt & Clark Expires April 28, 2009 [Page 7] Internet-Draft RTCP XR Discard October 2008 4. SDP Signaling [RFC3611] defines the use of SDP (Session Description Protocol) [RFC4566] for signaling the use of XR blocks. XR blocks MAY be used without prior signaling. This section augments the SDP [RFC4566] attribute "rtcp-xr" defined in [RFC3611] by providing an additional value of "xr-format" to signal the use of the report block defined in this document. rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF (defined in RFC3611) xr-format = xr-format / xr-pd-block xr-pd-block = "xr-pd" Hunt & Clark Expires April 28, 2009 [Page 8] Internet-Draft RTCP XR Discard October 2008 5. IANA Considerations This document creates a new block type within the IANA "RTCP XR Block Type Registry" called the Discard Metric Block, and a new parameter xr-pd within the "RTCP XR SDP Parameters Registry". Hunt & Clark Expires April 28, 2009 [Page 9] Internet-Draft RTCP XR Discard October 2008 6. Security Considerations It is believed that this proposed RTCP XR report block introduces no new security considerations beyond those described in [RFC3611]. This block does not provide per-packet statistics so the risk to confidentiality documented in Section 7, paragraph 3 of [RFC3611] does not apply. Hunt & Clark Expires April 28, 2009 [Page 10] Internet-Draft RTCP XR Discard October 2008 7. Contributors The authors gratefully acknowledge the comments and contributions made 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. Hunt & Clark Expires April 28, 2009 [Page 11] Internet-Draft RTCP XR Discard October 2008 8. References 8.1. Normative References [MEASIDENT] Hunt, G., "RTCP XR Measurement Identifier Block", ID draft-ietf-avt-rtcp-xr-measid-00, August 2008. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, March 1997. [RFC3550] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time Applications", RFC 3550, July 2003. [RFC3611] Friedman, T., "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, November 2003. [RFC4566] Handley, M., "SDP: Session Description Protocol", RFC 4566, July 2006. 8.2. Informative References [MONARCH] Hunt, G., "Monitoring Architectures for RTP", ID draft-hunt-avt-monarch-01, August 2008. [PMOLFRAME] Clark, A., "Framework for Performance Metric Development", ID draft-ietf-pmol-metrics-framework-00, July 2008. [POSTREPAIRLOSS] Hunt, G., "RTCP XR Report Block for Post-Repair Loss metric Reporting", ID draft-ietf-rtcp-xr-postrepair-loss-00, October 2008. [RFC4588] Rey, J., "RTP Retransmission Payload Format", RFC 4588, July 2006. [RFC5109] Li, A., "RTP Payload Format for Generic Forward Error Correction", RFC 5109, December 2007. Hunt & Clark Expires April 28, 2009 [Page 12] Internet-Draft RTCP XR Discard October 2008 Authors' Addresses Geoff Hunt BT Orion 1 PP9 Adastral Park Martlesham Heath Ipswich, Suffolk IP4 2TH United Kingdom Phone: +44 1473 608325 Email: geoff.hunt@bt.com Alan Clark Telchemy Incorporated 2905 Premiere Parkway, Suite 280 Duluth, GA 30097 USA Email: alan.d.clark@telchemy.com Hunt & Clark Expires April 28, 2009 [Page 13] Internet-Draft RTCP XR Discard October 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Hunt & Clark Expires April 28, 2009 [Page 14]