Audio/Video Transport Working G. Hunt Group BT Internet-Draft A. Clark Intended status: Standards Track Telchemy Expires: August 29, 2009 February 25, 2009 RTCP XR Report Block for Post-Repair Loss metric Reporting draft-ietf-avt-rtcp-xr-postrepair-loss-01.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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 August 29, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Hunt & Clark Expires August 29, 2009 [Page 1] Internet-Draft RTCP XR Post-Repair Loss February 2009 Abstract This document defines an RTCP XR Report Block that allows the reporting of a simple post-repair loss count metric for use in a range of RTP applications. It complements the pre-repair loss count metric "cumulative number of packets lost" provided by RFC3550. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Post-Repair Loss 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. Post-Repair Loss Metric Report Block . . . . . . . . . . . . . 6 3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 6 3.2. Definition of Fields in Post-Repair Loss Metric Report Block . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 9 5.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 9 5.3. Contact information for registrations . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11 8. Changes since last version . . . . . . . . . . . . . . . . . . 12 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 9.1. Normative References . . . . . . . . . . . . . . . . . . . 13 9.2. Informative References . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Hunt & Clark Expires August 29, 2009 [Page 2] Internet-Draft RTCP XR Post-Repair Loss February 2009 1. Introduction 1.1. Post-Repair Loss 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 remain unavailable to the application after the use of any available repair mechanism, such as forward error correction or retransmission. 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. [POSTREPAIRRLE] defines an RTCP XR block for more detailed packet-by- packet reporting of post-repair packet loss. The metric belongs to the class of post-repair loss 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 August 29, 2009 [Page 3] Internet-Draft RTCP XR Post-Repair Loss February 2009 1.4. Applicability This metric is believed to be applicable to all RTP applications which use a packet loss repair technique, such as FEC [RFC5109] or retransmission [RFC4588]. Hunt & Clark Expires August 29, 2009 [Page 4] Internet-Draft RTCP XR Post-Repair Loss February 2009 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. However the Post-Repair Loss Metric does not attempt to discriminate among the possible reasons which led to the lost packets' not being available in the post- repair stream. RTCP [RFC3550] reports on total lost packets. A separate metric [DISCARD] is available to report on total discarded packets. Hunt & Clark Expires August 29, 2009 [Page 5] Internet-Draft RTCP XR Post-Repair Loss February 2009 3. Post-Repair Loss 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=NPRL |I| tag | resv | block length=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | number of packets lost | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Report Block Structure 3.2. Definition of Fields in Post-Repair Loss Metric Report Block block type (BT): 8 bits A Post-Repair Loss Metric Report Block is identified by the constant NPRL. [Note to RFC Editor: please replace NPRL 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 Post-Repair Loss 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 Post- Repair Loss 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. Hunt & Clark Expires August 29, 2009 [Page 6] Internet-Draft RTCP XR Post-Repair Loss February 2009 block length: 16 bits The length of this report block in 32-bit words minus one. For the Post-Repair Loss Metric block, the block length is equal to 1. Number of packets lost: 32 bits Number of packets lost over the period (Interval or Cumulative) covered by this report, after application of repair procedures. Where repair procedures may achieve partial repair of a packet, a packet which is only partially repaired SHOULD be counted as lost. 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 August 29, 2009 [Page 7] Internet-Draft RTCP XR Post-Repair Loss February 2009 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-prl-block xr-prl-block = "post-repair-loss" Hunt & Clark Expires August 29, 2009 [Page 8] Internet-Draft RTCP XR Post-Repair Loss February 2009 5. IANA Considerations New block types for RTCP XR are subject to IANA registration. For general guidelines on IANA considerations for RTCP XR, refer to [RFC3611]. 5.1. New RTCP XR Block Type value This document assigns the block type value NPRL in the IANA "RTCP XR Block Type Registry" to the "Post-Repair Loss Metrics Block". [Note to RFC Editor: please replace NPRL with the IANA provided RTCP XR block type for this block.] 5.2. New RTCP XR SDP Parameter This document also registers a new parameter "post-repair-loss" in the "RTCP XR SDP Parameters Registry". 5.3. Contact information for registrations The contact information for the registrations is: Geoff Hunt (geoff.hunt@bt.com) Orion 2 PP3, Adastral Park, Martlesham Heath, Ipswich IP5 3RE, United Kingdom Hunt & Clark Expires August 29, 2009 [Page 9] Internet-Draft RTCP XR Post-Repair Loss February 2009 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 August 29, 2009 [Page 10] Internet-Draft RTCP XR Post-Repair Loss February 2009 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 August 29, 2009 [Page 11] Internet-Draft RTCP XR Post-Repair Loss February 2009 8. Changes since last version Expanded and clarified IANA Considerations section Changed SDP tag for block to "post-repair-loss". Hunt & Clark Expires August 29, 2009 [Page 12] Internet-Draft RTCP XR Post-Repair Loss February 2009 9. References 9.1. Normative References [MEASIDENT] Hunt, G., "RTCP XR Measurement Identifier Block", ID draft-ietf-avt-rtcp-xr-measid-01, February 2009. [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. 9.2. Informative References [DISCARD] Hunt, G., "RTCP XR Report Block for Discard metric Reporting", ID draft-ietf-rtcp-xr-discard-01, February 2009. [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. [POSTREPAIRRLE] Begen, A., "Post-Repair Loss RLE Report Block Type for RTCP XR", ID draft-ietf-avt-post-repair-rtcp-xr-04, 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 August 29, 2009 [Page 13] Internet-Draft RTCP XR Post-Repair Loss February 2009 Authors' Addresses Geoff Hunt BT Orion 2 PP3 Adastral Park Martlesham Heath Ipswich, Suffolk IP5 3RE United Kingdom Phone: +44 1473 651704 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 August 29, 2009 [Page 14]