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 Concealed Seconds metric Reporting draft-ietf-avt-rtcp-xr-concsec-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 Concealed Seconds October 2008 Abstract This document defines an RTCP XR Report Block that allows the reporting of Concealed Seconds metrics primarily for audio applications of RTP. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Concealed Seconds Block . . . . . . . . . . . . . . . . . 3 1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3 1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3 1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4 2. Concealed Seconds Metrics Block . . . . . . . . . . . . . . . 5 2.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5 2.2. Definition of Fields in Concealed Seconds Metrics Block . 5 3. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 9 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 12 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. Normative References . . . . . . . . . . . . . . . . . . . 13 7.2. Informative References . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 15 Hunt & Clark Expires April 28, 2009 [Page 2] Internet-Draft RTCP XR Concealed Seconds October 2008 1. Introduction 1.1. Concealed Seconds Block This draft defines a new block type to augment those defined in [RFC3611], for use primarily in audio applications of RTP. At any instant, the audio output at a receiver may be classified as either 'normal' or 'concealed'. 'Normal' refers to playout of audio payload received from the remote end, and also includes locally generated signals such as announcements, tones and comfort noise. Concealment refers to playout of locally-generated signals used to mask the impact of network impairments or to reduce the audibility of jitter buffer adaptations. The new block type provides metrics for concealment. Specifically, the first metric (Unimpaired Seconds) reports the number of whole seconds occupied only with normal playout of data which the receiver obtained from the sender's stream. The second metric (Concealed Seconds) reports the number of whole seconds during which the receiver played out any locally-generated media data. A third metric (Severely Concealed Seconds) reports the number of whole seconds during which the receiver played out locally-generated data for more than SCS Threshold (ms). 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. 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 Concealed Seconds October 2008 1.4. Applicability This metric is primarily applicable to audio applications of RTP. EDITOR'S NOTE: are there metrics for concealment of transport errors for video? Hunt & Clark Expires April 28, 2009 [Page 4] Internet-Draft RTCP XR Concealed Seconds October 2008 2. Concealed Seconds Metrics Block This sub-block provides a description of potentially audible impairments due to lost and discarded packets at the endpoint, expressed on a time basis analogous to a traditional PSTN T1/E1 errored seconds metric. The following metrics are based on successive one second intervals as declared by a local clock. This local clock does NOT need to be synchronized to any external time reference. The starting time of this clock is unspecified. Note that this implies that the same loss pattern could result in slightly different count values, depending on where the losses occur relative to the particular one-second demarcation points. For example, two loss events occurring 50ms apart could result in either one concealed second or two, depending on the particular 1000 ms boundaries used. The seconds in this sub-block are not necessarily calendar seconds. At the tail end of a call, periods of time of less than 1000ms shall be incorporated into these counts if they exceed 500ms and shall be disregarded if they are less than 500ms. 2.1. Report Block Structure Concealed seconds metrics block 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=NCS |I| tag |plc|rsv| block length = 3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Unimpaired Seconds | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Concealed Seconds | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Severely Concealed Seconds | RESERVED | SCS Threshold | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Report Block Structure 2.2. Definition of Fields in Concealed Seconds Metrics Block block type (BT): 8 bits A Concealed Seconds Metrics Report Block is identified by the constant NCS. [Note to RFC Editor: please replace NCS with the IANA provided RTCP XR block type for this block.] Hunt & Clark Expires April 28, 2009 [Page 5] Internet-Draft RTCP XR Concealed Seconds October 2008 Interval Metric flag (I): 1 bit This field is used to indicate whether the Concealed Seconds metric block is an Interval or a Cumulative report, that is, whether the reported values apply 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 Concealed Seconds Metrics block. Note that there may be more than one Measurement Identifier block per RTCP packet. Packet Loss Concealment Method (plc): 2 bits This field is used to identify the packet loss concealment method in use at the receiver, according to the following code: bits 0-3 0 = silence insertion 1 = simple replay, no attenuation 2 = simple replay, with attenuation 3 = enhanced Other values reserved Reserved (rsv): 2 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 Concealed Seconds block, the block length is equal to 3. Unimpaired Seconds: 32 bits A count of the number of unimpaired Seconds that have occurred. An unimpaired Second is defined as a continuous period of 1000ms during which no frame loss or discard due to late arrival has Hunt & Clark Expires April 28, 2009 [Page 6] Internet-Draft RTCP XR Concealed Seconds October 2008 occurred. Every second in a call must be classified as either OK or Concealed. Normal playout of comfort noise or other silence concealment signal during periods of talker silence, if VAD is used, shall be counted as unimpaired seconds. 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. Concealed Seconds: 32 bits A count of the number of Concealed Seconds that have occurred. A Concealed Second is defined as a continuous period of 1000ms during which any frame loss or discard due to late arrival has occurred. Equivalently, a concealed second is one in which some Loss-type concealment (defined in Section 3.6) has occurred. Buffer adjustment-type concealment SHALL not cause Concealed Seconds to be incremented, with the following exception. An implementation MAY cause Concealed Seconds to be incremented for 'emergency' buffer adjustments made during talkspurts. For clarification, the count of Concealed Seconds MUST include the count of Severely Concealed Seconds. 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. The duration, in milliseconds, of audio playout corresponding to Loss-type concealment. Severely Concealed Seconds: 16 bits A count of the number of Severely Concealed Seconds. A Severely Concealed Second is defined as a non-overlapping period of 1000 ms during which the cumulative amount of time that has been subject to frame loss or discard due to late arrival, exceeds the SCS Threshold. Hunt & Clark Expires April 28, 2009 [Page 7] Internet-Draft RTCP XR Concealed Seconds October 2008 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. RESERVED: 8 bits These bits are reserved. They SHOULD be set to zero by senders and MUST be ignored by receivers. SCS Threshold: 8 bits The SCS Threshold defines the amount of time corresponding to lost or discarded frames that must occur within a one second period in order for the second to be classified as a Severely Concealed Second. This is expressed in milliseconds and hence can represent a range of 0.1 to 25.5 percent loss or discard. A default threshold of 50ms (5% effective frame loss per second) is suggested. Hunt & Clark Expires April 28, 2009 [Page 8] Internet-Draft RTCP XR Concealed Seconds October 2008 3. 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. The SDP attribute for the block has an additional optional paremeter, "thresh", used to supply a value for the SCS Threshold parameter. If this parameter is present, the RTP system receiving the SDP SHOULD use this value for the current session. If the parameter is not present, the RTP system SHOULD use a locally configured value. rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF (defined in [RFC3611]) xr-format = xr-format / xr-conc-sec-block xr-conc-sec-block = "xr-concsec" ["=" thresh] thresh = 1*DIGIT ; threshold for SCS (ms) DIGIT = %x30-39 Hunt & Clark Expires April 28, 2009 [Page 9] Internet-Draft RTCP XR Concealed Seconds October 2008 4. IANA Considerations This document creates a new block type within the IANA "RTCP XR Block Type Registry" called the Concealed Seconds Metrics Block, and a new parameter xr-concsec within the "RTCP XR SDP Parameters Registry". Hunt & Clark Expires April 28, 2009 [Page 10] Internet-Draft RTCP XR Concealed Seconds October 2008 5. 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 11] Internet-Draft RTCP XR Concealed Seconds October 2008 6. 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 12] Internet-Draft RTCP XR Concealed Seconds October 2008 7. References 7.1. 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. 7.2. 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. Hunt & Clark Expires April 28, 2009 [Page 13] Internet-Draft RTCP XR Concealed Seconds 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 14] Internet-Draft RTCP XR Concealed Seconds 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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