One document matched: draft-wu-avt-retransmission-supression-rtp-01.txt
Differences from draft-wu-avt-retransmission-supression-rtp-00.txt
Network Working Group Q. Wu
Internet-Draft F. Xia
Intended status: Standards Track R. Even
Expires: September 9, 2010 Huawei
March 8, 2010
Proposal for an extension to RTCP Receiver Report for Feedback Storm
Suppression
draft-wu-avt-retransmission-supression-rtp-01
Abstract
This document specifies an extension to the messages defined in the
Audio-Visual Profile with Feedback (AVPF) designed to allow
intermediate node to suppress the feedback implosion from the
receivers. One of examples for feedback implosion is utilizing RTCP
NACK to request retransmission of the missing packets which may
result in NACK storm targeting to the same media sender. This issue
can be addressed to define one new RTCP message, which is referred to
as the Feedback Storm Suppression receiver report and carries the
information regarding feedback suppression early indication events to
the receiver before the receiver detects an original packet loss and
all the packet loss repair methods are applied. By using feedback
Suppression message together with RTCP based feedback message, the
delay for the receiver to recover from the packet loss can be reduced
and the risk of increasing network congestion can be mitigated or
diminished. This document also registers a new RTCP receiver report
for Feedback Storm Suppression.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Basic Operation . . . . . . . . . . . . . . . . . . . . . . . 5
4. Message Format . . . . . . . . . . . . . . . . . . . . . . . . 5
5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 5
6. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . . 7
Appendix A. Example scenarios for Feedback Storm Suppression . . 7
A.1. Scenario 1: One media Sender, one Distribution Source . . 7
A.2. Scenario 2: One Media Sender, more distribution sources . 8
Appendix B. Applicability of Feedback Storm Suppression . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
RTP retransmission is an effective packet loss recovery technique for
real-time applications with relaxed delay bounds [RFC4588],e.g.,
streaming media. The conventional RTCP feedback (NACK) message which
conveys the RTP sequence number of the lost packets can be used to
request the sender to compensate the missing RTP packets based on the
RTP sequence number of these packets[RFC4585].
However, in lots of multicast environments, packet loss occurs in the
upstream link or downstream aggregate link of the intermediate
network element (e.g., Retransmission server, Distribution Source)
due to oversaturated network link, faulty networking hardware or
corrupted packets rejected in-transit. It may result in NACK
implosion targeting at the same sender, i.e., massive NACK request to
the same multicast sender for retransmission of the same RTP packets
which is also known as "NACK storm" described in [DVB-IPTV]. To
increase the robustness to the loss of a NACK or of a retransmission
packet, a receiver may also send multiple NACKs for the same packet.
Another use case is Fast Update request storm occurs in the
conversational multimedia scenarios. In this case, packet loss may
happen in the upstream link or downstream aggregate link of
intermediate network element like Multipoint Control Unit(MCU) which
results in massive fast update request(i.e., Full Intra Request(FIR)
described in [RFC5104]) from receivers to the same media sender.
As these feedback storms progress (e.g., NACK implosion or Fast
update implosion), the network is overwhelmed with constant feedback
traffic, in the worsening case, RTCP feedback storm poses a risk of
increasing network congestion, with excessive traffic and degrading
network performance, this can eventually lead to a complete loss of
network connectivity as such feedback packets proliferate, the
network may become unusable.
In order to solve this, the current text in [I-D.ietf-avt-rtcpssm]
allows the distribution source to filter out the NACK messages while
this document propose an option to let the receivers know that
Feedback for packet loss is not needed in the specified cases. i.e.,
generating one new generic RTCP receiver report message, which
reflects the packet receipt/loss events and feedback suppression
early indication events before the receiver detects an original
packet loss and all the packet loss repair methods are applied.
This new RTCP receiver report, which we refer to as Feedback Storm
Suppression, indicates suppressing feedback request for the packet
loss(e.g., request retransmission of lost packets or request decoder
refresh point) before the receiver sends a request to the media
sender for the missing packet. In order to detect the original
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packet loss in the upstream direction before the receivers perceive
it, the intermediate node located between the media sender and
receiver may monitor a certain packet loss by reserving space to
replicate one copy of multicast data and checking the sequence number
consistency of the original multicast packets or configuring upstream
RTP client or a small subset of RTP receivers to act as immediate
reporters described in [DVB-IPTV]. Also this intermediate node
should take into account such factors as the tolerable application
delay, the network environment, and the media type. Upon the packet
loss is detected and initial latency is tolerable, in the upstream
direction towards the sender, the intermediate node may ask for
retransmission of the lost packet from the sender or re-asking for
the correct decoder refresh point, in the meanwhile, in the
downstream direction from the sender, the intermediate node may
convey Feedback Suppression Indication to all the receivers concerned
to indicate the receiver not to transmit feedback message. When the
sender receives the request from the intermediate node, the sender
resends the missing packet to the receiver via RTP using
retransmission payload format[RFC4588].
Similar to RTCP NACK, the Feedback Storm Suppression also conveys the
packet receipt/loss events at the packet level and considers missing
packets as unrepaired. But different from RTCP NACK, the Feedback
Storm Suppression is used by the intermediate node to multicast back
to the receivers in response to the RTCP feedback issued by the
receivers.
Note that the feedback storm suppression should collectively work
together with feedback to repair the lost source packets. Thus, the
delay for the receiver to recover from the packet loss can be reduced
and the risk of increasing network congestion can be mitigated or
diminished. The receiver may send a Feedback message before
receiving the indication but will not need to resend the Feedback
message after receiving the indication. Also the idea of Feedback
Storm Suppression can be further extended when the distributed
content distribution network are considered. That is to say several
intermediate node and media senders may constitute hierarchical
model. In this distributed content distribution environment, the
Feedback Storm Suppression not only can be used to suppress all the
receivers behind itself not to send packet loss request but also
suppress the neighboring node not to send packet loss request for the
missing packets via unicast. How the neighboring node is discovered
is beyond scope of this document.
This document registers a new RTCP receiver report message for
Feedback Storm Suppression. Applications that are employing one or
more loss-repair methods MAY use feedback Storm Suppression together
with these loss-repair methods for every packet they receive or for a
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set of specific packets they have received.
2. Terminology
The keywords "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. Basic Operation
The new RTCP receiver report, i.e., the Feedback Storm suppression
will work in Simple Feedback and in Distribution Source Feedback
Summary Models defined in [I-D.ietf-avt-rtcpssm]. The intermediate
node between media sender and receivers will include the support for
retransmission as part of the offered SDP and will expect such
support from the Media Sender.
The intermediate node may send this new RTCP receiver report FSEI
when detecting a loss on its incoming link while sending a packet
loss request to the media sender. The intermdidate node may receive
packet loss request messages(e.g., RTCP NACK) from the receivers and
may filter them out if it already sent a packet loss request for the
missing packet to the media source.
If the receiver understands this message it will not send packet loss
request(e.g., NACK) for the missing packets reported in the message
and will accept a retransmission stream. The receiver may send
packet loss request(e.g., NACK messages) if it did not understand
this new message.
4. Message Format
The Feedback Storm Suppression message is an extension to the RTCP
receiver report. [[The message format is to be decided based on the
AVT discussion.]]
5. SDP Signaling
TBD.
6. IANA Consideration
New message type and New parameters for RTCP receiver report are
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subject to IANA registration. For general guidelines on IANA
considerations for RTCP feedback, refer to [RFC4585]
The contact information for the registrations is:
Qin Wu
sunseawq@huawei.com
Site B, Floor 12F,Huihong Mansion, No.91,Baixia Rd.
Nanjing, JiangSu 210001 China
7. References
7.1. Normative References
[I-D.ietf-avt-rtcpssm]
Ott, J., Chesterfield , J., and E. Schooler, "RTCP
Extensions for Single- Source Multicast Sessions with
Unicast Feedback", September 2009.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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 4585,
July 2006.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
July 2006.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
"Codec Control Messages in the RTP Audio-Visual Profile
with Feedback (AVPF)", RFC 5104, February 2008.
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7.2. Informative References
[DVB-IPTV]
ETSI Standard, "Digital Video Broadcasting(DVB); Transport
of MPEG-2 TS Based DVB Services over IP Based Networks",
ETSI TS 102 034, V1.4.1 , August 2009.
[I-D.hunt-avt-monarch-01]
Hunt, G. and P. Arden, "Monitoring Architectures for RTP",
August 2008.
[I-D.ietf-pmol-metrics-framework-02]
Clark, A., "Framework for Performance Metric Development".
Appendix A. Example scenarios for Feedback Storm Suppression
A.1. Scenario 1: One media Sender, one Distribution Source
The general architecture is displayed below in Figure 1. In this
figure, one or more Media Senders send RTP packets to the
Distribution Source. The Distribution Source relays the RTP packets
to the receivers using a source-specific multicast channel. In the
reverse direction, the receivers transmit RTCP packets via unicast to
the distribution source. The Distribution Source in turn relays RTCP
packets to the media sender and then transmits the RTCP packets back
to the receivers, using source-specific multicast. When packet loss
happens between Media sender and distribution source, it may result
in massive retransmission request for the same RTP packets from all
the receivers using RTCP NACK to the same multicast sender. We refer
to it as Retransmission Storm.
+-------+
|---->|RTP_Rx1|
+--------+ | +-------+
| | +--------------+ |
| | | | | +-------+
| Media |-------| Distribution |-------|---->|RTP_Rx2|
| | | Source | | +-------+
| Sender | | | | .
| | +--------------+ | .
| | | .
+--------+ | +-------+
|---->|RTP_Rxn|
+-------+
Figure 1: One media Sender, one Distribution Source
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A.2. Scenario 2: One Media Sender, more distribution sources
The hierarchical model is displayed below in Figure 2. In this
figure, one media sender and two Distribution source constitute one
hierarchical model. In this model, one Media Senders send RTP
packets to two Distribution Sources respectively. These Distribution
Sources relay the RTP packets respectively to the receivers behind
itself using a source-specific multicast channel. In the reverse
direction, the receivers transmit RTCP packets via unicast to the
distribution source. The Distribution Source in turn relays RTCP
packets to the media sender and then transmits the RTCP packets back
to the receivers, using source-specific multicast. When packet loss
happens between Media sender and distribution source, it may result
in massive retransmission request for the same RTP packets from all
the receivers using RTCP NACK to the same multicast sender. We refer
to it as Retransmission Storm.
+--------+
|---->|RTP_Rx11|
| +--------+
+--------------+ |
| | | +--------+
|--->| Distribution |----|---->|RTP_Rx12|
| | Source1 | | +--------+
| | | | .
+--------+ | +--------------+ | .
| | | | .
| | | | +--------+
| Media | | |---->|RTP_Rx1k|
| |---| +--------+
| Sender | | +--------+
| | | |---->|RTP_Rx21|
| | | | +--------+
+--------+ | +--------------+ |
| | | | +--------+
| | Distribution |----|---->|RTP_Rx22|
|--->| Source2 | | +--------+
| | | .
+--------------+ | .
| .
| +--------+
|---->|RTP_Rx2j|
+--------+
Figure 2: One Media Sender, more distribution sources
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Appendix B. Applicability of Feedback Storm Suppression
This document defines new RTCP receiver report which we refer to as
Feedback Storm Suppression to deal with Retransmission Storm
mentioned above. Here we give two examples to show how this new RTCP
receiver report is applied into two scenarios described in section
A.1 for Retransmission Storm Suppression.
Applicability of Feedback Storm Suppression in Scenario 1 described
in Figure 1 is shown in the Figure 3. In this figure, the
distribution source detect the packet loss before the receiver
perceive it and ask for retransmission of the missing packets from
the media sender, in the meanwhile, the distribution source transmits
the RTCP Feedback Storm Suppression Indication back to the receivers
using source-specific multicast channel. In this way, the delay for
the receiver to recover from the packet loss can be reduced and the
risk of increasing network congestion can be mitigated.
+------+ +--------------+ +--------+
|Media | | Distribution | | |
|Sender| | Source | | RTP_Rx |
+--+---+ +------+-------+ +---+----+
| | |
| | |
|------------------->|------RTP Multicast---->|
| | |
| | |
| +--------+----------+ |
| |Detect Packet Loss | |
| |and Identify the SN| |
| |of missing Packets | |
| +--------+----------+ |
|<-----RTCP NACK-----| |
| | |
| +--Multicast RTCP FSEI-->|
| RTP Retransmission | |
|------------------->| |
| |------RTP Multicast---->|
| | Retransmission |
| | |
| | |
| | |
Figure 3: Applicability of Feedback Suppression Early Indication
Applicability of Feedback Storm Suppression in Scenario 2 described
in Figure 2 is shown in the figure A.2.2. The procedure in the
figure A.2.2 is similar to the one in the figure Figure 4. The only
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difference is distribution source should not only notify all the
receiver behind itself not to send NACK but also propagate the
retransmission suppression indication to the neighboring distribution
sources. In this way, all the receivers behind all the neighboring
distribution source can avoid sending massive retransmission request
to the media sender.
+------+ +-------+ +--------+ +-------+ +--------+
|Media | | | | RTP_Rx | | | | RTP_Rx |
|Sender| | DS1 | | (DS1) | | DS2 | | (DS2) |
+--+---+ +---+---+ +---+----+ +---+---+ +---+----+
| | | | |
| |RTP Multicast | | |
|----------->|------------->| | |
| | | | |
| | | |RTP Multicast|
|------------------------------------------->|------------>|
| | | | |
| +--------+------------+ | | |
| |Detect Packet Loss | | | |
| |and Identify the SN | | | |
| |of the missing Packets | | |
| +--------+------------+ | | |
| | | | |
|<-RTCP NACK-| Multicast RTCP RSSI | |
| |------------->| | |
| | | | |
| |-----Unicast RTCP RSSI-------->|Multicast RTCP FSEI
| | | |------------>|
|RTP Retransmission | | |
|----------->| | | |
| | | | |
| | RTP Retransmission | |
|------------+--------------+--------------->| |
| | | | |
| | RTP Multicast| | RTP Multicast
| |Retransmission| |Retransmission
| |------------->| |------------>|
| | | | |
DS1: Distribution Source 1
DS2: Distribution Source 2
Figure 4: Applicability of Retransmission Suppression Early
Indication
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Authors' Addresses
Qin Wu
Huawei
Site B,Floor 12F,Huihong Mansion, No.91 Baixia Rd.
Nanjing, Jiangsu 21001
China
Phone: +86-25-84565892
Email: sunseawq@huawei.com
Frank Xia
Huawei
1700 Alma Dr. Suite 500
Plano, TX 75075
USA
Phone: +1 972-509-5599
Email: xiayangsong@huawei.com
Roni Even
Huawei
14 David Hamelech
Tel Aviv 64953
Israel
Email: even.roni@huawei.com
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