Internet DRAFT - draft-ietf-xrblock-rtcp-xr-discard
draft-ietf-xrblock-rtcp-xr-discard
Audio/Video Transport Working Group A. Clark
Internet-Draft Telchemy
Intended status: Standards Track G. Zorn
Expires: December 30, 2013 Network Zen
Q. Wu
Huawei
June 28, 2013
RTP Control Protocol (RTCP) Extended Report (XR) Block for Discard Count
metric Reporting
draft-ietf-xrblock-rtcp-xr-discard-15.txt
Abstract
This document defines an RTP Control Protocol(RTCP) Extended Report
(XR) Block that allows the reporting of a simple discard count metric
for use in a range of RTP applications.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 30, 2013.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Discard Count Report Block . . . . . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 5
3. Discard Count Metric Report Block . . . . . . . . . . . . . . 6
3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 6
3.2. Definition of Fields in Discard Count Metric Report
Block . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 9
4.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 10
5.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 10
5.3. Contact information for registrations . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. Metrics represented using RFC6390 Template . . . . . 15
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 16
B.1. draft-ietf-xrblock-rtcp-xr-discard-14 . . . . . . . . . . 16
B.2. draft-ietf-xrblock-rtcp-xr-discard-13 . . . . . . . . . . 16
B.3. draft-ietf-xrblock-rtcp-xr-discard-12 . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
1.1. Discard Count Report Block
This document defines a new block type to augment those defined in
[RFC3611] for use in a range of RTP applications. The new block type
supports the reporting of the number of packets which are received
correctly but are never played out, typically because they arrive too
late to be played out (buffer underflow) or too early (buffer
overflow). The metric is applicable both to systems which use packet
loss repair techniques (such as forward error correction [RFC5109] or
retransmission [RFC4588]) and to those which do not.
This metric is useful for identifying the existence, and
characterizing the severity, of a packet transport problem which may
affect users' perception of a service delivered over RTP.
This block may be used in conjunction with [BGDISCARD] which provides
additional information on the pattern of discarded packets. However
the metric in [BGDISCARD] may be used independently of the metrics in
this block.
When a Discard Count Metrics Block is sent together with a Burst Gap
Discard Metrics Block (defined in [BGDISCARD] ) to the media sender
or RTP based network management system, the information carried in
the Discard Count Metrics Block and the Burst Gap Discard Metrics
Block allows systems receiving the blocks to calculate burst gap
summary statistics (e.g., the gap discard rate).
The metric belongs to the class of transport-related end system
metrics defined in [RFC6792].
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 document defines a new Extended Report block for
use with [RFC3550] and [RFC3611].
1.3. Performance Metrics Framework
The Performance Metrics Framework [RFC6390] provides guidance on the
definition and specification of performance metrics. The RTP
Monitoring Architectures [RFC6792] provides guideline for reporting
block format using RTCP XR. The metrics block described in this
document are in accordance with the guidelines in [RFC6390] and
[RFC6792].
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1.4. Applicability
This metric is believed to be applicable to a large class of RTP
applications which use a de-jitter buffer [RFC5481].
Discards due to late or early arriving packets affects user
experience. The reporting of discards alerts senders and other
receivers to the need to adjust their transmission or reception
strategies. The reports allow network managers to diagnose these
user experience problems.
The ability to detect duplicate packets can be used by managers to
detect network layer or sender behavior which may indicate network or
device issues. Based on the reports, these issues may be addressed
prior to any impact on user experience.
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2. Terminology
2.1. Standards Language
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 RFC 2119 [RFC2119].
In addition, the following terms are defined:
Received, Lost and Discarded
A packet shall be regarded as lost if it fails to arrive within an
implementation-specific time window. A packet that arrives within
this time window but is either too early to be played out or too
late to be played out or thrown away before playout due to packet
duplication or redundancy shall be regarded as discarded. A
packet shall not be regarded as discarded if it arrives within
this time window but is dropped during decoding by some higher
layer decoder, e.g., due to a decoding error. A packet shall be
classified as one of received (or OK), discarded or lost. The
Discard Count Metric counts only discarded packets. The metric
"cumulative number of packets lost" defined in [RFC3550] reports a
count of packets lost from the media stream (single
Synchronization source (SSRC) within single RTP session).
Similarly the metric "number of packets discarded" reports a count
of packets discarded from the media stream (single SSRC within
single RTP session) arriving at the receiver. Another metric
defined in [RFC5725] is available to report on packets which are
not recovered by any repair techniques which may be in use.
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3. Discard Count Metric Report Block
Metrics in this block report on the number of packets discarded in
the stream arriving at the RTP end system. The measurement of these
metrics is made at the receiving end of the RTP stream. Instances of
this metrics block refer by SSRC to the separate auxiliary
Measurement Information Block [RFC6776] which describes measurement
Intervals in use. This metrics block relies on the measurement
interval in the Measurement Information Block indicating the span of
the report and MUST be sent in the same compound RTCP packet as the
measurement information block. If the measurement interval is not
received in the same compound RTCP packet as this metrics block, this
metrics block MUST be discarded.
3.1. Report Block Structure
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=PDC | I |DT | resv.| block length = 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| discard count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
3.2. Definition of Fields in Discard Count Metric Report Block
Block type (BT): 8 bits
A Discard Count Metric Report Block is identified by the constant
PDC.
[Note to RFC Editor: please replace PDC with the IANA provided
RTCP XR block type for this block.]
Interval Metric Flag (I): 2 bits
This field indicates whether the reported metric is an interval,
cumulative, or sampled metric [RFC6792]:
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I=10: Interval Duration - the reported value applies to the
most recent measurement interval duration between successive
metrics reports.
I=11: Cumulative Duration - the reported value applies to the
accumulation period characteristic of cumulative measurements.
I=01: Sampled Value - the reported value is a sampled
instantaneous value.
In this document, the Discard Count Metric can only be measured
over definite intervals, and cannot be sampled. Accordingly, the
value I=01, indicating a sampled value, MUST NOT be sent, and MUST
be discarded when received. In addition, the value I=00 is
reserved and also MUST NOT be sent, and MUST be discarded when
received.
Discard Type (DT): 2bits
This field is used to identify the discard type used in this
report block. The discard type is defined as follows:
00: Report packet discarded or being thrown away before playout
due to packets duplication.
01: Report packet discarded due to too early to be played out.
10: Report packet discarded due to too late to be played out.
The value DT=11 is reserved for future definition and MUST NOT be
Sent,and MUST be discarded when received.
An endpoint MAY report any combination of discard types in each
reporting interval by including several Discard Count Metric
Report Blocks in a single RTCP XR packet.
Some systems send duplicate RTP packets for robustness or error
resilience. This is NOT RECOMMENDED since it breaks RTCP packet
statistics. If duplication is desired for error resilience, the
mechanism described in [RTPDUP] can be used, since this will not
cause breakage of RTP streams or RTCP statistics.
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Reserved (resv): 4 bits
These bits are reserved. They MUST be set to zero by senders and
ignored by receivers (See RFC6709 section 4.2).
block length: 16 bits
The length of this report block in 32-bit words, minus one, in
accordance with the definition in [RFC3611]. This field MUST be
set to 2 to match the fixed length of the report block. The block
MUST be discarded if the block length is set to a different value.
SSRC of source: 32 bits
As defined in Section 4.1 of [RFC3611].
discard count
Number of packets discarded over the period (Interval or
Cumulative) covered by this report.
The measured value is unsigned value. If the measured value
exceeds 0xFFFFFFFD, the value 0xFFFFFFFE MUST be reported to
indicate an over-range measurement. If the measurement is
unavailable, the value 0xFFFFFFFF MUST be reported.
Note that the number of packets expected in the period associated
with this metric (whether interval or cumulative) is available
from the difference between a pair of extended sequence numbers in
the Measurement Information block [RFC6776], so need not be
repeated in this block.
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4. SDP Signaling
[RFC3611] defines the use of SDP (Session Description Protocol)
[RFC4566] for signaling the use of XR blocks. However XR blocks MAY
be used without prior signaling (see section 5 of RFC3611).
4.1. SDP rtcp-xr-attrib Attribute Extension
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.
xr-format =/ xr-pdc-block
xr-pdc-block = "pkt-discard-count"
4.2. Offer/Answer Usage
When SDP is used in offer-answer context, the SDP Offer/Answer usage
defined in [RFC3611] for unilateral "rtcp-xr" attribute parameters
applies. For detailed usage of Offer/Answer for unilateral
parameter, refer to section 5.2 of [RFC3611].
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5. 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].
5.1. New RTCP XR Block Type value
This document assigns the block type value PDC in the IANA " RTP
Control Protocol Extended Reports (RTCP XR) Block Type Registry " to
the "Discard Count Metrics Block".
[Note to RFC Editor: please replace PDC with the IANA provided RTCP
XR block type for this block.]
5.2. New RTCP XR SDP Parameter
This document also registers a new parameter "pkt-discard-count" in
the " RTP Control Protocol Extended Reports (RTCP XR) Session
Description Protocol (SDP) Parameters Registry ".
5.3. Contact information for registrations
The following contact information is provided for all registrations
in this document:
Qin Wu (sunseawq@huawei.com)
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
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6. Security Considerations
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. Where this is a concern, the implementation should apply
authentication to this report block. This can be achieved by using
the AVPF profile together with the Secure RTP profile as defined in
[RFC3711]; as a prerequisite, an appropriate combination of those two
profiles (an "SAVPF") is being specified [RFC5124].
Besides this, 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.
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7. Contributors
Geoff Hunt wrote the initial draft of this document.
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8. Acknowledgments
The authors gratefully acknowledge reviews and feedback provided 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, Kevin
Gross, Varun Singh, Claire Bi, Roni Even, Dan Romascanu and Jonathan
Lennox.
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[RFC3550] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time
Applications", RFC 3550, July 2003.
[RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", November 2003.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", July 2006.
[RFC6709] Carpenter, B., Aboba, B., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC 6709,
September 2012.
[RFC6776] Hunt, G., "Measurement Identity and information Reporting
using SDES item and XR Block", RFC 6776, October 2012.
9.2. Informative References
[BGDISCARD]
Hunt, G., "RTCP XR Report Block for Burst Gap Discard
metric Reporting",
ID draft-ietf-xrblock-rtcp-xr-burst-gap-discard-14,
April 2013.
[RFC4588] Rey, J., "RTP Retransmission Payload Format", RFC 4588,
July 2006.
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error
Correction", RFC 5109, July 2006.
[RFC5725] Begen, A., "RTCP XR Report Block for Post-Repair Loss
metric Reporting", RFC 5725, February 2010.
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric
Development", RFC 6390, October 2011.
[RFC6792] Wu, Q., "Monitoring Architectures for RTP", RFC 6792,
November 2012.
[RTPDUP] Begen, A. and C. Perkins, "Duplicating RTP Streams",
ID draft-ietf-avtext-rtp-duplication-02, March 2013.
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Appendix A. Metrics represented using RFC6390 Template
RFC EDITOR NOTE: please change XXXX in [RFCXXXX] by the new RFC
number, when assigned.
a. Number of packets discarded Metric
* Metric Name: Number of RTP packets discarded Metric
* Metric Description: Number of RTP packets discarded over the
period covered by this report.
* Method of Measurement or Calculation: See section 3.2, number
of packets discarded definition [RFCXXXX].
* Units of Measurement: See section 3.2, number of packets
discarded definition [RFCXXXX].
* Measurement Point(s) with Potential Measurement Domain: See
section 3, 1st paragraph [RFCXXXX].
* Measurement Timing: See section 3, 1st paragraph [RFCXXXX] for
measurement timing and section 3.2 [RFCXXXX] for Interval
Metric flag.
* Use and applications: See section 1.4 [RFCXXXX].
* Reporting model: See RFC3611.
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Appendix B. Change Log
Note to the RFC-Editor: please remove this section prior to
publication as an RFC.
B.1. draft-ietf-xrblock-rtcp-xr-discard-14
The following are the major changes compared to previous version:
o Editorial changes to paragraph 4 of section 1.1.
B.2. draft-ietf-xrblock-rtcp-xr-discard-13
The following are the major changes compared to previous version:
o Some editorial changes to get in line with burst gap drafts.
B.3. draft-ietf-xrblock-rtcp-xr-discard-12
The following are the major changes compared to previous version:
o Incorporate some changes to burst gap draft that applies to this
document.
o Use RFC6390 template to the metrics in the appendix.
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Authors' Addresses
Alan Clark
Telchemy Incorporated
2905 Premiere Parkway, Suite 280
Duluth, GA 30097
USA
Email: alan.d.clark@telchemy.com
Glen Zorn
Network Zen
77/440 Soi Phoomjit, Rama IV Road
Phra Khanong, Khlong Toie
Bangkok 10110
Thailand
Phone: +66 (0) 87 502 4274
Email: gwz@net-zen.net
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
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