XR Block Working Group J. Ott
Internet-Draft V. Singh
Intended status: Standards Track Aalto University
Expires: June 22, 2013 I. Curcio
Nokia Research Center
December 19, 2012
RTP Control Protocol (RTCP) Extended Reports (XR) for Run Length
Encoding (RLE) of Discarded Packets
draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-05.txt
Abstract
The RTP Control Protocol (RTCP) is used in conjunction with the Real-
time Transport Protocol (RTP) in to provide a variety of short-term
and long-term reception statistics. The available reporting may
include aggregate information across longer periods of time as well
as individual packet reporting. This document specifies a per-packet
report metric capturing individual packets discarded from the jitter
buffer after successful reception.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on June 22, 2013.
Copyright Notice
Copyright (c) 2012 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
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. XR Discard RLE Report Block . . . . . . . . . . . . . . . . . 4
4. XR Bytes Discarded Report Block . . . . . . . . . . . . . . . 5
5. Protocol Operation . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Reporting Node (Receiver) . . . . . . . . . . . . . . . . 7
5.2. Media Sender . . . . . . . . . . . . . . . . . . . . . . . 7
6. SDP signaling . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. XR Report Block Registration . . . . . . . . . . . . . . . 9
8.2. SDP Parameter Registration . . . . . . . . . . . . . . . . 9
8.3. Contact information for IANA registrations . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 10
A.1. changes in
draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-00 . . . . 10
A.2. changes in
draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-01 . . . . 10
A.3. changes in
draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-02 . . . . 11
A.4. changes in
draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-03 . . . . 11
A.5. changes in
draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-04 . . . . 11
A.6. changes in
draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-05 . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
RTP [RFC3550] provides a transport for real-time media flows such as
audio and video together with the RTP control protocol (RTCP) which
provides periodic feedback about the media streams received in a
specific duration. In addition, RTCP can be used for timely feedback
about individual events to report (e.g., packet loss) [RFC4585].
Both long-term and short-term feedback enable a sender to adapt its
media transmission and/or encoding dynamically to the observed path
characteristics.
RFC3611 [RFC3611] defines RTCP Extended Reports as a detailed
reporting framework to provide more than just the coarse RR
statistics. The detailed reporting may enable a sender to react more
appropriately to the observed networking conditions as these can be
characterized better, although at the expense of extra overhead.
Among many other report blocks, RFC3611 specifies the Loss RLE block
which reports runs of packets received and lost with the granularity
of individual packets. This can help both error recovery and path
loss characterization. In addition to lost packets, RFC3611 defines
the notion of "discarded" packets: packets that were received but
dropped from the jitter buffer because they were either too early
(for buffering) or too late (for playout). The "discard rate" metric
is part of the VoIP metrics report block even though it is not just
applicable to audio: it is specified as the fraction of discarded
packets since the beginning of the session. See section 4.7.1 of
RFC3611 [RFC3611].
Recently proposed extensions to the XR reporting suggest enhancing
this discard metric:
o Reporting the number of discarded packets in a measurement
interval, i.e., during either the last reporting interval or since
the beginning of the session, as indicated by a flag in the
suggested XR report [I-D.ietf-xrblock-rtcp-xr-discard]. If an
endpoint needs to report packet discard due to other reasons than
early- and late-arrival (for example, discard due to duplication,
redundancy, etc.) then it should consider using the Discarded
Packets Report Block [I-D.ietf-xrblock-rtcp-xr-discard].
o Reporting gaps and bursts of discarded packets during a
measurement interval, i.e., the last reporting interval or the
duration of the session
[I-D.ietf-xrblock-rtcp-xr-burst-gap-discard].
However, none of these metrics allow a receiver to report precisely
which packets were discarded. While this information could in theory
be derived from high-frequency reporting on the number of discarded
packets [I-D.ietf-xrblock-rtcp-xr-discard] or from the gap/burst
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report [I-D.ietf-xrblock-rtcp-xr-burst-gap-discard], these two
mechanisms do not appear feasible: The former would require an unduly
high amount of reporting which still might not be sufficient due to
the non-deterministic scheduling of RTCP packets. The latter incur
significant complexity and reporting overhead and might still not
deliver the desired accuracy.
This document defines a discard report block following the idea of
the run-length encoding applied for lost and received packets in
[RFC3611].
Complementary to or instead of the indication which packets were
discarded, an XR block is defined to indicate the number of bytes
discarded, per interval or for the duration of the session, similar
to other XR report blocks.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119
[RFC2119] and indicate requirement levels for compliant
implementations.
The terminology defined in RTP [RFC3550] and in the extensions for XR
reporting [RFC3611] applies.
3. XR Discard RLE Report Block
The XR Discard RLE report block uses the same format as specified for
the loss and duplicate report blocks in [RFC3611]. Figure 1 recaps
the packet format. The fields "BT", "T", "block length", "SSRC of
source", "begin_seq", and "end_seq" SHALL have the same semantics and
representation as defined in [RFC3611]. The "chunks" encoding the
run length SHALL have the same representation as in RFC3611, but
encode discarded packets.
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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=DRLE |rsvd |E| T | block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| begin_seq | end_seq |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| chunk 1 | chunk 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| chunk n-1 | chunk n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: XR Discard Report Block
Block Type (BT, 8 bits): A Run-length encoded Discarded Packets
Report Block is identified by the constant DRLE.
[Note to RFC Editor: please replace DRLE with the IANA provided RTCP
XR block type for this block. Please remove this note prior to
publication as an RFC.]
rsvd (3 bits): These reserved bits SHOULD be set to zero by receivers
and MUST be ignored by senders.
The 'E' bit is introduced to distinguish between packets discarded
due to early arrival and those discarded due to late arrival. The
'E' bit MUST be set to '1' if the chunks represent packets discarded
due to too early arrival and MUST be set to '0' otherwise.
In case both early and late discarded packets shall be reported, two
Discard RLE report blocks MUST be included; their sequence number
range MAY overlap, but individual packets MUST only be reported as
either early or late and not appear marked in both. Packets reported
in neither are considered to be properly received and not discarded.
Discard RLE Report Blocks SHOULD be sent in conjunction with an RTCP
RR as a compound RTCP packet.
4. XR Bytes Discarded Report Block
The XR Bytes Discarded report block uses the following format which
follows the model of the framework for performance metric development
[RFC6390].
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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=BDR | I |E|reserved | block length=2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| number of bytes discarded |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: XR Bytes Discarded Report Block
Block Type (BT, 8 bits): A Bytes Discarded Packets Report Block is
identified by the constant BDR.
[Note to RFC Editor: please replace BDR with the IANA provided RTCP
XR block type for this block. Please remove this note prior to
publication as an RFC.]
The Interval Metric flag (I) (2 bits) is used to indicate whether the
discard metric is Interval, or a Cumulative metric, that is, whether
the reported value applies to the most recent measurement interval
duration between successive reports (I=10, the Interval Duration) or
to the accumulation period characteristic of cumulative measurements
(I=11, the Cumulative Duration). Since the bytes discarded are not
measured at a particular time instance but over one or several
reporting intervals, the metric MUST NOT be reported as a Sampled
Metric (I=01).
The 'E' bit is introduced to distinguish between packets discarded
due to early arrival and those discarded due to late arrival. The
'E' bit MUST be set to '1' if it reports bytes discarded due to early
arrival and MUST be set to '0' if it reports bytes discarded due to
late arrival. In case both early and late discarded packets shall be
reported, two Bytes Discarded report blocks MUST be included.
These reserved bits (5 bits) SHOULD be set to zero by receivers and
MUST be ignored by senders.
block length (16 bits) MUST be set to 2, in accordance with the
definition of this field in [RFC3611]. The block MUST be discarded
if the block length is set to a different value.
The 'number of bytes discarded' is a 32-bit unsigned integer value
indicating the total number of bytes discarded.
If Interval Metric flag (I=11) is set, the value in the field
indicates the number of bytes discarded from the start of the
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session, if Interval Metric flag (I=01) is set, it indicates the
number of bytes discarded since the last RTCP XR Byte Discarded Block
was received.
If the XR block follows a measurement identity block [RFC6776] in the
same RTCP compound packet then the cumulative (I=11) or the interval
(I=10) for this report block corresponds to the values of the
"measurement duration" in the measurement information block.
If the receiver sends the Bytes Discarded Report Block without the
measurement identity block then the discard block MUST be sent in
conjunction with an RTCP RR as a compound RTCP packet.
5. Protocol Operation
This section describes the behavior of the reporting (= receiver)
node and the media sender.
5.1. Reporting Node (Receiver)
Transmission of RTCP XR Discard RLE Reports is up to the discretion
of the receiver, as is the reporting granularity. However, it is
RECOMMENDED that the receiver signals all discarded packets using the
method defined in this document. If all packets over a reporting
period were lost, the receiver MAY use the Discard Report Block
[I-D.ietf-xrblock-rtcp-xr-discard] instead. In case of limited
available reporting bandwidth, it is up to the receiver whether or
not to include RTCP XR Discard RLE reports.
The receiver MAY send the Discard RLE Reports as part of the
regularly scheduled RTCP packets as per RFC3550. It MAY also include
Discard RLE Reports in immediate or early feedback packets as per
RFC4585.
5.2. Media Sender
The media sender MUST be prepared to operate without receiving any
Discard RLE reports. If Discard RLE reports are generated by the
receiver, the sender cannot rely on all these reports being received,
nor can the sender rely on a regular generation pattern from the
receiver side.
However, if the sender receives any RTCP reports but no Discard RLE
report blocks and is aware that the receiver supports Discard RLE
report blocks, it MAY assume that no packets were discarded at the
receiver.
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The sender SHOULD accept the Bytes Discarded Report Block only if it
is received in a compound RTCP receiver report or if it is preceded
by a measurement identity block [RFC6776]. Under all other
circumstances it MUST ignore the block.
6. SDP signaling
A participant of a media session MAY use SDP to signal its support
for the two report blocks specified in this document or use them
without any prior signaling (see section 5 of [RFC3611]).
For signaling in SDP, the RTCP XR attribute as defined in [RFC3611]
MUST be used. The SDP [RFC4566] attribute 'xr-format' defined in
RFC3611 is augmented as described in the following to indicate the
RLE discard metric and bytes discarded metric.
rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)]
CRLF ; defined in [RFC3611]
xr-format =/ xr-discard-rle
/ xr-discard-bytes
xr-discard-rle = "discard-rle"
xr-discard-bytes = "discard-bytes"
The parameter 'discard-rle' MUST be used to indicate support for the
Discard RLE Report Block defined in Section 3, the parameter
'discard-bytes' to indicate support for the Bytes Discarded Report
Block defined in Section 4
When SDP is used in Offer/Answer context, the mechanism defined in
[RFC3611] for unilateral "rtcp-xr" attribute parameters applies (see
section 5.2 of [RFC3611]).
7. Security Considerations
The security considerations of [RFC3550], [RFC3611], and [RFC4585]
apply. Since this document offers only a more precise reporting for
an already existing metric, no further security implications are
foreseen.
8. IANA Considerations
New block types for RTCP XR are subject to IANA registration. For
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general guidelines on IANA considerations for RTCP XR, refer to
[RFC3611].
8.1. XR Report Block Registration
This document extends the IANA "RTP Control Protocol Extended Reports
(RTCP XR) Block Type Registry" by two new values: DRLE and BDR.
[Note to RFC Editor: please replace DRLE and BDR with the IANA
provided RTCP XR block type for this block here and in the diagrams
above. Please remove this note prior to publication as an RFC.]
8.2. SDP Parameter Registration
This document registers two new parameters for the Session
Description Protocol (SDP), "discard-rle" and "discard-bytes", in the
"RTP Control Protocol Extended Reports (RTCP XR) Session Description
Protocol (SDP) Parameters Registry".
8.3. Contact information for IANA registrations
Joerg Ott (jo@comnet.tkk.fi)
Aalto University Comnet, Otakaari 5A, 02150 Espoo, Finland.
9. Acknowledgements
Thanks to Qin Wu, Colin Perkins, Dan Romascanu, Roni Even and Dan
Wing for providing valuable feedback on earlier versions of this
draft
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", RFC 3611,
November 2003.
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[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
July 2006.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
October 2011.
[RFC6776] Clark, A. and Q. Wu, "Measurement Identity and Information
Reporting Using a Source Description (SDES) Item and an
RTCP Extended Report (XR) Block", RFC 6776, October 2012.
10.2. Informative References
[I-D.ietf-xrblock-rtcp-xr-discard]
Clark, A., Zorn, G., and W. Wu, "RTP Control Protocol
(RTCP) Extended Report (XR) Block for Discard Count metric
Reporting", draft-ietf-xrblock-rtcp-xr-discard-11 (work in
progress), December 2012.
[I-D.ietf-xrblock-rtcp-xr-burst-gap-discard]
Clark, A., Huang, R., and W. Wu, "RTP Control
Protocol(RTCP) Extended Report (XR) Block for Burst/Gap
Discard metric Reporting",
draft-ietf-xrblock-rtcp-xr-burst-gap-discard-08 (work in
progress), December 2012.
Appendix A. Change Log
Note to the RFC-Editor: please remove this section prior to
publication as an RFC.
A.1. changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-00
o Changed the interval flag from 1 to 2 bits in the discarded bytes
report. Also added the measurement identification tag to the
block.
o Added this section.
A.2. changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-01
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o Removed the measurement identification tag in the bytes discarded
block.
A.3. changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-02
o Removed the extra Tag bits from the Discarded bytes XR block.
o Clarified use of measurement identity block in Section 4 and 5.2
A.4. changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-03
o Added explanation for block length in bytes discarded block.
o Added an acknowledgement section.
A.5. changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-04
o Added Block Type definition to each XRBlock.
o Made changes requested in WGLC.
A.6. changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-05
o Made changes requested by SDP directorate.
Authors' Addresses
Joerg Ott
Aalto University
School of Electrical Engineering
Otakaari 5 A
Espoo, FIN 02150
Finland
Email: jo@comnet.tkk.fi
Varun Singh
Aalto University
School of Electrical Engineering
Otakaari 5 A
Espoo, FIN 02150
Finland
Email: varun@comnet.tkk.fi
URI: http://www.netlab.tkk.fi/~varun/
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Igor D.D. Curcio
Nokia Research Center
P.O. Box 1000 (Visiokatu 3)
Tampere, FIN 33721
Finland
Email: igor.curcio@nokia.com
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