One document matched: draft-begen-avt-post-repair-rtcp-xr-01.txt
Differences from draft-begen-avt-post-repair-rtcp-xr-00.txt
AVT A. Begen
Internet-Draft D. Hsu
Intended status: Standards Track M. Lague
Expires: November 26, 2008 Cisco Systems
May 25, 2008
Post-Repair Loss RLE Report Block Type for RTCP XR
draft-begen-avt-post-repair-rtcp-xr-01
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Copyright (C) The IETF Trust (2008).
Abstract
This document defines a new report block type within the framework of
RTP Control Protocol (RTCP) Extended Reports (XR). One of the
initial XR report block types is the Loss Run Length Encoding (RLE)
Report Block. This report conveys the information regarding the
individual Real-time Transport Protocol (RTP) packet receipt and loss
events experienced during the RTCP interval preceding the
transmission of the report. The new report, which is referred to as
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the Post-repair Loss RLE Report, carries the information regarding
the remaining lost packets after all error-repair techniques are
applied. By comparing the RTP packet receipts/losses before and
after the error repair is completed, one can determine the
effectiveness of the error-repair techniques in an aggregated
fashion. This document also defines the signaling of the Post-repair
Loss RLE Report in the Session Description Protocol (SDP).
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 4
3. Post-Repair Loss RLE Report Block . . . . . . . . . . . . . . . 4
4. Session Description Protocol Signaling . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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1. Introduction
RTP Control Protocol (RTCP) is the out-of-band control protocol for
the applications that are using the Real-time Transport Protocol
(RTP) for media delivery and communications [RFC3550]. RTCP allows
the RTP entities to monitor the data delivery and provides them
minimal control functionality via sender and receiver reports as well
as other control packets. [RFC3611] expands the RTCP functionality
further by introducing the RTCP Extended Reports (XR).
One of the initial XR report block types defined in [RFC3611] is the
Loss Run Length Encoding (RLE) Report Block. This report conveys the
information regarding the individual RTP packet receipt and loss
events experienced during the RTCP interval preceding the
transmission of the report. However, the Loss RLE in an RTCP XR
report is usually collected only on the primary source stream before
any error-repair technique is applied. Once one or more error-repair
techniques, e.g., Forward Error Correction (FEC)
[I-D.begen-fecframe-1d2d-parity-scheme] and/or retransmission
[RFC4588], are applied, some or all of the lost packets on the
primary source stream may be recovered. However, the pre-repair Loss
RLE cannot indicate which source packets were recovered and which are
still missing. Thus, the pre-repair Loss RLE cannot specify how well
the error repair performed.
This issue can be addressed by generating an additional report block
(within the same RTCP XR report), which reflects the packet receipt/
loss events after all error-repair techniques are applied. This
report block, which we refer to as the Post-repair Loss RLE,
indicates the remaining missing, i.e., unrepairable, source packets.
When the pre- and post-repair Loss RLEs are compared, the RTP sender
or another 3rd party entity can evaluate the effectiveness of the
error-repair techniques in an aggregated fashion.
Note that the idea of using pre- and post-repair Loss RLEs can be
further extended when multiple sequential error-repair techniques are
applied to the primary source stream. Reporting the Loss RLEs before
and after each error-repair technique can provide specific
information about the individual performances of these techniques.
However, it can be a difficult task to quantify the specific
contribution made by each error-repair technique in hybrid systems,
where different techniques collectively work together to repair the
lost source packets. Thus, in this specification we only consider
reporting the Loss RLE after all error-repair techniques are applied.
This document registers a new report block type to cover the Post-
repair Loss RLE within the framework of RTCP XR.
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2. Requirements Notation
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 [RFC2119].
3. Post-Repair Loss RLE Report Block
The Post-repair Loss RLE Report Block is similar to the existing Loss
RLE Report Block defined in [RFC3611]. The report is formatted as
sketched in Figure 1.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BT=TBD | rsvd. | T | block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| begin_seq | end_seq |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| chunk 1 | chunk 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| chunk n-1 | chunk n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format for the post-repair loss RLE report block
o block type (BT): 8 bits
A Post-repair Loss RLE Report Block is identified by the constant
TBD.
o rsvd.: 4 bits
This field is reserved for future definition. In the absence of
such definition, the bits in this field MUST be set to zero and
MUST be ignored by the receiver.
o thinning (T): 4 bits
The amount of thinning performed on the sequence number space.
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,
and all packets are reported on. The maximum thinning is one
packet in every 32,768 (amounting to two packets within each 16-
bit sequence space).
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o block length: 16 bits
The length of this report block, including the header, in 32-bit
words minus one.
o SSRC of source: 32 bits
The SSRC of the RTP data packet source being reported upon by this
report block.
o begin_seq: 16 bits
The first sequence number that this block reports on.
o end_seq: 16 bits
The last sequence number that this block reports on plus one.
o chunk i: 16 bits
There are three chunk types: run length, bit vector, and
terminating null, defined in [RFC3611] (Section 4). If the chunk
is all zeroes, then it is a terminating null chunk. Otherwise,
the left most bit of the chunk determines its type: 0 for run
length and 1 for bit vector.
4. Session Description Protocol Signaling
A new parameter is defined for the Post-repair Loss RLE Report Block
to be used with Session Description Protocol (SDP) [RFC4566]. It has
the following syntax within the "rtcp-xr" attribute:
rtcp-xr-attrib = "a=rtcp-xr:" [xr-format *(SP xr-format)] CRLF
xr-format = "post-repair-loss-rle" ["=" max-size]
max-size = 1*DIGIT ; maximum block size in octets
DIGIT = %x30-39
CRLF = %d13.10
Figure 2
Refer to Section 5.1 of [RFC3611] for a detailed description of the
full syntax of the "rtcp-xr" attribute.
5. Security Considerations
The security considerations of [RFC3611] apply.
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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].
This document assigns the block type value TBD in the RTCP XR Block
Type Registry to "Post-repair Loss RLE Report Block." This document
also registers the SDP [RFC4566] parameter "post-repair-loss-rle" for
the "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry.
The contact information for the registrations is:
Ali Begen
abegen@cisco.com
170 West Tasman Drive
San Jose, CA 95134 USA
7. Acknowledgments
The authors would like to thank the members of the VQE Team at Cisco
and Colin Perkins for their inputs and suggestions.
8. References
8.1. Normative References
[RFC2119] 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., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", RFC 3611,
November 2003.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
8.2. Informative References
[I-D.begen-fecframe-1d2d-parity-scheme]
Begen, A. and R. Asati, "1-D and 2-D Parity FEC Scheme for
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FEC Framework", draft-begen-fecframe-1d2d-parity-scheme-00
(work in progress), February 2008.
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
July 2006.
Authors' Addresses
Ali Begen
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
USA
Email: abegen@cisco.com
Dong Hsu
Cisco Systems
1414 Massachusetts Ave.
Boxborough, MA 01719
USA
Email: dohsu@cisco.com
Michael Lague
Cisco Systems
1414 Massachusetts Ave.
Boxborough, MA 01719
USA
Email: mlague@cisco.com
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