Internet DRAFT - draft-ietf-xrblock-rtcp-xr-post-repair-loss-count
draft-ietf-xrblock-rtcp-xr-post-repair-loss-count
INTERNET-DRAFT R. Huang
Intended Status: Standards Track Huawei
Expires: August 23, 2015 V. Singh
Aalto University
February 19, 2015
RTP Control Protocol (RTCP) Extended Report (XR) for Post-Repair
Loss Count Metrics
draft-ietf-xrblock-rtcp-xr-post-repair-loss-count-11
Abstract
This document defines an RTP Control Protocol (RTCP) Extended Report
(XR) Block that allows reporting of post-repair loss count metric for
a range of RTP applications. In addition, another metric, repaired
loss count, is also introduced in this report block for calculating
the pre-repair loss count when needed so that the RTP sender or a
third-party entity is able to evaluate the effectiveness of the
repair methods used by the system.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
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Copyright and License Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
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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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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Post-Repair Loss Count Metrics Report Block . . . . . . . . . . 4
3.1 Report Block Structure . . . . . . . . . . . . . . . . . . 4
3.2 Example Usage . . . . . . . . . . . . . . . . . . . . . . . 5
4 SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1 SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 7
4.2 Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 7
5 Security Considerations . . . . . . . . . . . . . . . . . . . . 7
6 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
6.1 New RTCP XR Block Type value . . . . . . . . . . . . . . . 7
6.2 New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . . 8
6.3 Contact Information for registrations . . . . . . . . . . . 8
7 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1 Normative References . . . . . . . . . . . . . . . . . . . 8
8.2 Informative References . . . . . . . . . . . . . . . . . . 9
Appendix A. Metrics Represented Using the Template from RFC 6390 . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1 Introduction
RTCP Sender Reports (SR)/Receiver Reports (RR) [RFC3550] contain some
rough statistics about the data received from the particular source
indicated in that block. One of them is the cumulative number of
packets 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] or 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 the reporting overhead for the packet-by-packet
report block is higher compared to other report blocks.
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
applications. This new block type reports the post-repair loss count
metric which records the number of primary source RTP packets that
are still lost after applying one or more loss repair mechanisms. In
addition, another metric, repaired loss count, is also introduced in
this report block for calculating the pre-repair loss count during
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.
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.
The metrics defined in this document belong to the class of
transport-related metrics defined in [RFC6792] and are specified 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",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS].
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 (e.g., FEC). It complements the RTCP XR metrics defined
in [RFC5725]. As noted in [RFC5725], ambiguity may occur when
comparing this metric with pre-repair loss metric reported in an RTCP
SR/RR, i.e., some packets were not repaired in the current RTCP
interval, but they may be repaired later. Therefore, this block uses
a begin sequence number and an end sequence number to explicitly
indicate the actual sequence number range reported by this RTCP XR.
Accordingly, only packets that have no further chance of being
repaired and that have been repaired are included in this report
block.
3.1 Report Block Structure
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| post-repair loss count | repaired loss count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.]
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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. It can
remain fixed when calculating metrics over several RTCP reporting
intervals.
end_seq: 16 bits
The last sequence number that this block reports on plus one.
post-repair loss count: 16 bits
Total number of packets finally lost after applying one or more
loss-repair methods, e.g., FEC and/or retransmission, during the
actual sequence number range indicated by begin_seq and end_seq.
This metric MUST NOT count the lost packets for which repair might
still be possible. Note that this metric MUST measure only primary
source RTP packets.
repaired loss count: 16 bits
Total number of packets fully repaired after applying one or more
loss-repair methods, e.g., FEC and/or retransmission, during the
actual sequence number range indicated by begin_seq and end_seq.
Note that this metric MUST measure only primary source RTP
packets.
3.2 Example Usage
The metrics defined in this report block are all measured at the RTP
receiver. However, the receiving endpoint can report the metrics in
two different ways:
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1. Cumulative report
In this case, implementations may set begin_seq to the first packet
in the RTP session and it will remain fixed across all reports.
Hence, the "post-repair loss count" and "repaired loss count",
respectively will correspond to "cumulative post-repair loss count"
and "cumulative repaired loss count" in this case. These cumulative
metrics when combined with the cumulative loss metrics reported in an
RTCP RR (pre-repair) assists in calculating the still to be repaired
lost packets:
still to be repaired lost packet = cumulative number of packets
lost - cumulative post-repair loss count - cumulative repaired
loss count
2. Interval report
Some implementations may align the begin_seq and end_seq number with
the highest sequence numbers of consecutive RTCP RRs (RTCP interval).
This is NOT RECOMMENDED as packets that are not yet repaired in this
current RTCP interval and may be repaired in the subsequent intervals
will not be reported. It is illustrated in the following example:
Interval A: The extended highest sequence number received in RTCP
RR is 20. Begin_seq is 10 and end_seq is 20.
Interval B: The extended highest sequence number received in RTCP
RR is 30. Begin_seq is 20 and end_seq is 30.
If packets 17 and 19 are lost and not yet repaired in interval A and
subsequently repaired in interval B, they will not then be reported
because their sequence numbers do not belong in the interval B.
Therefore, if implementations want these packets to be reported as
repaired, they MUST NOT align the begin_seq and end_seq to the RTCP
intervals.
Alternatively, implementations may choose the begin_seq and end_seq
numbers that cover several RTCP intervals. Additionally, the reported
range of sequence numbers may overlap with the previous report
blocks, so that the packets that were not yet repaired in one
interval but were subsequently repaired or deemed unrepairable were
reported in subsequent intervals.
In this case, the "cumulative number of packets lost" cannot be
easily compared with the post-repair metrics. However, the sending
endpoint can calculate the efficiency of the error resilience
algorithm using the post-repair and repaired lost count,
respectively.
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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
parameters, refer to section 5.2 of [RFC3611].
5 Security Considerations
This proposed 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 confidentiality 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
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
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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 contact information for the registration is :
RAI Area Directors <rai-ads@tools.ietf.org>
7 Acknowledgments
The author would like to thank Roni Even, Colin Perkins, and Qin Wu
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.
[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.
[RFC5725] Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE
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Report Block Type for RTP Control Protocol (RTCP) Extended
Reports (XRs)", RFC 5725, February 2010.
8.2 Informative References
[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.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
October 2011.
[RFC6709] Carpenter, B., Aboba, B., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC6709,
September 2012.
[RFC6792] Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
RTP Monitoring Framework", RFC 6792, November 2012.
[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.
Appendix A. Metrics Represented Using the Template from RFC 6390
a. Post-Repair RTP Packet Loss Count Metric
* Metric Name: Post-Repair 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: See section 3.1, Post-
Repair RTP Packet Loss Count Metric definition. It is directly
measured and must be measured for the primary source RTP packets
with no further chance of repair.
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* Units of Measurement: This metric is expressed as a 16-bit
unsigned integer value giving the number of RTP packets.
* Measurement Point(s) with Potential Measurement Domain: It is
measured at the receiving end of the RTP stream.
* Measurement Timing: This metric relies on the sequence number
interval to determine measurement timing. See Section 3, 3rd
paragraph, for details.
* Use and Applications: These metrics are applicable to any RTP
application, especially those that use loss repair mechanisms. See
Section 1 for details.
* 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: See section 3.1, Repaired
RTP Packet Loss Count Metric definition. It is directly measured
and must be measured for the primary source RTP packets with no
further chance of repair.
* Units of Measurement: This metric is expressed as a 16-bit
unsigned integer value giving the number of RTP packets.
* Measurement Point(s) with Potential Measurement Domain: It is
measured at the receiving end of the RTP stream.
* Measurement Timing: This metric relies on the sequence number
interval to determine measurement timing. See Section 3, 3rd
paragraph, for details.
* Use and Applications: These metrics are applicable to any RTP
application, especially those that use loss repair mechanisms. See
Section 1 for details.
* Reporting Model: See RFC3611.
Authors' Addresses
Rachel Huang
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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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