STRAW Working Group L. Miniero
Internet-Draft Meetecho
Intended status: Standards Track S. Garcia Murillo
Expires: October 21, 2016 Medooze
V. Pascual
Quobis
April 19, 2016
Guidelines to support RTCP end-to-end in Back-to-Back User Agents
(B2BUAs)
draft-ietf-straw-b2bua-rtcp-10
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
messages 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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 21, 2016.
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Copyright Notice
Copyright (c) 2016 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
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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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Signalling/Media Plane B2BUAs . . . . . . . . . . . . . . . . 4
3.1. Media Relay . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Media-aware Relay . . . . . . . . . . . . . . . . . . . . 6
3.3. Media Terminator . . . . . . . . . . . . . . . . . . . . 10
4. Media Path Security . . . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Change Summary . . . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
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 [RFC7667]. These topologies are
currently being updated to address new commonly encountered scenarios
as well [RFC7667].
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 can be quite easily relayed,
it definitely can cause serious issue for RTCP messages, which carry
important information and feedback on the communication quality the
participants are experiencing. 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) in the RTP header of her RTP source
stream. The B2BUA rewrites the SSRC (SSRC3) before relaying the
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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, she will place the related
received RTP stream SSRC she is aware of (SSRC2), together with her
own (SSRC1), in RTCP Reports and/or NACKs. 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 these RTCP
messages 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 messages he received
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. This 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 simple mishandling
of precious information may lead to serious consequences. This is
especially true if we picture more complex scenarios involving
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 [RFC7656].
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: a B2BUA, in fact, may act as a simple
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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 messages as they flow by; or it may be a full-fledged
media termination entity, terminating and generating RTP and RTCP
messages as needed.
While [RFC3550] and [RFC7667] already mandate some specific
behaviours in the presence of certain topologies, not all deployments
strictly adhere to the specifications. 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 not to impact any end-to-end
RTCP effectiveness.
3.1. Media Relay
A media relay, as identified in [RFC7092], basically just forwards
all RTP and RTCP messages 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. This means
that both packet payloads and packet headers are opaque to them.
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 still happen,
though, for different reasons, as for instance if the session
description ends up providing incorrect information. This may
happen, for example, if the SDP on either side contains 'ssrc'
[RFC5576] attributes that don't match the actual SSRC being
advertized on the media plane, or in case the B2BUA advertized
support for NACK because it implements it, while the original INVITE
didn't. Such issues 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. This may cause participants to find a
mismatch between the SSRCs advertized in SDP and the ones actually
observed in RTP and RTCP messages (which may indeed change during a
multimedia session anyway, but having them synced during setup would
help nonetheless), or to have 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
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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 messages, 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.
It is worth mentioning that, leaving RTCP messages 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. Besides, these CNAME items may actually contain IP addresses
instead: this means that, should a NAT be involved in the
communication, this may actually result in CNAME collisions, which
could indeed break the end-to-end RTCP behaviour. While [RFC7022]
can prevent this from happening, there may be implementations that
don't make use of it. As such, a B2BUA MAY rewrite CNAME items if
any potential collision is detected, even in the Media Relay case.
If a B2BUA does indeed decide to rewrite CNAME items, though, then it
MUST generate new CNAMEs following [RFC7022].
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 messages
flowing by, and may even be able to modify their headers. Using the
RFC3550 terminology, this can be seen as a RTP Translator. A B2BUA
implementing this role, though, typically does not 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/CSRC, sequence numbers, timestamps and others in an RTP
stream, before forwarding the modified packets to the other
interested participants. 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
for a B2BUA modifying RTP-related information across two related RTP
streams to also modify, in a coherent way, the same information in
RTCP messages as well.
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It is worthwile to point out that such a B2BUA may not necessarily
forward all the packets it is receiving, though. Selective
Forwarding Units (SFU) [RFC7667], for instance, may 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 the SSRC of the sender RTP stream a
Sender Report refers to, it MUST update the SSRC in the SR packet
header as well. If the B2BUA has changed the SSRCs of other RTP
streams too, and any of these streams are addressed in any of the
SR report blocks, it MUST update the related values in the SR
report blocks as well. 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 the SSRC of any RTP stream addressed in
any of the chunks of an incoming SDES message, it MUST update the
related SSRCs in all the chunks. The same considerations made
with respect to CNAME collisions at the end of Section 3.1 apply
here as well.
BYE: [RFC3550]
If the B2BUA has changed the SSRC of any RTP stream addressed in
the SSRC/CSRC identifiers included in a BYE packet, it MUST update
them in the message.
APP: [RFC3550]
If the B2BUA has changed the SSRC of any RTP stream addressed in
the header of an APP packet, it MUST update the identifier in the
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 accordingly.
Extended Reports (XR): [RFC3611]
If the B2BUA has changed the SSRC of the RTP stream associated
with the originator of an XR packet, it MUST update the SSRC in
the XR message header. The same guidelines given for SR/RR, with
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respect to SSRC identifiers in report blocks, apply for all the
Report Block types in the XR message as well. 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 of RTP streams addressed in a
RSI packet, it MUST update the SSRC identifiers in the message.
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 of RTP streams addressed in a
TOKEN packet, it MUST update the SSRC identifiers in the message.
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 identifier of the packet sender and the SSRC identifier
of the media source the feedack is related to. Just as described
for the previous messages, these SSRC identifiers MUST be updated
in the message if the B2BUA has changed the SSRC of the RTP
streams addressed there. It MUST NOT, though, change a media
source SSRC that was originally set to zero, unless zero is
actually the SSRC that was chosen by one of the involved
endpoints, in which case the above mentioned rules as to SSRC
rewriting apply. 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.
TMMBR/TMMBN/FIR/TSTR/TSTN/VBCM: [RFC5104]
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Besides the common packet format management for feedback messages,
a media-aware B2BUA MUST also properly rewrite the additional SSRC
identifier in the 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) in REMB packets, if it changed the related RTP SSRC
of the media sender.
Explicit Congestion Notification (ECN): [RFC6679]
Besides the common packet format management for feedback messages,
the same guidelines given for SR/RR management apply as well,
considering the presence of sequence numbers in the ECN Feedback
Report format. For what concerns the management of RTCP XR ECN
Summary Report messages, the same guidelines given for generic XR
messages apply.
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 present, before sending it
to the recipient. Besides, it MUST rewrite the 'rtcp' attribute if
provided. At the same time, while a media-aware B2BUA is typically
able to inspect/modify RTCP messages, it may not support all RTCP
messages. This means that a B2BUA may choose to drop RTCP messages
it can't parse. In that case, a media-aware B2BUA MUST 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. It's important to
point out that, in case any RTCP message needs to be dropped, then
the B2BUA SHOULD NOT drop the whole compound RTCP message it may
belong to, but only the RTCP message itself.
A different set of considerations, instead, is worthwhile for what
concerns RTP/RTCP multiplexing [RFC5761] and Reduced-Size RTCP
[RFC5506]. While the former allows for a better management of
network resources by multiplexing RTP packets and RTCP messages over
the same transport, the latter allows for a compression of RTCP
messages, thus leading to less network traffic. For what concerns
RTP/RTCP multiplexing, a B2BUA acting as a Media Relay may use it on
either RTP session independently. This means that, for instance, a
Media Relay B2BUA may use RTP/RTCP multiplexing on one side of the
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communication, and not use it on the other side, if it's not
supported. This allows for a better management of network resources
on the side that does support it. In case any of the parties in the
communications supports it and the B2BUA does too, the related 'rtcp-
mux' SDP attribute MUST be forwarded on the other side(s). If the
B2BUA detects that any of the parties in the communication does not
support the feature, it may decide to either disable it entirely or
still advertize it for the RTP sessions with parties that do support
it. In case the B2BUA decides to involve RTP/RTCP multiplexing, it
MUST ensure that there are no conflicting RTP payload type numbers on
both sides. In case there are, it MUST rewrite RTP payload type
numbers to ensure no conflict in the domain where the RTP/RTCP
multiplexing is applied. Should RTP payload types be rewritten, the
related information in the SDP MUST be updated accordingly.
For what concerns Reduced-Size RTCP, instead, the considerations are
a bit different. In fact, while a Media Relay B2BUA may choose to
use it on the side that supports it and not on the side that doesn't,
there are other aspects to take into account before doing so. While
Reduced-Size allows indeed for less network traffic related to RTCP
messaging in general, this gain may lead a Reduced-Size RTCP
implementation to also issue a higher rate of RTCP feedback messages.
This would result in an increased RTCP traffic on the side that does
not support Reduced-Size, and could as a consequence be actually
counterproductive if the available bandwidth is different on the two
sides. That said, the B2BUA can choose whether or not to advertize
support for Reduced-Size RTCP on either side by means of the 'rtcp-
rsize' SDP attribute. Should a B2BUA decide to allow the sides to
independently use Reduced-Size or not, then the B2BUA MUST advertize
support for the feature on the sides that support it, and MUST NOT
advertize it on the sides that don't, by removing the related
attribute from the SDP before forwarding it. Should the B2BUA decide
to disable the feature on all sides, instead, it MUST NOT advertize
support for the Reduced-Size RTCP functionality on either side, by
removing the 'rtcp-rsize' attribute from the SDP.
3.3. Media Terminator
A Media Terminator B2BUA, unlike simple relays and media-aware ones,
is also able to terminate media itself. As such, it can inspect and/
or modify RTP payloads as well. 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 topology can also be seen as a Back-to-
back RTP sessions through a Middlebox, as described in Section 3.2.2
of [RFC7667]. Such a capability makes them quite different from the
previously introduced B2BUA typologies. Since such a B2BUA would
terminate RTP itself, it can take care of the related statistics and
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feedback functionality directly, with no need to simply relay any
message between the 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 in the first place. Nevertheless, should any
RTCP message actually need to be forwarded to another participant in
the multimedia session, the same guidelines provided for the media-
aware B2BUA case apply.
For what concerns RTP/RTCP multiplexing support, the same
considerations already given for the Media Relay management basically
apply for a Media Terminator as well. Some different considerations
might be given as to the Reduced-Size RTCP functionality, instead: in
fact, in the Media Terminator case it is safe to use the feature
independently on each side. In that case, the same considerations
about advertizing the support, or lack of, of the feature on either
side as described for the Media Relay case apply here as well.
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 may not be once any security is
enforced on RTP packets and RTCP messages by means of SRTP [RFC3711].
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 envisage 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.
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, only the Media-
unaware Relay scenario can be properly addressed. Attempting to
cover Media-aware Relay and Media Terminarion scenarios when
involving secure sessions will inevitably lead to the B2BUA acting as
a man-in-the-middle, and as such its behaviour is unspecified and
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discouraged. More considerations on this are provided in
[I-D.ietf-straw-b2bua-dtls-srtp].
5. IANA Considerations
This document makes no request of IANA.
6. Security Considerations
This document, being a summary and a best common practice overview
that covers different standards, does not introduce any additional
consideration to those described by the aforementioned standard
documents.
It is worth pointing out, though, that there are scenarios where an
improper management of RTCP messaging across a B2BUA may lead,
willingly or not, to situations not unlike an attack. To make a
simple example, an improper management of a REMB feedback message
containing, e.g., information on the limited bandwidth availability
for a user, may lead to missing or misleading information to its
peer. This may cause the peer to increase the encoder bitrate, maybe
up to a point where a user with poor connectivity will inevitably be
choked by an amount of data it cannot process. This scenario may as
such result in what looks like a Denial of Service (DOS) attack
towards the user.
7. Change Summary
Note to RFC Editor: Please remove this whole section.
The following are the major changes between the 09 and the 10
versions of the draft:
o Replaced references to obsoleted RFC 5117 with [RFC7667].
o Made reference to [RFC7656] normative.
o Clarified text across the whole document to address Ben's review.
The following are the major changes between the 08 and the 09
versions of the draft:
o Updated references to documents which have become RFC in the
meanwhile, [RFC7667] and [RFC7656].
The following are the major changes between the 06 and the 07
versions of the draft:
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o Clarified the suggested changed by Colin Perkins on the management
of CNAME items in SDES, and added reference to [RFC7022].
o Addressed comment by Simon Perreault on CNAME collisions
management.
The following are the major changes between the 05 and the 06
versions of the draft:
o Addressed comment by Colin Perkins on the management of CNAME
items in SDES.
The following are the major changes between the 04 and the 05
versions of the draft:
o Clarified behaviour when SSRC is zero.
o Fixed a couple of nits found by the Idnits tool.
The following are the major changes between the 03 and the 04
versions of the draft:
o Addressed review by Magnus Westerlund.
o Added guidelines for ECN RTCP messages.
o Clarified that if an RTCP message is dropped because unsupported,
only the unsupported packet is dropped and not the compound packet
that contains it.
o Added reference to Section 3.2.2 of [RFC7667] to Section 3.3.
o Added considerations on RTP/RTCP multiplexing and Reduced-Size
RTCP.
The following are the major changes between the 02 and the 03
versions of the draft:
o Rephrased the Media Path Security section to take into account the
MITM-related discussion in Honolulu.
o Added some Security Considerations.
The following are the major changes between the 01 and the 02
versions of the draft:
o Updated terminology to better adhere to [RFC7656].
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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 message 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
The authors would like to thank Flavio Battimo and Pierluigi Palma
for their invaluable feedback in the early stages of the document.
The authors would also like to thank Colin Perkins, Bernard Aboba,
Albrecht Schwarz, Hadriel Kaplan, Keith Drage, Jonathan Lennox,
Stephen Farrell, Magnus Westerlund and Simon Perreault for their
constructive comments, suggestions, and reviews that were critical to
the formulation and refinement of this document.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <http://www.rfc-editor.org/info/rfc4566>.
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[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002,
<http://www.rfc-editor.org/info/rfc3264>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <http://www.rfc-editor.org/info/rfc3550>.
[RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
DOI 10.17487/RFC7656, November 2015,
<http://www.rfc-editor.org/info/rfc7656>.
9.2. Informative References
[RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session
Initiation Protocol (SIP) Back-to-Back User Agents",
RFC 7092, DOI 10.17487/RFC7092, December 2013,
<http://www.rfc-editor.org/info/rfc7092>.
[RFC7667] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667,
DOI 10.17487/RFC7667, November 2015,
<http://www.rfc-editor.org/info/rfc7667>.
[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,
DOI 10.17487/RFC4585, July 2006,
<http://www.rfc-editor.org/info/rfc4585>.
[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
"Codec Control Messages in the RTP Audio-Visual Profile
with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104,
February 2008, <http://www.rfc-editor.org/info/rfc5104>.
[RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific
Media Attributes in the Session Description Protocol
(SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009,
<http://www.rfc-editor.org/info/rfc5576>.
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[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute
in Session Description Protocol (SDP)", RFC 3605,
DOI 10.17487/RFC3605, October 2003,
<http://www.rfc-editor.org/info/rfc3605>.
[RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed.,
"RTP Control Protocol Extended Reports (RTCP XR)",
RFC 3611, DOI 10.17487/RFC3611, November 2003,
<http://www.rfc-editor.org/info/rfc3611>.
[RFC5760] Ott, J., Chesterfield, J., and E. Schooler, "RTP Control
Protocol (RTCP) Extensions for Single-Source Multicast
Sessions with Unicast Feedback", RFC 5760,
DOI 10.17487/RFC5760, February 2010,
<http://www.rfc-editor.org/info/rfc5760>.
[RFC6284] Begen, A., Wing, D., and T. Van Caenegem, "Port Mapping
between Unicast and Multicast RTP Sessions", RFC 6284,
DOI 10.17487/RFC6284, June 2011,
<http://www.rfc-editor.org/info/rfc6284>.
[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.,
and K. Carlberg, "Explicit Congestion Notification (ECN)
for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <http://www.rfc-editor.org/info/rfc6679>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<http://www.rfc-editor.org/info/rfc3711>.
[RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session
Description Protocol (SDP) Security Descriptions for Media
Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006,
<http://www.rfc-editor.org/info/rfc4568>.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
Control Packets on a Single Port", RFC 5761,
DOI 10.17487/RFC5761, April 2010,
<http://www.rfc-editor.org/info/rfc5761>.
[RFC5506] Johansson, I. and M. Westerlund, "Support for Reduced-Size
Real-Time Transport Control Protocol (RTCP): Opportunities
and Consequences", RFC 5506, DOI 10.17487/RFC5506, April
2009, <http://www.rfc-editor.org/info/rfc5506>.
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[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,
DOI 10.17487/RFC5764, May 2010,
<http://www.rfc-editor.org/info/rfc5764>.
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
DOI 10.17487/RFC4588, July 2006,
<http://www.rfc-editor.org/info/rfc4588>.
[RFC7022] Begen, A., Perkins, C., Wing, D., and E. Rescorla,
"Guidelines for Choosing RTP Control Protocol (RTCP)
Canonical Names (CNAMEs)", RFC 7022, DOI 10.17487/RFC7022,
September 2013, <http://www.rfc-editor.org/info/rfc7022>.
[I-D.ietf-straw-b2bua-dtls-srtp]
R, R., Reddy, T., Salgueiro, G., Pascual, V., and P.
Ravindran, "DTLS-SRTP Handling in Session Initiation
Protocol (SIP) Back-to-Back User Agents (B2BUAs)", draft-
ietf-straw-b2bua-dtls-srtp-12 (work in progress), April
2016.
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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