Network Working Group Q. Wu
Internet-Draft F. Xia
Intended status: Standards Track R. Even
Expires: June 12, 2011 Huawei
December 9, 2010
RTCP Extension for Feedback Suppression Indication
draft-wu-avt-retransmission-supression-rtp-08
Abstract
In a large RTP session using the RTCP feedback mechanism defined in
RFC 4585, a media source or middlebox may experience transient
overload if some event causes a large number of receivers to send
feedback at once. This feedback implosion can be mitigated if the
device suffering from overload can send a third party loss report
message to the receivers to inhibit further feedback. This memo
defines RTCP extensions for third party loss report, to suppress NACK
and FIR feedback requests. It also defines associated SDP
signalling.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 12, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
Wu, et al. Expires June 12, 2011 [Page 1]
Internet-Draft Third Party Loss Report December 2010
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Wu, et al. Expires June 12, 2011 [Page 2]
Internet-Draft Third Party Loss Report December 2010
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
4. RTCP Feedback Report Extension . . . . . . . . . . . . . . . . 7
4.1. Transport Layer Feedback: Third-party Loss Report . . . . 7
4.2. Payload Specific Feedback: Third-party Loss Report . . . . 8
5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Example Use Cases . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Source Specific Multicast (SSM) use case . . . . . . . . . 9
6.1.1. Simple Feedback Model . . . . . . . . . . . . . . . . 10
6.1.2. Distribution Source Feedback Summary Model . . . . . . 11
6.2. Unicast based Rapid Acquisition of Multicast Stream
(RAMS) use case . . . . . . . . . . . . . . . . . . . . . 12
6.3. RTP transport translator use case . . . . . . . . . . . . 13
6.4. Multipoint Control Unit (MCU) use case . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
10.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Wu, et al. Expires June 12, 2011 [Page 3]
Internet-Draft Third Party Loss Report December 2010
1. Introduction
RTCP feedback messages [RFC4585] allow the receivers in an RTP
session to report events and ask for action from the media source (or
a delegated feedback target defined in SSM [RFC5760]). There are
cases where multiple receivers may initiate the same, or an
equivalent message towards the same media source. When the receiver
count is large, this behavior may cause transient overload of the
media source, the network or both. This is known as a "feedback
storm" or a "NACK storm". One common cause of such a feedback storm
is receivers utilizing RTP retransmission [RFC4588] as a packet loss
recovery technique based, sending feedback using RTCP NACK messages
[RFC4585] without proper dithering of the retransmission requests.
Another use case involves video Fast Update requests. A storm of
these feedback messages can occur in conversational multimedia
scenarios like Topo-Video-switch-MCU [RFC5117]. In this scenario,
packet loss may happen on an upstream link of an intermediate network
element such as a Multipoint Control Unit(MCU). Poorly designed
receivers that blindly issue fast update requests (i.e., Full Intra
Request (FIR) described in [RFC5104]), can cause an implosion of FIR
requests from receivers to the same media source.
RTCP feedback storms may cause short term overload and, and in
extreme cases to pose a possible risk of increasing network
congestion on the control channel (e.g. RTCP feedback), the data
channel, or both. It is therefore desirable to provide a way of
suppressing unneeded feedback.
One approach to this, suggested in [DVB-IPTV], involves sending a
NACK message to the other clients (or receiver) in the same group as
the sender of NACK. However sending multicast NACK to the group can
not prevent large amount of unicast NACK addressed to the same media
source or middlebox, for example when the NACK is used as a
retransmission request [RFC4588]. Also NACK is defined as a receiver
report sent from a receiver observing a packet loss, therefore it
only inform others that sender of NACK detected loss while the case
the sender of the feedback has received reports that the indicated
packets were lost is not covered. This document specifies a new
message for this function. It further is more precise in the
intended uses and less likely to be confusing to receivers. It tells
receivers explicitly that feedback for a particular packet or frame
loss is not needed for a period of time and can provide an early
indication before the receiver reacts to the loss and invokes its
packet loss repair machinery.
Wu, et al. Expires June 12, 2011 [Page 4]
Internet-Draft Third Party Loss Report December 2010
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. Protocol Overview
This document extends the RTCP feedback messages defined in the
Audio-Visual Profile with Feedback (AVPF) and define the Third Party
Loss Report message. The Third Party Loss Report message informs the
receiver in the downstream path of the middlebox that the sender of
the Third Party Loss Report has received reports that the indicated
packets were lost and asks a receiver to not send feedback messages
for particular packets (indicated by their RTP sequence numbers)
independent of whether the receiver detected the packet loss or
detected a need for a decoder refresh point.
In order to observe packet loss before the receivers perceive it, one
or more intermediate nodes may be placed between the media source and
the receivers. These intermediates are variously referred to as
Distribution servers, MCUs, RTP translator, or RTP mixers, depending
on the precise use case. These intermediaries monitor for packet
loss upstream of themselves by checking RTP sequence numbers, just as
receivers do. Upon observing (or suspecting) an upstream loss, the
intermediary may send Loss Party Loss Report message towards the
receivers as defined in this specification.
These intermediate nodes need to take into account such factors as
the tolerable application delay, the network dynamics, and the media
type. When the packet loss is detected upstream of the intermediary
and additional latency is tolerable, the intermediate node may itself
send a feedback message asking for the suspected lost packet or ask
for the correct decoder refresh point. Because it has already
provided the necessary feedback toward the source, the intermediate
node can be reasonably certain that it will help the situation by
sending a Third Party Loss Report message to all the relevant
receivers, thereby indicating to the receivers that they should not
transmit feedback messages for a period of time.
Alternatively, the media source may directly monitor the amount of
feedback requests it receives, and send Third Party Loss Report
messages to the receivers.
When a receiver gets such a Third Party Loss Report message, it
should refrain from sending a feedback request (e.g., NACK or FIR)
for the missing packets reported in the message for a period of time.
Wu, et al. Expires June 12, 2011 [Page 5]
Internet-Draft Third Party Loss Report December 2010
A receiver may still have sent a Feedback message according to the
AVPF scheduling algorithm of [RFC4585]before receiving a Third Party
Loss Report message, but further feedback messages for those sequence
numbers will be suppressed by this technique for a period of time.
Nodes that do not understand the Third Party Loss Report message will
ignore it, and might therefore still send feedback according to the
AVPF scheduling algorithm of [RFC4585]. The media source or
intermediate nodes cannot assume that the use of a Third Party Loss
Report message actually reduces the amount of feedback it receives.
RTCP Third Party Loss Report follows the similar format of message
type as RTCP NACK. But unlike RTCP NACK, the third party loss report
is defined as an indication that the sender of the feedback has
received reports that the indicated packets were lost and conveys the
packet receipt/loss events at the sequence number level from the
middlebox to the receivers in the downstream path of middlebox while
NACK [RFC4585]just indicates that the sender of the NACK observed
that these packets were lost. The Third Party Loss Report message
can also be generated by RTP middleboxs that has not seen the actual
packet loss and sent to the corresponding receivers. Intermediaries
downstream of an intermediary detecting loss obviously SHOULD NOT
initiate their own additional Third Party Loss Report messages for
the same packet sequence numbers. They may either simply forward the
Third Party Loss Report message received from upstream, or replace it
with a Third Party Loss Report message that reflects the loss pattern
they have themselves seen. The Third Party Loss Report does not have
the retransmission request [rfc4588] semantics.
Since Third Party Loss Report interacts strongly with repair timing,
it has to work together with feedback to not adversely impact the
repair of lost source packets. One example is the middle box gets
the retransmitted packet by sending a NACK upstream and sent it
downstream. This retransmitted packet was lost on the downstream
link. In order to deal with this, the downstream receiver can start
a timeout in which it expected to get a retransmission packet. When
this timeout expires and there is no retransmitted packet or a new
third party loss report message, it can take its normal behavior as
if there is no current retransmission suppression. In some cases
where the loss was detected and repair initiated much closer to the
source, the delay for the receiver to recover from packet loss can be
reduced through the combination of intermediary feedback to the
source and Third Party Loss Report downstream. In all (properly
operating) cases, the risk of increasing network congestion is
decreased.
Wu, et al. Expires June 12, 2011 [Page 6]
Internet-Draft Third Party Loss Report December 2010
4. RTCP Feedback Report Extension
This document registers two new RTCP Feedback messages for Third
Party Loss Report. Applications that are employing one or more loss-
repair methods MAY use Third Party Loss Report together with their
existing loss-repair methods either for every packet they expect to
receive, or for an application-specific subset of the RTP packets in
a session. In other words, receivers MAY ignore Third Party Loss
Report messages, but SHOULD react to them unless they have good
reason to still send feedback messages despite having been requested
to suppress them.
4.1. Transport Layer Feedback: Third-party Loss Report
This Third Party Loss Report message is an extension to the RTCP
Transport Layer Feedback Report and identified by RTCP packet type
value PT=RTPFB and FMT=TBD.
The FCI field MUST contain one or more entries of transport layer
third party loss Early Indication (TLLEI). Each entry applies to a
different media source, identified by its SSRC.
The Feedback Control Information (FCI) for TLLEI uses the similar
format of message Types defined in the section 4.3.1.1 of [RFC5104].
The format is shown 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PID | BLP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Message Format for the Third Party Loss Report
Packet ID (PID): 16 bits
The PID field is used to specify a lost packet. The PID field
refers to the RTP sequence number of the lost packet.
bitmask of proceeding lost packets (BLP): 16 bits
The BLP allows for reporting losses of any of the 16 RTP packets
immediately following the RTP packet indicated by the PID. The
BLP's definition is identical to that given in [RFC4585].
Wu, et al. Expires June 12, 2011 [Page 7]
Internet-Draft Third Party Loss Report December 2010
4.2. Payload Specific Feedback: Third-party Loss Report
This message is an extension to the RTCP Payload Specific Feedback
report and identified by RTCP packet type value PT=PSFB and FMT=TBD.
The FCI field MUST contain a Payload Specific Third Party Loss Early
Indication (PSLEI) entry. Each entry applies to a different media
source, identified by its SSRC.
The Feedback Control Information (FCI) for PSLEI uses the similar
format of message Types defined in the section 4.3.1.1 of [RFC5104].
The format is shown in Figure 2.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seq nr. | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Message Format for the Third Party Loss Report
SSRC (32 bits):
The SSRC value of the media source that is requested to send a
decoder refresh point.
Seq nr:8bits Command sequence number. The sequence number space is
unique for each pairing of the SSRC of command source and the SSRC
of the command target. The sequence number SHALL be increased by
1 modulo 256 for each new request.
Reserved: 24 bits
All bits SHALL be set to 0 by the media source and SHALL be
ignored on reception.
5. SDP Signaling
A new feedback value "tplr" needs to be defined for the Third Party
Loss Report message to be used with Session Description Protocol
(SDP) [RFC4566] using the Augmented Backus-Naur Form (ABNF)
[RFC4585].
The "tplr" feedback value SHOULD be used with parameters that
Wu, et al. Expires June 12, 2011 [Page 8]
Internet-Draft Third Party Loss Report December 2010
indicate the third party loss supported. In this document, we define
two such parameter, namely:
o "tllei" denotes support of transport layer third party loss early
indication (fsei).
o "pslei" denotes support of payload specific third party loss early
indication.
In the ABNF for rtcp-fb-val defined in [RFC4585], there is a
placeholder called rtcp-fb-id to define new feedback types. "tplr" is
defined as a new feedback type in this document, and the ABNF for the
parameters for tplr is defined here (please refer to section 4.2 of
[RFC4585] for complete ABNF syntax).
rtcp-fb-val =/ "tplr" rtcp-fb-tplr-param
rtcp-fb-tplr-param = SP "tllei";transport layer third party loss early indication
/ SP "pslei";payload specific third party loss early indication
/ SP token [SP byte-string]
; for future commands/indications
byte-string = <as defined in section 4.2 of [RFC4585] >
Refer to Section 4.2 of [RFC4585] for a detailed description and the
full syntax of the "rtcp-fb" attribute.
6. Example Use Cases
The operation of feedback suppression is similar for all types of RTP
sessions and topologies [RFC5117], however the exact messages used
and the scenarios in which suppression is employed differ for various
use cases. The following sections outline the intended use cases of
using Third Party Loss Report for feedback suppression and give an
overview of the particular mechanisms.
6.1. Source Specific Multicast (SSM) use case
In SSM RTP sessions as described in [RFC5760], one or more Media
Sources send RTP packets to a Distribution Source. The Distribution
Source relays the RTP packets to the receivers using a source-
specific multicast group.
In order to avoid the forms of Feedback implosion described in
section 1,the distribution source should be told that the indicated
packets were lost. How the distribution source know the indicated
packets were lost is beyond of scope of this document. When upstream
link or downstream aggregate link packet loss occurs, the
distribution source creates a Third Party Loss Report and sent it to
Wu, et al. Expires June 12, 2011 [Page 9]
Internet-Draft Third Party Loss Report December 2010
all the RTP receivers, over the multicast channel. Another
possibility is when there may be multiple distribution sources placed
between the media source and the receivers, the upstream distribution
source may inform downstream distribution sources of the detected
packet loss using Third Party Loss Report messages. In response, the
downstream distribution sources forward Third Party Loss Report
received from upstream to all the RTP receivers, over the multicast
channel. This Third Party Loss Report message tells the receivers
that the sender of the third party loss report has received reports
that the indicated packets were lost. The distribution source then
can (optionally) ask for the lost packets from the media source on
behalf of all the RTP receivers. The lost packets will either be
forthcoming from distribution source, or it irretrievably lost such
that there is nothing to be gained by the receiver sending a NACK to
the media source.
The distribution source must be able to communicate with all group
members in order for either mechanism to be effective at suppressing
feedback.
As outlined in the [RFC5760], there are two Unicast Feedback models
that may be used for reporting, - the Simple Feedback model and the
Distribution Source Feedback Summary Model. The RTCP Feedback
extension for Third Party Loss Report specified in the Section 4 of
this document will work in both Feedback models. Details of
operation in each are specified below.
6.1.1. Simple Feedback Model
In the simple Feedback Model, NACKs from the receiver observing the
loss will be reflected to the other receivers, and there's no need
for distribution source to create the third-party loss report. The
distribution source that has not seen the actual packet loss should
pass through any Third Party Loss Report message it receives from the
upstream direction.
This RTCP Third Party Loss Report message lets the receivers know
that the sender of the Third party Loss Report has received reports
that the indicated packets were lost and feedback for this packet
loss is not needed and should not be sent to the media source(s). If
the media source(s) are part of the SSM group for RTCP packet
reflection, the Distribution Source must filter this packet out. If
the media source(s) are not part of the SSM group for RTCP packets,
the Distribution Source must not forward this RTCP Third Party Loss
Report message to the media source(s).
Wu, et al. Expires June 12, 2011 [Page 10]
Internet-Draft Third Party Loss Report December 2010
6.1.2. Distribution Source Feedback Summary Model
In the distribution source feedback summary model, there may be
multiple distribution sources and the Loss Detection instances are
distributed into different distribution sources. In some cases,
these Loss Detection instances for the same session can exist at the
same time, e.g., one Loss Detection instance is implemented in the
upstream distribution source A, a second Loss Detection instance for
the same session is part of feedback target A and feedback target B
respectively within the distribution source B. The distribution
source B is placed in the path between distribution A and downstream
receivers. In this section, we focus on this generic case to discuss
the distribution Source Feedback Summary Model.
The distribution source A must listen on the RTP channel for data.
When the distribution source A observes RTP packets from a media
source are not consecutive by checking the sequence number of
packets, the distribution source A generates the new RTCP Third Party
Loss Report message described in the Section 4, and then send it to
receivers in the downstream path via the multicast channel. Note
that the distribution source A must use its own SSRC value as packet
sender SSRC for transmitting the new RTCP Third Party Loss Report
message.
a second detection instance within the Distribution Source B must
also listen for RTCP data sent to the RTCP port. Upon receiving the
RTCP Third Party Loss Report from the Distribution Source A, the
distribution source B needs to check whether it sees upstream third
party loss report from distribution source A reporting the same
event. If the upstream Third Party Loss Report reports the different
event, the distribution source B passes through any Third Party Loss
Report message it receives from the upstream direction. If the same
event is reported from distribution source A, the distribution source
B replaces it with the summary Third Party Loss Report with the
information summarization received from two loss detection instances
within the Distribution Source B. In order to reduce the processing
load at the distribution source, each loss detection instance may
provide preliminary summarization report.
During the summary third party loss report creating, the Distribution
Source B must use its own SSRC value as packet sender SSRC for
transmitting summarization information and MUST perform proper SSRC
collision detection and resolution.
The distribution source B may send this new RTCP summary third party
loss report described in the Section 4to the group on the multicast
RTCP channel and meanwhile send a packet loss request to the media
source.
Wu, et al. Expires June 12, 2011 [Page 11]
Internet-Draft Third Party Loss Report December 2010
In some case, the distribution source B may receive RTCP NACK
messages from the receivers behind the Distribution Source before the
distribution source detects the packet loss which may cause potential
Feedback implosion. In such case, the distribution source B may
filter them out if it already detected the same loss or sent a packet
loss request for the missing packet to the media source.
When the host receives the RTCP Third Party Loss Report message, if
the host understands this message it will not send packet loss
request (e.g., NACK) for the missing packets reported in the message.
If it did not understand this new message, the host MAY send packet
loss request(e.g., NACK messages) to the specified media source.
6.2. Unicast based Rapid Acquisition of Multicast Stream (RAMS) use
case
The typical RAMS architecture
[I-D.ietf-avt-rapid-acquisition-for-rtp]may have several Burst/
Retransmission Sources(BRS) behind the multicast source (MS) These
BRSes will receive the multicast SSM stream from the media source.
If one of the BRSes detects packet loss (i.e., First loss in
Figure 3) on its upstream link between the MS and BRS, but the others
BRSes have not, as the packet loss took place on SSM tree branch that
does not impact the other BRSes. In such case, the BRSes with loss
detection functionality support cannot detect packet loss at their
upstream link, therefore these BRSes will not create new Third Party
Loss Report message and send it to receivers in their downstream
path. If the BRS impacted by packet loss has loss detection support,
the BRS MAY choose to create new Third Party Loss Report message and
send it to the receivers in the downstream link. Note that BRS must
use its own SSRC as packet sender SSRC for transmitting the feedback
suppress message.
The BRS may also send a NACK upstream to request the retransmitted
packet. Upon receiving the retransmitted packet, the BRS sent it
downstream. Note that this retransmitted packet may get lost (i.e.,
second loss in the Figure 3) on the downstream link. In order to
deal with this issue, the downstream receiver can start a timeout
clock in which it expected to get a retransmission packet. When this
timeout expires and there is no retransmitted packet or a new Third
Party Loss Report message, it can take its normal behavior as if
there is no current retransmission suppression in place.
Wu, et al. Expires June 12, 2011 [Page 12]
Internet-Draft Third Party Loss Report December 2010
First +------------+ +----------+
loss |Burst and |Second Loss | |
+-----X-----| Retrans. |----X------>| |
| Upstream |Source1(BRS)| Downstream | |
Link close | link 1 +------------+ link 1 | |
to multicast | | |
source | | |
| | | |
| | +------------+ | RTP |
+---------+ | +-----++ |Burst and | | Receiver |
|Multicast| V| | +----------| Retrans. |----------->| |
| Source +-----|Router|Upstream |Source2(BRS)| Downstream | RTP_Rx |
+---------+ | |link 2 +------------+ link 2 | |
+-----++ | |
| | |
| | |
| | |
| +------------+ | |
| |Burst and | | |
+-----------+ Retrans. |----------->| |
Upstream |Source k(BRS| Downstream | |
link k +------------+ link k +----------+
Figure 3: RAMS Use Case
6.3. RTP transport translator use case
A Transport Translator (Topo-Trn-Translator), as defined in [RFC5117]
is typically forwarding the RTP and RTCP traffic between RTP clients,
for example converting between multicast and unicast for domains that
do not support multicast. The translator can identify packet loss
from the upstream and send the Third Party Loss Report message to the
unicast receivers. Note that the translator must be a participant in
the session and can then use it's own SSRC as packet sender SSRC for
transmitting the Third Party Loss Report message
6.4. Multipoint Control Unit (MCU) use case
In point to multipoint topologies using video switching MCU (Topo-
Video-switch-MCU) [RFC5117], the MCU typically forwards a single
media stream to each participant, selected from the available input
streams. The selection of the input stream is often based on voice
activity in the audio-visual conference, but other conference
management mechanisms (like presentation mode or explicit floor
control) exist as well.
In this case the MCU may detect packet loss from the sender or may
decide to switch to a new source. In both cases the receiver may
Wu, et al. Expires June 12, 2011 [Page 13]
Internet-Draft Third Party Loss Report December 2010
lose synchronization with the video stream and may send a FIR
request. If the MCU itself can detect the mis-synchronization of the
video, the MCU can send the FIR suppression message to the receivers
and send a FIR request to the video source. As suggested in RFC
5117, this topology is better implemented as an Topo-mixer, in which
case the mixer's SSRC is used as packet sender SSRC for transmitting
Third Party Loss Report message.
7. Security Considerations
The defined messages have certain properties that have security
implications. These must be addressed and taken into account by
users of this protocol.
Spoofed or maliciously created feedback messages of the type defined
in this specification can have the following implications:
Sending Third Party Loss Report with wrong sequence number of lost
packet that makes missing RTP packets can not be compensated.
To prevent these attacks, there is a need to apply authentication and
integrity protection of the feedback messages. This can be
accomplished against threats external to the current RTP session
using the RTP profile that combines Secure RTP [RFC3711] and AVPF
into SAVPF [RFC5124].
Note that middleboxes that are not visible at the RTP layer that wish
to send Third Party Loss Reports on behalf of the media source can
only do so if they spoof the SSRC of the media source. This is
difficult in case SRTP is in use. If the middlebox is visible at the
RTP layer, this is not an issue, provided the middlebox is part of
the security context for the session.
Also note that endpoints that receive a Third Party Loss Report would
be well-advised to ignore it, unless it is authenticated via SRTCP or
similar. Accepting un-authenticated Third Party Loss Report can lead
to a denial of service attack, where the endpoint accepts poor
quality media that could be repaired.
8. IANA Consideration
New feedback type and New parameters for RTCP Third Party Loss Report
are subject to IANA registration. For general guidelines on IANA
considerations for RTCP feedback, refer to [RFC4585].
This document assigns one new feedback type value x in the RTCP
Wu, et al. Expires June 12, 2011 [Page 14]
Internet-Draft Third Party Loss Report December 2010
feedback report registry to "Third Party Loss Report" with the
following registrations format:
Name: TPLR
Long Name: Third Party Loss Report
Value: TBD
Reference: This document.
This document also assigns the parameter value y in the RTCP TPLR
feedback report Registry to " Transport Layer Third Party Loss Early
Indication ", with the following registrations format:
Name: TLLEI
Long name: Transport Layer Third Party Loss Early Indication
Value: TBD
Reference: this document.
This document also assigns the parameter value z in the RTCP TPLR
feedback report Registry to "Payload Specific Third Party Loss Early
Indication ", with the following registrations format:
Name: PSLEI
Long name: Payload Specific Third Party Loss Early Indication
Value: TBD
Reference: this document.
The contact information for the registrations is:
Qin Wu
sunseawq@huawei.com
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012, China
9. Acknowledgement
The authors would like to thank David R Oran, Ali C. Begen, Colin
Perkins,Tom VAN CAENEGEM, Ingemar Johansson S, Bill Ver Steeg, WeeSan
Lee for their valuable comments and suggestions on this document.
10. References
10.1. Normative References
[RFC5760] Ott, J., Chesterfield, J., and E. Schooler, "RTP Control
Protocol (RTCP) Extensions for Single-Source Multicast
Sessions with Unicast Feedback", RFC 5760, February 2010.
Wu, et al. Expires June 12, 2011 [Page 15]
Internet-Draft Third Party Loss Report December 2010
[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.
[RFC5117] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117,
January 2008.
[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.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for
Real-time Transport Control Protocol (RTCP)-Based Feedback
(RTP/SAVPF)", RFC 5124, February 2008.
10.2. Informative References
[RFC5740] Adamson, B., Bormann, C., Handley, M., and J. Macker,
"NACK-Oriented Reliable Multicast (NORM) Transport
Protocol", November 2009.
[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.
Wu, et al. Expires June 12, 2011 [Page 16]
Internet-Draft Third Party Loss Report December 2010
[I-D.ietf-avt-rapid-acquisition-for-rtp]
Steeg, B., Begen, A., Caenegem, T., and Z. Vax, "Unicast-
Based Rapid Acquisition of Multicast RTP Sessions",
November 2010.
[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".
Authors' Addresses
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
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
Wu, et al. Expires June 12, 2011 [Page 17]