draft-ietf-avt-post-repair-rtcp-xr-04.txt   draft-ietf-avt-post-repair-rtcp-xr-05.txt 
AVT A. Begen AVT A. Begen
Internet-Draft D. Hsu Internet-Draft D. Hsu
Intended status: Standards Track M. Lague Intended status: Standards Track M. Lague
Expires: April 30, 2009 Cisco Systems Expires: December 18, 2009 Cisco Systems
October 27, 2008 June 16, 2009
Post-Repair Loss RLE Report Block Type for RTCP XR Post-Repair Loss RLE Report Block Type for RTCP XR
draft-ietf-avt-post-repair-rtcp-xr-04 draft-ietf-avt-post-repair-rtcp-xr-05
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Abstract Abstract
This document defines a new report block type within the framework of This document defines a new report block type within the framework of
RTP Control Protocol (RTCP) Extended Reports (XR). One of the RTP Control Protocol (RTCP) Extended Reports (XR). One of the
initial XR report block types is the Loss Run Length Encoding (RLE) initial XR report block types is the Loss Run Length Encoding (RLE)
Report Block. This report conveys the information regarding the Report Block. This report conveys the information regarding the
individual Real-time Transport Protocol (RTP) packet receipt and loss individual Real-time Transport Protocol (RTP) packet receipt and loss
events experienced during the RTCP interval preceding the events experienced during the RTCP interval preceding the
transmission of the report. The new report, which is referred to as transmission of the report. The new report, which is referred to as
the Post-repair Loss RLE Report, carries the information regarding the Post-repair Loss RLE Report, carries the information regarding
the remaining lost packets after all loss-repair methods are applied. the remaining lost packets after all loss-repair methods are applied.
By comparing the RTP packet receipts/losses before and after the loss By comparing the RTP packet receipts/losses before and after the loss
repair is completed, one can determine the effectiveness of the loss- repair is completed, one can determine the effectiveness of the loss-
repair methods in an aggregated fashion. This document also defines repair methods in an aggregated fashion. This document also defines
the signaling of the Post-repair Loss RLE Report in the Session the signaling of the Post-repair Loss RLE Report in the Session
Description Protocol (SDP). Description Protocol (SDP).
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 4 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 5
3. Post-Repair Loss RLE Report Block . . . . . . . . . . . . . . . 4 3. Post-Repair Loss RLE Report Block . . . . . . . . . . . . . . 5
4. Session Description Protocol Signaling . . . . . . . . . . . . 6 4. Session Description Protocol Signaling . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 9
1. Introduction 1. Introduction
RTP Control Protocol (RTCP) is the out-of-band control protocol for RTP Control Protocol (RTCP) is the out-of-band control protocol for
the applications that are using the Real-time Transport Protocol the applications that are using the Real-time Transport Protocol
(RTP) for media delivery and communications [RFC3550]. RTCP allows (RTP) for media delivery and communications [RFC3550]. RTCP allows
the RTP entities to monitor the data delivery and provides them the RTP entities to monitor the data delivery and provides them
minimal control functionality via sender and receiver reports as well minimal control functionality via sender and receiver reports as well
as other control packets. [RFC3611] expands the RTCP functionality as other control packets. [RFC3611] expands the RTCP functionality
further by introducing the RTCP Extended Reports (XR). further by introducing the RTCP Extended Reports (XR).
skipping to change at page 3, line 42 skipping to change at page 4, line 42
This report block, which we refer to as the Post-repair Loss RLE, This report block, which we refer to as the Post-repair Loss RLE,
indicates the remaining missing, i.e., unrepairable, source packets. indicates the remaining missing, i.e., unrepairable, source packets.
When the pre-repair and post-repair Loss RLEs are compared, the RTP When the pre-repair and post-repair Loss RLEs are compared, the RTP
sender or another third party entity can evaluate the effectiveness sender or another third party entity can evaluate the effectiveness
of the loss-repair methods in an aggregated fashion. To avoid any of the loss-repair methods in an aggregated fashion. To avoid any
ambiguity in the evaluation, it is RECOMMENDED that the post-repair ambiguity in the evaluation, it is RECOMMENDED that the post-repair
Loss RLE is generated for the source packets that have no further Loss RLE is generated for the source packets that have no further
chance of being repaired. If the loss-repair method(s) may still chance of being repaired. If the loss-repair method(s) may still
recover one or more missing source packets, the post-repair Loss RLE recover one or more missing source packets, the post-repair Loss RLE
SHOULD NOT be sent until the loss-recovery process has been SHOULD NOT be sent until the loss-recovery process has been
completed. completed. However, a potential ambiguity may result from sequence
number wrapping in the primary source stream. Thus, the post-repair
Loss RLE reports may not be delayed arbitrarily. In case of an
ambiguity in the incoming reports, it is the sender's or the
monitoring entity's responsibility to understand which packets the
post-repair Loss RLE report is related to.
Similar to the pre-repair Loss RLE, the post-repair Loss RLE conveys Similar to the pre-repair Loss RLE, the post-repair Loss RLE conveys
the receipt/loss events at the packet level and considers partially the receipt/loss events at the packet level and considers partially
repaired packets as unrepaired. Thus, the methods that can partially repaired packets as unrepaired. Thus, the methods that can partially
recover the missing data SHOULD NOT be evaluated based on the recover the missing data SHOULD NOT be evaluated based on the
information provided by the Post-repair Loss RLE Reports since such information provided by the Post-repair Loss RLE Reports since such
information may underestimate the effectiveness of such methods. information may underestimate the effectiveness of such methods.
Note that the idea of using pre-repair and post-repair Loss RLEs can Note that the idea of using pre-repair and post-repair Loss RLEs can
be further extended when multiple sequential loss-repair methods are be further extended when multiple sequential loss-repair methods are
skipping to change at page 5, line 40 skipping to change at page 6, line 40
MUST be ignored by the receiver. MUST be ignored by the receiver.
o thinning (T): 4 bits o thinning (T): 4 bits
The amount of thinning performed on the sequence number space. The amount of thinning performed on the sequence number space.
Only those packets with sequence numbers 0 mod 2^T are reported on Only those packets with sequence numbers 0 mod 2^T are reported on
by this block. A value of 0 indicates that there is no thinning, by this block. A value of 0 indicates that there is no thinning,
and all packets are reported on. The maximum thinning is one and all packets are reported on. The maximum thinning is one
packet in every 32,768 (amounting to two packets within each 16- packet in every 32,768 (amounting to two packets within each 16-
bit sequence space). bit sequence space).
If thinning is desired, It is RECOMMENDED to use the same thinning
value in the pre-repair and post-repair Loss RLE reports. This
will allow easier report processing and correlation. However,
based on the specific needs of the application or the monitoring
entity, different values of thinning MAY be used for pre-repair
and post-repair Loss RLE reports.
o block length: 16 bits o block length: 16 bits
The length of this report block, including the header, in 32-bit The length of this report block, including the header, in 32-bit
words minus one. words minus one.
o SSRC of source: 32 bits o SSRC of source: 32 bits
The SSRC of the RTP data packet source being reported upon by this The SSRC of the RTP data packet source being reported upon by this
report block. report block.
o begin_seq: 16 bits o begin_seq: 16 bits
The first sequence number that this block reports on. The first sequence number that this block reports on.
o end_seq: 16 bits o end_seq: 16 bits
The last sequence number that this block reports on plus one. The last sequence number that this block reports on plus one.
skipping to change at page 6, line 19 skipping to change at page 7, line 25
o chunk i: 16 bits o chunk i: 16 bits
There are three chunk types: run length, bit vector, and There are three chunk types: run length, bit vector, and
terminating null, defined in [RFC3611] (Section 4). If the chunk terminating null, defined in [RFC3611] (Section 4). If the chunk
is all zeroes, then it is a terminating null chunk. Otherwise, is all zeroes, then it is a terminating null chunk. Otherwise,
the left most bit of the chunk determines its type: 0 for run the left most bit of the chunk determines its type: 0 for run
length and 1 for bit vector. length and 1 for bit vector.
Note that the sequence numbers that are included in the report refer Note that the sequence numbers that are included in the report refer
to the primary source stream. to the primary source stream.
When using post-repair Loss RLE reports, the amount of bandwidth
consumed by the detailed reports should be considered carefully. The
bandwidth usage rules as they are described in [RFC3611] apply to
post-repair Loss RLE reports as well.
4. Session Description Protocol Signaling 4. Session Description Protocol Signaling
A new parameter is defined for the Post-repair Loss RLE Report Block A new parameter is defined for the Post-repair Loss RLE Report Block
to be used with Session Description Protocol (SDP) [RFC4566]. It has to be used with Session Description Protocol (SDP) [RFC4566]. It has
the following syntax within the "rtcp-xr" attribute: the following syntax within the "rtcp-xr" attribute:
rtcp-xr-attrib = "a=rtcp-xr:" [xr-format *(SP xr-format)] CRLF rtcp-xr-attrib = "a=rtcp-xr:" [xr-format *(SP xr-format)] CRLF
xr-format = "post-repair-loss-rle" ["=" max-size] xr-format = "post-repair-loss-rle" ["=" max-size]
skipping to change at page 6, line 41 skipping to change at page 8, line 8
CRLF = %d13.10 CRLF = %d13.10
Figure 2 Figure 2
Refer to Section 5.1 of [RFC3611] for a detailed description and the Refer to Section 5.1 of [RFC3611] for a detailed description and the
full syntax of the "rtcp-xr" attribute. full syntax of the "rtcp-xr" attribute.
5. Security Considerations 5. Security Considerations
The security considerations of [RFC3611] apply in this document as The security considerations of [RFC3611] apply in this document as
well. well. Additional security considerations are briefly mentioned
below.
An attacker who monitors the regular pre-repair Loss RLE reports sent
by a group of receivers in the same multicast distribution network
may infer the network characteristics (Multicast Inference of Network
Characteristics). However, monitoring the post-repair Loss RLE
reports will not reveal any further information about the network.
Without the regular pre-repair Loss RLE reports, the post-repair ones
will not be any use to attackers. Even when used with the regular
pre-repair Loss RLE reports, the post-repair Loss RLE reports only
reveal the effectiveness of the repair process. However, this does
not enable any new attacks nor does it provide information to an
attacker that could not be similarly obtained by watching the RTP
packets fly by himself, performing the repair algorithms and
computing the desired output.
An attacker may interfere with the repair process for an RTP stream.
In that case, if the attacker is able to see the post-repair Loss
RLEs, the attacker may infer whether the attack is effective or not,
in which case the attacker may continue attacking or alter the
attack. In practice, however, this does not pose a security risk.
Similar to other RTCP XR reports, the post-repair Loss RLE reports
MAY be protected by using SRTP and SRTCP [RFC3711].
6. IANA Considerations 6. IANA Considerations
New block types for RTCP XR are subject to IANA registration. For New block types for RTCP XR are subject to IANA registration. For
general guidelines on IANA considerations for RTCP XR, refer to general guidelines on IANA considerations for RTCP XR, refer to
[RFC3611]. [RFC3611].
This document assigns the block type value 10 in the RTCP XR Block This document assigns the block type value 10 in the RTCP XR Block
Type Registry to "Post-repair Loss RLE Report Block." This document Type Registry to "Post-repair Loss RLE Report Block." This document
also registers the SDP [RFC4566] parameter "post-repair-loss-rle" for also registers the SDP [RFC4566] parameter "post-repair-loss-rle" for
skipping to change at page 8, line 5 skipping to change at page 9, line 45
8.2. Informative References 8.2. Informative References
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error [RFC5109] Li, A., "RTP Payload Format for Generic Forward Error
Correction", RFC 5109, December 2007. Correction", RFC 5109, December 2007.
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588, Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
July 2006. July 2006.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
Authors' Addresses Authors' Addresses
Ali Begen Ali Begen
Cisco Systems Cisco Systems
170 West Tasman Drive 170 West Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
USA USA
Email: abegen@cisco.com Email: abegen@cisco.com
skipping to change at page 9, line 4 skipping to change at line 370
Email: dohsu@cisco.com Email: dohsu@cisco.com
Michael Lague Michael Lague
Cisco Systems Cisco Systems
1414 Massachusetts Ave. 1414 Massachusetts Ave.
Boxborough, MA 01719 Boxborough, MA 01719
USA USA
Email: mlague@cisco.com Email: mlague@cisco.com
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