wdiff rfc4637.original rfc4637.txt

INTERNET-DRAFT
Network Working Group J. Ott/C. Ott
Request for Comments: 4637 Helsinki University of Technology
Category: Informational C. Perkins
Expires: November 2003 TZI/ISI
15 May 2003

SDPng
University of Glasgow
January 2007

Transition
draft-ietf-mmusic-sdpng-trans-04.txt from the Session Description Protocol (SDP) to
SDP Next Generation (SDPng)

Status of this memo This document is an Internet-Draft and is subject to all provisions
of Section 10 of RFC2026.

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This document is a product of the Multiparty Multimedia Session
Control (MMUSIC) working group of the Internet Engineering Task
Force. Comments are solicited and should be addressed to the working
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Abstract

Today, the Session Description Protocol (SDP) is today widely used in the
Internet to announce as well as negotiate multimedia sessions and
exchange capabilities. Having originally been designed for session
announcements only, as opposed to announcements and capabilities
negotiation announcements, native SDP lacks numerous features to be
applicable in many session scenarios. Numerous extensions have been
developed to circumvent SDP's shortcomings -- shortcomings, but they have also
repeatedly shown its inherent limitations. A successor protocol -- protocol,
termed "SDPng" for the time being -- is being, has been developed to address the
aforementioned needs of Internet applications in a more structured
manner. With the huge installed base of SDP-based applications, a
migration path needs to be developed to move from SDP to SDPng over
time. This document outlines how this migration can be achieved: in
general as well as for the various IETF control protocols that
potentially make use of SDP and SDPng.

1. Introduction

SDP is now widely used within the Internet community to describe
media sessions and, in a limited fashion, system capabilities
relating to (multi)media sessions, for a variety of application
scenarios: session announcements, interactive session setup,
capability assessment assessment, and remote control of media streams. All but
the first of these are rather different from what SDP was originally
designed for -- for, but all of them share the idea of setting up and
configuring media streams. Over time, its wide range of uses has
revealed numerous shortcomings -- shortcomings, most of which stem from the fact that
SDP has been used for lack of a better alternative and its semantics
have been re-interpreted to make it fit the respective scenarios'
needs. In many cases, workrounds workarounds (typically called "extensions")
for those shortcomings could be found which that are often rather
cumbersome. While this practice has extended SDP's lifetime and
provided at least a suitable basis for numerous applications, in
parallel, a successor protocol -- protocol, currently referred to as "SDPng"
-- "SDPng", has
been developed.

It is worthwhile noting

Note that the aforementioned applications' needs are sufficiently
similar for a single description protocol to take care of them if
it was designed for this purpose from the beginning. As a lesson
learned from SDP, any further expansion in scope should be avoided
where no clear fit can be
seen -- seen, and specific (different) solutions
should be developed instead.

The design of SDPng takes into account the requirements arising from
the above application scenarios and puts particular emphasis on
protocol extensibility and modularization of extensions, at the same
time keeping the core description format simple. SDPng uses a
different (more expressive) syntax than SDP does and hence is not
backward compatible at the syntax level. Nevertheless, the concepts
of SDPng take into account the migration issues from SDP to SDPng by
providing straightforward mappings between the two formats where
possible and try to maximize compatibility from a semantics
perspective.

The current revisions of SDP and SDPng are documented in

o draft-ietf-mmusic-sdp-new-12.txt SDP: Session Description Protocol [1] and

o draft-ietf-mmusic-sdpng-06.txt Session Description and Capability Negotiation [9].

For SDP, a number of additional features are defined in the following
documents that need to be taken into account:
account are defined in the following documents:

o the offer/answer scheme of interpreting and matching media session
descriptions to negotiate media sessions to be used in call or
conference in a single round-trip (RFC 3264 [6]);

o full support for IPv6 as the network layer protocol (RFC 3266
[2]);

o SDP extensions to allow selecting ATM Asynchronous Transfer Mode (ATM)
virtual circuits as an additional network protocol and specifying
ATM-specific parameters (RFC 3108 [3]);
o a general extension to deal with connection-oriented transport
protocols such as TCP [12];

o an extension to support SCTP Stream Control Transmission Protocol
(SCTP) as a media transport protocol in addition to UDP and TCP
[17];

o an SDP extension to explicitly specify RTCP the RTP Control Protocol
(RTCP) port number to enable the necessary expressiveness for NAT
Network Address Translation (NAT) traversal [8];

o a mechanism (media identification, "mid") for naming and grouping
("group") SDP media lines according to one or more criteria, e.g. e.g.,
for the purpose of lip-synchronization or for identifying media
sessions carrying the same content (RFC 3388 [4], [10]);

o the capability to indicate which media sessions shall be mapped
into the same resource reservation context [13];

o an extension to allow expression of simultanous simultaneous capabilities
across media sessions and formats (RFC 3407 [5])

o attributes for passing parameters of a keying protocol (such as
MIKEY)
Multimedia Internet KEYing (MIKEY)) as part of a session
description [11];

o support for conveying cryptographic parameters as part of a
session description [15];

o a mechanism to explicitly specify the sources allowed to provide
input to media sessions [16]; and

o a simple language to provide instructions to media mixers on which
incoming media streams shall be combined to produce which outgoing
ones (and possbily possibly how they shall be combined) [14].

This document outlines a migration path from SDP to SDPng, starting
from a short overview of the current application scenarios. In the
next step, we highlight which design decisions taken for SDPng should
simplify a smooth migration and describe how mappings between the two
description formats can be performed at an abstract level. We then
address procedural issues for integrating SDP and SDPng into the
various protocols relying on those media description formats.
Finally, we summarize work items on the agenda for SDPng.

2. Application Scenarios

The following session control protocols that make use of SDP have
been standardized in the IETF so far:

1. SDP was originally developed to announce (Mbone-based) multimedia
sessions via session directories using the Session Announcement
Protocol (SAP) -- (SAP), but other mechanisms for disseminating the session
descriptions (such as HTTP, SMTP,
NNTP, etc.) and Network News Transfer
Protocol (NNTP)) are conceivable as well.

The major property of this application scenario is that the
creator of the session description defines a (set of) fixed
choice(s) for all media types in a conference and the conference
partipants
participants have no way to influence these. If they support at
least one of the codecs for a particular media type they can
participate in this media session, otherwise they cannot. There
is no interaction between sender(s) and receiver(s) to negotiate
the media stream codecs and parameters.

This scenario is referred to as "announcement".

2. Another use of SDP is in conjunction with the Real-Time Streaming
Protocol (RTSP). In RTSP, SDP is used to convey descriptions of a
media stream interactively requested to be played from a server
(or recorded by a server). SDP itself is not used for capability
negotiation, not even for the addresses to be used; those are
negotiated within RTSP and may override the addresses specified as
part of SDP.

This scenario is referred to as "retrieval".

3. With SIP, SDP is used to propose media stream configurations and
choose out of these (i.e. (i.e., enable a subset of these). By
proposing and accepting media stream configurations, endpoints use
SDP to implicitly describe their capabilities and carry out a
negotiation procedure on the media streams to use.

In the context of SIP, specific meanings (including required
extensions) have been defined for use of SDP with unicast
addresses, for connection-oriented transports, and for certain
media level
media-level attributes (such as the direction attribute send-
only, send-only,
receive-only, and inactive).

Numerous extensions have been proposed to extend SDP to better
suit SIP's needs. Besides a description of the offer/answer
model, these extensions particularly include the ability to
describe simultaneous capabilites capabilities and to group media stream
semantically.

This scenario is referred to as "offer/answer".

4. SDP is used to convey the capability descriptions of a MEGACO
media gateway (MG) to its media gateway controller (MGC) as well
as for the MGC to instruct the MG where to send media streams to
and from where to receive media streams, including codec and
parameter choice.

For this purpose, SDP has been modified/extended to some degree to
fit the MEGACO needs.

This scenario is referred to as "gateway control".

It should noted

Note that the original SDP concept already provided an extension
mechanism to cover other network types than IPv4 and IPv6; however,
specific extensions have only been defined recently for ATM and are
now under discussion for TDM. time division multiplexing (TDM) networks.
Extensions to other transport (including radio interfaces or next next-
generation wireless networks) as well as to new types of session
descriptions (e.g. (e.g., electronic program guides) are conceivable.

3. Mapping SDP to SDPng

On a transition path from SDP to SDPng, allowing for a somewhat
straightforward mapping of (parts of) one description format onto the
other is of crucial importance. SDPng has been designed in a way
that allows many of the session description features of SDP to be
easily mapped onto the SDPng format and vice versa -- versa, except that SDPng
is more expressive than SDP and hence information loss is not
unlikely to occur when doing the reverse mapping. The final mapping
rules between SDP and SDPng to be drawn up shall ensure that when mapping
SDP to SDPng and then back to SDP will produce an SDP that is
functionally identical to the one originally fed into the mapping
process. Note that the use of a number of SDP extensions (FID,
SIMCAP) may be implied in this mapping process, depending on the use
of SDP. The mapping rules will ensure that no information loss will
occur when translating from SDP to SDPng.

The SDPng design uses a structure of four sections: definitions,
potential or actual configurations, constraints constraints, and session
attributes. Of these, the "Configurations" and "Session Attributes"
sections map well onto the current SDP. The "Definitions" and
"Constraints" sections provide additional structure which that is not
directly expressible in SDP.

o At the media description level, the Potential and Actual
Configurations specified in the "Configurations" section maps well
to media descriptions ("m=", possibly "c=", and associated
attributes ("a=") lines).

o At the session description level, the SDP session parameters are
largely reflected in the "Session Attributes" section of SDPng.
The attributes proven suitable for session announcements have been
used as the basis when for defining SDPng.

In SDPng, media descriptions are explicitly tagged with identifiers
and thus are easily referenced for semantically grouping media
streams (e.g. (e.g., to describe alternative audio in different languages,
media streams to be synchronized, or media streams to carry the same
information simultaneously but with different encodings) -- encodings), as has been
defined for SDP in a limited fashion by the "fid" attribute set.
SDPng allows for an even to more formally describe formal description of the syntax of
individual or compound media streams in the "Session Attributes"
section. Furthermore, SDPng supports a superset of additional
constraints that may be realized by the "simcap" extensions for SDP
in the "Constraints" section.

Additional address families such as ATM or TDM bearers, next
generation wireless network bearers, DVB channels, etc. can be
incorporated into SDPng by defining the appropriate extensions for
the SDPng transports.

Similarly, new codecs can be added by just defining new codec
specifications or defining entire new classes of applications to be
described as new content types ("codec") to be carried in a media
session (including e.g. (including, e.g., text, fax, slide presentations, and shared
editors, etc).
editors). If necessary, sophisticated parameter structures can be
supported (even though the authors believe that simplicity is key to
interoperability here). This is similar to, but more structured
than, the definition of new codec attributes in MIME registrations
for SDP.

Note that it is expected that the MIME namespace for codecs will
be mapped into the SDPng namespace, and a consistent mapping from
SDP "a=fmtp:" attributes to SDPng codec parameters will be
defined.

By means of its conceptual differentiation into Potential and Actual
Configurations, SDPng supports both 1) indicating a system's
capabilities (without specifying transport addresses) separately from
the instantiation of a particular media stream as well as and 2) conveying
capability descriptions and instantiation proposals at the same time
-- time,
thereby providing a good fit for all the above session control
scenarios: the "announcement" and "retrieval" scenarios will just use
rather fixed Actual Configurations. The "offer/answer" model will
use use Actual Configuration Configurations but use them to negotiate media
strams streams in
a two-way handshake but may in addition use Potential Configurations
to indicate capabilities that shall not be used immediately. The
"gateway control" scenario will use both: Potential Configurations
to describe an MG's capabilities and Actual Configurations for
setting up media sessions at MGs as well as retrieving information
about currently active media sessions. This differentiation is not
directly expressible in SDP, although various extensions can be used
to overload SDP semantics to achieve at least part of this effect.

Finally, while the short-term SDPng specification aims at supporting
only the widespread offer/answer model for capability negotiation, a
future extension will also allow for content-independent negotiation
of session parameters by defining collapsing/intersection rules. In
particular, SDPng will take the need for multicast-based distributed
calculation of joint capabilities into account for those rules (but
note that it is *not* intended as a generic format for describing
conference state information). Such functionality is not covered by
current SDP -- SDP, but there is also no perceived urgent demand demand, so that this
sophisticated functional component of SDPng is left to a future
protocol extension. The base SDPng protocol will provide the
necessary flexibility, however.

4. Integration with Session Control Protocols

This section outlines for

For each of the session control protocols described above above, this
section outlines how SDP and SDPng can be used in parallel and
indicates how a suitable transition could be achieved.

4.1. Session Announcement Protocol (SAP)

There are two revisions of SAP specified, version 0 0, which is
implemented in a number of experimental tools, and version 1 1, which
is defined in RFC 2972.

SAPv0:SAPv0 2974 [18].

SAPv0: SAPv0 does not support a mechanism to identify the content
type of a session announcement but implicitly assumes SDP.
Proper parsers will note that the contents of the SAPv0
message does not begin with a "v=" line and hence will ignore
the entire announcement. SDPng contents MAY may be identified by
a different character sequence in the beginning of the
announcement body, but this is not recommended. Instead,
SAPv1 should be used, since it contains an explicit payload
identifier.

SAPv1:In

SAPv1: In SAPv1, an explicit payload type field (containing a MIME
type) is available and should be used to differentiate between
SDP anf and SDPng contents. Two approaches are conceivable:
Either multipart MIME message is used with two parts
containing the same session descriptions -- descriptions, one expressing it in
SDP and the other in SDPng. Alternatively, SDPng or, alternatively, two alternate
session announcements may be used (being properly
distinguished by the SDP "o=" field and the SDPng equivalent).

It is recommended that implementations recognize the MIME
multipart/alternative type in SAPv1 announcements, allowing
for a simple transition to SDPng.

It should be noted

Note that current session directory implementations only support SDP.
Nevertheless, using the SAP Message Identifier Hash and the source
address, they should be able to perform session deletions and
modifications properly -- properly, even without understanding the format
contained in the SAP message body.

For the introduction of SDPng, session announcements should be made
"bi-lingual", i.e. i.e., in SDP and SDPng. If a SAP announcer for some
reason knows that all its potential audience will support SDPng, the
SDP announcement should be omitted.

It should be noted that,

Note that for IPv4-based multicast sessions, session directories
still may rely on parsing the session specifications to avoid clashes
in the multicast address space. Introducing a new session
description language will prevent older implementations from
continuing this practice successfully -- successfully, assuming that only SDPng
announcements are used and/or that old implementations do not support
MIME multipart/alternative message bodies. This use of SAP is
deprecated, however.

4.2. Real-Time Streaming Protocol (RTSP)

RTSP uses SDP to provide presentation descriptions (with a
presentation comprising one or more media sessions), typically
communicated from the server to the client (for playing) for playing and in the
opposite direction for recording. The presentation description may
also include initialization data for the various media streams and
URLs to be used for controlling the entire presentation as well as
the individual media sessions. Transport parameters -- such (such as IP
addresses, port numbers, etc. -- etc.) are conveyed as part of the RTSP
header fields.

RTSP uses the Content-Type: header field to indicate the format of
the enclosed entity. This provides a straightforward means for
distinguishing SDP and SDPng-based presentation descriptions. In
addition, the Accept: header should be used by the client to indicate
which content types it supports. If the client specifies both SDP
and SDPng as acceptable, the server should provide only the SDPng-
based presentation description.

If the client does not indicate a particular Content-Type: Content-Type:, the
server can, theoretically, use MIME multipart bodies (e.g. (e.g.,
"multipart/alternative") to convey both description types
simultaneously. However, it is generally not expected that today's
RTSP clients and servers will be able to handle multipart bodies.
Hence, if no hint is provided by the client by means of the Accept:
header, the server must provide only an SDP description.

In general, it would be preferrable preferable to have the servers migrate to
always supporting both description formats, thus enabling the clients
to choose. The servers should indicate SDPng support by means of
suitable header fields whenever possible.

Finally, RTSP makes special provision provisions to interwork with firewalls by
including the crucial transport parameters in a separate RTSP header
field _in_addition_ in addition to the presentation description. This practice, in
principle, allows to change for changing the presentation description format
without having to worry about the operation of firewalls and similar
devices.

4.3. Session Initiation Protocol (SIP)

The use of SDP with SIP follows the offer/anser offer/answer model and is
described in [6]. It is key to the (efficiency of the) offer/answer
model that a complete capability exchange and media stream
instantiation be carried out in one round-trip -- round-trip, which is supported
by SDP. While SDPng allows to separate a separating capability exchange from
media sesssion session instantiation, those two pieces are also easily
integrated in a single step.

SIP also uses a Content-Type: header to indicate the nature of data
carried in its message body; body, and SIP explicitly calls for supporting
MIME multipart message bodies. While, again, the use of MIME
multipart/alternative would in principle be possible (from a
theoretical perspective), issues regarding the actual implementation
of multipart/alternative in SIP entities have been raised. As
backward compatibility has to be achieved, a different approach is
suggested:

A SIP UAC MAY User Agent Client (UAC) may use an SDPng message body in a SIP
INVITE (or other) message. If the SIP UAS User Agent Server (UAS) does
not support SDPng, it will return a "415 Unsupported Media Type"
response to the UAC and indicate acceptable content types in the
Accept: header (probably including "application/sdp"). The SIP UAC
must then retry the INVITE (or other) message using the indicated
session description language. The SIP UAC should cache knowledge
about which peers did not understand SDPng as session description
formats for a limited amount of time (e.g. (e.g., several days) so that
extra round-trips for session setup are only incurred infrequently.
Whenever a peer has sent an SDPng description (or it is known from
other means that the peer supports SDPng), this information should
also be cached.

The SIP Accept: header can be exploited to determine the capability
of a peer to understand SDPng in addition to (or instead) instead of) plain
SDP. Methods such as OPTIONS MAY may be used to determine a peer's
support for SDPng. However, a peer's capabilities may not be known
when the first message is sent sent, which may introduce an extra round-trip round-
trip if including SDP and SDPng in the initial INVITE message is not
an option. Further approaches to make a UA's support for SDPng known
ahead of time should be explored.

A number of SDP extensions have been motivated by SIP-based
applications
applications, and these need to be accommodated in SDPng as well.
Features such as "simcap" and "FID" are inherently supported by
SDPng; proper definitions for connection-oriented media need to be
fully understood and then incorporated. Key management attributes as
(as defined in [11] [11]) need to be included (not just for SIP) and so
general mechanisms may also need to be general mechanisms included to signal security
capabilities [11] [15] and to indicate their optional or mandatory
use. The same applies to quality Quality of service Service (QoS) parameters [13]
(which are largely also motivated by SIP but are also useful with
control protocols).

Numerous extensions to SDP have been developed for the purpose of
supporting certain SIP requirements -- actually requirements; actually, most of those listed
in section 1. 1 fall into this category. The following paragraphs
address how those are handled by and mapped to SDPng.

IPv6 is natively supported by SDPng. For other network protocols -- protocols,
such as ATM and TDM, which have only come up in the context of
MEGACO, see below -- similar below. Similar SDPng packages need to be defined that
provide the same information as the corresponding SDP extensions.

Support for connection-oriented media in general will be supported in
SDPng using a similar parameterization. Support for SCTP will be
equivalent to the approach taken for SDP as the parameters are
comparable.

SDP's explicit RTCP port number parameter (that helps with NAT
traversal) is inherently available in the RTP Real-time Transport
Protocol (RTP) transport specification of SDPng.

Media session identification is also provided by the SDPng spec by
means of naming attributes in the potential as well as actual
configurations. The "Session Attributes" section of SDPng is meant
to provide meta-information about the media sessions such as grouping
of lip synchronization, lip-synchronization, indicating streams semantics, etc. This
section is also the place to express media "mixing" attributes as
discussed in [14]. QoS parameterizations for SDPng are developed
separately as package enhancements and are still under discussion.

Simultaneous capabilities are dealt with by the Constraints section
of SDPng where restrictions across several components as well as
within a single component can be expressed.

Security parameters have not yet been developed for the SDPng
specification. The intention is to define a separate security
package (similar to codec and transport definitions). Security
parameters may be provided in the definition section for later
reference from within the component specification or may be specified
inline
in-line in a component.

Indicating permissible sources for unicast and particularly multicast
media sessions is already covered in the basic SDPng transport
specification.

In summary, most of the newly developed SDP attributes and their
usages have either have been considered in the SDPng base specification
and the transport packagaes packages or will be added as additional attributes
or as separate packages.

Note that the above discussions are not just applicable to SIP but
may be used in a broader scope (e.g. (e.g., with RTSP or MEGACO).

4.4. Media Gateway Control Protocol (MEGACOP)

The MEGACO specification already supports two different encodings for
capability and media stream descriptions: a text-based variant based
upon (a modified) SDP and a binary representation of the same
information set. MGCs are required to implement both encodings while encodings,
whereas MGs have the choice to pick either or both. Differentiation
between the protocol encoding variants is done using different port
numbers: 2944 for the text-based and 2945 for the binary encoding.

Unfortunately, within the text-based encoding, there is no means to
differentiate several description formats. SDP messages are carried
as an "octet string" without any type identifier. Defining a third
port number for this further differentiation does not seem to be
appropriate, particularly since the message encoding is still a text
format.

The remaining means for distinction is that an SDP specification
would start with a "v=0" line while an SDPng document would begin
with a different character sequence.

Note that MEGACOP also supports a binary encoding for SDP
messages; current practice seems to favor the text encoding for
SDP and hence we will not address a binary encoding for SDPng.

Within the context of MEGACO, various extensions to SDP have been
defined, addressing its use for capability description and also
defining support for further network types (presently, ATM and TDM).
Capability descriptions are inherently supported by SDPng. To add
support for further networks, the respective parameters need to be
defined as network-specific SDNng packages.

5. SDPng and Middleboxes

Middleboxes (e.g. (e.g., firewalls, NATs, and NAPTs) are of significant
importance for many deployment scenarios for SDP-based signaling
protocols. The SDP description typically carries addressing
paramaters
parameters for media sessions which that may be invalidated by middleboxes:
by firewalls because they block packet destined at the respective
addresses and by NA(P)Ts because they change the addresses that must
actually be used.

A number of approaches have been devised to deal with currently
deployed and, eventually, future middleboxes: 1) co-locating a proxy
for the respective signaling protocol(s) with a middlebox, 2) using
extra protocols to determine the presence and the mode of operation
of a NA(P)T (which does not work for firewalls), and 3) the
definition of a control protocol for middleboxes. While approach 1)
is entirely up to the manufacturers of middleboxes, 2) and 3) are
subject to IETF standardization in the MIDCOM WG. Working Group.

1) Proxies that are incorporated in middleboxes to parse and (in the
case of NATs) possibly alter the contents of session descriptions
exchanged in the signaling path will need to implement SDPng in
the future. For a (potentially long) interim period, both SDP and
SDPng need to be supported by such devices.

2) If entities involved in the respective signaling path use
protocols such as STUN Simple Traversal of the UDP Protocol through NAT
(STUN) to determine the presence of a NAT and its mode of
operation, it is up to these entities to include the correct
addressing information in the SDP or SDPng session descriptions.
NATs continue to operate as before and do not require any changes
because of a migration from SDP to SDPng.

3) If local signaling servers or other entities use a MIDCOM protocol
to configure a firewall or NAT to allow certain media streams to
pass through, again, no changes need to be made to MIDCOM-enabled
firewalls. The migration from SDP to SDPng is transparent to
them; only the involved signaling component need needs to support --
SDPng, but they would need to do so anyway.

6. Directing the Evolution of SDP

With the transition from SDP to SDPng, there is the question of the
evolution of SDP, SDP and the legacy systems which that use it.

The SDP specification [1] is stable, and mostly corrects errors in
the original specification, with the addition of very few new
features. The revision is expected to be published as a proposed
standard RFC shortly, obsoleting RFC 2327.

A number of extensions to
SDP for use in offer/answer scenarios are also available. These
include grouping [4] and capability negotiation [5], which have recently been approved
published as proposed standard RFCs, bringing minimal
capability/alternative descriptions to SDP.

Related is the SDP offer/answer model for SDP, published as RFC3264 RFC 3264
[6]. This defines the model used to complete the steps of a
negotiation using SDP. A similar mode of operation will be provided
for SDPng for baseline operation with SIP (and possibly RTSP).

All these are subsumed into SDPng, so there should be no further need
for development in these areas; applications with requirements that
are not met by these specifications should use SDPng.

There have recently been proposals to add quality of service
negotiation for SDP and, similarly, we expect other extensions to be
proposed over time. Due to the well-known limitations of SDP, we do
not believe it appropriate to continue development of more elaborate
extensions: for negotiation, for QoS, for security, and for other
general-purpose or application-specific needs.

The exceptions to this rule are clearly the addition of security
features to SDP (which are required for many current SDP deployment
scenarios) as well as minor extensions for media session attributes
(e.g.
(e.g., indicating the use of joint vs. separate resource reservations
as documented in [7]).

Overall, new work should be done in the framework of SDPng where
applications and their requirements for (new) expressiveness in end-
to-end exchanges to negotiate and configure media sessions will
hopefully act as a driver for that process.

7. IANA Considerations

The transition from SDP to SDPng will require IANA to define new
parameter registries, which will be created and populated as SDPng
evolves. This memo does not, in itself, require any action by IANA.

8. Security Considerations

Since SDPng performs largely the same role as SDP+extensions, it is
not expected that there will be significant new security
considerations as a result of the transition. The security
considerations section of [9] provides further details.

During the transition process process, it is likely that dual descriptions
will be common. There is a potential for inconsistancy inconsistency between
definitions, which may have unintended consequences if one part of
the system, for example a middlebox, interprets the SDP format whilst
definition while another interprets the SDPng format definition.

9. Author's Addresses

Joerg Ott <jo@tzi.org>
Universitaet Bremen
MZH 5180
Bibliothekstr. 1
D-28359 Bremen
Germany
tel:+49-421-201-7028
sip:jo@tzi.org

Colin Perkins <csp@csperkins.org>
USC Information Sciences Institute
3811 North Fairfax Drive, Suite 200
Arlington, VA 22203
USA
tel:+1-703-812-3705

10. References

9.1. Normative References

[1] Mark Handley, Van M., Jacobson, Colin V., and C. Perkins, "SDP: Session
Description Protocol," Internet Draft draft-ietf-mmusic-sdp-
new-11.txt, Work in Progress, November 2002. Protocol", RFC 4566, July 2006.

[2] Sean Olson, Gonzalo S., Camarillo, Adam G., and A.B. Roach, "Support for IPv6 in
Session Description Protocol (SDP)", RFC 3266, June 2002.

[3] 3108 Kumar, R. Kumar and M. Mostafa, "Conventions for the use of the
Session Description Protocol (SDP) for ATM Bearer Connections," Connections",
RFC 3108, May 2001.

[4] Gonzalo Camarillo, Jan Holler, Goran AP G., Eriksson, Henning G., Holler, J., and H. Schulzrinne,
"Grouping of media lines Media Lines in SDP," the Session Description Protocol
(SDP)", RFC 3388, December 2002.

[5] Flemming Andreasen, "SDP F., "Session Description Protocol (SDP) Simple
Capability Declaration," Declaration", RFC 3407, October 2002.

[6] Jonathan Rosenberg Rosenberg, J. and Henning H. Schulzrinne, "An Offer/Answer Model with SDP,"
Session Description Protocol (SDP)", RFC 3264, June 2002.

[7] Camarillo, G. Camarillo and A. Monrad, "Mapping of Media Streams to
Resource Reservation Flows", RFC 3524, April 2003.

[8] Christian Huitema, "RTCP C., "Real Time Control Protocol (RTCP) attribute in SDP," Internet Draft
draft-ietf-mmusic-sdp4nat-03.txt, Work in Progress, September
2002.

10.1.
Session Description Protocol (SDP)", RFC 3605, October 2003.

9.2. Informative References

[9] Dirk Kutscher, Joerg D., Ott, Carsten J., and C. Bormann, "Session Description and
Capability Negotiation", Internet Draft draft-ietf-mmusic-
sdpng-06.txt, Work in Progress, March 2003. Progress.

[10] Gonzalo Camarillo Camarillo, G. and Jonathan J. Rosenberg, "The Alternative Semantics for
the Session Description Protocol Grouping
Framework," Internet Draft draft-camarillo-mmusic-alt-00.txt, Framework", Work in
Progress, February 2003.

[11] Jari Arkko, Elisabetta Carrarra, Fredrik J., Lindholm, Mats F., Naslund,
and Karl M., Norrman, K. and E.
Carrara, "Key Management Extensions for SDP Session Description
Protocol (SDP) and
RTSP," Internet Draft draft-ietf-mmusic-kmgmt-ext-06.txt, Work
in Progress, February 2003. Real Time Streaming Protocol (RTSP)", RFC
4567, July 2006.

[12] David Yon, "Connection-Oriented D. and G. Camarillo, "TCP-Based Media Transport in SDP,"
Internet Draft draft-ietf-mmusic-sdp-comedia-05.txt, Work in
Progress, March 2003. the
Session Description Protocol (SDP)", RFC 4145, September 2005.

[13] G. Camarillo (ed), W. Marshall (ed), Camarillo, G., Marshall, W., and J. Rosenberg, "Integration of
Resource Management and SIP", Internet Draft draft-ietf-sip-
manyfolks-resource-03.txt, Work in Progress, November 2001. Session Initiation Protocol (SIP)", RFC
3312, October 2002.

[14] G. Camarillo, H. G., Schulzrinne, H., and E. Burger, "The source and
sink attributes for the Session Description Protocol", Internet
Draft draft-camarillo-mmusic-source-sink-00.txt, Work in
Progress, September 2002.

[15] Mark Andreasen, F., Baugher, "SDP M., and D. Wing, "Session Description
Protocol (SDP) Security Descriptions for Media Streams",
Internet Draft draft-ietf-mmusic-sdescriptions-00.txt, Work in
Progress, February 2003. RFC
4568, July 2006.

[16] Quinn, B. Quinn and R. Finlayson, "SDP "Session Description Protocol (SDP)
Source-Filters", Internet
Draft draft-ietf-mmusic-sdp-srcfilter-04.txt, Work in Progress,
April 2003. RFC 4570, July 2006.

[17] Robert Fairlie-Cuninghame, R., "Guidelines for specifying SCTP-
based SCTP-based
media transport using SDP," Internet Draft draft-fairlie-
mmusic-sdp-sctp-00.txt, SDP", Work in Progress, May 2001.

11.

[18] Handley, M., Perkins, C., and E. Whelan, "Session Announcement
Protocol", RFC 2974, October 2000.

Authors' Addresses

Joerg Ott
Helsinki University of Technology
Networking Laboratory
PO Box 3000
02015 TKK
Finland

EMail: jo@acm.org

Colin Perkins
Department of Computing Science
University of Glasgow
17 Lilybank Gardens
Glasgow G12 8QQ
UK

EMail: csp@csperkins.org

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