AVT Working Group J. Ott
Internet-Draft Helsinki University of Technology
Intended status: Standards Track I. Curcio
Expires: March 18, 2010 Nokia Research Center
V. Singh
Helsinki University of Technology
September 14, 2009
Real-time Transport Control Protocol Extension Report for Run Length
Encoding of Discarded Packets
draft-ott-avt-rtcp-xt-discard-metrics-01.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 March 18, 2010.
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.
Ott, et al. Expires March 18, 2010 [Page 1]
Internet-Draft RTCP XR Discard RLE September 2009
Abstract
The Real-time Transport 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.
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 . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Reporting Node (Receiver) . . . . . . . . . . . . . . . . 7
5.2. Media Sender . . . . . . . . . . . . . . . . . . . . . . . 7
6. SDP signaling . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. XR Report Block Registration . . . . . . . . . . . . . . . 8
8.2. SDP Parameter Registration . . . . . . . . . . . . . . . . 9
8.3. Contact information for IANA registrations . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Ott, et al. Expires March 18, 2010 [Page 2]
Internet-Draft RTCP XR Discard RLE September 2009
1. Introduction
RTP [RFC3550] provides a transport for real-time media flows such as
audio and video together with the RTP control porotocl 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 eXtension 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, albeit at the expense of extra overhead.
Among many other fields, RFC3611 specifies the Loss RLE block which
define 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, RFC 3611 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). This 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 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-avt-rtcp-xr-discard].
o Reporting gaps and bursts of discarded packets during the last
reporting interval or cumulatively since the beginning of the
session [I-D.ietf-avt-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 or from the gap/burst report, 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 accurary.
Ott, et al. Expires March 18, 2010 [Page 3]
Internet-Draft RTCP XR Discard RLE September 2009
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
lost, an XR block is defined to indicate the number of bytes lost,
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 [RFC3611]. Figure
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.
Ott, et al. Expires March 18, 2010 [Page 4]
Internet-Draft RTCP XR Discard RLE September 2009
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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
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. Packets reported in both MUST be considered as
discarded without further information available, 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.
Editor's node: is it acceptable to use one of the 'reserved' bits for
this purpose or should two block types be used?
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
[I-D.ietf-pmol-metrics-framework].
Ott, et al. Expires March 18, 2010 [Page 5]
Internet-Draft RTCP XR Discard RLE September 2009
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| resv | block length=2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| number of bytes discarded |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: XR Bytes Discarded Report Block
The Interval Metric flag (I) (1 bit) is used to indicate whether the
Post-Repair Loss 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.
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 Bytes
Discarded report blocks MUST be included.
The 'number of bytes discarded' is a 32-bit unsigned integer value
indicating the total number of bytes discarded (I=0) or the number of
bytes discarded since the last RTCP XR Bytes Discarded block was
sent.
Bytes Discarded Report Blocks SHOULD be sent in conjunction with an
RTCP RR as a compound RTCP packet.
Editor's note: is it acceptable to use one of the 'reserved' bits for
this purpose or should two block types be used?
5. Protocol Operation
This section describes the behavior of the reporting (= receiver) RTP
node and the sender RTP node.
Ott, et al. Expires March 18, 2010 [Page 6]
Internet-Draft RTCP XR Discard RLE September 2009
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-avt-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 or not.
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.
6. SDP signaling
The report blocks specified in this document define extensions to
RTCP XR reporting. Whether or not this specific extended report is
sent is left to the discretion of the receiver. Its presence may
enable better operation of the sender since more detailed information
is available. Not providing this information will make the sender
rely on other RTCP report metrics.
A participant of a media session MAY use SDP to signal its support
for this attribute. In this case, the RTCP XR attribute as defined
in RFC3611 [RFC3611] MUST be used. The SDP RFC4566 [RFC4566]
attribute 'xr-format' defined in RFC3611 is augmented as described in
the following to indicate the discard metric.
Ott, et al. Expires March 18, 2010 [Page 7]
Internet-Draft RTCP XR Discard RLE September 2009
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 literal 'discard-rle' MUST be used to indicate support for the
Discard RLE Report Block defined in section Section 3, the literal
'discard-bytes' to indicate support for the Bytes Discarded Report
Block defined in section Section 4
For signaling support for the discard metric, the rules defined in
RFC3611 apply. Generally, senders and receivers SHOULD indicate this
capability if they support this metric and would like to use it in
the specific media session being signaled. The receiver MAY decide
not to send discard information unless it knows about the sender's
support to save on RTCP reporting bandwidth.
A participant in a media session MAY use the two report blocks
specified in this document without any explicit (SDP) signaling.
7. Security Considerations
The security considerations of RFC3550, RFC3611, and RFC4585 apply.
Since this document offers only a more precide 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
general guidelines on IANA considerations for RTCP XR, refer to
RFC3611 [RFC3611].
8.1. XR Report Block Registration
This document extends the IANA "RTCP XR Block Type Registry" by two
new values: DRLE and DBR.
[Note to RFC Editor: please replace DRLE and DBR with the IANA
provided RTCP XR block type for this block here and in the diagrams
above.]
Ott, et al. Expires March 18, 2010 [Page 8]
Internet-Draft RTCP XR Discard RLE September 2009
8.2. SDP Parameter Registration
This document registers two new parameters for the Session
Description Protocol (SDP), "discard-rle" and "discard-bytes", in the
"RTCP XR SDP Parameters Registry".
8.3. Contact information for IANA registrations
Joerg Ott (jo@comnet.tkk.fi)
TKK Comnet, Otakaari 5A, 02150 Espoo, Finland.
9. 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.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551,
July 2003.
[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.
[RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", RFC 3611,
November 2003.
[I-D.ietf-avt-rtcpssm]
Schooler, E., Ott, J., and J. Chesterfield, "RTCP
Extensions for Single-Source Multicast Sessions with
Unicast Feedback", draft-ietf-avt-rtcpssm-18 (work in
progress), March 2009.
[I-D.ietf-avt-rtcp-xr-discard]
Hunt, G. and A. Clark, "RTCP XR Report Block for Discard
metric Reporting", draft-ietf-avt-rtcp-xr-discard-02 (work
in progress), May 2009.
Ott, et al. Expires March 18, 2010 [Page 9]
Internet-Draft RTCP XR Discard RLE September 2009
[I-D.ietf-avt-rtcp-xr-burst-gap-discard]
Hunt, G. and A. Clark, "RTCP XR Report Block for Burst/Gap
Discard metric Reporting",
draft-ietf-avt-rtcp-xr-burst-gap-discard-02 (work in
progress), May 2009.
[I-D.ietf-pmol-metrics-framework]
Clark, A., "Framework for Performance Metric Development",
draft-ietf-pmol-metrics-framework-02 (work in progress),
March 2009.
Authors' Addresses
Joerg Ott
Helsinki University of Technology
Otakaari 5 A
Espoo, FIN 02150
Finland
Email: jo@netlab.hut.fi
Igor D.D. Curcio
Nokia Research Center
P.O. Box 1000 (Visiokatu 1)
Tampere, FIN 33721
Finland
Email: igor.curcio (at) nokia.com
Varun Singh
Helsinki University of Technology
Otakaari 5 A
Espoo, FIN 02150
Finland
Email: varun@netlab.tkk.fi
Ott, et al. Expires March 18, 2010 [Page 10]