Audio/Video Transport Working G. Hunt Group BT Internet-Draft A. Clark Intended status: Standards Track Telchemy Expires: November 16, 2009 May 15, 2009 RTCP XR Report Block for Burst/Gap Discard metric Reporting draft-ietf-avt-rtcp-xr-burst-gap-discard-02.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 November 16, 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 November 16, 2009 [Page 1] Internet-Draft RTCP XR Burst/Gap Discard May 2009 Abstract This document defines an RTCP XR Report Block that allows the reporting of Burst and Gap Discard metrics for use in a range of RTP applications. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Burst and Gap 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. Burst/Gap Discard Block . . . . . . . . . . . . . . . . . . . 6 3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 6 3.2. Definition of Fields in Burst/Gap Discard Report Block . . 6 3.3. Derived metrics based on reported metrics . . . . . . . . 8 4. Considerations for Voice-over-IP applications . . . . . . . . 10 5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 6.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 12 6.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 12 6.3. Contact information for registrations . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 14 9. Changes from previous version . . . . . . . . . . . . . . . . 15 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 10.1. Normative References . . . . . . . . . . . . . . . . . . . 16 10.2. Informative References . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Hunt & Clark Expires November 16, 2009 [Page 2] Internet-Draft RTCP XR Burst/Gap Discard May 2009 1. Introduction 1.1. Burst and Gap 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 proportion of packets discarded by the receiver due to jitter. The discards during discard bursts are reported, together with the number of bursts and additional data allowing the calculation of statistical parameters (mean and variance) of the distribution of burst lengths. This block is intended to be used in conjunction with [DISCARD] which provides the total packets discarded, and on which this block therefore depends. However the metric in [DISCARD] may be used independently of the metrics in this block. This block provides information on transient IP problems. Burst/Gap metrics are typically used in Cumulative reports however MAY be used in Interval reports. The burstiness of packet discard affects user experience, may influence any sender strategies to mitigate the problem, and may also have diagnostic value. The metric belongs to the class of transport-related terminal metrics defined in [MONARCH] (work in progress). The definitions of Burst, Gap, Loss and Discard are consistent with definitions in [RFC3611], with the clarification that Loss and Discard are defined in terms of frames. To accomodate the range of jitter buffer algorithms and packet discard logic that may be used by implementors, the method used to distinguish between bursts and gaps may be an equivalent method to that defined in [RFC3611]. 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. 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 Hunt & Clark Expires November 16, 2009 [Page 3] Internet-Draft RTCP XR Burst/Gap Discard May 2009 described in this draft either reference external definitions or define metrics generally in accordance with the guidelines in [PMOLFRAME]. 1.4. Applicability This metric is believed to be applicable to the large class of RTP applications which contain jitter buffers. Hunt & Clark Expires November 16, 2009 [Page 4] Internet-Draft RTCP XR Burst/Gap Discard May 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. Bursts and Gaps The terms Burst and Gap are used in a manner consistent with that of RTCP XR [RFC3611]. Hunt & Clark Expires November 16, 2009 [Page 5] Internet-Draft RTCP XR Burst/Gap Discard May 2009 3. Burst/Gap Discard 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=NBGD |I| tag | resv | block length = 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Threshold | Sum of Burst Durations (ms) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Packets Discarded in Bursts | Total... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ...Packets expected in bursts | Number of bursts | Sum of| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ...Squares of Burst Durations (ms-squared) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Report Block Structure 3.2. Definition of Fields in Burst/Gap Discard Report Block block type (BT): 8 bits A Burst/Gap Discard Report Block is identified by the constant NBGD. [Note to RFC Editor: please replace NBGD 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 Burst/Gap 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 Burst/ Gap Discard block. Note that there may be more than one Measurement Identifier block per RTCP packet. Hunt & Clark Expires November 16, 2009 [Page 6] Internet-Draft RTCP XR Burst/Gap Discard May 2009 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 The length of this report block in 32-bit words, minus one. For the Burst/Gap Discard block, the block length is equal to 4. Threshold: 8 bits The Threshold is equivalent to Gmin in [RFC3611], i.e. the number of successive frames that must not be discarded prior to and following a discarded frame in order for this discarded frame to be regarded as part of a gap. Sum of Burst Durations (ms): 24 bits The total duration of bursts of discarded frames in the period of the report (Interval or Cumulative). If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF SHOULD be reported. Packets discarded in bursts: 24 bits The total number of packets discarded during discard bursts. If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF SHOULD be reported. Total packets expected in bursts: 24 bits The total number of packets expected during discard bursts (that is, the sum of received packets and lost packets). If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF SHOULD be reported. Number of bursts: 16 bits The number of bursts in the period of the report (Interval or Cumulative). Hunt & Clark Expires November 16, 2009 [Page 7] Internet-Draft RTCP XR Burst/Gap Discard May 2009 If the measured value exceeds 0xFFFD, the value 0xFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF SHOULD be reported. Sum of Squares of Burst Durations (ms-squared): 36 bits The sum of the squares of burst durations (where individual burst durations are expressed in ms) over in the period of the report (Interval or Cumulative). The units for this quantity are milliseconds-squared. If the measured value exceeds 0xFFFFFFFFD, the value 0xFFFFFFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFFFFF SHOULD be reported. 3.3. Derived metrics based on reported metrics The metrics described here are intended to be used as described in this section, in conjunction with information from the Measurement Identity block (which MUST be present in the same RTCP packet as the Burst/Gap Discard block) and also with the metric "number of packets discarded" provided in the RTCP XR Discard Block [DISCARD]. The RTCP XR Discard Block SHOULD be sent if the Burst/Gap Discard block is sent, but the converse does not apply. The fraction of packets discarded during bursts is the quotient: Packets Discarded in Bursts / Total Packets expected in Bursts The fraction of packets discarded during gaps is the quotient: (number of packets discarded - Packets Discarded in Bursts) / (Packets Expected - Total Packets expected in Bursts) where "number of packets discarded" is obtained from the RTCP XR Discard Block [DISCARD] and Packets Expected is calculated as the difference between "extended last sequence number" and "extended first sequence number" (Interval or Cumulative) provided in the Measurement Identity block [MEASIDENT] associated with this Burst/Gap Discard block. The mean burst duration is obtained as the quotient: mean = Sum of Burst Durations / Number of Bursts The variance of the burst duration is obtained using the standard result: var = ( Sum of Squares of Burst Durations - Number of Bursts * mean^2 Hunt & Clark Expires November 16, 2009 [Page 8] Internet-Draft RTCP XR Burst/Gap Discard May 2009 ) / (Number of Bursts - 1) Hunt & Clark Expires November 16, 2009 [Page 9] Internet-Draft RTCP XR Burst/Gap Discard May 2009 4. Considerations for Voice-over-IP applications This metric block is applicable to a broad range of RTP applications. Where the metric is used with a Voice-overIP (VoIP) application, the following considerations apply. RTCP XR views a call as being divided into bursts, which are periods during which the discard rate is high enough to cause noticeable call quality degradation (generally over 5 percent discard rate), and gaps, which are periods during which discarded packets are infrequent and hence call quality is generally acceptable. If Voice Activity Detection is used the Burst and Gap Duration shall be determined as if silence frames had been sent, i.e. a period of silence in excess of Gmin frames MUST terminate a burst condition. The recommended value for the threshold Gmin in [RFC3611] results in a Burst being a period of time during which the call quality is degraded to a similar extent to a typical PCM Severely Errored Second. Hunt & Clark Expires November 16, 2009 [Page 10] Internet-Draft RTCP XR Burst/Gap Discard May 2009 5. 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-bgd-block xr-bgd-block = "brst-gap-dscrd" Hunt & Clark Expires November 16, 2009 [Page 11] Internet-Draft RTCP XR Burst/Gap Discard May 2009 6. 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]. 6.1. New RTCP XR Block Type value This document assigns the block type value NBGD in the IANA "RTCP XR Block Type Registry" to the "Concealed Seconds Metrics Block". [Note to RFC Editor: please replace NBGD with the IANA provided RTCP XR block type for this block.] 6.2. New RTCP XR SDP Parameter This document also registers a new parameter "brst-gap-dscrd" in the "RTCP XR SDP Parameters Registry". 6.3. 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 November 16, 2009 [Page 12] Internet-Draft RTCP XR Burst/Gap Discard May 2009 7. 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 November 16, 2009 [Page 13] Internet-Draft RTCP XR Burst/Gap Discard May 2009 8. 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 November 16, 2009 [Page 14] Internet-Draft RTCP XR Burst/Gap Discard May 2009 9. Changes from previous version Changed BNF for SDP following Christian Groves' and Tom Taylor's comments (4th and 5th May 2009), now aligned with RFC 5234 section 3.3 "Incremental Alternatives". Hunt & Clark Expires November 16, 2009 [Page 15] Internet-Draft RTCP XR Burst/Gap Discard May 2009 10. References 10.1. Normative References [MEASIDENT] Hunt, G., "RTCP XR Measurement Identifier Block", ID draft-ietf-avt-rtcp-xr-meas-identity-02, May 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. 10.2. Informative References [DISCARD] Hunt, G., "RTCP XR Report Block for Discard metric Reporting", ID draft-ietf-rtcp-xr-discard-02, May 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-02, March 2009. Hunt & Clark Expires November 16, 2009 [Page 16] Internet-Draft RTCP XR Burst/Gap Discard May 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 November 16, 2009 [Page 17]