Internet DRAFT - draft-singh-xrblock-rtcp-xr-bytes-discarded-metric
draft-singh-xrblock-rtcp-xr-bytes-discarded-metric
XR Block Working Group V. Singh, Ed.
Internet-Draft J. Ott
Intended status: Standards Track Aalto University
Expires: February 02, 2014 I. Curcio
Nokia Research Center
August 01, 2013
RTP Control Protocol (RTCP) Extended Reports (XR) for Bytes Discarded
Metric
draft-singh-xrblock-rtcp-xr-bytes-discarded-metric-00
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 report
computing the bytes discarded from the de-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 February 02, 2014.
Copyright Notice
Copyright (c) 2013 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. XR Bytes Discarded Report Block . . . . . . . . . . . . . . . 4
4. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 5
4.1. Reporting Node (Receiver) . . . . . . . . . . . . . . . . 5
4.2. Media Sender . . . . . . . . . . . . . . . . . . . . . . 6
5. SDP signaling . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7.1. XR Report Block Registration . . . . . . . . . . . . . . 7
7.2. SDP Parameter Registration . . . . . . . . . . . . . . . 7
7.3. Contact information for IANA registrations . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Metrics represented using RFC6390 Template . . . . . 9
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 10
B.1. changes in draft-singh-xrblock-rtcp-xr-bytes-
discarded-metric-00 . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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 media 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 Receiver
Report (RR) statistics. The detailed reporting may enable a media
sender to react more appropriately to the observed networking
conditions as these can be characterized better, although at the
expense of extra overhead.
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In addition to lost packets, RFC3611 defines the notion of
"discarded" packets: packets that were received but dropped from the
de-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].
The discard metric is believed to be applicable to a large class of
RTP applications which use a de-jitter buffer RFC5481 [RFC5481].
Recently proposed extensions to the Extended Reports (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].
o Reporting run-length encoding of discarded packet during a
measurement interval, i.e., between a set of sequence numbers
[I-D.ietf-xrblock-rtcp-xr-discard-rle-metrics].
However, none of these metrics allow a receiver to report precisely
the number of bytes that 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 Discard RLE report
[I-D.ietf-xrblock-rtcp-xr-discard-rle-metrics], 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 incurs
significant complexity (by storing a map of sequence numbers and
packet sizes) and reporting overhead.
An XR block is defined in this document to indicate the number of
bytes discarded, per interval or for the duration of the session,
similar to other XR report blocks.
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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].
The terminology defined in RTP [RFC3550] and in the extensions for XR
reporting [RFC3611] applies.
3. 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].
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 1: 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). In addition, the value I=00 is reserved and MUST NOT
be sent, and MUST be discarded when received.
The 'E' bit is introduced to distinguish between packets discarded
due to early arrival and those discarded due to late arrival. The
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'E' bit is set to '1' if it reports bytes discarded due to early
arrival and is set to '0' if it reports bytes discarded due to late
arrival. If a duplicate packet is received and discarded, these
duplicate packets are ignored and not reported. In case both early
and late discarded packets shall be reported, two Bytes Discarded
report blocks MUST be included.
reserved (5 bits): This field is reserved for future definition. In
the absence of such definition, the bits in this field MUST be set to
zero and MUST be ignored by the receiver.
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. Bytes discarded
corresponds to the RTP payload size of every RTP packet that is
discarded (due to early or late arrival). Hence, the bytes discarded
ignores the size of any RTP header extensions and the size of the
padding bits. Also the discarded packet is associated to the
interval in which it was discarded and not when it was expected.
If Interval Metric flag (I=11) is set, the value in the field
indicates the number of bytes discarded from the start of the
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 Receiver Report (RR) as a compound RTCP
packet.
4. Protocol Operation
This section describes the behavior of the reporting node (= media
receiver) and the media sender.
4.1. Reporting Node (Receiver)
Transmission of RTCP XR Bytes Discarded Report is up to the
discretion of the media receiver, as is the reporting granularity.
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However, it is RECOMMENDED that the media receiver signals all
discarded packets using the method defined in this document. If all
packets over a reporting period were discarded, the media receiver
MAY use the Discard Report Block [I-D.ietf-xrblock-rtcp-xr-discard]
instead.
The media receiver MAY send the Bytes Discard Reports as part of the
regularly scheduled RTCP packets as per RFC3550. It MAY also include
Bytes Discard Reports in immediate or early feedback packets as per
RFC4585.
4.2. Media Sender
The media sender MUST be prepared to operate without receiving any
Bytes Discarded reports. If Bytes Discarded reports are generated by
the media receiver, the media sender cannot rely on all these reports
being received, nor can the media sender rely on a regular generation
pattern from the media receiver.
However, if the media sender receives any RTCP reports but no Bytes
Discard report blocks and is aware that the media receiver supports
Bytes Discard report blocks, it MAY assume that no packets were
discarded at the media receiver.
The media 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.
5. SDP signaling
A participant of a media session MAY use SDP to signal its support
for the report block 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
bytes discarded metric.
rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)]
CRLF ; defined in [RFC3611]
xr-format =/ xr-discard-bytes
xr-discard-bytes = "discard-bytes"
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The parameter 'discard-bytes' to indicate support for the Bytes
Discarded Report Block defined in Section 3.
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]).
6. Security Considerations
The Bytes Discarded block does not provide per-packet statistics,
hence the risk to confidentiality documented in Section 7, paragraph
3 of [RFC3611] does not apply. In some situations, returning very
detailed error information (e.g., over-range measurement or
measurement unavailable) using this report block can provide an
attacker with insight into the security processing. Implementers
should consider the guidance in [I-D.ietf-avt-srtp-not-mandatory] for
using appropriate security mechanisms, i.e., where security is a
concern, the implementation should apply encryption and
authentication to the report block. For example this can be achieved
by using the AVPF profile together with the Secure RTP profile as
defined in [RFC3711]; an appropriate combination of the two profiles
(an "SAVPF") is specified in [RFC5124]. However, other mechanisms
also exist (documented in [I-D.ietf-avtcore-rtp-security-options])
and might be more suitable.
Additionally, The security considerations of [RFC3550], [RFC3611],
and [RFC4585] apply.
7. 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].
7.1. XR Report Block Registration
This document extends the IANA "RTP Control Protocol Extended Reports
(RTCP XR) Block Type Registry" by a new value: BDR (Bytes Discarded
Report).
[Note to RFC Editor: please replace 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.]
7.2. SDP Parameter Registration
This document registers a new parameters for the Session Description
Protocol (SDP), "discard-bytes" in the "RTP Control Protocol Extended
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Reports (RTCP XR) Session Description Protocol (SDP) Parameters
Registry".
7.3. Contact information for IANA registrations
Varun Singh (varun.singh@iki.fi)
Aalto University Comnet, Otakaari 5A, 02150 Espoo, Finland.
8. Acknowledgments
The authors would like to thank Alan Clark, Roni Even, Sam Hartman,
Colin Perkins, Dan Romascanu, Dan Wing, and Qin Wu for providing
valuable feedback on earlier versions of this draft.
9. References
9.1. 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.
[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.
[I-D.ietf-xrblock-rtcp-xr-discard]
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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-15 (work in
progress), June 2013.
9.2. Informative References
[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-14 (work in progress), April 2013.
[I-D.ietf-xrblock-rtcp-xr-discard-rle-metrics]
Ott, J., Singh, V., and I. Curcio, "RTP Control Protocol
(RTCP) Extended Reports (XR) for Run Length Encoding (RLE)
of Discarded Packets", draft-ietf-xrblock-rtcp-xr-discard-
rle-metrics-06 (work in progress), July 2013.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
Applicability Statement", RFC 5481, March 2009.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for
Real-time Transport Control Protocol (RTCP)-Based Feedback
(RTP/SAVPF)", RFC 5124, February 2008.
[I-D.ietf-avt-srtp-not-mandatory]
Perkins, C. and M. Westerlund, "Securing the RTP Protocol
Framework: Why RTP Does Not Mandate a Single Media
Security Solution", draft-ietf-avt-srtp-not-mandatory-13
(work in progress), May 2013.
[I-D.ietf-avtcore-rtp-security-options]
Westerlund, M. and C. Perkins, "Options for Securing RTP
Sessions", draft-ietf-avtcore-rtp-security-options-04
(work in progress), July 2013.
Appendix A. Metrics represented using RFC6390 Template
RFC EDITOR NOTE: please change XXXX in [RFCXXXX] by the new RFC
number, when assigned.
a. Bytes Discarded Metric
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* Metric Name: Bytes Discarded Metric
* Metric Description: Total number of bytes discarded over the
period covered by this report.
* Method of Measurement or Calculation: See section 4, number of
bytes discarded definition [RFCXXXX].
* Units of Measurement: See section 4, number of bytes discarded
definition [RFCXXXX].
* Measurement Point(s) with Potential Measurement Domain: See
section 4, 1st paragraph [RFCXXXX].
* Measurement Timing: See section 4, last three paragraphs of
[RFCXXXX] for measurement timing and for the Interval Metric
flag.
* Use and applications: See section 1, paragraph 1 of [RFCXXXX].
* Reporting model: See RFC3611.
Appendix B. Change Log
Note to the RFC-Editor: please remove this section prior to
publication as an RFC.
B.1. changes in draft-singh-xrblock-rtcp-xr-bytes-discarded-metric-00
o Bytes discarded metric split from
[I-D.ietf-xrblock-rtcp-xr-discard-rle-metrics].
Authors' Addresses
Varun Singh (editor)
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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Joerg Ott
Aalto University
School of Electrical Engineering
Otakaari 5 A
Espoo, FIN 02150
Finland
Email: jo@comnet.tkk.fi
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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