STRAW Working Group L. Miniero
Internet-Draft Meetecho
Intended status: Standards Track S. Garcia Murillo
Expires: April 27, 2015 Medooze
V. Pascual
Quobis
October 24, 2014
Guidelines to support RTCP end-to-end in Back-to-Back User Agents
(B2BUAs)
draft-ietf-straw-b2bua-rtcp-02
Abstract
SIP Back-to-Back User Agents (B2BUAs) are often envisaged to also be
on the media path, rather than just intercepting signalling. This
means that B2BUAs often implement an RTP/RTCP stack as well, whether
to act as media transcoders or to just passthrough the media
themselves, thus leading to separate multimedia sessions that the
B2BUA correlates and bridges together. If not disciplined, though,
this behaviour can severely impact the communication experience,
especially when statistics and feedback information contained in RTCP
packets get lost because of mismatches in the reported data.
This document defines the proper behaviour B2BUAs should follow when
also acting on the signalling/media plane in order to preserve the
end-to-end functionality of RTCP.
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 April 27, 2015.
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Copyright Notice
Copyright (c) 2014 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Signalling/Media Plane B2BUAs . . . . . . . . . . . . . . . . 5
3.1. Media Relay . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Media-aware Relay . . . . . . . . . . . . . . . . . . . . 6
3.3. Media Terminator . . . . . . . . . . . . . . . . . . . . 9
4. Media Path Security . . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Change Summary . . . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Session Initiation Protocol [RFC3261] Back-to-Back User Agents
(B2BUAs) are SIP entities that can act as a logical combination of
both a User Agent Server (UAS) and a User Agent Client (UAC). As
such, their behaviour is not always completelely adherent to the
standards, and can lead to unexpected situations the IETF is trying
to address. [RFC7092] presents a taxonomy of the most deployed B2BUA
implementations, describing how they differ in terms of the
functionality and features they provide.
Such components often do not only act on the signalling plane, that
is intercepting and possibly modifying SIP messages, but also on the
media plane. This means that, when on the signalling path between
two or more participants willing to communicate, such components also
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manipulate the session description [RFC4566] in order to have all RTP
and RTCP [RFC3550] pass through it as well within the context of an
SDP offer/answer [RFC3264]. The reasons for such a behaviour can be
different: the B2BUA may want, for instance, to provide transcoding
functionality for participants with incompatible codecs, or it may
need the traffic to be directly handled for different reasons like
billing, lawful interception, session recording and so on. This can
lead to several different topologies for RTP-based communication, as
documented in [RFC5117]. These topologies are currently being
updated to address new commonly encountered scenarios as well
[I-D.ietf-avtcore-rtp-topologies-update].
Whatever the reason, such a behaviour does not come without a cost.
In fact, whenever a media-aware component is placed on the path
between two or more participants that want to communicate by means of
RTP/RTCP, the end-to-end nature of such protocols is broken, and
their effectiveness may be affected as a consequence. While this may
not be a problem for RTP packets, which from a protocol point of view
just contain opaque media packets and as such can be quite easily
relayed, it definitely can cause serious issue for RTCP packets,
which carry important information and feedback on the communication
quality the participants are experiencing. In fact, RTCP packets
make use of specific ways to address the media they are referring to.
Consider, for instance, the simple scenario only involving two
participants and a single RTP session depicted in Figure 1:
+--------+ +---------+ +---------+
| |=== SSRC1 ===>| |=== SSRC3 ===>| |
| Alice | | B2BUA | | Bob |
| |<=== SSRC2 ===| |<=== SSRC4 ===| |
+--------+ +---------+ +---------+
Figure 1: B2BUA modifying RTP headers
In this common scenario, a participant (Alice) is communicating with
another participant (Bob) as a result of a signalling session managed
by a B2BUA: this B2BUA is also on the media path between the two, and
is acting as a media relay. This means that two separate RTP
sessions are involved (one per side), each carrying two RTP streams
(one per media direction). As part of this process, though, it is
also rewriting some of the RTP header information on the way, for
instance because that's how its RTP relaying stack works: in this
example, just the SSRC of the incoming RTP audio streams is changed,
but more information may be changed as well (e.g., sequence numbers,
timestamps, etc.). In particular, whenever Alice sends an audio RTP
packet, she sets her SSRC (SSRC1) to the RTP header of her RTP source
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stream; the B2BUA rewrites the SSRC (SSRC3) before relaying the
packet to Bob. At the same time, RTP packets sent by Bob (SSRC4) get
their SSRC rewritten as well (SSRC2) before being relayed to Alice.
Assuming now that Alice needs to inform Bob she has lost several
audio packets in the last few seconds, maybe because of a network
congestion, she would of course place the related received RTP stream
SSRC she is aware of (SSRC2), together with her own (SSRC1), in RTCP
Reports and/or NACKS to do so, hoping for a retransmission or for Bob
to slow down. Since the B2BUA is making use of different SSRCs for
the RTP streams in the RTP session it established with each
participant, a blind relaying of the RTCP packets to Bob would in
this case result, from Bob's perspective, in unknown SSRCs being
addressed, thus resulting in the precious information being dropped.
In fact, Bob is only aware of SSRCs SSRC4 (the one his source RTP
stream uses) and SSRC3 (the one he's receiving from the B2BUA in the
received RTP stream), and knows nothing about SSRCs SSRC1 and SSRC2
in the RTCP packets he would receive instead. As a consequence of
the feedback being dropped, unaware of the issue Bob may continue to
flood Alice with even more media packets and/or not retransmit Alice
the packets she missed, which may easily lead to a very bad
communication experience, if not eventually to an unwanted
termination of the communication itself.
This is just a trivial example that, together with additional
scenarios, will be addressed in the following sections.
Nevertheless, it is a valid example of how such a trivial mishandling
of precious information may lead to serious consequences, especially
considering that more complex scenarios may involve several
participants at the same time, multiple RTP sessions (e.g., a video
stream along audio) rather than a single one, redundancy RTP streams,
SSRC multiplexing and so on. Considering how common B2BUA
deployments are, it is very important for them to properly address
such feedback, in order to be sure that their activities on the media
plane do not break anything they're not supposed to.
2. Terminology
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].
Besides, this document addresses, where relevant, the RTP-related
terminology as disciplined in
[I-D.ietf-avtext-rtp-grouping-taxonomy].
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3. Signalling/Media Plane B2BUAs
As anticipated in the introductory section, it's very common for
B2BUA deployments to also act on the media plane, rather than just
signalling alone. In particular, [RFC7092] describes three different
categories of such B2BUAs, according to the level of activities
performed on the media plane: a B2BUA, in fact, may act as a simple
media relay (1), effectively unaware of anything that is transported;
it may be a media-aware relay (2), also inspecting and/or modifying
RTP and RTCP packets as they flow by; or it may be a full-fledged
media termination entity, terminating and generating RTP and RTCP
packets as needed.
While [RFC3550] and [RFC5117] already mandate some specific
behaviours when specific topologies are deployed, not all deployments
strictly adhere to the specifications and as such it's not rare to
encounter issues that may be avoided with a more disciplined
behaviour in that regard. For this reason, the following subsections
will describe the proper behaviour B2BUAs, whatever above category
they fall in, should follow in order to avoid, or at least minimize,
any impact on end-to-end RTCP effectiveness.
3.1. Media Relay
A media relay as identified in [RFC7092] basically just forwards,
from an application level point of view, all RTP and RTP packets it
receives, without either inspecting or modifying them. Using the RTP
Topologies terminology, this can be seen as a RTP Transport
Translator. As such, B2BUA acting as media relays are not aware of
what traffic they're handling, meaning that not only the packet
payloads are opaque to them, but headers as well. Many Session
Border Controllers (SBC) implement this kind of behaviour, e.g., when
acting as a bridge between an inner and outer network.
Considering all headers and identifiers in both RTP and RTCP are left
untouched, issues like the SSRC mismatch described in the previous
section would not occur. Similar problems could occur, though,
should the session description end up providing incorrect information
about the media flowing (e.g., if the SDP on either side contain
'ssrc' [RFC5576] attributes that don't match the actual SSRC being
advertized on the media plane) or about the supported RTCP mechanisms
(e.g., in case the B2BUA advertized support for NACK because it
implements it, but the original INVITE didn't). Such an issue might
occur, for instance, in case the B2BUA acting as a media relay is
generating a new session description when bridging an incoming call,
rather than taking into account the original session description in
the first place. This may cause the participants to find a mismatch
between the SSRCs advertized in SDP and the ones actually observed in
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RTP and RTCP packets (which may indeed change during a multimedia
session anyway, but having them synced during setup would help
nonetheless), or having them either ignore or generate RTCP feedback
packets that were not explicitly advertized as supported.
In order to prevent such an issue, a media-relay B2BUA SHOULD forward
all the SSRC- and RTCP-related SDP attributes when handling a
multimedia session setup between interested participants: this
includes attributes like 'ssrc' [RFC3261], 'rtcp-fb' [RFC4585],
'rtcp-xr-attrib' [RFC3611] and others. It SHOULD NOT, though,
blindly forward all SDP attributes, as some of them (e.g.,
candidates, fingerprints, crypto, etc.) may lead to call failures for
different reasons out of scope to this document. One notable example
is the 'rtcp' [RFC3605] attribute that UAC may make use of to
explicitly state the port they're willing to use for RTCP:
considering the B2BUA would relay RTCP packets, the port as seen by
the other UAC involved in the communication would differ from the one
negotiated originally, and as such it MUST be rewritten accordingly.
Besides, it is worth mentioning that, leaving RTCP packets untouched,
a media relay may also let through information that, according to
policies, may be best left hidden or masqueraded, e.g., domain names
in CNAME items. Nevertheless, that information cannot break the end-
to-end RTCP behaviour.
3.2. Media-aware Relay
A Media-aware relay, unlike the the Media Relay addressed in the
previous section, is actually aware of the media traffic it is
handling. As such, it is able to inspect RTP and RTCP packets
flowing by, and may even be able to modify the headers in any of them
before forwarding them. Using the RFC3550 terminology, this can be
seen as a RTP Translator. A B2BUA implementing this role would
typically not, though, inspect the RTP payloads as well, which would
be opaque to them: this means that the actual media would not be
manipulated (e.g, transcoded).
This makes them quite different from the Media Relay previously
discussed, especially in terms of the potential issues that may occur
at the RTCP level. In fact, being able to modify the RTP and RTCP
headers, such B2BUAs may end up modifying RTP related information
like SSRC (and hence CSRC lists, that must of course be updated
accordingly), sequence numbers, timestamps and the like in an RTP
stream, before forwarding the modified packets to the other
interested participants in the multimedia sessions on the RTP streams
they're using to receive the media. This means that, if not properly
disciplined, such a behaviour may easily lead to issues like the one
described in the introductory section. As such, it is very important
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for a B2BUA modifying RTP-related information across two related RTP
streams to also modify the same information in RTCP packets as well,
and in a coherent way, so that not to confuse any of the participants
involved in a communication.
It is worthwile to point out that such a B2BUA would not necessarily
forward all the packets it is receiving, though: Selective Forwarding
Units (SFU) [I-D.ietf-avtcore-rtp-topologies-update], for instance,
could aggregate or drop incoming RTCP messages, while at the same
time originating new ones on their own. For the messages that are
forwarded and/or aggregated, though, it's important to make sure the
information is coherent.
Besides the behaviour already mandated for RTCP translators in
Section 7.2 of [RFC3550], a media-aware B2BUA MUST also handle
incoming RTCP messages to forward following this guideline:
SR: [RFC3550]
If the B2BUA has changed any SSRC in any RTP streams relation, it
MUST update the SSRC-related information in the incoming SR packet
before forwarding it. This includes the sender SSRC, which MUST
be rewritten with the one the B2BUA uses in the RTP stream used to
receive RTP packets from each participant, and the SSRC
information in all the blocks, which MUST be rewritten using the
related sender participant(s) SSRC. If the B2BUA has also changed
the base RTP sequence number when forwarding RTP packets, then
this change needs to be properly addressed in the 'extended
highest sequence number received' field in the Report Blocks.
RR: [RFC3550]
The same guidelines given for SR apply for RR as well.
SDES: [RFC3550]
If the B2BUA has changed any SSRC in any direction, it MUST update
the SSRC-related information in all the chunks in the incoming
SDES packet before forwarding it.
BYE: [RFC3550]
If the B2BUA has changed any SSRC in any direction, it MUST update
the SSRC in the BYE message.
APP: [RFC3550]
If the B2BUA has changed any SSRC in any direction, it MUST update
the SSRC in the BYE message. Should the B2BUA be aware of any
specific APP message format that contains additional information
related to SSRCs, it SHOULD update them as well.
Extended Reports (XR): [RFC3611]
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If the B2BUA has changed any SSRC in any direction, it MUST update
the SSRC-related information in the incoming XR message header
before forwarding it. This includes the source SSRC, which MUST
be rewritten with the one the B2BUA uses to send RTP packets to
each sender participant, and the SSRC information in all the block
types that include it, which MUST be rewritten using the related
sender participant(s) SSRC. If the B2BUA has also changed the
base RTP sequence number when forwarding RTP packets, then this
change needs to be properly addressed in the 'begin_seq' and
'end_seq' fields that are available in most of the Report Block
types that are part of the XR specification.
Receiver Summary Information (RSI): [RFC5760]
If the B2BUA has changed any SSRC in any direction, it MUST update
the SSRC-related information in the incoming RSI message header
before forwarding it. This includes the distribution source SSRC,
which MUST be rewritten with the one the B2BUA uses to send RTP
packets to each sender participant, the summarized SSRC and, in
case a Collision Sub-Report Block is available, the SSRCs in the
related list.
Port Mapping (TOKEN): [RFC6284]
If the B2BUA has changed any SSRC in any direction, it MUST update
the SSRC-related information in the incoming TOKEN message before
forwarding it. This includes the Packet Sender SSRC, which MUST
be rewritten with the one the B2BUA uses to send RTP packets to
each sender participant, and the Requesting Client SSRC in case
the message is a response, which MUST be rewritten using the
related sender participant(s) SSRC.
Feedback messages: [RFC4585]
All Feedback messages have a common packet format, which includes
the SSRC of the packet sender and the one of the media source the
feedack is related to. Just as described for the previous
messages, these SSRC identifiers MUST be updated if the B2BUA has
changed any SSRC in any direction. It MUST NOT, though, change a
media source SSRC that was originally set to zero. Besides,
considering that many feedback messages also include additional
data as part of their specific Feedback Control Information (FCI),
a media-aware B2BUA MUST take care of them accordingly, if it can
parse and regenerate them, according to the following guidelines.
NACK: [RFC4585]
Besides the common packet format management for feedback messages,
a media-aware B2BUA MUST also properly rewrite the Packet ID (PID)
of all addressed lost packets in the NACK FCI if it changed the
RTP sequence numbers before forwarding a packet.
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TMMBR/TMMBN/FIR/TSTR/TSTN/VBCM: [RFC5104]
Besides the common packet format management for feedback messages,
a media-aware B2BUA MUST also properly rewrite the additional SSRC
identifier all those messages envisage as part of their specific
FCI if it changed the related RTP SSRC of the media sender.
REMB: [I-D.alvestrand-rmcat-remb]
Besides the common packet format management for feedback messages,
a media-aware B2BUA MUST also properly rewrite the additional SSRC
identifier(s) REMB packets envisage as part of their specific FCI
if it changed the related RTP SSRC of the media sender.
Apart from the generic guidelines related to Feedback messages, no
additional modifications are needed for PLI, SLI and RPSI feedback
messages instead.
Of course, the same considerations about the need for SDP and RTP/
RTCP information to be coherent also applies to media-aware B2BUAs.
This means that, if a B2BUA is going to change any SSRC, it SHOULD
update the related 'ssrc' attributes if they were present in the
original description before sending it to the recipient, just as it
MUST rewrite the 'rtcp' attribute if provided. At the same time, the
ability for a media-aware B2BUA to inspect/modify RTCP packets may
also mean such a B2BUA may choose to drop RTCP packets it can't
parse: in that case, a media-aware B2BUA SHOULD also advertize its
RTCP level of support in the SDP in a coherent way, in order to
prevent, for instance, a UAC to make use of NACK messages that would
never reach the intended recipients.
3.3. Media Terminator
A Media Terminator B2BUA, unlike simple relays and media-aware ones,
is also able to terminate media itself, that is taking care of RTP
payloads as well and not only headers. This means that such
components, for instance, can act as media transcoders and/or
originate specific RTP media. Using the RTP Topologies terminology,
this can be seen as a RTP Media Translator. Such a capability makes
them quite different from the previously introduced B2BUA typologies,
as this means they are going to terminate RTCP as well: in fact,
since the media is terminated by themselves, the related statistics
and feedback functionality can be taken care directly by the B2BUA,
and does not need to be relayed to the other participants in the
multimedia session.
For this reason, no specific guideline is needed to ensure a proper
end-to-end RTCP behaviour in such scenarios, mostly because most of
the times there would be no end-to-end RTCP interaction among the
involved participants at all, as the B2BUA would terminate them all
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and take care of them accordingly. Nevertheless, should any RTCP
packet actually need to be forwarded to another participant in the
multimedia session, the same guidelines provided for the media-aware
B2BUA case apply.
4. Media Path Security
The discussion made in the previous sections on the management of
RTCP messages by a B2BUA has so far mostly worked under the
assumption that the B2BUA has actually access to the RTP/RTCP
information itself. This is indeed true if we assume that plain RTP
and RTCP is being handled, but this may not be true once any security
is enforced on RTP packets and RTCP messages by means of SRTP
[RFC3711], whether the keying is done using Secure Descriptions
[RFC4568] or DTLS-SRTP [RFC5764].
While typically not an issue in the Media Relay case, where RTP and
RTCP packets are forwarded without any modification no matter whether
security is involved or not, this could definitely have an impact on
Media-aware Relays and Media Terminator B2BUAs. To make a simple
example, if we think of a SRTP/SRTCP session across a B2BUA where the
B2BUA itself has no access to the keys used to secure the session,
there would be no way to manipulate SRTP headers without violating
the hashing on the packet; at the same time, there would be no way to
rewrite the RTCP information accordingly either, as most of the
packet (especially when RTCP compound packets are involved) would be
encrypted.
For this reason, it is important to point out that the operations
described in the previous sections are only possible if the B2BUA has
a way to effectively manipulate the packets and messages flowing by.
This means that, in case media security is involved, the B2BUA
willing to act as either a Media-aware Relay or a Media Terminator
can only do so when acting as an intermediary with respect to the
secure sessions. As such, different secure sessions would need to be
negotiated (either via SDES or DTLS-SRTP) with the involved
participants, in order to be able to have access to the unencrypted
packets and, if needed, modify them before encrypting them again and
forwarding them.
Of course, this is only a viable solution if all the involved
participants trust the B2BUA. In fact, it is very important to point
out that a B2BUA acting as an intermediary would break any end-to-end
security mechanism that may be in place, as all the involved
participants would have a secure communication up to the B2BUA and
would have to rely on the B2BUA actually encrypting the communication
on the other end(s) as well. This means that the participants
involved in a multimedia session through a B2BUA have to trust the
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B2BUA to secure the session on the other end(s), taking care of any
validation and protection that may be required as part of the
process.
It is worth noting that some additional care may be needed, with
respect to RTCP, when acting as an intermediary between two secure
sessions. Specifically, issues may arise when relaying NACK feedback
originated by a user who failed to receive some RTP packets, that
were instead received by the B2BUA: such an issue might occur when
the packet loss happens between the user and the B2BUA itself, and
not between the RTP packet sender and the B2BUA. Such a situation
might result in the RTP media sender retransmitting the encrypted
packet, which would then be rejected by the B2BUA as a replayed one.
However, this issue is well known and addressed in [RFC4588], which
both the B2BUA and the involved participants in the communication
SHOULD make use of to prevent it from happening. This mechanism
allows for a Redundancy RTP Stream to be used for the purpose, which
would prevent the replay error. Of course, all recommendations given
previously with respect to managing SSRCs across the B2BUA still
apply here as well: in fact, such a redundant RTP stream would make
use of a different SSRC, that would need to be taken care of both at
the RTP and the SDP level. If [RFC4588] is not supported, the B2BUA
SHOULD handle NACK packets directly, and only forward feedback on
lost packets it has not access to.
5. IANA Considerations
This document makes no request of IANA.
6. Security Considerations
TBD. Not any additional consideration to what the standards already
give? Probably this section will need a few words about how NOT
following the guidelines can lead to security issues: e.g., not
properly translating REMB messages can cause an increasing flow of
media packets, that may be seen as attacks to devices that can't
handle the amount of data.
7. Change Summary
Note to RFC Editor: Please remove this whole section.
The following are the major changes between the 01 and the 02
versions of the draft:
o Updated terminology to better adhere to
[I-D.ietf-avtext-rtp-grouping-taxonomy].
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o Rephrased the Media Path Security section to take into account the
MITM-related discussion in Toronto.
o Clarified that NACK management might be trickier when SRTP is
involved.
The following are the major changes between the 00 and the 01
versions of the draft:
o Updated references and mapping per taxonomy RFC (7092).
o Added a reference to RTP topologies, and tried a mapping as per-
discussion in London.
o Added more RTCP packet types to the Media-Aware section.
o Clarified that fixing the 'rtcp' SDP attribute is important.
o Added a new section on the impact of media security.
8. Acknowledgements
TBD.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, June
2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
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[RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session
Initiation Protocol (SIP) Back-to-Back User Agents", RFC
7092, December 2013.
9.2. Informative References
[RFC5117] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117,
January 2008.
[I-D.ietf-avtcore-rtp-topologies-update]
Westerlund, M. and S. Wenger, "RTP Topologies", draft-
ietf-avtcore-rtp-topologies-update-04 (work in progress),
August 2014.
[I-D.ietf-avtext-rtp-grouping-taxonomy]
Lennox, J., Gross, K., Nandakumar, S., and G. Salgueiro,
"A Taxonomy of Grouping Semantics and Mechanisms for Real-
Time Transport Protocol (RTP) Sources", draft-ietf-avtext-
rtp-grouping-taxonomy-02 (work in progress), June 2014.
[I-D.alvestrand-rmcat-remb]
Alvestrand, H., "RTCP message for Receiver Estimated
Maximum Bitrate", draft-alvestrand-rmcat-remb-03 (work in
progress), October 2013.
[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.
[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.
[RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific
Media Attributes in the Session Description Protocol
(SDP)", RFC 5576, June 2009.
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute
in Session Description Protocol (SDP)", RFC 3605, October
2003.
[RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", RFC 3611, November
2003.
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[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.
[RFC6284] Begen, A., Wing, D., and T. Van Caenegem, "Port Mapping
between Unicast and Multicast RTP Sessions", RFC 6284,
June 2011.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session
Description Protocol (SDP) Security Descriptions for Media
Streams", RFC 4568, July 2006.
[RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer
Security (DTLS) Extension to Establish Keys for the Secure
Real-time Transport Protocol (SRTP)", RFC 5764, May 2010.
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
July 2006.
Authors' Addresses
Lorenzo Miniero
Meetecho
Email: lorenzo@meetecho.com
Sergio Garcia Murillo
Medooze
Email: sergio.garcia.murillo@gmail.com
Victor Pascual
Quobis
Email: victor.pascual@quobis.com
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