Internet DRAFT - draft-westerlund-avtcore-multi-media-rtp-session
draft-westerlund-avtcore-multi-media-rtp-session
AVTCORE WG M. Westerlund
Internet-Draft Ericsson
Updates: 3550 (if approved) C. Perkins
Intended status: Standards Track University of Glasgow
Expires: January 10, 2013 J. Lennox
Vidyo
July 9, 2012
Multiple Media Types in an RTP Session
draft-westerlund-avtcore-multi-media-rtp-session-00
Abstract
This document specifies how an RTP session can contain media streams
with media from multiple media types such as audio, video, and text.
This has been restricted by the RTP Specification, and thus this
document updates RFC 3550 to enable this behavior for applications
that satisfy the applicability for using multiple media types in a
single RTP session.
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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This Internet-Draft will expire on January 10, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. NAT and Firewalls . . . . . . . . . . . . . . . . . . . . 4
3.2. No Transport Level QoS . . . . . . . . . . . . . . . . . . 5
3.3. Architectural Equality . . . . . . . . . . . . . . . . . . 5
4. Overview of Solution . . . . . . . . . . . . . . . . . . . . . 5
5. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Usage of the RTP session . . . . . . . . . . . . . . . . . 6
5.2. Signalled Support . . . . . . . . . . . . . . . . . . . . 6
5.3. Homogeneous Multi-party . . . . . . . . . . . . . . . . . 7
5.4. Reduced number of Payload Types . . . . . . . . . . . . . 8
5.5. Stream Differentiation . . . . . . . . . . . . . . . . . . 8
5.6. Non-compatible Extensions . . . . . . . . . . . . . . . . 8
6. RTP Session Specification . . . . . . . . . . . . . . . . . . 9
6.1. RTP Session . . . . . . . . . . . . . . . . . . . . . . . 9
6.2. Sender Source Restrictions . . . . . . . . . . . . . . . . 10
6.3. Payload Type Applicability . . . . . . . . . . . . . . . . 10
6.4. RTCP . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7. Extension Considerations . . . . . . . . . . . . . . . . . . . 11
7.1. RTP Retransmission . . . . . . . . . . . . . . . . . . . . 12
7.2. Generic FEC . . . . . . . . . . . . . . . . . . . . . . . 12
8. Signalling . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. SDP-Based Signalling . . . . . . . . . . . . . . . . . . . 13
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . . 14
12.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
When the Real-time Transport Protocol (RTP) [RFC3550] was designed,
close to 20 years ago, IP networks were very different compared to
the ones in 2012 when this is written. The almost ubiquitous
deployment of Network Address Translators (NAT) and Firewalls has
increased the cost and likely-hood of communication failure when
using many different transport flows. Thus there exists a pressure
to reduce the number of concurrent transport flows.
RTP [RFC3550] as defined recommends against having multiple media
types, like audio and video, in the same RTP session. The motivation
for this is dependent on particular usage or dependencies on lower
layer Quality of Service (QoS). When these aren't present, there are
no strong RTP reasons for not allowing multiple media types in one
RTP session. However, the Session Description Protocol (SDP)
[RFC4566], as one of the dominant signalling method for establishing
RTP session, has enforced this rule, by not allowing multiple media
types for a given receiver destination or set of ICE candidates,
which is the most common method to determine which RTP session the
packets are intended for.
The fact that these limitations have been in place for so long a
time, in addition to RFC 3550 being written without fully considering
multiple media types in an RTP session, does result in a number of
considerations being needed. This document provides such
considerations regarding applicability as well as functionality,
including normative specification of behavior.
First, some basic definitions are provided. This is followed by a
background that discusses the motivation in more detail. A overview
of the solution of how to provide multiple media types in one RTP
session is then presented. Next is the formal applicability this
specification have followed by the normative specification. This is
followed by a discussion how some RTP/RTCP Extensions should function
in the case of multiple media types in one RTP session. A
specification of the requirements on signalling from this
specification and a look how this is realized in SDP using Bundle
[I-D.ietf-mmusic-sdp-bundle-negotiation]. The document ends with the
security considerations.
2. Definitions
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2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2.2. Terminology
The following terms are used with supplied definitions:
Endpoint: A single entity sending or receiving RTP packets. It may
be decomposed into several functional blocks, but as long as it
behaves as a single RTP stack entity it is classified as a single
endpoint.
Media Stream: A sequence of RTP packets using a single SSRC that
together carries part or all of the content of a specific Media
Type from a specific sender source within a given RTP session.
Media Type: Audio, video, text or application whose form and meaning
are defined by a specific real-time application.
RTP Session: As defined by [RFC3550], the endpoints belonging to the
same RTP Session are those that share a single SSRC space. That
is, those endpoints can see an SSRC identifier transmitted by any
one of the other endpoints. An endpoint can receive an SSRC
either as SSRC or as CSRC in RTP and RTCP packets. Thus, the RTP
Session scope is decided by the endpoints' network interconnection
topology, in combination with RTP and RTCP forwarding strategies
deployed by endpoints and any interconnecting middle nodes.
3. Motivation
This section discusses in more detail the main motivations why
allowing multiple media types in the same RTP session is suitable.
3.1. NAT and Firewalls
The existence of NATs and Firewalls at almost all Internet access has
had implications on protocols like RTP that were designed to use
multiple transport flows. First of all, the NAT/FW traversal
solution one uses needs to ensure that all these transport flows are
established. This has three different impacts:
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1. Increased delay to perform the transport flow establishment
2. The more transport flows, the more state and the more resource
consumption in the NAT and Firewalls. When the resource
consumption in NAT/FWs reaches their limits, unexpected behaviors
usually occur.
3. More transport flows means a higher risk that some transport flow
fails to be established, thus preventing the application to
communicate.
Using fewer transport flows reduces the risk of communication
failure, improved establishment behavior and less load on NAT and
Firewalls.
3.2. No Transport Level QoS
Many RTP-using applications don't utilize any network level Quality
of Service functions. Nor do they expect or desire any separation in
network treatment of its media packets, independent of whether they
are audio, video or text. When an application has no such desire, it
doesn't need to provide a transport flow structure that simplifies
flow based QoS.
3.3. Architectural Equality
For applications that don't desire any type of different treatment,
neither on the transport level nor in RTP or RTCP reporting, using
the same RTP session for both media types appears a reasonable
choice. The architecture should be neutral to media type, rather
look at what it provides based on the application users choice.
Therefore this bias should be removed and let the application
designer make the choice if they need multiple RTP sessions or not
based on other aspects.
4. Overview of Solution
The goal of the solution is to enable having one or more RTP
sessions, where each RTP session may contain two or more media types.
This includes having multiple RTP sessions containing a given media
type, for example having three sessions containing video and audio.
The solution is quite straightforward. The first step is to override
the SHOULD and SHOULD NOT language of the RTP specification
[RFC3550]. This is done by appropriate exception clauses given that
this specification is followed.
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Within an RTP session where multiple media types have been configured
for use, a SSRC may only send one media type during its lifetime.
Different SSRCs must be used for the different media sources, the
same way multiple media sources of the same media type already have
to do. The payload type will inform a receiver which media type the
SSRC is being used for. Thus the payload type must be unique across
all of the payload configurations independent of media type that may
be used in the RTP session.
Some few extra considerations within the RTP sessions also needs to
be considered. RTCP bandwidth and regular reporting suppression
(AVPF and SAVPF) should be considered to be configured. Certain
payload types like FEC also need additional rules.
The final important part of the solution to this is to use signalling
and ensure that agreement on using multiple media types in an RTP
session exists, and how that then is configured. Thus document
documents some existing requirements, while an external reference
defines how this is accomplished in SDP.
5. Applicability
This specification has limited applicability and any one intending to
use must ensure that their application and usage meets the below
criteria for usage.
5.1. Usage of the RTP session
Before choosing to use this specification, an application implementer
needs to ensure that they don't have a need for different RTP
sessions between the media types for some reason. The main rule is
that if one expects to have equal treatment of all media packets,
then this specification might be suitable. The equal treatment
include anything from network level up to RTCP reporting and
feedback. The document Guidance on RTP Multiplexing Architecture
[I-D.westerlund-avtcore-multiplex-architecture] gives more detailed
guidance on aspects to consider when choosing how to use RTP and
specifically sessions. RTP-using applications that need or would
prefer multiple RTP sessions, but do not require the functionalities
or behaviors that multiple transport flows give, can consider using
Multiple RTP Sessions on a Single Lower-Layer Transport
[I-D.westerlund-avtcore-transport-multiplexing].
5.2. Signalled Support
Usage of this specification is not compatible with anyone following
RFC 3550 and intending to have different RTP sessions for each media
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type. Therefore there must be mutual agreement to use multiple media
types in one RTP session by all participants within an RTP session.
This agreement must in most cases be determined using signalling.
This requirement can be a problem for signalling solutions that can't
negotiate with all participants. For declarative signalling
solutions, mandating that the session is using multiple media types
in one RTP session can be a way of attempting to ensure that all
participants in the RTP session follow the requirement. However, for
signalling solutions that lack methods for enforcing that a receiver
supports a specific feature, this can still cause issues.
5.3. Homogeneous Multi-party
In multiparty communication scenarios it is important to separate two
different cases. One case is where the RTP session contains multiple
participants in a common RTP session. This occurs for example in Any
Source Multicast (ASM) and Transport Translator topologies as defined
in RTP Topologies [RFC5117]. It may also occur in some
implementations of RTP mixers that share the same SSRC/CSRC space
across all participants. The second case is when the RTP session is
terminated in a middlebox and the other participants sources are
projected or switched into each RTP session and rewritten on RTP
header level including SSRC mappings.
For the first case, with a common RTP session or at least shared
SSRC/CSRC values, all participants in multiparty communication are
required to support multiple media types in an RTP session. An
participant using two or more RTP sessions towards a multiparty
session can't be collapsed into a single session with multiple media
types. The reason is that in case of multiple RTP sessions, the same
SSRC value can be use in both RTP sessions without any issues, but
when collapsed to a single session there is an SSRC collision. In
addition some collisions can't be represented in the multiple
separate RTP sessions. For example, in a session with audio and
video, an SSRC value used for video will not show up in the Audio RTP
session at the participant using multiple RTP sessions, and thus not
trigger any collision handling. Thus any application using this type
of RTP session structure must have a homogeneous support for multiple
media types in one RTP session, or be forced to insert a translator
node between that participant and the rest of the RTP session.
For the second case of separate RTP sessions for each multiparty
participant and a central node it is possible to have a mix of single
RTP session users and multiple RTP session users as long as one is
willing to remap the SSRCs used by a participant with multiple RTP
sessions into non-used values in the single RTP session SSRC space
for each of the participants using a single RTP session with multiple
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media types. It can be noted that this type of implementation is
required to understand any type of RTP/RTCP extension being used in
the RTP sessions to correctly be able to translate them between the
RTP sessions.
5.4. Reduced number of Payload Types
An RTP session with multiple media types in it have only a single
7-bit Payload Type range for all its payload types. Within the 128
available values, only 96 or less if "Multiplexing RTP Data and
Control Packets on a Single Port" [RFC5761] is used, all the
different RTP payload configurations for all the media types must
fit. For most applications this will not be a real problem, but the
limitation exists and could be encountered.
5.5. Stream Differentiation
If network level differentiation of the media streams of different
media types are desired using this specification can cause severe
limitations. All media streams in an RTP session, independent of the
media type, will be sent over the same underlying transport flow.
Any flow-based Quality of Service (QoS) mechanism will be unable to
provide differentiated treatment between different media types, e.g.
to prioritize audio over video. If that is desired, separate RTP
sessions over different underlying transport flows needs to be used.
Any marking-based QoS scheme like DiffServ is not affected unless a
network ingress marks based on flows.
5.6. Non-compatible Extensions
There exist some RTP and RTCP extensions that rely on the existence
of multiple RTP sessions. If the goal of using an RTP session with
multiple media types is to have only a single RTP session, then these
extensions can't be used. If one has no need to have different RTP
sessions for the media types but is willing to have multiple RTP
sessions, one for the main media transmission and one for the
extension, they can be used. It should be noted that this assumes
that it is possible to get the extension working when the related RTP
session contains multiple media types.
Identified RTP/RTCP extensions that require multiple RTP Sessions
are:
RTP Retransmission: RTP Retransmission [RFC4588] has a session
multiplexed mode. It also has a SSRC multiplexed mode that can be
used instead. So use the mode that is suitable for the RTP
application.
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XOR-Based FEC: The RTP Payload Format for Generic Forward Error
Correction [RFC5109] and its predecessor [RFC2733] requires a
separate RTP session unless the FEC data is carried in RTP Payload
for Redundant Audio Data [RFC2198] which has another set of
restrictions.
Note that the Source-Specific Media Attributes [RFC5576]
specification defines an SDP syntax (the "FEC" semantic of the
"ssrc-group" attribute) to signal FEC relationships between
multiple media streams within a single RTP session. However, this
can't be used as the FEC repair packets are required to have the
same SSRC value as the source packets being protected. [RFC5576]
does not normatively update and resolve that restriction.
6. RTP Session Specification
This section defines what needs to be done or avoided to make an RTP
session with multiple media types function without issues.
6.1. RTP Session
Section 5.2 of "RTP: A Transport Protocol for Real-Time Applications"
[RFC3550] states:
For example, in a teleconference composed of audio and video media
encoded separately, each medium SHOULD be carried in a separate
RTP session with its own destination transport address.
Separate audio and video streams SHOULD NOT be carried in a single
RTP session and demultiplexed based on the payload type or SSRC
fields.
This specification changes both of these sentences. The first
sentence is changed to:
For example, in a teleconference composed of audio and video media
encoded separately, each medium SHOULD be carried in a separate
RTP session with its own destination transport address, unless
specification [RFCXXXX] is followed and the application meets the
applicability constraints.
The second sentence is changed to:
Separate audio and video streams SHOULD NOT be carried in a single
RTP session and demultiplexed based on the payload type or SSRC
fields, unless multiplexed based on both SSRC and payload type and
usage meets what Multiple Media Types in an RTP Session [RFCXXXX]
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specifies.
RFC-Editor Note: Please replace RFCXXXX with the RFC number of this
specification when assigned.
TBD: Discussion of the motivations in Section 5.2 of the RTP
Specification [RFC3550].
6.2. Sender Source Restrictions
A SSRC in the RTP session MUST only send one media type (audio,
video, text etc.) during the SSRC's lifetime. The main motivation is
that a given SSRC has its own RTP timestamp and sequence number
spaces. The same way that you can't send two streams of encoded
audio on the same SSRC, you can't send one audio and one video
encoding on the same SSRC. Each media encoding when made into an RTP
stream needs to have the sole control over the sequence number and
timestamp space. If not, one would not be able to detect packet loss
for that particular stream. Nor can one easily determine which clock
rate a particular SSRCs timestamp shall increase with.
6.3. Payload Type Applicability
Most Payload Types have a native media type, like an audio codec is
natural belonging to the audio media type. However, there exist a
number of RTP payload types that don't have a native media type. For
example, transport robustification mechanisms like RTP Retransmission
[RFC4588] and Generic FEC [RFC5109] inherit their media type from
what they protect. RTP Retransmission is explicitly bound to the
payload type it is protecting, and thus will inherit it. However
Generic FEC is a excellent example of an RTP payload type that has no
natural media type. The media type for what it protects is not
relevant as it is the recovered RTP packets that have a particular
media type, and thus Generic FEC is best categorized as an
application media type.
The above discussion is relevant to what limitations exist for RTP
payload type usage within an RTP session that has multiple media
types. When it comes to Generic FEC, is an configured payload type
allowed to be used to protect both audio SSRCs and Video SSRCs? Note
a particular SSRC carrying Generic FEC will clearly only protect a
specific SSRC and thus that instance is bound to the SSRC's media
type. For this specific case, it appears possible to have one be
applicable to both. However, in cases when the signalling is setup
to enable fallback to using separate RTP sessions, then using a
different media type, e.g. application, than the media being
protected can create issues.
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TBD: What recommendations are needed here?
6.4. RTCP
All SSRCs in an RTP session fall under the same set of RTCP
configuration parameters, such as the RR and RS bandwidth and the
trr-int parameter if AVPF or SAVPF is used. This means that at least
the regular reporting period by, and on, a source will be equal,
independent of the media type for that source. This should in most
cases not be an issue, but it may result in more frequent reporting
than is considered necessary for a particular media type or set of
media sources. Having multiple media types in one RTP session also
results in more SSRCs being present in this RTP session. This
increasing the amount of cross reporting between the SSRCs. From an
RTCP perspective, two RTP sessions with half the number of SSRCs in
each will be slightly more efficient. If someone needs either the
higher efficiency due to the lesser number of SSRCs or the fact that
one can't tailor RTCP usage per media type, they need to use
independent RTP sessions.
When it comes to handling multiple SSRCs in an RTP session there is a
clarification under discussion in Real-Time Transport Protocol (RTP)
Considerations for Multi-Stream Endpoints
[I-D.lennox-avtcore-rtp-multi-stream]. When it comes to configuring
RTCP the need for regular periodic reporting needs to be weighted
against any feedback or control messages being sent. The
applications using AVPF or SAVPF are RECOMMENDED to consider setting
trr-int parameter to a value suitable for the applications needs,
thus potentially reducing the need for regular reporting and thus
releasing more bandwidth for use for feedback or control.
Another aspect of an RTP session with multiple media types is that
the used RTCP packets, RTCP Feedback Messages, or RTCP XR metrics
used may not be applicable to all media types. Instead all RTP/RTCP
endpoints need to correlate the media type of the SSRC being
referenced in an messages/packet and only use those that apply to
that particular SSRC and its media type. Signalling solutions may
have shortcomings when it comes to indicate that a particular set of
RTCP reports or feedback messages only apply to a particular media
type within an RTP session.
7. Extension Considerations
This section discusses the impact on some RTP/RTCP extensions due to
usage of multiple media types in on RTP session. Only extensions
where something worth noting has been included.
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7.1. RTP Retransmission
SSRC-multiplexed RTP retransmission [RFC4588] is actually very
straightforward. Each retransmission RTP payload type is explicitly
connected to an associated payload type. If retransmission is only
to be used with a subset of all payload types, this is not a problem,
as it will be evident from the retransmission payload types which
payload types that have retransmission enabled for them.
Session-multiplexed RTP retransmission is also possible to use where
an retransmission session contains the retransmissions of the
associated payload types in the source RTP session. The only
difference to previously is that the source RTP session is one which
contains multiple media types. Thus it is even more likely that only
a subset of the source RTP session's payload types and SSRCs are
actually retransmitted.
Open Issue: When using SDP to signal retransmission for one RTP
session with multiple media types and one RTP session for the
retransmission data will cause a situation where one will have
multiple m= lines grouped using FID and the ones belonging to
respective RTP session being grouped using BUNDLE. This usage may
contradict both the FID semantics [RFC5888] and an assumption in the
RTP retransmission specification [RFC4588].
7.2. Generic FEC
TBW:
8. Signalling
The Signalling requirements
Establishing an RTP session with multiple media types requires
signalling. This signalling needs to fulfill the following
requirements:
1. Ensure that any participant in the RTP session is aware that this
is an RTP session with multiple media types.
2. Ensure that the payload types in use in the RTP session are using
unique values, with no overlap between the media types.
3. Configure the RTP session level parameters, such as RTCP RR and
RS bandwidth, AVPF trr-int, underlying transport, the RTCP
extensions in use, and security parameters, commonly for the RTP
session.
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4. RTP and RTCP functions that can be bound to a particular media
type should be reused when possible also for other media types,
instead of having to be configured for multiple code-points.
Note: In some cases one will not have a choice but to use
multiple configurations.
8.1. SDP-Based Signalling
The signalling of multiple media types in one RTP session in SDP is
specified in "Multiplexing Negotiation Using Session Description
Protocol (SDP) Port Numbers"
[I-D.ietf-mmusic-sdp-bundle-negotiation].
9. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
10. Security Considerations
Having an RTP session with multiple media types doesn't change the
methods for securing a particular RTP session. One possible
difference is that the different media have often had different
security requirements. When combining multiple media types in one
session, their security requirements must also be combined by
selecting the most demanding for each property. Thus having multiple
media types may result in increased overhead for security for some
media types to ensure that all requirements are meet.
Otherwise, the recommendations for how to configure and RTP session
do not add any additional requirements compared to normal RTP, except
for the need to be able to ensure that the participants are aware
that it is a multiple media type session. If not that is ensured it
can cause issues in the RTP session for both the unaware and the
aware one. Similar issues can also be produced in an normal RTP
session by creating configurations for different end-points that
doesn't match each other.
11. Acknowledgements
The authors would like to thank Christer Holmberg for the feedback on
the document.
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12. References
12.1. Normative References
[I-D.ietf-mmusic-sdp-bundle-negotiation]
Holmberg, C. and H. Alvestrand, "Multiplexing Negotiation
Using Session Description Protocol (SDP) Port Numbers",
draft-ietf-mmusic-sdp-bundle-negotiation-00 (work in
progress), February 2012.
[I-D.lennox-avtcore-rtp-multi-stream]
Lennox, J. and M. Westerlund, "Real-Time Transport
Protocol (RTP) Considerations for Multi-Stream Endpoints",
July 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
12.2. Informative References
[I-D.westerlund-avtcore-multiplex-architecture]
Westerlund, M., Burman, B., and C. Perkins, "RTP
Multiplexing Architecture",
draft-westerlund-avtcore-multiplex-architecture-01 (work
in progress), March 2012.
[I-D.westerlund-avtcore-transport-multiplexing]
Westerlund, M. and C. Perkins, "Multiple RTP Sessions on a
Single Lower-Layer Transport",
draft-westerlund-avtcore-transport-multiplexing-02 (work
in progress), March 2012.
[RFC2198] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V.,
Handley, M., Bolot, J., Vega-Garcia, A., and S. Fosse-
Parisis, "RTP Payload for Redundant Audio Data", RFC 2198,
September 1997.
[RFC2733] Rosenberg, J. and H. Schulzrinne, "An RTP Payload Format
for Generic Forward Error Correction", RFC 2733,
December 1999.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
Westerlund, et al. Expires January 10, 2013 [Page 14]
Internet-Draft Multiple Media Types in an RTP Session July 2012
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
July 2006.
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error
Correction", RFC 5109, December 2007.
[RFC5117] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117,
January 2008.
[RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific
Media Attributes in the Session Description Protocol
(SDP)", RFC 5576, June 2009.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
Control Packets on a Single Port", RFC 5761, April 2010.
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description
Protocol (SDP) Grouping Framework", RFC 5888, June 2010.
Authors' Addresses
Magnus Westerlund
Ericsson
Farogatan 6
SE-164 80 Kista
Sweden
Phone: +46 10 714 82 87
Email: magnus.westerlund@ericsson.com
Colin Perkins
University of Glasgow
School of Computing Science
Glasgow G12 8QQ
United Kingdom
Email: csp@csperkins.org
Westerlund, et al. Expires January 10, 2013 [Page 15]
Internet-Draft Multiple Media Types in an RTP Session July 2012
Jonathan Lennox
Vidyo, Inc.
433 Hackensack Avenue
Seventh Floor
Hackensack, NJ 07601
US
Email: jonathan@vidyo.com
Westerlund, et al. Expires January 10, 2013 [Page 16]
