draft-ietf-avt-post-repair-rtcp-xr-07.txt   rfc5725.txt 
AVT A. Begen Internet Engineering Task Force (IETF) A. Begen
Internet-Draft D. Hsu Request for Comments: 5725 D. Hsu
Intended status: Standards Track M. Lague Category: Standards Track M. Lague
Expires: May 15, 2010 Cisco Systems ISSN: 2070-1721 Cisco
November 11, 2009 February 2010
Post-Repair Loss RLE Report Block Type for RTCP XR Post-Repair Loss RLE Report Block Type for
draft-ietf-avt-post-repair-rtcp-xr-07 RTP Control Protocol (RTCP) Extended Reports (XRs)
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 (XRs). 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 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 information regarding the
the remaining lost packets after all loss-repair methods are applied. packets that remain lost 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).
Status of this Memo Status of This Memo
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 4 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 4
3. Post-Repair Loss RLE Report Block . . . . . . . . . . . . . . . 4 3. Post-Repair Loss RLE Report Block . . . . . . . . . . . . . . . 4
4. Session Description Protocol Signaling . . . . . . . . . . . . 6 4. Session Description Protocol Signaling . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 8 8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
RTP Control Protocol (RTCP) is the out-of-band control protocol for The RTP Control Protocol (RTCP) is the out-of-band control protocol
the applications that are using the Real-time Transport Protocol for 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 RTP entities to monitor data delivery and provides them minimal
minimal control functionality via sender and receiver reports as well control functionality via sender and receiver reports as well as
as other control packets. [RFC3611] expands the RTCP functionality other control packets. [RFC3611] expands the RTCP functionality
further by introducing the RTCP Extended Reports (XR). further by introducing the RTCP Extended Reports (XRs).
One of the initial XR report block types defined in [RFC3611] is the One of the initial XR report block types defined in [RFC3611] is the
Loss Run Length Encoding (RLE) Report Block. This report conveys the Loss Run Length Encoding (RLE) Report Block. This report conveys
information regarding the individual RTP packet receipt and loss information regarding the individual 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. However, the Loss RLE in an RTCP XR transmission of the report. However, the Loss RLE in an RTCP XR
report is usually collected only on the primary source stream before report is usually collected only on the primary source stream before
any loss-repair method is applied. Once one or more loss-repair any loss-repair method is applied. Once one or more loss-repair
methods, e.g., Forward Error Correction (FEC) [RFC5109] and/or methods, e.g., Forward Error Correction (FEC) [RFC5109] and/or
retransmission [RFC4588], are applied, some or all of the lost retransmission [RFC4588], are applied, some or all of the lost
packets on the primary source stream may be recovered. However, the packets on the primary source stream may be recovered. However, the
pre-repair Loss RLE cannot indicate which source packets were pre-repair Loss RLE cannot indicate which source packets were
recovered and which are still missing. Thus, the pre-repair Loss RLE recovered and which are still missing. Thus, the pre-repair Loss RLE
cannot specify how well the loss repair performed. cannot specify how well the loss repair performed.
This issue can be addressed by generating an additional report block This issue can be addressed by generating an additional report block
(within the same or a different RTCP XR report), which reflects the (within the same or a different RTCP XR report), which reflects the
packet receipt/loss events after all loss-repair methods are applied. packet receipt/loss events after all loss-repair methods are applied.
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 be 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. However, a potential ambiguity may result from sequence completed. However, a potential ambiguity may result from sequence-
number wrapping in the primary source stream. Thus, the post-repair number wrapping in the primary source stream. Thus, the Post-repair
Loss RLE reports may not be delayed arbitrarily. In case of an Loss RLE reports may not be delayed arbitrarily. In case of an
ambiguity in the incoming reports, it is the sender's or the ambiguity in the incoming reports, it is the sender's or the
monitoring entity's responsibility to understand which packets the monitoring entity's responsibility to understand which packets the
post-repair Loss RLE report is related to. 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
applied to the primary source stream. Reporting the Loss RLEs before applied to the primary source stream. Reporting the Loss RLEs before
and after each loss-repair method can provide specific information and after each loss-repair method can provide specific information
about the individual performances of these methods. However, it can about the individual performances of these methods. However, it can
be a difficult task to quantify the specific contribution made by be a difficult task to quantify the specific contribution made by
each loss-repair method in hybrid systems, where different methods each loss-repair method in hybrid systems, where different methods
collectively work together to repair the lost source packets. Thus, collectively work together to repair the lost source packets. Thus,
in this specification we only consider reporting the Loss RLE after in this specification we only consider reporting the Loss RLE after
all loss-repair methods are applied. all loss-repair methods have been applied.
This document registers a new report block type to cover the post- This document registers a new report block type to cover the post-
repair Loss RLE within the framework of RTCP XR. Applications that repair Loss RLE within the framework of RTCP XR. Applications that
are employing one or more loss-repair methods MAY use Post-repair are employing one or more loss-repair methods MAY use Post-repair
Loss RLE Reports for every packet they receive or for a set of Loss RLE reports for every packet they receive or for a set of
specific packets they have received. In other words, the coverage of specific packets they have received. In other words, the coverage of
the post-repair Loss RLEs may or may not be contiguous. the post-repair Loss RLEs may or may not be contiguous.
2. Requirements Notation 2. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Post-Repair Loss RLE Report Block 3. Post-Repair Loss RLE Report Block
skipping to change at page 6, line 21 skipping to change at page 5, line 21
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| begin_seq | end_seq | | begin_seq | end_seq |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| chunk 1 | chunk 2 | | chunk 1 | chunk 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... : : ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| chunk n-1 | chunk n | | chunk n-1 | chunk n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format for the post-repair loss RLE report block Figure 1: Format for the Post-repair Loss RLE Report Block
o block type (BT): 8 bits o block type (BT): 8 bits
A Post-repair Loss RLE Report Block is identified by the constant A Post-repair Loss RLE Report Block is identified by the constant
10. 10.
o rsvd.: 4 bits o rsvd.: 4 bits
This field is reserved for future definition. In the absence of This field is reserved for future definition. In the absence of
such definition, the bits in this field MUST be set to zero and such definition, the bits in this field MUST be set to zero and
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 by
by this block. A value of 0 indicates that there is no thinning, this block. A value of 0 indicates that there is no thinning and
and all packets are reported on. The maximum thinning is one all packets are reported. The maximum thinning is one packet in
packet in every 32,768 (amounting to two packets within each 16- every 32,768 (amounting to two packets within each 16-bit sequence
bit sequence space). space).
If thinning is desired, It is RECOMMENDED to use the same thinning If thinning is desired, it is RECOMMENDED to use the same thinning
value in the pre-repair and post-repair Loss RLE reports. This value in the Pre-repair and Post-repair Loss RLE reports. This
will allow easier report processing and correlation. However, will allow easier report processing and correlation. However,
based on the specific needs of the application or the monitoring based on the specific needs of the application or the monitoring
entity, different values of thinning MAY be used for pre-repair entity, different values of thinning MAY be used for Pre-repair
and post-repair Loss RLE reports. 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.
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. These are defined in Section 4 of [RFC3611].
is all zeroes, then it is a terminating null chunk. Otherwise, If the chunk is all zeroes, then it is a terminating null chunk.
the left most bit of the chunk determines its type: 0 for run Otherwise, the left-most bit of the chunk determines its type: 0
length and 1 for bit vector. for run 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 When using Post-repair Loss RLE reports, the amount of bandwidth
consumed by the detailed reports should be considered carefully. The consumed by the detailed reports should be considered carefully. The
bandwidth usage rules as they are described in [RFC3611] apply to bandwidth usage rules, as they are described in [RFC3611], apply to
post-repair Loss RLE reports as well. 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] using to be used with Session Description Protocol (SDP) [RFC4566] using
the Augmented Backus-Naur Form (ABNF) [RFC5234]. It has the the Augmented Backus-Naur Form (ABNF) [RFC5234]. It has the
following syntax within the "rtcp-xr" attribute [RFC3611]: following syntax within the "rtcp-xr" attribute [RFC3611]:
rtcp-xr-attrib = "a=rtcp-xr:" [xr-format *(SP xr-format)] CRLF pkt-loss-rle-post = "post-repair-loss-rle" ["=" max-size]
xr-format =/ "post-repair-loss-rle" ["=" max-size]
max-size = 1*DIGIT ; maximum block size in octets
Figure 2 max-size = 1*DIGIT ; maximum block size in octets
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. The "pkt-loss-rle-post"
parameter is compatible with the definition of "format-ext" in 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. Additional security considerations are briefly mentioned well. Additional security considerations are briefly mentioned
below. below.
An attacker who monitors the regular pre-repair Loss RLE reports sent An attacker who monitors the regular Pre-repair Loss RLE reports sent
by a group of receivers in the same multicast distribution network by a group of receivers in the same multicast distribution network
may infer the network characteristics (Multicast Inference of Network may infer the network characteristics (Multicast Inference of Network
Characteristics). However, monitoring the post-repair Loss RLE Characteristics). However, monitoring the Post-repair Loss RLE
reports will not reveal any further information about the network. reports will not reveal any further information about the network.
Without the regular pre-repair Loss RLE reports, the post-repair ones 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 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 Pre-repair Loss RLE reports, the Post-repair Loss RLE reports only
reveal the effectiveness of the repair process. However, this does reveal the effectiveness of the repair process. However, this does
not enable any new attacks nor does it provide information to an not enable any new attacks, nor does it provide information to an
attacker that could not be similarly obtained by watching the RTP attacker that could not be similarly obtained by watching the RTP
packets fly by himself, performing the repair algorithms and packets fly by himself, performing the repair algorithms and
computing the desired output. computing the desired output.
An attacker may interfere with the repair process for an RTP stream. 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 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, RLEs, the attacker may infer whether or not the attack is effective.
in which case the attacker may continue attacking or alter the If not, the attacker may continue attacking or alter the attack. In
attack. In practice, however, this does not pose a security risk. practice, however, this does not pose a security risk.
An attacker may put incorrect information in the regular pre-repair An attacker may put incorrect information in the regular Pre-repair
and post-repair Loss RLE reports such that it impacts the proactive and Post-repair Loss RLE reports such that it impacts the proactive
decisions made by the sender in the repair process or the reactive decisions made by the sender in the repair process or the reactive
decisions when responding to the feedback messages coming from the decisions when responding to the feedback messages coming from the
receiver. A sender application should be aware of such risks and receiver. A sender application should be aware of such risks and
should take the necessary precautions to minimize the chances for (or should take the necessary precautions to minimize the chances for
better eliminate) such attacks. (or, better, eliminate) such attacks.
Similar to other RTCP XR reports, the post-repair Loss RLE reports Similar to other RTCP XR reports, the Post-repair Loss RLE reports
MAY be protected by using SRTP and SRTCP [RFC3711]. MAY be protected by using the Secure RTP (SRTP) and Secure RTP
Control Protocol (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
the "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry. the "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry.
The contact information for the registrations is: The contact information for the registrations is:
Ali Begen Ali Begen
abegen@cisco.com abegen@cisco.com
170 West Tasman Drive 170 West Tasman Drive
San Jose, CA 95134 USA San Jose, CA 95134 USA
skipping to change at page 9, line 41 skipping to change at page 8, line 41
November 2003. November 2003.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 2006.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
8.2. Informative References 8.2. Informative References
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Correction", RFC 5109, December 2007. Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[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. [RFC5109] Li, A., "RTP Payload Format for Generic Forward Error
Norrman, "The Secure Real-time Transport Protocol (SRTP)", Correction", RFC 5109, December 2007.
RFC 3711, March 2004.
Authors' Addresses Authors' Addresses
Ali Begen Ali Begen
Cisco Systems Cisco
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
Dong Hsu Dong Hsu
Cisco Systems Cisco
1414 Massachusetts Ave. 1414 Massachusetts Ave.
Boxborough, MA 01719 Boxborough, MA 01719
USA USA
Email: dohsu@cisco.com EMail: dohsu@cisco.com
Michael Lague Michael Lague
Cisco Systems Cisco
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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