INTERNET-DRAFT R. Huang
Intended Status: Standard Huawei
Expires: June 12, 2014 V. Singh
Aalto University
December 9, 2013
RTP Control Protocol (RTCP) Extended Report (XR) for Post-Repair
Loss Count Metrics
draft-ietf-xrblock-rtcp-xr-post-repair-loss-count-00
Abstract
This document defines an RTP Control Protocol (RTCP) Extended Report
(XR) Block that allows reporting of post-repair loss count metrics
for a range of RTP applications.
Status of this Memo
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Copyright and License 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
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Post-Repair Loss Count Metrics Report Block . . . . . . . . . . 4
4 SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1 SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 6
4.2 Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 6
5 Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6.1 New RTCP XR Block Type value . . . . . . . . . . . . . . . 7
6.2 New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . . 7
6.3 Contact Information for registrations . . . . . . . . . . . 7
7 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1 Normative References . . . . . . . . . . . . . . . . . . . 7
8.2 Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. Metrics Represented Using the Template from RFC 6390 . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1 Introduction
RTCP SR/RR [RFC3550] contains some rough statistics about the data
received from the particular source indicated in that block. One of
them is the cumulative number of packet lost, which is called pre-
repair loss metric in this document. This metric conveys information
regarding the total number of RTP data packets that have been lost
since the beginning of the RTP session. However, this metric is
measured on media stream before any loss repair mechanism, e.g.,
retransmission [RFC4588] and Forward Error Correction (FEC)
[RFC5109], is applied. Using a repair mechanism usually results in
recovering some or all of the lost packets. Hence, the sending
endpoint cannot assess the performance of the repair mechanism by
observing the change in fraction loss and the cumulative loss
statistics. Consequently, [RFC5725] specifies a post-repair loss Run-
length Encoding (RLE) XR report block to address this issue. The
sending endpoint is able to infer which packets were repaired from
the RLE report block, but at the cost of higher overhead. When
applications use multiple XR blocks, the endpoints require more
concise reporting to save bandwidth.
This document defines a new XR block type to augment those defined in
[RFC3611] and complement the report block defined in [RFC5725] for
use in a range of RTP application. This new block type reports the
number of RTP packets on the primary source stream that are still
lost after applying one or more loss repair mechanisms. When
comparing this metric with pre-repair loss metric of RTCP SR/RR, it
may bring ambiguity as noted in [RFC5725]: Some packets will not be
repaired in current RTCP interval. So in [RFC5725] it is suggested to
delay report block to wait for packets to be repaired. However, it is
not wise to delay this report block arbitrarily until those packets
have been fully repaired. Thus it is RECOMMENDED that this report
block should be generated for those source packets that have no
further chance of being repaired. But a potential ambiguity may
result from sequence number range inconsistent. To address this
issue, we use begin sequence number and end sequence number to
explicitly indicate the actual sequence number range that the report
block reports on. In addition, another metric, repaired loss count,
is also introduced in this report block for calculating the pre-
repair loss count during the this range. Note that the metrics in
this report block MUST NOT be directly compared with the pre-repair
loss metric of RFC3550.
The metrics defined in this document belongs to the class of
transport-related metrics defined in [RFC6792]. And it is in
accordance with the guidelines in [RFC6390] and [RFC6792]. These
metrics are applicable to any RTP application, especially those that
use loss repair mechanisms.
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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 RFC 2119 [RFC2119].
3 Post-Repair Loss Count Metrics Report Block
This block describes the residual number of packets lost after
applying repair mechanisms. The report block is complementary to the
RTCP XR metrics defined in [RFC5725] as it uses a non-RLE format.
The post-repair loss count metrics report block has the following
format:
0 1 2 3 4
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 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BT=PRLR | Reserved | block length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| begin_seq | end_seq |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| unrepaired loss count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| repaired loss count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format for the Post-Repair Loss Count Metrics Report
Block
Block Type (BT): 8 bits
A Post-Repair Loss Count Metrics Report Block is identified by the
constant PRLR.
[Note to RFC Editor: Please replace PRLR with the IANA provided
RTCP XR block type for this block.]
Reserved: 8 bits
These bits are reserved for future use. They MUST be set to zero
by senders and ignored by receivers (see [RFC6709], Section 4.2).
block length: 16 bits
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This field is in accordance with the definition in [RFC3611]. In
this report block, it MUST be set to 4. 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].
begin_seq: 16 bits
The sequence number of the first packet in the session or the
sequence number of the first packet fully repaired that this block
reports on.
end_seq: 16 bits
The sequence number of the last packet fully repaired that this
block reports on plus one.
unrepaired loss count: 32 bits
Total number of packets finally lost after one or more loss-repair
methods, e.g., FEC and/or retransmission, during this interval.
This metric MUST NOT count the lost packets that haven't finished
repairing. Note that this metric must be measured in the primary
source stream.
repaired loss count: 32 bits
Total number of packets fully repaired after one or more loss-
repair methods, e.g., FEC and/or retransmission, during this
interval. Note that this metric must be measured in the primary
source stream.
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4 SDP Signaling
[RFC3611] defines the use of SDP (Session Description Protocol) for
signaling the use of RTCP 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 session augments the SDP attribute "rtcp-xr" defined in Section
5.1 of [RFC3611] by providing an additional value of "xr-format" to
signal the use of the report block defined in this document.
xr-format =/ xr-prlr-block
xr-prlr-block = "post-repair-loss-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].
5 Security Considerations
It is believed that this RTCP XR block introduces no new security
considerations beyond those described in [RFC3611]. This block does
not provide per-packet statistics, so the risk to confidentially
documented in Section 7, paragraph 3 of [RFC3611] does not apply.
An attacker may put incorrect information in the Post-Repair Loss
Count reports, which will be affect the performance of loss repair
mechanisms. Implementers should consider the guidance in [I-D.ietf-
avtcore-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.
6 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].
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6.1 New RTCP XR Block Type value
This document assigns the block type value PRLR in the IANA "RTP
Control Protocol Extended Reports (RTCP XR) Block Type Registry" to
the "Post-Repair Loss Count Metrics Report Block".
[Note to RFC Editor: please replace PRLR with the IANA provided RTCP
XR block type for this block.]
6.2 New RTCP XR SDP Parameter
This document also registers a new parameter "post-repair-loss-count"
in the "RTP Control Protocol Extended Reports (RTCP XR) Session
Description Protocol (SDP) Parameters Registry".
6.3 Contact Information for registrations
The following contact information is provided for all registrations
in this document:
Rachel Huang (rachel.huang@huawei.com)
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
7 Acknowledgments
The author would like to thank Roni Even for giving valuable comments
and suggestions.
8 References
8.1 Normative References
[KEYWORDS] 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., Ed., Caceres, R., Ed., and A. Clark, Ed.,
"RTP Control Protocol Extended Reports (RTCP XR)",
RFC 3611, November 2003.
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[RFC5725] Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE
Report Block Type for RTP Control Protocol (RTCP) Extended
Reports (XRs)", RFC 5725, February 2010.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
8.2 Informative References
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
October 2011.
[RFC6792] Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
RTP Monitoring Framework", RFC 6792, November 2012.
Appendix A. Metrics Represented Using the Template from RFC 6390
a. Unrepaired RTP Packet Loss Count Metric
* Metric Name: Unrepaired RTP Packet Loss Count Metric
* Metric Description: Total number of RTP packets still lost after
loss repair methods are applied
* Method of Measurement or Calculation: It must be measured in the
primary source stream. It must be measured for the packets that
have no further chance of being repaired.
* Units of Measurement: See section 3, unrepaired loss count
definition.
* Measurement Point(s) with Potential Measurement Domain: See
section 3, 1st paragraph.
* Measurement Timing: See Section 4 for measurement timing.
* Use and Applications: See Section 1
* Reporting Model: See RFC3611.
b. Repaired RTP Packet Loss Count Metric
* Metric Name: Repaired RTP Packet Count Metric
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* Metric Description: The number of RTP packets lost but repaired
after applying loss repair methods.
* Method of Measurement or Calculation: It must be measured in the
primary source stream.
* Units of Measurement: See section 3, repaired loss count
definition.
* Measurement Point(s) with Potential Measurement Domain: See
section 3, 1st paragraph.
* Measurement Timing: See Section 4 for measurement timing.
* Use and Applications: See Section 1
* Reporting Model: See RFC3611.
Authors' Addresses
Rachel Huang
Huawei
101 Software Avenue, Yuhua District
Nanjing 210012
China
EMail: rachel.huang@huawei.com
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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