INTERNET-DRAFT R. Huang
Intended Status: Standard Huawei
Expires: December 25, 2014 V. Singh
Aalto University
June 23, 2014
RTP Control Protocol (RTCP) Extended Report (XR) for Post-Repair
Loss Count Metrics
draft-ietf-xrblock-rtcp-xr-post-repair-loss-count-04
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) 2014 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 3
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 from RTCP SR/RR [RFC3550]. 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 may 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 primary source RTP packets that are still lost after
applying one or more loss repair mechanisms. The metrics defined in
this document are packet level rather than slice/picture level, which
means the partial recovery of a packet will not be regarded as a
repaired packet. 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, so that the RTP sender or a
third-party entity is able to evaluate the effectiveness of the
repair methods used by the system. 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.
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 [KEYWORDS].
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primary source RTP packet: The original RTP packet sent from the RTP
sender for the first time. A lost primary source RTP packet may be
repaired by some other RTP packets used in repair mechanisms like FEC
or retransmission.
3 Post-Repair Loss Count Metrics Report Block
This block reports the number of packets lost after applying repair
mechanisms to complement the RTCP XR metrics defined in [RFC5725].
This packet may be stacked with other RTCP packets to form compound
RTCP packets and share the average reporting interval calculated by
the RTCP method described in [RFC3550]. When comparing this metric
with pre-repair loss metric of RTCP SR/RR, ambiguity may occur as
noted in [RFC5725]: Some packets will not be repaired in current RTCP
interval. 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. The sequence number range reported by RTCP
SR/RR may contain some sequence numbers of packets for which repair
might still be possible. To address this issue, we use begin sequence
number and end sequence number to explicitly indicate the actual
sequence number range that this RTCP XR report block reports on as
the measurement timing. These metrics defined in this report block
are all interval metrics and the measurement of them is made at the
RTP receiver. The relationship between the metrics in this report
block and the pre-repair loss metric of RTCP XR could be expressed in
the following formula:
cumulative number of packets lost = unrepaired loss count +
repaired loss count + to be repaired lost packet
"cumulative number of packets lost" is the metric from RTCP SR/RR.
"unrepaired loss count" and "repaired loss count" are the metrics
defined in this draft.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 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
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 first sequence number that this block reports on.
end_seq: 16 bits
The last sequence number that this block reports on plus one.
unrepaired loss count: 16 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 for which repair might
still be possible. Note that this metric must be measured in the
primary source RTP packets.
repaired loss count: 16 bits
Total number of packets fully repaired after one or more loss-
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repair methods, e.g., FEC and/or retransmission, during this
interval. Note that this metric must be measured in the primary
source RTP packets.
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 [RFC7202]
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 [RFC7201]) and might be more suitable.
6 IANA Considerations
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New block types for RTCP XR are subject to IANA registration. For
general guidelines on IANA considerations for RTCP XR, refer to
[RFC3611].
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 and Colin Perkins 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.
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[RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed.,
"RTP Control Protocol Extended Reports (RTCP XR)",
RFC 3611, November 2003.
[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.
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
July 2006.
[RFC5109] Li, A., Ed., "RTP Payload Format for Generic Forward Error
Correction", RFC 5109, December 2007.
[RFC7201] Westerlund, M. and C., Perkins, "Qptions for Securing RTP
Sessions", RFC 7201, April 2014.
[RFC7202] Perkins, C. and M., Westerlund, "Securing the RTP
Framework: Why RTP Does Not Mandate a Single Media
Security Solution", RFC 7202, April 2014.
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 for
the primary source RTP packets with no further chance of repair
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* 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 3, 1st paragraph, 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
* Metric Description: The number of RTP packets lost but repaired
after applying loss repair methods
* Method of Measurement or Calculation: It must be measured for
the primary source RTP packets with no further chance of repair
* 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 3, 1st paragraph, 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
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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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