Audio/Video Transport Working Group Q. Wu
Internet-Draft R. Even
Intended status: Standards Track Huawei
Expires: April 25, 2013 October 22, 2012
Advertisement for multi-source endpoint multiplexing multiple media type
in the same RTP session
draft-wu-avtcore-multisrc-endpoint-adver-02.txt
Abstract
When two endpoints with multiple media sources are in communication,
each media source or each receiver within either endpoint may send or
receive reception report independently. This may incur a lot of
duplicated reception report to and from the endpoint with multiple
sources. This document discusses how to tackle these problems and
propose three phases for suppressing reception reports.
Status of this Memo
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This Internet-Draft will expire on April 25, 2013.
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Report Source Grouping . . . . . . . . . . . . . . . . . . 5
3.2. Report Source Election . . . . . . . . . . . . . . . . . . 5
3.3. Report Source Advertisement . . . . . . . . . . . . . . . 5
4. Protocol formats . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. SDES item for Reception Report Sending . . . . . . . . . . 7
4.1.1. RRS: Reception Report Sending SDES Item . . . . . . . 7
4.2. SDES item for Reception Report Monitoring . . . . . . . . 7
4.2.1. RRM: Reception Report Monitoring SDES Item . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6.1. New RTCP SDES Type values . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
For some applications that use unicast transport, e.g., in RTCWeb
application, an endpoint with multiple media sources (i.e.,multiple-
source hosts, e.g., a client with several cameras) may use a
different SSRC for each medium but sending them in the same RTP
session, which reduces communication failure due to NAT and firewall
when using multiple RTP sessions or transport flows.
However when two endpoints with multiple media sources are in
communication, each media source within either endpoint may send
reception report independently and the receiving endpoint may not
know the reception reports received from different media source are
from the same sending endpoint. This creates the following three
problems:
o An endpoint with multiple media sources involved in one RTP
session may send the reception report with duplicated information
about the same remote media source from each of local media
sources.
o An endpoint with multiple media sources involved in one RTP
session may receive the reception report with duplicated
information about the same local media source from each of remote
media sources.
o An endpoint with multiple media sources involved in one RTP
session also may send reception reports about one of its own media
sources from another of its own (This is also referred to as RTCP
self-reporting). Such reception reports cause additional
redundant traffic travelling over the link between sending
endpoints and receiving endpoint, which changes the report
interval and may affect the media qualities.
This document discusses how to tackle these problems. Three phases
for suppressing reception reports are proposed.
o Grouping of media sources originate from a single endpoint and
classifying these media sources into multiple groups.
o Electing one single SSRC for reception report sending and one
single SSRC for reception report monitoring based on local policy.
o Advertising the SSRC that is used either for reception report
sending or reception report monitoring.
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2. Terminology
2.1. Standards Language
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 RFC 2119 [RFC2119].
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3. Protocol Overview
In order to suppress unnecessary reception reports to and from multi-
source endpoint, multi-source endpoint should group media sources
originating from a single endpoint and elect one or a set of
specified SSRCs for reception report processing (e.g., reception
report sending, reception report receiving and reception report
monitoring).
3.1. Report Source Grouping
When an endpoint with multiple sources multiplexes multiple media
types in the same RTP session, the media source originating from the
same endpoint should be grouped together. Similarly the endpoint
with multiple sources may have multiple one or more than one report
source for monitoring. These report sources for monitoring should
also be grouped together. Therefore an endpoint with multiple
sources should at least split all its own media sources or receivers
into two groups(i.e., split SSRCs into two groups): One is sending
group, the other is monitoring group. Each group may have one or
several group members. Each group member is identified by a
different SSRC.
3.2. Report Source Election
When grouping for each endpoint with multiple sources is available,
in order to prevent group members receiving duplicated data, one or
more than one group member MUST be elected from sending group as
report source for reception report sending. When one report source
leaves the session or is down, another candidate report source can
replace instead. If the monitoring is used, each endpoint with
multiple sources MUST have at least one report source for monitoring
purpose. One or more than one reporting sources MUST be selected
from monitoring group for monitoring use.
Each endpoint with multiple sources at least has one SSRC for
reception report sending. If the monitoring is used, the endpoint
with multiple sources should choose another SSRC from monitoring
group as monitoring report source.
3.3. Report Source Advertisement
When report sources are elected for reception report sending, and
monitoring purpose respectively, it is necessary to signal which
report source is used for which purpose.
In this document we define two new SDES items to advertise the
reporting sources from endpoint with multiple sources that are used
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for reception report sending and monitoring respectively (See section
5.1 and section 5.2 for protocol format details).
When those report sources are advertised, the selected report source
can send reception report about the same remote media source on
behalf of the media sources of its own, which prevent duplicated
reception report sent from all the local media sources of its own for
the same event.
If the other media source which is not selected as report source
knows or understands the advertised report source, it should suppress
the reception report for the same event.
If the other media source which is not selected as report source does
not know or understand the advertised report source and detects the
need to send reception report, this media source should wait for a
(short) random dithering interval to check whether it sees a
corresponding reception report message from any other receiver or
other media sources of its own reporting the same event. If a
corresponding reception report for the same event is received from
other media sources or any other receivers, it should refrain from
sending the reception report message.
In order to prevent duplicated reception report sent from one of its
own media sources to another of its own within the same endpoint with
multiple sources(i.e., self-reporting), the report source should know
the other media sources of its own and suppress sending the reception
report on the remote source to its own media sources.
Editor's note: Current draft does not discuss topologies like source
projection mixer where the mixer keeps the original ssrc so even
though they arrive from the mixer they have different CNAMEs. It
will be useful to discuss those topologies in the future version.
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4. Protocol formats
Editor's note: It is not clear if you need to signal which one is
used or what is the group but if needed it may be better to allow the
sender to indicate which SSRCs are part of a group. It will also
require an negotiation in the offer/answer to verify that this mode
is supported by the stream senders.
4.1. SDES item for Reception Report Sending
This sub-section defines the format of the Reception Report Sending
SDES item. The SDES item is carried in the RTCP SDES packet. The
packet format for the RTCP SDES is defined in Section 6.5 of
[RFC3550]. Each SDES packet is composed of a header with fixed-
length fields for version, source count, packet type (PT), and
length, followed by zero or more chunks. Each chunk consists of an
SSRC/CSRC identifier followed by zero or more SDES items. If this
SDES item is carried, the CNAME SDES item should also be carried
together with this SDES item in the same chunk. In the SDES packet,
the PT field is set to SDES(202).
4.1.1. RRS: Reception Report Sending SDES Item
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RRS=TBD | length | Candidate Report Source SSRC
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ....
+-+-+-+-+-+-+-+-+
The Reception Report Sending Item is not mandatory item and intended
for indicating the elected report source for an endpoint with
multiple sources, which is responsible for reception report sending.
The SSRC/CSRC identifier included in the same chunk (at the beginning
of this chunk) as the item is the SSRC of elected sending report
source. Additionally, this item may carry one or more than one
Candidate Report Source SSRCs. The candidate Report Source SSRC
follows the same format as SSRC/CSRC identifier defined in RFC3550.
Its length is described by the length field. The value of the length
field does not include the two octet SDES item header. This item
MUST be ignored by applications that are not configured to make use
of it.
4.2. SDES item for Reception Report Monitoring
This sub-section defines the format of the Reception Report
Monitoring SDES item. The SDES item is carried in the RTCP SDES
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packet. The packet format for the RTCP SDES is defined in Section
6.5 of [RFC3550].Each SDES packet is composed of a header with fixed-
length fields for version, source count, packet type (PT), and
length, followed by zero or more chunks. Each chunk consists of an
SSRC/CSRC identifier followed by zero or more SDES items. If this
SDES item is carried, the CNAME SDES item should also be carried
together with this SDES item in the same chunk. In the SDES packet,
the PT field is set to SDES(202).
4.2.1. RRM: Reception Report Monitoring SDES Item
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RRM=TBD | length | Candidate Report Source SSRC
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ....
+-+-+-+-+-+-+-+-+
The Reception Report Sending Item is not mandatory item and intended
for indicating the report source for an endpoint, which is
responsible for reception report monitoring. The SSRC/CSRC
identifier included in the same chunk as the item (at the beginning
of this chunk) is the SSRC of elected sending report source.
Additionally, this item may carry one or more than one Candidate
Report Source SSRCs. The candidate Report Source SSRC follows the
same format as SSRC/CSRC identifier defined in RFC3550. Its length
is described by the length field. The value of the length field does
not include the two octet SDES item header. This item MUST be
ignored by applications that are not configured to make use of it.
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5. Security Considerations
RTCP reports can contain sensitive information, including information
about report source grouping for endpoint with multiple source and
member of a session established between two or more endpoints.
Therefore, the use of security mechanisms with RTP, as documented in
Section 9 of [RFC3550] applies.
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6. IANA Considerations
New SDES types for RTCP SDES are subject to IANA registration. For
general guidelines on IANA considerations for RTCP SDES, refer
to[RFC3550].
6.1. New RTCP SDES Type values
This document assigns two additional SDES type in the IANA "RTCP SDES
Item Types Registry" to the new SDES items as follow:
abbrev. name value
RRSS: Reception Report Sending Source TBD
RRRS: Reception Report Monitoring Source TBD
[Note to RFC Editor: please replace RRSS and RRMS with the IANA
provided RTCP SDES Item Types.]
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[RFC3550] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time
Applications", RFC 3550, July 2003.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4595,
July 2006.
[RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP
Header Extensions", RFC 5285, July 2008.
7.2. Informative References
[I-D.ietf-avtcore-multi-media-rtp-session-00]
Westerlund, M., "Multiple Media Types in an RTP Session",
ID draft-ietf-avtcore-multi-media-rtp-session-00,
October 2012.
[I-D.lennox-avtcore-rtp-multi-stream]
Lennox, J. and M. Westerlund, "Real-Time Transport
Protocol (RTP) Considerations for Endpoints Sending
Multiple Media Streams",
ID draft-lennox-avtcore-rtp-multi-stream-00, July 2012.
[I-D.wu-avtcore-multiplex-multisource-endpoint]
Wu, Q., "Bandwidth and RTCP timing issues for multi-source
endpoint",
ID draft-wu-avtcore-multiplex-multisource-endpoint-01,
October 2012.
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Authors' Addresses
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
Roni Even
Huawei
14 David Hamelech
Tel, Aviv 64953
Israel
Email: ron.even.tlv@gmail.com
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