RTP Control Protocol (RTCP) Extended Report (XR) for Post-Repair Loss Count Metrics
RFC 7509

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Internet Engineering Task Force (IETF)                          R. Huang
Request for Comments: 7509                                        Huawei
Category: Standards Track                                       V. Singh
ISSN: 2070-1721                                         Aalto University
                                                                May 2015

            RTP Control Protocol (RTCP) Extended Report (XR)
                   for Post-Repair Loss Count Metrics

Abstract

   This document defines an RTP Control Protocol (RTCP) Extended Report
   (XR) block that allows reporting of a post-repair loss count metric
   for a range of RTP applications.  In addition, another metric,
   repaired loss count, is also introduced in this report block for
   calculating the pre-repair loss count when needed, so that the RTP
   sender or a third-party entity is able to evaluate the effectiveness
   of the repair methods used by the system.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc7509.

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Singh & Huang                Standards Track                    [Page 1]
RFC 7509             Post-Repair Non-RLE Loss Count             May 2015

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
   3. Post-Repair Loss Count Metrics Report Block .....................3
      3.1. Report Block Structure .....................................4
      3.2. Example Usage ..............................................5
   4. SDP Signaling ...................................................6
      4.1. SDP rtcp-xr-attrib Attribute Extension .....................6
      4.2. Offer/Answer Usage .........................................7
   5. Security Considerations .........................................7
   6. IANA Considerations .............................................7
      6.1. New RTCP XR Block Type Value ...............................7
      6.2. New RTCP XR SDP Parameter ..................................7
      6.3. Contact Information for Registrations ......................7
   7. References ......................................................8
      7.1. Normative References .......................................8
      7.2. Informative References .....................................9
   Appendix A. Metrics Represented Using the Template from RFC 6390 ..10
   Acknowledgments ...................................................11
   Authors' Addresses ................................................11

1.  Introduction

   RTCP Sender Reports (SRs) / Receiver Reports (RRs) [RFC3550] contain
   some rough statistics about the data received from the particular
   source indicated in that block.  One of them is the cumulative number
   of packets lost, which is called the pre-repair loss metric in this
   document.  This metric conveys information regarding the total number
   of RTP data packets that have been lost since the beginning of the
   RTP session.

   However, this metric is measured on the media stream before any loss-
   repair mechanism, e.g., retransmission [RFC4588] or Forward Error
   Correction (FEC) [RFC5109], is applied.  Using a repair mechanism
   usually results in recovering some or all of the lost packets.  The
   recovery process does not reduce the values reported by the two loss
   metrics in RTCP RR [RFC3550] -- namely, the fraction lost and the
   cumulative loss.  Hence, the sending endpoint cannot infer the
   performance of the repair mechanism based on the aforementioned
   metrics in [RFC3550].

   Consequently, [RFC5725] specifies a post-repair loss Run-Length
   Encoding (RLE) XR report block to address this issue.  The sending
   endpoint is able to infer which packets were repaired from the RLE