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 Packet Delay Variation Metric Reporting draft-ietf-avt-rtcp-xr-pdv-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 Packet Delay Variation October 2008 Abstract This document defines an RTCP XR Report Block that allows the reporting of Packet Delay Variation metrics for a range of RTP applications. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Packet Delay Variation Metrics Block . . . . . . . . . . . 3 1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3 1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3 1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 3 2. Packet Delay Variation Metrics Block . . . . . . . . . . . . . 4 2.1. Report Block Structure . . . . . . . . . . . . . . . . . . 4 2.2. Definition of Fields in PDV Metrics Block . . . . . . . . 4 2.3. Examples of use . . . . . . . . . . . . . . . . . . . . . 7 3. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 8 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1. Normative References . . . . . . . . . . . . . . . . . . . 11 6.2. Informative References . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Intellectual Property and Copyright Statements . . . . . . . . . . 13 Hunt & Clark Expires April 28, 2009 [Page 2] Internet-Draft RTCP XR Packet Delay Variation October 2008 1. Introduction 1.1. Packet Delay Variation Metrics 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 provides information on Packet Delay Variation using one of several standard metrics. The metrics belong to the class of transport 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]. 1.4. Applicability These metrics are applicable to a range of RTP applications. Hunt & Clark Expires April 28, 2009 [Page 3] Internet-Draft RTCP XR Packet Delay Variation October 2008 2. Packet Delay Variation Metrics Block Metrics in this block report on packet delay variation in the stream arriving at the RTP system. 2.1. Report Block Structure PDV 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=NPDV |I| tag |pdvtyp | block length=3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Pos Threshold/Peak PDV | Pos PDV Percentile | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Neg Threshold/Peak PDV | Neg PDV Percentile | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mean PDV | unused | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Report Block Structure 2.2. Definition of Fields in PDV Metrics Block block type (BT): 8 bits A Packet Delay Variation Metrics Report Block is identified by the constant NJB. [Note to RFC Editor: please replace NPDV 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 Packet Delay Variation metrics 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 Packet Hunt & Clark Expires April 28, 2009 [Page 4] Internet-Draft RTCP XR Packet Delay Variation October 2008 Delay Variation Metrics block. Note that there may be more than one Measurement Identifier block per RTCP packet. Packet Delay Variation Metric Type (pdvtyp): 4 bits This field is used to identify the Packet Delay Variation Metric Type used in this report block, according to the following code: bits 014-017 0: PPDV according to [RFC3550], 1: MAPDV according to [G.1020], 2: IPDV according to [Y.1540] Other values reserved block length: 16 bits The length of this report block in 32-bit words, minus one. For the Packet Delay Variation Metrics block, the block length is equal to 3. Positive Threshold/Peak PDV: 16 bit, S11:4 format The PDV associated with the Positive PDV percentile expressed in milliseconds. The term Positive is associated with packets arriving later than the expected time. If the measured value is more negative than -2047.9375 (the value which would be coded as 0x8001), the value 0x8000 SHOULD be reported to indicate an over-range negative measurement. If the measured value is more positive than +2047.8125 (the value which would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to indicate an over-range positive measurement. If the measurement is unavailable, the value 0x7FFF SHOULD be reported. Positive PDV Percentile: 16 bit, 8:8 format The percentage of packets on the call for which individual packet delays were less than the Positive Threshold PDV. If the measurement is unavailable, the value 0xFFFF SHOULD be reported. Negative Threshold/Peak PDV: 16 bit, S11:4 format The PDV associated with the Negative PDV percentile expressed in milliseconds. The term Negative is associated with packets arriving earlier than the expected time. Hunt & Clark Expires April 28, 2009 [Page 5] Internet-Draft RTCP XR Packet Delay Variation October 2008 If the measured value is more negative than -2047.9375 (the value which would be coded as 0x8001), the value 0x8000 SHOULD be reported to indicate an over-range negative measurement. If the measured value is more positive than +2047.8125 (the value which would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to indicate an over-range positive measurement. If the measurement is unavailable, the value 0x7FFF SHOULD be reported. Negative PDV Percentile: 16 bit, 8:8 format The percentage of packets on the call for which individual packet delays were more than the Negative Threshold PDV. If the measurement is unavailable, the value 0xFFFF SHOULD be reported. If the PDV Type indicated is IPDV and the Positive and Negative PDV Percentiles are set to 100.0 then the Positive and Negative Threshold/Peak PDV values are the peak values measured during the reporting interval (which may be from the start of the call for cumulative reports). In this case, the difference between the Positive and Negative Threshold/Peak values defines the range of IPDV. Mean PDV: (16 bit, S11:4 format) expressed in milliseconds For MAPDV this value is generated according to [G.1020]. For interval reports the MAPDV value is reset at the start of the interval. For PPDV the value reported is the value of J(i) calculated according to [RFC3550] at the time the report is generated. For IPDV, the value reported is the mean of per-packet IPDV values. This metric indicates the arrival time of the first media packet of the session with respect to the mean of the arrival times of every packet of the session. A single value of the metric (for a single session) may not be useful by itself, but its average over a number of sessions may be useful in diagnosing media delay at session startup. For example, this might occur if media packets are often delayed behind signalling packets due to head-of-line blocking. If the measured value is more negative than -2047.9375 (the value which would be coded as 0x8001), the value 0x8000 SHOULD be reported to indicate an over-range negative measurement. If the measured value is more positive than +2047.8125 (the value which would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to Hunt & Clark Expires April 28, 2009 [Page 6] Internet-Draft RTCP XR Packet Delay Variation October 2008 indicate an over-range positive measurement. If the measurement is unavailable, the value 0x7FFF SHOULD be reported. unused: 16 bits These bits are unused. They SHOULD be set to zero by the sender and MUST be ignored by the receiver. 2.3. Examples of use (a) To report PPDV (RFC3550): Threshold PDV = FFFF (Undefined); PDV Percentile = FFFF (Undefined); PDV type = 0 (PPDV) causes PPDV to be reported in the Mean PDV field. (b) To report MAPDV (G.1020): Pos Threshold PDV = 50.0; Pos PDV Percentile = 95.3; Neg Threshold PDV = 50.0 (note - implies -50ms); Neg PDV Percentile = 98.4; PDV type = 1 (MAPDV) causes average MAPDV to be reported in the Mean PDV field. Note that implementations may either fix the reported percentile and calculate the associated PDV level OR may fix a threshold PDV level and calculate the associated percentile. From a practical implementation perspective it is simpler to use the second of these approaches (except of course in the extreme case of a 100% percentile). IPDV, according to Y.1540 is the difference in delay between the current packet and the first packet of the stream. If the sending and receiving clocks are not synchronized, this metric includes the effect of relative timing drift. Hunt & Clark Expires April 28, 2009 [Page 7] Internet-Draft RTCP XR Packet Delay Variation 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. rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF (defined in [RFC3611]) xr-format = xr-format / xr-pdv-block xr-pdv-block = "delay" [ "," pdvtype ] [ "," nspec "," pspec ] pdvtype = "pdv=" 0 ; ppdv RFC 3550 / 1 ; mapdv ITU-T G.1020 / 2 ; ipdv ITU-T Y.1540 nspec = "nthr=" fixpoint ; negative threshold PDV (ms) / "npc=" fixpoint ; negative PDV percentile pspec = "pthr=" fixpoint ; positive threshold PDV (ms) / "ppc=" fixpoint ; positive PDV percentile fixpoint = 1*DIGIT "." 1*DIGIT ; fixed point decimal DIGIT = %x30-39 When SDP is used in offer-answer, a system sending SDP may request a specific type of PDV measurement. In addition, they may state a specific percentile or threshold value, and expect to receive the corresponding threshold or percentile metric, respectively. The system receiving the SDP SHOULD send the PDV metrics requested, but if the metric is not available, the system receiving the SDP SHOULD send the flag value indicating that the metric is unavailable. Hunt & Clark Expires April 28, 2009 [Page 8] Internet-Draft RTCP XR Packet Delay Variation October 2008 4. IANA Considerations This document creates a new block type within the IANA "RTCP XR Block Type Registry" called the Packet Delay Variation Metrics Block, and a new parameter xr-pdv within the "RTCP XR SDP Parameters Registry". Hunt & Clark Expires April 28, 2009 [Page 9] Internet-Draft RTCP XR Packet Delay Variation 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 10] Internet-Draft RTCP XR Packet Delay Variation October 2008 6. References 6.1. Normative References [G.1020] ITU-T, "ITU-T Rec. G.1020, Performance parameter definitions for quality of speech and other voiceband applications utilizing IP networks", November 2003. [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. 6.2. 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 11] Internet-Draft RTCP XR Packet Delay Variation 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 12] Internet-Draft RTCP XR Packet Delay Variation 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 13]