draft-ietf-mmusic-sdp-new-18.txt   draft-ietf-mmusic-sdp-new-19.txt 
Network Working Group M. Handley Network Working Group M. Handley
Internet-Draft UCL Internet-Draft UCL
Obsoletes: 2327, 3266 (if V. Jacobson Obsoletes: 2327, 3266 (if V. Jacobson
approved) Packet Design approved) Packet Design
Expires: December 10, 2004 C. Perkins Expires: February 9, 2005 C. Perkins
University of Glasgow University of Glasgow
June 11, 2004 August 11, 2004
SDP: Session Description Protocol SDP: Session Description Protocol
draft-ietf-mmusic-sdp-new-18.txt draft-ietf-mmusic-sdp-new-19.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, I certify that any applicable By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed, patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with and any of which I become aware will be disclosed, in accordance with
RFC 3668. RFC 3668.
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This Internet-Draft will expire on December 10, 2004. This Internet-Draft will expire on February 9, 2005.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract Abstract
This memo defines the Session Description Protocol (SDP). SDP is This memo defines the Session Description Protocol (SDP). SDP is
intended for describing multimedia sessions for the purposes of intended for describing multimedia sessions for the purposes of
session announcement, session invitation, and other forms of session announcement, session invitation, and other forms of
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . 3 2. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . 3
3. Examples of SDP Usage . . . . . . . . . . . . . . . . . . . 3 3. Examples of SDP Usage . . . . . . . . . . . . . . . . . . . 3
3.1 Multicast Session Announcement . . . . . . . . . . . . . . 3 3.1 Multicast Session Announcement . . . . . . . . . . . . . . 3
3.2 Session Initiation . . . . . . . . . . . . . . . . . . . . 4 3.2 Session Initiation . . . . . . . . . . . . . . . . . . . . 4
3.3 Streaming media . . . . . . . . . . . . . . . . . . . . . 4 3.3 Streaming media . . . . . . . . . . . . . . . . . . . . . 4
3.4 Email and the World Wide Web . . . . . . . . . . . . . . . 4 3.4 Email and the World Wide Web . . . . . . . . . . . . . . . 4
4. Requirements and Recommendations . . . . . . . . . . . . . . 5 4. Requirements and Recommendations . . . . . . . . . . . . . . 5
4.1 Media Information . . . . . . . . . . . . . . . . . . . . 5 4.1 Media and Transport Information . . . . . . . . . . . . . 5
4.2 Timing Information . . . . . . . . . . . . . . . . . . . . 6 4.2 Timing Information . . . . . . . . . . . . . . . . . . . . 6
4.3 Private Sessions . . . . . . . . . . . . . . . . . . . . . 6 4.3 Private Sessions . . . . . . . . . . . . . . . . . . . . . 6
4.4 Obtaining Further Information about a Session . . . . . . 6 4.4 Obtaining Further Information about a Session . . . . . . 7
4.5 Categorisation . . . . . . . . . . . . . . . . . . . . . . 6 4.5 Categorisation . . . . . . . . . . . . . . . . . . . . . . 7
4.6 Internationalization . . . . . . . . . . . . . . . . . . . 7 4.6 Internationalization . . . . . . . . . . . . . . . . . . . 7
5. SDP Specification . . . . . . . . . . . . . . . . . . . . . 7 5. SDP Specification . . . . . . . . . . . . . . . . . . . . . 7
5.1 Protocol Version ("v=") . . . . . . . . . . . . . . . . . 9 5.1 Protocol Version ("v=") . . . . . . . . . . . . . . . . . 10
5.2 Origin ("o=") . . . . . . . . . . . . . . . . . . . . . . 10 5.2 Origin ("o=") . . . . . . . . . . . . . . . . . . . . . . 10
5.3 Session Name ("s=") . . . . . . . . . . . . . . . . . . . 11 5.3 Session Name ("s=") . . . . . . . . . . . . . . . . . . . 11
5.4 Session Information ("i=") . . . . . . . . . . . . . . . . 11 5.4 Session Information ("i=") . . . . . . . . . . . . . . . . 12
5.5 URI ("u=") . . . . . . . . . . . . . . . . . . . . . . . . 11 5.5 URI ("u=") . . . . . . . . . . . . . . . . . . . . . . . . 12
5.6 Email Address and Phone Number ("e=" and "p=") . . . . . . 11 5.6 Email Address and Phone Number ("e=" and "p=") . . . . . . 12
5.7 Connection Data ("c=") . . . . . . . . . . . . . . . . . . 12 5.7 Connection Data ("c=") . . . . . . . . . . . . . . . . . . 13
5.8 Bandwidth ("b=") . . . . . . . . . . . . . . . . . . . . . 14 5.8 Bandwidth ("b=") . . . . . . . . . . . . . . . . . . . . . 15
5.9 Timing ("t=") . . . . . . . . . . . . . . . . . . . . . . 15 5.9 Timing ("t=") . . . . . . . . . . . . . . . . . . . . . . 16
5.10 Repeat Times ("r=") . . . . . . . . . . . . . . . . . . 16 5.10 Repeat Times ("r=") . . . . . . . . . . . . . . . . . . 17
5.11 Time Zones ("z=") . . . . . . . . . . . . . . . . . . . 17 5.11 Time Zones ("z=") . . . . . . . . . . . . . . . . . . . 18
5.12 Encryption Keys ("k=") . . . . . . . . . . . . . . . . . 18 5.12 Encryption Keys ("k=") . . . . . . . . . . . . . . . . . 19
5.13 Attributes ("a=") . . . . . . . . . . . . . . . . . . . 19 5.13 Attributes ("a=") . . . . . . . . . . . . . . . . . . . 20
5.14 Media Descriptions ("m=") . . . . . . . . . . . . . . . 21 5.14 Media Descriptions ("m=") . . . . . . . . . . . . . . . 21
6. Suggested Attributes . . . . . . . . . . . . . . . . . . . . 24 6. Suggested Attributes . . . . . . . . . . . . . . . . . . . . 23
7. Communicating Conference Control Policy . . . . . . . . . . 29 7. Communicating Conference Control Policy . . . . . . . . . . 30
8. Security Considerations . . . . . . . . . . . . . . . . . . 30 8. Security Considerations . . . . . . . . . . . . . . . . . . 31
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 31 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 32
9.1 The "application/sdp" media type . . . . . . . . . . . . . 31 9.1 The "application/sdp" media type . . . . . . . . . . . . . 32
9.2 Registration of Parameters . . . . . . . . . . . . . . . . 32 9.2 Registration of Parameters . . . . . . . . . . . . . . . . 33
9.3 Encryption Key Access Methods . . . . . . . . . . . . . . 36 9.3 Encryption Key Access Methods . . . . . . . . . . . . . . 37
A. SDP Grammar . . . . . . . . . . . . . . . . . . . . . . . . 37 A. SDP Grammar . . . . . . . . . . . . . . . . . . . . . . . . 38
B. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 42 B. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 43
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 42 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
10.1 Normative References . . . . . . . . . . . . . . . . . . . 42 10.1 Normative References . . . . . . . . . . . . . . . . . . . 43
10.2 Informative References . . . . . . . . . . . . . . . . . . 42 10.2 Informative References . . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 43 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 45
Intellectual Property and Copyright Statements . . . . . . . 45 Intellectual Property and Copyright Statements . . . . . . . 46
1. Introduction 1. Introduction
[Note to RFC Editor: All references to RFC XXXX should be replaced by
the RFC number of this document, when published.]
When initiating multimedia teleconferences, voice-over-IP calls, When initiating multimedia teleconferences, voice-over-IP calls,
streaming video, or other sessions, there is a requirement to convey streaming video, or other sessions, there is a requirement to convey
media details, transport addresses, and other session description media details, transport addresses, and other session description
metadata to the participants. metadata to the participants.
SDP provides a standard representation for such information, SDP provides a standard representation for such information,
irrespective of how that information is transported. SDP is purely a irrespective of how that information is transported. SDP is purely a
format for session description - it does not incorporate a transport format for session description - it does not incorporate a transport
protocol, and is intended to use different transport protocols as protocol, and is intended to use different transport protocols as
appropriate, including the Session Announcement Protocol [8], Session appropriate, including the Session Announcement Protocol [9], Session
Initiation Protocol [9], Real-Time Streaming Protocol [10], Initiation Protocol [10], Real-Time Streaming Protocol [11],
electronic mail using the MIME extensions, and the Hypertext electronic mail using the MIME extensions, and the Hypertext
Transport Protocol. Transport Protocol.
SDP is intended to be general purpose so that it can be used in a SDP is intended to be general purpose so that it can be used in a
wide range of network environments and applications. However, it is wide range of network environments and applications. However, it is
not intended to support negotiation of session content or media not intended to support negotiation of session content or media
encodings: this is viewed as outside the scope of session encodings: this is viewed as outside the scope of session
description. description.
2. Glossary of Terms 2. Glossary of Terms
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conferences and other multicast sessions, and to communicate the conferences and other multicast sessions, and to communicate the
relevant session setup information to prospective participants, a relevant session setup information to prospective participants, a
distributed session directory may be used. An instance of such a distributed session directory may be used. An instance of such a
session directory periodically sends packets containing a description session directory periodically sends packets containing a description
of the session to a well known multicast group. These advertisements of the session to a well known multicast group. These advertisements
are received by other session directories such that potential remote are received by other session directories such that potential remote
participants can use the session description to start the tools participants can use the session description to start the tools
required to participate in the session. required to participate in the session.
One protocol commonly used to implement such a distributed directory One protocol commonly used to implement such a distributed directory
is the Session Announcement Protocol, SAP [8]. SDP provides the is the Session Announcement Protocol, SAP [9]. SDP provides the
recommended session description format for such session recommended session description format for such session
announcements. announcements.
3.2 Session Initiation 3.2 Session Initiation
The Session Initiation Protocol, SIP [9] is an application layer The Session Initiation Protocol, SIP [10] is an application layer
control protocol for creating, modifying and terminating sessions control protocol for creating, modifying and terminating sessions
such as Internet multimedia conferences, Internet telephone calls and such as Internet multimedia conferences, Internet telephone calls and
multimedia distribution. The SIP messages used to create sessions multimedia distribution. The SIP messages used to create sessions
carry session descriptions which allow participants to agree on a set carry session descriptions which allow participants to agree on a set
of compatible media types. These session descriptions are commonly of compatible media types. These session descriptions are commonly
formatted using SDP. When used with SIP, the offer/answer model [11] formatted using SDP. When used with SIP, the offer/answer model [12]
provides a limited framework for negotiation using SDP. provides a limited framework for negotiation using SDP.
3.3 Streaming media 3.3 Streaming media
The Real Time Streaming Protocol, RTSP [10], is an application-level The Real Time Streaming Protocol, RTSP [11], is an application-level
protocol for control over the delivery of data with real-time protocol for control over the delivery of data with real-time
properties. RTSP provides an extensible framework to enable properties. RTSP provides an extensible framework to enable
controlled, on-demand delivery of real-time data, such as audio and controlled, on-demand delivery of real-time data, such as audio and
video. An RTSP client and server negotiate an appropriate set of video. An RTSP client and server negotiate an appropriate set of
parameters for media delivery, partially using SDP syntax to describe parameters for media delivery, partially using SDP syntax to describe
those parameters. those parameters.
3.4 Email and the World Wide Web 3.4 Email and the World Wide Web
Alternative means of conveying session descriptions include Alternative means of conveying session descriptions include
electronic mail and the World Wide Web. For both email and WWW electronic mail and the World Wide Web. For both email and WWW
distribution, the MIME content type "application/sdp" is used. This distribution, the MIME content type "application/sdp" is used. This
enables the automatic launching of applications for participation in enables the automatic launching of applications for participation in
the session from the WWW client or mail reader in a standard manner. the session from the WWW client or mail reader in a standard manner.
Note that announcements of multicast sessions made only via email or Note that announcements of multicast sessions made only via email or
the World Wide Web (WWW) do not have the property that the receiver the World Wide Web (WWW) do not have the property that the receiver
of a session announcement can necessarily receive the session because of a session announcement can necessarily receive the session because
the multicast sessions may be restricted in scope, and access to the the multicast sessions may be restricted in scope, and access to the
WWW server or reception of email is possible outside this scope. WWW server or reception of email is possible outside this scope.
Session announcements made using SAP do not suffer this mismatch.
Session announcements made using SAP do not suffer from this
mismatch.
4. Requirements and Recommendations 4. Requirements and Recommendations
The purpose of SDP is to convey information about media streams in The purpose of SDP is to convey information about media streams in
multimedia sessions to allow the recipients of a session description multimedia sessions to allow the recipients of a session description
to participate in the session. SDP is primarily intended for use in to participate in the session. SDP is primarily intended for use in
an internetwork, although it is sufficiently general that it can an internetwork, although it is sufficiently general that it can
describe conferences in other network environments. Media streams can describe conferences in other network environments. Media streams
be many-to-many. The times during which the session is active need can be many-to-many. The times during which the session is active
not be continuous. need not be continuous.
Thus far, multicast based sessions on the Internet have differed from Thus far, multicast based sessions on the Internet have differed from
many other forms of conferencing in that anyone receiving the traffic many other forms of conferencing in that anyone receiving the traffic
can join the session (unless the session traffic is encrypted). In can join the session (unless the session traffic is encrypted). In
such an environment, SDP serves two primary purposes. It is a means such an environment, SDP serves two primary purposes. It is a means
to communicate the existence of a session, and is a means to convey to communicate the existence of a session, and is a means to convey
sufficient information to enable joining and participating in the sufficient information to enable joining and participating in the
session. In a unicast environment, only the latter purpose is likely session. In a unicast environment, only the latter purpose is likely
to be relevant. to be relevant.
Thus SDP includes: An SDP session description includes:
o Session name and purpose o Session name and purpose
o Time(s) the session is active o Time(s) the session is active
o The media comprising the session o The media comprising the session
o Information needed to receive those media (addresses, ports, o Information needed to receive those media (addresses, ports,
formats and so on) formats and so on)
As resources necessary to participate in a session may be limited, As resources necessary to participate in a session may be limited,
some additional information may also be desirable: some additional information may also be desirable:
o Information about the bandwidth to be used by the conference
o Information about the bandwidth to be used by the session
o Contact information for the person responsible for the session o Contact information for the person responsible for the session
In general, SDP must convey sufficient information to enable In general, SDP must convey sufficient information to enable
applications to join a session (with the possible exception of applications to join a session (with the possible exception of
encryption keys) and to announce the resources to be used to non- encryption keys), and to announce the resources to be used to any
participants that may need to know. non-participants that may need to know (this latter feature is
primarily useful when SDP is used with a multicast session
announcement protocol).
4.1 Media Information 4.1 Media and Transport Information
An SDP session description includes the following media information:
SDP includes:
o The type of media (video, audio, etc) o The type of media (video, audio, etc)
o The transport protocol (RTP/UDP/IP, H.320, etc) o The transport protocol (RTP/UDP/IP, H.320, etc)
o The format of the media (H.261 video, MPEG video, etc) o The format of the media (H.261 video, MPEG video, etc)
For an IP multicast session, the following are also conveyed: In addition to media format and transport protocol, SDP conveys
o Multicast address for media address and port details. For an IP multicast session, these
o Transport port for media comprise:
o The multicast group address for media
o The transport port for media
This address and port are the destination address and destination This address and port are the destination address and destination
port of the multicast stream, whether being sent, received, or both. port of the multicast stream, whether being sent, received, or both.
For an IP unicast session, the following are conveyed: For unicast IP sessions, the following are conveyed:
o Remote address for media
o Transport port for media o The remote address for media
o The transport port for media
The semantics of this address and port depend on the media and The semantics of this address and port depend on the media and
transport protocol defined. By default, this is the remote address transport protocol defined. By default, this SHOULD be the remote
and remote port to which data is sent, however some media types may address and remote port to which data is sent. Some media types MAY
redefine this behaviour. redefine this behaviour, but this is NOT RECOMMENDED.
4.2 Timing Information 4.2 Timing Information
Sessions may either be bounded or unbounded in time. Whether or not Sessions may either be bounded or unbounded in time. Whether or not
they are bounded, they may be only active at specific times. they are bounded, they may be only active at specific times. SDP can
convey:
SDP can convey:
o An arbitrary list of start and stop times bounding the session o An arbitrary list of start and stop times bounding the session
o For each bound, repeat times such as "every Wednesday at 10am for o For each bound, repeat times such as "every Wednesday at 10am for
one hour" one hour"
This timing information is globally consistent, irrespective of local This timing information is globally consistent, irrespective of local
time zone or daylight saving time. time zone or daylight saving time.
4.3 Private Sessions 4.3 Private Sessions
It is possible to create both public sessions and private sessions. It is possible to create both public sessions and private sessions.
SDP itself does not distinguish between these: private sessions are SDP itself does not distinguish between these: private sessions are
typically conveyed by encrypting the session description during typically conveyed by encrypting the session description during
distribution. The details of how encryption is performed are distribution. The details of how encryption is performed are
dependent on the mechanism used to convey SDP - e.g. mechanisms are dependent on the mechanism used to convey SDP: mechanisms are
defined for SDP transported using SAP [8] and SIP [9]. currently defined for SDP transported using SAP [9] and SIP [10],
others may be defined in future.
If a session announcement is private it is possible to use that If a session announcement is private it is possible to use that
private announcement to convey encryption keys necessary to decode private announcement to convey encryption keys necessary to decode
each of the media in a conference, including enough information to each of the media in a conference, including enough information to
know which encryption scheme is used for each media. know which encryption scheme is used for each media.
4.4 Obtaining Further Information about a Session 4.4 Obtaining Further Information about a Session
A session description should convey enough information to decide A session description should convey enough information to decide
whether or not to participate in a session. SDP may include whether or not to participate in a session. SDP may include
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"application/sdp" (See Section 9). "application/sdp" (See Section 9).
An SDP session description is entirely textual using the ISO 10646 An SDP session description is entirely textual using the ISO 10646
character set in UTF-8 encoding. SDP field names and attribute names character set in UTF-8 encoding. SDP field names and attribute names
use only the US-ASCII subset of UTF-8, but textual fields and use only the US-ASCII subset of UTF-8, but textual fields and
attribute values MAY use the full ISO 10646 character set. Field and attribute values MAY use the full ISO 10646 character set. Field and
attribute values which use the full UTF-8 character set are never attribute values which use the full UTF-8 character set are never
directly compared, hence there is no requirement for UTF-8 directly compared, hence there is no requirement for UTF-8
normalization. The textual form, as opposed to a binary encoding normalization. The textual form, as opposed to a binary encoding
such as ASN.1 or XDR, was chosen to enhance portability, to enable a such as ASN.1 or XDR, was chosen to enhance portability, to enable a
variety of transports to be used (e.g, session description in a MIME variety of transports to be used, and to allow flexible, text-based
email message) and to allow flexible, text-based toolkits (e.g., Tcl/ toolkits to be used to generate and process session descriptions.
Tk) to be used to generate and to process session descriptions.
However, since SDP may be used in environments where the maximum However, since SDP may be used in environments where the maximum
permissable size of a session description is limited (e.g. SAP permissable size of a session description is limited, the encoding is
announcements), the encoding is deliberately compact. Also, since deliberately compact. Also, since announcements may be transported
announcements may be transported via very unreliable means or damaged via very unreliable means or damaged by an intermediate caching
by an intermediate caching server, the encoding was designed with server, the encoding was designed with strict order and formatting
strict order and formatting rules so that most errors would result in rules so that most errors would result in malformed session
malformed session announcements which could be detected easily and announcements which could be detected easily and discarded. This
discarded. This also allows rapid discarding of encrypted session also allows rapid discarding of encrypted session announcements for
announcements for which a receiver does not have the correct key. which a receiver does not have the correct key.
An SDP session description consists of a number of lines of text of An SDP session description consists of a number of lines of text of
the form: the form:
<type>=<value> <type>=<value>
where <type> MUST be exactly one case-significant character and where <type> MUST be exactly one case-significant character and
<value> is structured text whose format depends on <type>. In <value> is structured text whose format depends on <type>. In
general <value> is either a number of fields delimited by a single general <value> is either a number of fields delimited by a single
space character, or a free format string. Whitespace MUST NOT be used space character, or a free format string. Whitespace MUST NOT be
either side of the "=" sign. used either side of the "=" sign.
An SDP session description consists of a session-level section An SDP session description consists of a session-level section
followed by zero or more media-level sections. The session-level followed by zero or more media-level sections. The session-level
part starts with a "v=" line and continues to the first media-level part starts with a "v=" line and continues to the first media-level
section. The media description starts with an "m=" line and section. The media description starts with an "m=" line and
continues to the next media description or end of the whole session continues to the next media description or end of the whole session
description. In general, session-level values are the default for description. In general, session-level values are the default for
all media unless overridden by an equivalent media-level value. all media unless overridden by an equivalent media-level value.
Some lines in each description are REQUIRED and some are OPTIONAL but Some lines in each description are REQUIRED and some are OPTIONAL but
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v= (protocol version) v= (protocol version)
o= (owner/creator and session identifier). o= (owner/creator and session identifier).
s= (session name) s= (session name)
i=* (session information) i=* (session information)
u=* (URI of description) u=* (URI of description)
e=* (email address) e=* (email address)
p=* (phone number) p=* (phone number)
c=* (connection information - not required if included in c=* (connection information - not required if included in
all media) all media)
b=* (zero or more bandwidth information lines) b=* (zero or more bandwidth information lines)
One or more time descriptions (see below) One or more time descriptions ("t=" and "r=" lines, see below)
z=* (time zone adjustments) z=* (time zone adjustments)
k=* (encryption key) k=* (encryption key)
a=* (zero or more session attribute lines) a=* (zero or more session attribute lines)
Zero or more media descriptions (see below) Zero or more media descriptions
Time description Time description
t= (time the session is active) t= (time the session is active)
r=* (zero or more repeat times) r=* (zero or more repeat times)
Media description Media description
m= (media name and transport address) m= (media name and transport address)
i=* (media title) i=* (media title)
c=* (connection information - optional if included at c=* (connection information - optional if included at
session-level) session-level)
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o=<username> <sess-id> <sess-version> <nettype> <addrtype> o=<username> <sess-id> <sess-version> <nettype> <addrtype>
<unicast-address> <unicast-address>
The "o=" field gives the originator of the session (her username and The "o=" field gives the originator of the session (her username and
the address of the user's host) plus a session identifier and version the address of the user's host) plus a session identifier and version
number: number:
<username> is the user's login on the originating host, or it is "-" <username> is the user's login on the originating host, or it is "-"
if the originating host does not support the concept of user ids. if the originating host does not support the concept of user ids.
The <username> MUST NOT contain spaces. The <username> MUST NOT contain spaces.
<sess-id> is a numeric string such that the tuple of <username>, <sess-id> is a numeric string such that the tuple of <username>,
<sess-id>, <nettype>, <addrtype> and <unicast-address> form a <sess-id>, <nettype>, <addrtype> and <unicast-address> form a
globally unique identifier for the session. The method of globally unique identifier for the session. The method of
<sess-id> allocation is up to the creating tool, but it has been <sess-id> allocation is up to the creating tool, but it has been
suggested that a Network Time Protocol (NTP) format timestamp be suggested that a Network Time Protocol (NTP) format timestamp be
used to ensure uniqueness [7]. used to ensure uniqueness [8].
<sess-version> is a version number for this session description. Its <sess-version> is a version number for this session description. Its
usage is up to the creating tool, so long as <sess-version> is usage is up to the creating tool, so long as <sess-version> is
increased when a modification is made to the session data. Again, increased when a modification is made to the session data. Again,
it is RECOMMENDED that an NTP format timestamp is used. it is RECOMMENDED that an NTP format timestamp is used.
<nettype> is a text string giving the type of network. Initially "IN"
is defined to have the meaning "Internet", but other values MAY be <nettype> is a text string giving the type of network. Initially
registered in future (see Section 9). "IN" is defined to have the meaning "Internet", but other values
MAY be registered in future (see Section 9).
<addrtype> is a text string giving the type of the address that <addrtype> is a text string giving the type of the address that
follows. Initially "IP4" and "IP6" are defined, but other values follows. Initially "IP4" and "IP6" are defined, but other values
MAY be registered in future (see Section 9). MAY be registered in future (see Section 9).
<unicast-address> is the address of the machine from which the <unicast-address> is the address of the machine from which the
session was created. For an address type of IP4, this is either session was created. For an address type of IP4, this is either
the fully-qualified domain name of the machine, or the the fully-qualified domain name of the machine, or the
dotted-decimal representation of the IP version 4 address of the dotted-decimal representation of the IP version 4 address of the
machine. For an address type of IP6, this is either the machine. For an address type of IP6, this is either the
fully-qualified domain name of the machine, or the compressed fully-qualified domain name of the machine, or the compressed
textual representation of the IP version 6 address of the machine. textual representation of the IP version 6 address of the machine.
For both IP4 and IP6, the fully-qualified domain name is the form For both IP4 and IP6, the fully-qualified domain name is the form
that SHOULD be given unless this is unavailable, in which case the that SHOULD be given unless this is unavailable, in which case the
globally unique address MAY be substituted. A local IP address globally unique address MAY be substituted. A local IP address
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modifications. modifications.
5.3 Session Name ("s=") 5.3 Session Name ("s=")
s=<session name> s=<session name>
The "s=" field is the textual session name. There MUST be one and The "s=" field is the textual session name. There MUST be one and
only one "s=" field per session description. The "s=" field MUST NOT only one "s=" field per session description. The "s=" field MUST NOT
be empty and SHOULD contain ISO 10646 characters (but see also the be empty and SHOULD contain ISO 10646 characters (but see also the
"a=charset" attribute). If a session has no meaningful name, the "a=charset" attribute). If a session has no meaningful name, the
value "s= " SHOULD be used (i.e. a single space as the session name). value "s= " SHOULD be used (i.e. a single space as the session
name).
5.4 Session Information ("i=") 5.4 Session Information ("i=")
i=<session description> i=<session description>
The "i=" field provides textual information about the session. There The "i=" field provides textual information about the session. There
may be at most one session-level "i=" field per session description, may be at most one session-level "i=" field per session description,
and at most one "i=" field per media. If the "a=charset" attribute is and at most one "i=" field per media. If the "a=charset" attribute
present, it specifies the character set used in the "i=" field. If is present, it specifies the character set used in the "i=" field.
the "a=charset" attribute is not present, the "i=" field MUST contain If the "a=charset" attribute is not present, the "i=" field MUST
ISO 10646 characters in UTF-8 encoding. contain ISO 10646 characters in UTF-8 encoding.
A single "i=" field MAY also be used for each media definition. In A single "i=" field MAY also be used for each media definition. In
media definitions, "i=" fields are primarily intended for labeling media definitions, "i=" fields are primarily intended for labeling
media streams. As such, they are most likely to be useful when a media streams. As such, they are most likely to be useful when a
single session has more than one distinct media stream of the same single session has more than one distinct media stream of the same
media type. An example would be two different whiteboards, one for media type. An example would be two different whiteboards, one for
slides and one for feedback and questions. slides and one for feedback and questions.
The "i=" field is intended to provide a free-form human readable
description of the session or the purpose of a media stream. It is
not suitable for parsing by automata.
5.5 URI ("u=") 5.5 URI ("u=")
u=<uri> u=<uri>
A URI is a Universal Resource Identifier as used by WWW clients [4]. A URI is a Universal Resource Identifier as used by WWW clients [4],
The URI should be a pointer to additional information about the [6]. The URI should be a pointer to additional information about the
conference. This field is OPTIONAL, but if it is present it MUST be conference. This field is OPTIONAL, but if it is present it MUST be
specified before the first media field. No more than one URI field is specified before the first media field. No more than one URI field
allowed per session description. is allowed per session description.
5.6 Email Address and Phone Number ("e=" and "p=") 5.6 Email Address and Phone Number ("e=" and "p=")
e=<email-address> e=<email-address>
p=<phone-number> p=<phone-number>
The "e=" and "p=" lines specify contact information for the person The "e=" and "p=" lines specify contact information for the person
responsible for the conference. This is not necessarily the same responsible for the conference. This is not necessarily the same
person that created the conference announcement. person that created the conference announcement.
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If the email addres or phone number are present, they MUST be If the email addres or phone number are present, they MUST be
specified before the first media field. More than one email or phone specified before the first media field. More than one email or phone
field can be given for a session description. field can be given for a session description.
Phone numbers SHOULD be given in the form of an international public Phone numbers SHOULD be given in the form of an international public
telecommunication number (see ITU-T Recommendation E.164) preceded by telecommunication number (see ITU-T Recommendation E.164) preceded by
a "+". Spaces and hyphens may be used to split up a phone field to a "+". Spaces and hyphens may be used to split up a phone field to
aid readability if desired. For example: aid readability if desired. For example:
p=+44-171-380-7777 or p=+1 617 555 6011 p=+1 617 555-6011
Both email addresses and phone numbers can have an OPTIONAL free text Both email addresses and phone numbers can have an OPTIONAL free text
string associated with them, normally giving the name of the person string associated with them, normally giving the name of the person
who may be contacted. This MUST be enclosed in parenthesis if it is who may be contacted. This MUST be enclosed in parenthesis if it is
present. For example: present. For example:
e=j.doe@example.com (Jane Doe) e=j.doe@example.com (Jane Doe)
The alternative RFC 2822 name quoting convention is also allowed for The alternative RFC 2822 name quoting convention is also allowed for
both email addresses and phone numbers. For example: both email addresses and phone numbers. For example:
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It MAY contain a single session-level "c=" field and additional "c=" It MAY contain a single session-level "c=" field and additional "c="
field(s) per media description, in which case the per-media values field(s) per media description, in which case the per-media values
override the session-level settings for the respective media. override the session-level settings for the respective media.
The first sub-field ("<nettype>") is the network type, which is a The first sub-field ("<nettype>") is the network type, which is a
text string giving the type of network. Initially "IN" is defined to text string giving the type of network. Initially "IN" is defined to
have the meaning "Internet", but other values MAY be registered in have the meaning "Internet", but other values MAY be registered in
the future (see Section 9). the future (see Section 9).
The second sub-field ("<addrtype>") is the address type. This allows The second sub-field ("<addrtype>") is the address type. This allows
SDP to be used for sessions that are not IP based. Currently only IP4 SDP to be used for sessions that are not IP based. Currently only
and IP6 are defined, but other values MAY be registered in the future IP4 and IP6 are defined, but other values MAY be registered in the
(see Section 9). future (see Section 9).
The third sub-field ("<connection-address>") is the connection The third sub-field ("<connection-address>") is the connection
address. OPTIONAL sub-fields MAY be added after the connection address. OPTIONAL sub-fields MAY be added after the connection
address depending on the value of the <addrtype> field. address depending on the value of the <addrtype> field.
When the <addrtype> is IP4 and IP6, the connection address is defined When the <addrtype> is IP4 and IP6, the connection address is defined
as follows: as follows:
o If the session is multicast, the connection address will be an IP o If the session is multicast, the connection address will be an IP
multicast group address. If the session is not multicast, then multicast group address. If the session is not multicast, then
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c=IN IP6 FF15::102 c=IN IP6 FF15::102
c=IN IP6 FF15::103 c=IN IP6 FF15::103
(remembering that the TTL field is not present in IPv6 multicast). (remembering that the TTL field is not present in IPv6 multicast).
Multiple addresses or "c=" lines MAY be specified on a per-media Multiple addresses or "c=" lines MAY be specified on a per-media
basis only if they provide multicast addresses for different layers basis only if they provide multicast addresses for different layers
in a hierarchical or layered encoding scheme. They MUST NOT be in a hierarchical or layered encoding scheme. They MUST NOT be
specified for a session-level "c=" field. specified for a session-level "c=" field.
The slash notation described above MUST NOT be used for IP unicast The slash notation for multiple addresses described above MUST NOT be
addresses. used for IP unicast addresses.
5.8 Bandwidth ("b=") 5.8 Bandwidth ("b=")
b=<bwtype>:<bandwidth> b=<bwtype>:<bandwidth>
This OPTIONAL field denotes the proposed bandwidth to be used by the This OPTIONAL field denotes the proposed bandwidth to be used by the
session or media. The <bwtype> is an alphanumeric modifier giving session or media. The <bwtype> is an alphanumeric modifier giving
the meaning of the <bandwidth> figure. Two values are initially the meaning of the <bandwidth> figure. Two values are defined in
defined, but other values MAY be registered in future (see Section this specification, but other values MAY be registered in future (see
9): Section 9 and [22], [16]):
CT If the bandwidth of a session or media in a session is different CT If the bandwidth of a session or media in a session is different
from the bandwidth implicit from the scope, a "b=CT:..." line from the bandwidth implicit from the scope, a "b=CT:..." line
SHOULD be supplied for the session giving the proposed upper limit SHOULD be supplied for the session giving the proposed upper limit
to the bandwidth used. The primary purpose of this is to give an to the bandwidth used. The primary purpose of this is to give an
approximate idea as to whether two or more sessions can co-exist approximate idea as to whether two or more sessions can co-exist
simultaneously. When using the CT modifier with RTP, if several simultaneously. When using the CT modifier with RTP, if several
RTP sessions are part of the conference, the conference total RTP sessions are part of the conference, the conference total
refers to total bandwidth of all RTP sessions. refers to total bandwidth of all RTP sessions.
AS The bandwidth is interpreted to be application-specific (it will AS The bandwidth is interpreted to be application-specific (it will
be the application's concept of maximum bandwidth). Normally this be the application's concept of maximum bandwidth). Normally this
will coincide with what is set on the application's "maximum will coincide with what is set on the application's "maximum
bandwidth" control if applicable. For RTP based applications, AS bandwidth" control if applicable. For RTP based applications, AS
gives the RTP "session bandwidth" as defined in section 6.2 of gives the RTP "session bandwidth" as defined in section 6.2 of
[12]. [14].
Note that CT gives a total bandwidth figure for all the media at all Note that CT gives a total bandwidth figure for all the media at all
sites. AS gives a bandwidth figure for a single media at a single sites. AS gives a bandwidth figure for a single media at a single
site, although there may be many sites sending simultaneously. site, although there may be many sites sending simultaneously.
A prefix "X-" is defined for <bwtype> names. This is intended for A prefix "X-" is defined for <bwtype> names. This is intended for
experimental purposes only. For example: experimental purposes only. For example:
b=X-YZ:128 b=X-YZ:128
Use of the "X-" prefix is NOT RECOMMENDED: instead new modifiers Use of the "X-" prefix is NOT RECOMMENDED: instead new modifiers
SHOULD be registered with IANA in the standard namespace. SDP parsers SHOULD be registered with IANA in the standard namespace. SDP
MUST ignore bandwidth fields with unknown modifiers. Modifiers MUST parsers MUST ignore bandwidth fields with unknown modifiers.
be alpha-numeric and, although no length limit is given, they are Modifiers MUST be alpha-numeric and, although no length limit is
recommended to be short. given, they are recommended to be short.
The <bandwidth> is in kilobits per second by default. Modifiers MAY The <bandwidth> is in kilobits per second by default. Modifiers MAY
specify that alternative units are to be used (the modifiers defined specify that alternative units are to be used (the modifiers defined
in this memo use the default units). in this memo use the default units).
5.9 Timing ("t=") 5.9 Timing ("t=")
t=<start-time> <stop-time> t=<start-time> <stop-time>
The "t=" lines specify the start and stop times for a session. The "t=" lines specify the start and stop times for a session.
Multiple "t=" lines MAY be used if a session is active at multiple Multiple "t=" lines MAY be used if a session is active at multiple
irregularly spaced times; each additional "t=" lines specifies an irregularly spaced times; each additional "t=" lines specifies an
additional period of time for which the session will be active. If additional period of time for which the session will be active. If
the session is active at regular times, an "r=" line (see below) the session is active at regular times, an "r=" line (see below)
should be used in addition to, and following, a "t=" line - in which should be used in addition to, and following, a "t=" line - in which
case the "t=" line specifies the start and stop times of the repeat case the "t=" line specifies the start and stop times of the repeat
sequence. sequence.
The first and second sub-fields give the start and stop times for the The first and second sub-fields give the start and stop times for the
session respectively. These values are the decimal representation of session respectively. These values are the decimal representation of
Network Time Protocol (NTP) time values in seconds [7]. To convert Network Time Protocol (NTP) time values in seconds since 1900 [8].
these values to UNIX time, subtract decimal 2208988800. To convert these values to UNIX time, subtract decimal 2208988800.
NTP timestamps are 64 bit values which wrap sometime in the year NTP timestamps are elsewhere represented by 64 bit values which wrap
2036. Since SDP uses an arbitrary length decimal representation, sometime in the year 2036. Since SDP uses an arbitrary length
this should not cause an issue (SDP timestamps will continue counting decimal representation, this should not cause an issue (SDP
seconds since 1900, NTP will use the value modulo the 64 bit limit). timestamps MUST continue counting seconds since 1900, NTP will use
the value modulo the 64 bit limit).
If the <stop-time> is set to zero, then the session is not bounded, If the <stop-time> is set to zero, then the session is not bounded,
though it will not become active until after the <start-time>. If though it will not become active until after the <start-time>. If
the <start-time> is also zero, the session is regarded as permanent. the <start-time> is also zero, the session is regarded as permanent.
User interfaces SHOULD strongly discourage the creation of unbounded User interfaces SHOULD strongly discourage the creation of unbounded
and permanent sessions as they give no information about when the and permanent sessions as they give no information about when the
session is actually going to terminate, and so make scheduling session is actually going to terminate, and so make scheduling
difficult. difficult.
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corresponding "t=" field would be the NTP representation of 10am on corresponding "t=" field would be the NTP representation of 10am on
the first Monday, the <repeat interval> would be 1 week, the <active the first Monday, the <repeat interval> would be 1 week, the <active
duration> would be 1 hour, and the offsets would be zero and 25 duration> would be 1 hour, and the offsets would be zero and 25
hours. The corresponding "t=" field stop time would be the NTP hours. The corresponding "t=" field stop time would be the NTP
representation of the end of the last session three months later. By representation of the end of the last session three months later. By
default all fields are in seconds, so the "r=" and "t=" fields might default all fields are in seconds, so the "r=" and "t=" fields might
be: be:
t=3034423619 3042462419 t=3034423619 3042462419
r=604800 3600 0 90000 r=604800 3600 0 90000
To make description more compact, times may also be given in units of To make description more compact, times may also be given in units of
days, hours or minutes. The syntax for these is a number immediately days, hours or minutes. The syntax for these is a number immediately
followed by a single case-sensitive character. Fractional units are followed by a single case-sensitive character. Fractional units are
not allowed - a smaller unit should be used instead. The following not allowed - a smaller unit should be used instead. The following
unit specification characters are allowed: unit specification characters are allowed:
d - days (86400 seconds) d - days (86400 seconds)
h - hours (3600 seconds) h - hours (3600 seconds)
m - minutes (60 seconds) m - minutes (60 seconds)
s - seconds (allowed for completeness but not recommended) s - seconds (allowed for completeness but NOT RECOMMENDED)
Thus, the above session announcement could also have been written: Thus, the above session announcement could also have been written:
r=7d 1h 0 25h r=7d 1h 0 25h
Monthly and yearly repeats cannot be directly specified with a single Monthly and yearly repeats cannot be directly specified with a single
SDP repeat time - instead separate "t=" fields should be used to SDP repeat time - instead separate "t=" fields should be used to
explicitly list the session times. explicitly list the session times.
5.11 Time Zones ("z=") 5.11 Time Zones ("z=")
z=<adjustment time> <offset> <adjustment time> <offset> .... z=<adjustment time> <offset> <adjustment time> <offset> ....
To schedule a repeated session which spans a change from daylight- To schedule a repeated session which spans a change from daylight
saving time to standard time or vice-versa, it is necessary to saving time to standard time or vice-versa, it is necessary to
specify offsets from the base time. This is required because specify offsets from the base time. This is required because
different time zones change time at different times of day, different different time zones change time at different times of day, different
countries change to or from daylight time on different dates, and countries change to or from daylight time on different dates, and
some countries do not have daylight saving time at all. some countries do not have daylight saving time at all.
Thus in order to schedule a session that is at the same time winter Thus in order to schedule a session that is at the same time winter
and summer, it must be possible to specify unambiguously by whose and summer, it must be possible to specify unambiguously by whose
time zone a session is scheduled. To simplify this task for time zone a session is scheduled. To simplify this task for
receivers, we allow the sender to specify the NTP time that a time receivers, we allow the sender to specify the NTP time that a time
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5.12 Encryption Keys ("k=") 5.12 Encryption Keys ("k=")
k=<method> k=<method>
k=<method>:<encryption key> k=<method>:<encryption key>
If transported over a secure and trusted channel, the session If transported over a secure and trusted channel, the session
description protocol MAY be used to convey encryption keys. A simple description protocol MAY be used to convey encryption keys. A simple
mechanism for key exchange is provided by the key field ("k=") mechanism for key exchange is provided by the key field ("k=")
although this is primarily supported for compatibility with older although this is primarily supported for compatibility with older
implementations and its use is NOT RECOMMENDED. Work is in progress implementations and its use is NOT RECOMMENDED. Work is in progress
to define new key exchange mechanisms for use with SDP [18][17] and to define new key exchange mechanisms for use with SDP [20][21] and
it is expected that new applications will use those mechanisms. it is expected that new applications will use those mechanisms.
A key field is permitted before the first media entry (in which case A key field is permitted before the first media entry (in which case
it applies to all media in the session), or for each media entry as it applies to all media in the session), or for each media entry as
required. The format of keys and their usage is outside the scope of required. The format of keys and their usage is outside the scope of
this document, and the key field provides no way to indicate the this document, and the key field provides no way to indicate the
encryption algorithm to be used, key type, or other information about encryption algorithm to be used, key type, or other information about
the key: this is assumed to be provided by the higher-level protocol the key: this is assumed to be provided by the higher-level protocol
using SDP. If there is a need to convey this information within SDP, using SDP. If there is a need to convey this information within SDP,
the extensions mentioned previously SHOULD be used. Many security the extensions mentioned previously SHOULD be used. Many security
protocols require two keys, one for confidentiality and another for protocols require two keys: one for confidentiality, another for
integrity. This specification does not support the transfer of two integrity. This specification does not support transfer of two keys.
keys.
The method indicates the mechanism to be used to obtain a usable key The method indicates the mechanism to be used to obtain a usable key
by external means, or from the encoded encryption key given. The by external means, or from the encoded encryption key given. The
following methods are defined: following methods are defined:
k=clear:<encryption key> k=clear:<encryption key>
The encryption key is included untransformed in this key field. The encryption key is included untransformed in this key field.
This method MUST NOT be used unless it can be guaranteed that This method MUST NOT be used unless it can be guaranteed that
the SDP is conveyed over a secure channel. the SDP is conveyed over a secure channel. The encryption key
is interpreted as text according to the charset attribute, use
the "k=base64:" method to convey characters that are otherwise
prohibited in SDP.
k=base64:<encoded encryption key> k=base64:<encoded encryption key>
The encryption key is included in this key field but has been The encryption key is included in this key field but has been
base64 encoded because it includes characters that are base64 encoded [13] because it includes characters that are
prohibited in SDP. This method MUST NOT be used unless it can prohibited in SDP. This method MUST NOT be used unless it can
be guaranteed that the SDP is conveyed over a secure channel. be guaranteed that the SDP is conveyed over a secure channel.
k=uri:<URI to obtain key> k=uri:<URI to obtain key>
A Universal Resource Identifier is included in the key field. A Universal Resource Identifier is included in the key field.
The URI refers to the data containing the key, and may require The URI refers to the data containing the key, and may require
additional authentication before the key can be returned. When additional authentication before the key can be returned. When
a request is made to the given URI, the reply should specify a request is made to the given URI, the reply should specify
the encoding for the key. The URI is often a secure HTTP URI, the encoding for the key. The URI is often a secure HTTP URI,
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No key is included in this SDP description, but the session or No key is included in this SDP description, but the session or
media stream referred to by this key field is encrypted. The media stream referred to by this key field is encrypted. The
user should be prompted for the key when attempting to join the user should be prompted for the key when attempting to join the
session, and this user-supplied key should then be used to session, and this user-supplied key should then be used to
decrypt the media streams. The use of user-specified keys is decrypt the media streams. The use of user-specified keys is
NOT RECOMMENDED, since such keys tend to have weak security NOT RECOMMENDED, since such keys tend to have weak security
properties. properties.
The key field MUST NOT be used unless it can be guaranteed that the The key field MUST NOT be used unless it can be guaranteed that the
SDP is conveyed over a secure and trusted channel. An example of such SDP is conveyed over a secure and trusted channel. An example of
a channel might be SDP embedded inside an S/MIME message or a TLS such a channel might be SDP embedded inside an S/MIME message or a
protected HTTP or SIP session. It is important to ensure that the TLS protected HTTP or SIP session. It is important to ensure that
secure channel is with the party that is authorized to join the the secure channel is with the party that is authorized to join the
session, not an intermediary: if a caching proxy server is used, it session, not an intermediary: if a caching proxy server is used, it
is important to ensure that the proxy is either trusted or unable to is important to ensure that the proxy is either trusted or unable to
access the SDP. Definition of appropriate security measures is beyond access the SDP. Definition of appropriate security measures is
the scope of this specification, and should be defined by the users beyond the scope of this specification, and should be defined by the
of SDP. users of SDP.
5.13 Attributes ("a=") 5.13 Attributes ("a=")
a=<attribute> a=<attribute>
a=<attribute>:<value> a=<attribute>:<value>
Attributes are the primary means for extending SDP. Attributes may Attributes are the primary means for extending SDP. Attributes may
be defined to be used as "session-level" attributes, "media-level" be defined to be used as "session-level" attributes, "media-level"
attributes, or both. attributes, or both.
A media description may have any number of attributes ("a=" fields) A media description may have any number of attributes ("a=" fields)
which are media specific. These are referred to as "media-level" which are media specific. These are referred to as "media-level"
attributes and add information about the media stream. Attribute attributes and add information about the media stream. Attribute
fields can also be added before the first media field; these fields can also be added before the first media field; these
"session-level" attributes convey additional information that applies "session-level" attributes convey additional information that applies
to the conference as a whole rather than to individual media; an to the conference as a whole rather than to individual media; an
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A media description may have any number of attributes ("a=" fields) A media description may have any number of attributes ("a=" fields)
which are media specific. These are referred to as "media-level" which are media specific. These are referred to as "media-level"
attributes and add information about the media stream. Attribute attributes and add information about the media stream. Attribute
fields can also be added before the first media field; these fields can also be added before the first media field; these
"session-level" attributes convey additional information that applies "session-level" attributes convey additional information that applies
to the conference as a whole rather than to individual media; an to the conference as a whole rather than to individual media; an
example might be the conference's floor control policy. example might be the conference's floor control policy.
Attribute fields may be of two forms: Attribute fields may be of two forms:
o property attributes: o A property attribute is simply of the form "a=<flag>". These are
A property attribute is simply of the form "a=<flag>". binary attributes, and the presence of the attribute conveys that
These are binary attributes, and the presence of the the attribute is a property of the session. An example might be
attribute conveys that the attribute is a property of "a=recvonly".
the session. An example might be "a=recvonly".
o value attributes: o A value attribute is of the form "a=<attribute>:<value>". For
A value attribute is of the form "a=<attribute>:<value>". example, a whiteboard could have the value attribute
For example, a whiteboard could have the value attribute
"a=orient:landscape" "a=orient:landscape"
Attribute interpretation depends on the media tool being invoked. Attribute interpretation depends on the media tool being invoked.
Thus receivers of session descriptions should be configurable in Thus receivers of session descriptions should be configurable in
their interpretation of session descriptions in general and of their interpretation of session descriptions in general and of
attributes in particular. attributes in particular.
Attribute names MUST be in the US-ASCII subset of ISO-10646/UTF-8. Attribute names MUST use the US-ASCII subset of ISO-10646/UTF-8.
Attribute values are octet strings, and MAY use any octet value Attribute values are octet strings, and MAY use any octet value
except 0x00 (Nul), 0x0A (LF), and 0x0D (CR). By default, attribute except 0x00 (Nul), 0x0A (LF), and 0x0D (CR). By default, attribute
values are to be interpreted as in ISO-10646 character set with UTF-8 values are to be interpreted as in ISO-10646 character set with UTF-8
encoding. Unlike other text fields, attribute values are NOT encoding. Unlike other text fields, attribute values are NOT
normally affected by the "charset" attribute as this would make normally affected by the "charset" attribute as this would make
comparisons against known values problematic. However, when an comparisons against known values problematic. However, when an
attribute is defined, it can be defined to be charset-dependent, in attribute is defined, it can be defined to be charset-dependent, in
which case it's value should be interpreted in the session charset which case it's value should be interpreted in the session charset
rather than in ISO-10646. rather than in ISO-10646.
Attributes MUST be registered with IANA (see Section 9). If an Attributes MUST be registered with IANA (see Section 9). If an
attribute is received that is not understood, it MUST be ignored by attribute is received that is not understood, it MUST be ignored by
the receiver. the receiver.
5.14 Media Descriptions ("m=") 5.14 Media Descriptions ("m=")
m=<media> <port> <proto> <fmt> m=<media> <port> <proto> <fmt> ...
A session description may contain a number of media descriptions. A session description may contain a number of media descriptions.
Each media description starts with an "m=" field, and is terminated Each media description starts with an "m=" field, and is terminated
by either the next "m=" field or by the end of the session by either the next "m=" field or by the end of the session
description. A media field has several sub-fields. description. A media field has several sub-fields:
The first sub-field ("<media>") is the media type. Currently defined <media> is the media type. Currently defined media are "audio",
media are "audio", "video", "text", "application", "data" and "video", "text", "application", "data" and "control", although
"control", though this list may be extended in future (see Section this list may be extended in future (see Section 9). The
9). The difference between "application" and "data" is that the difference between "application" and "data" is that the former is
former is a media flow such as whiteboard information, and the latter a media flow such as whiteboard information, and the latter is
is bulk-data transfer such as multicasting of program executables bulk-data transfer such as multicasting of program executables
which will not typically be displayed to the user. "control" is used which will not typically be displayed to the user. "control" is
to specify an additional conference control channel for the session. used to specify an additional conference control channel for the
session.
The second sub-field ("<port>") is the transport port to which the <port> is the transport port to which the media stream is sent. The
media stream is sent. The meaning of the transport port depends on meaning of the transport port depends on the network being used as
the network being used as specified in the relevant "c=" field, and specified in the relevant "c=" field, and on the transport
on the transport protocol defined in the third sub-field. Other protocol defined in the <proto> sub-field of the media field.
ports used by the media application (such as the RTCP port [12]) MAY Other ports used by the media application (such as the RTCP port
be derived algorithmically from the base media port or MAY be [14]) MAY be derived algorithmically from the base media port or
specified in a separate attribute (e.g. "a=rtcp:" as defined in MAY be specified in a separate attribute (for example "a=rtcp:" as
[14]). defined in [17]).
For applications where hierarchically encoded streams are being sent For applications where hierarchically encoded streams are being
to a unicast address, it may be necessary to specify multiple sent to a unicast address, it may be necessary to specify multiple
transport ports. This is done using a similar notation to that used transport ports. This is done using a similar notation to that
for IP multicast addresses in the "c=" field: used for IP multicast addresses in the "c=" field:
m=<media> <port>/<number of ports> <transport> <fmt list> m=<media> <port>/<number of ports> <transport> <fmt list>
In such a case, the ports used depend on the transport protocol. For In such a case, the ports used depend on the transport protocol.
RTP, the default is that only the even numbered ports are used for For RTP, the default is that only the even numbered ports are used
data with the corresponding one-higher odd ports used for the RTCP for data with the corresponding one-higher odd ports used for the
belonging to the RTP session, and the <number of ports> denoting the RTCP belonging to the RTP session, and the <number of ports>
number of RTP sessions. For example: denoting the number of RTP sessions. For example:
m=video 49170/2 RTP/AVP 31 m=video 49170/2 RTP/AVP 31
would specify that ports 49170 and 49171 form one RTP/RTCP pair and would specify that ports 49170 and 49171 form one RTP/RTCP pair
49172 and 49173 form the second RTP/RTCP pair. RTP/AVP is the and 49172 and 49173 form the second RTP/RTCP pair. RTP/AVP is the
transport protocol and 31 is the format (see below). If non- transport protocol and 31 is the format (see below). If
contiguous ports are required, they must be signalled using a non-contiguous ports are required, they must be signalled using a
separate attribute (e.g. "a=rtcp:" as defined in [14]). separate attribute (for example "a=rtcp:" as defined in [17]).
If multiple addresses are specified in the "c=" field and multiple If multiple addresses are specified in the "c=" field and multiple
ports are specified in the "m=" field, a one-to-one mapping from port ports are specified in the "m=" field, a one-to-one mapping from
to the corresponding address is implied. For example: port to the corresponding address is implied. For example:
c=IN IP4 224.2.1.1/127/2 c=IN IP4 224.2.1.1/127/2
m=video 49170/2 RTP/AVP 31 m=video 49170/2 RTP/AVP 31
would imply that address 224.2.1.1 is used with ports 49170 and would imply that address 224.2.1.1 is used with ports 49170 and
49171, and address 224.2.1.2 is used with ports 49172 and 49173. 49171, and address 224.2.1.2 is used with ports 49172 and 49173.
The third sub-field ("<proto>") is the transport protocol. The <proto> is the transport protocol. The meaning of the transport
transport protocol values are dependent on the address type field in protocol is dependent on the address type field in the relevant
the "c=" fields. Thus a "c=" field of IP4 defines that the transport "c=" field. Thus a "c=" field of IP4 indicates that the transport
protocol runs over IP4. For IP4, it is normally expected that most protocol runs over IP4. The following transport protocols are
media traffic will be carried as RTP over UDP. The following defined, but may be extended through registration of new protocols
transport protocols are defined, but may be extended through with IANA (see Section 9):
registration of new protocols with IANA (see Section 9):
RTP/AVP - the IETF's Realtime Transport Protocol using the
Audio/Video profile carried over UDP.
udp - User Datagram Protocol
If an application uses a single combined proprietary media format and
transport protocol over UDP, then simply specifying the transport
protocol as udp and using the format field to distinguish the
combined protocol is recommended. If a transport protocol is used
over UDP to carry several distinct media types that need to be
distinguished by a session directory, then specifying the transport
protocol and media format separately is necessary. RTP is an example
of a transport-protocol that carries multiple payload formats that
must be distinguished by the session directory for it to know how to
start appropriate tools, relays, mixers or recorders.
The main reason to specify the transport-protocol in addition to the
media format is that the same standard media formats may be carried
over different transport protocols even when the network protocol is
the same - a historical example is vat PCM audio and RTP PCM audio.
In addition, relays and monitoring tools that are
transport-protocol-specific but format-independent are possible.
For RTP media streams operating under the RTP Audio/Video Profile
[13], the protocol field is "RTP/AVP". Should other RTP profiles be
defined in the future, their profiles will be specified in the same
way. For example, the protocol field "RTP/XYZ" would specify RTP
operating under a profile whose short name is "XYZ".
The fourth and subsequent sub-fields ("<fmt>") are media formats.
For audio, text and video, these SHOULD reference a MIME sub-type
describing the format under the "audio", "text" and "video" top-level
MIME types.
When a list of payload formats is given, this implies that all of
these formats may be used in the session, but the first of these
formats SHOULD be used as the default format for the session.
For media whose transport protocol is not RTP or UDP the format field
is protocol specific. Such formats should be defined in an
additional specification document.
For media whose transport protocol is RTP, SDP can be used to provide
a dynamic binding of media encoding to RTP payload type. The encoding
names in the RTP AV Profile do not specify unique audio encodings (in
terms of clock rate and number of audio channels), and so they are
not used directly in SDP format fields. Instead, the payload type
number should be used to specify the format for static payload types
and the payload type number along with additional encoding
information should be used for dynamically allocated payload types.
An example of a static payload type is u-law PCM coded single channel
audio sampled at 8kHz. This is completely defined in the RTP Audio/
Video profile as payload type 0, so the media field for such a stream
sent to UDP port 49232 is:
m=audio 49232 RTP/AVP 0
An example of a dynamic payload type is 16 bit linear encoded stereo
audio sampled at 16 kHz. If we wish to use dynamic RTP/AVP payload
type 98 for such a stream, additional information is required to
decode it:
m=audio 49232 RTP/AVP 98
a=rtpmap:98 L16/16000/2
The general form of an rtpmap attribute is:
a=rtpmap:<payload type> <encoding name>/<clock rate>
[/<encoding parameters>]
For audio streams, <encoding parameters> may specify the number of
audio channels. This parameter may be omitted if the number of
channels is one provided no additional parameters are needed.
For video streams, no encoding parameters are currently specified.
Additional parameters may be defined in the future, but codec- * udp: denotes an unspecified protocol running over UDP.
specific parameters SHOULD NOT be added. Parameters added to an
rtpmap attribute SHOULD only be those required for a session
directory to make the choice of appropriate media to participate in a
session. Codec-specific parameters should be added in other
attributes (for example, "a=fmtp:").
Up to one rtpmap attribute can be defined for each media format * RTP/AVP: denotes RTP [14] used under the RTP Profile for Audio
specified. Thus we might have: and Video Conferences with Minimal Control [15] running over
UDP.
m=audio 49230 RTP/AVP 96 97 98 * RTP/SAVP: denotes the Secure Real-time Transport Protocol [18]
a=rtpmap:96 L8/8000 running over UDP.
a=rtpmap:97 L16/8000
a=rtpmap:98 L16/11025/2
RTP profiles that specify the use of dynamic payload types MUST The main reason to specify the transport-protocol in addition to
define the set of valid encoding names and/or a means to register the media format is that the same standard media formats may be
encoding names if that profile is to be used with SDP. carried over different transport protocols even when the network
protocol is the same - a historical example is vat PCM audio and
RTP PCM audio. In addition, relays and monitoring tools that are
transport-protocol-specific but format-independent are possible.
Note that RTP audio formats typically do not include information <fmt> is a media format description. The fourth and any subsequent
about the number of samples per packet. If a non-default (as defined sub-fields describe the format of the media. The interpretation
in the RTP Audio/Video Profile) packetisation is required, the of the media format depends on the value of the <proto> sub-field.
"ptime" attribute is used as given below.
For more details on RTP audio and video formats, see [13]. If the <proto> sub-field is "RTP/AVP" or "RTP/SAVP" the <fmt>
sub-fields contain RTP payload type numbers. When a list of
payload type numbers is given, this implies that all of these
payload formats MAY be used in the session, but the first of these
formats SHOULD be used as the default format for the session. For
dynamic payload type assignments the "a=rtpmap:" attribute (see
Section 6) SHOULD be used to map from an RTP payload type number
to a media encoding name that identifies the payload format. The
"a=fmtp:" attribute MAY be used to specify format parameters (see
Section 6).
Predefined application formats for the UDP protocol with non-RTP If the <proto> sub-field is "udp" the <fmt> sub-fields MUST
media are as below: reference a media type describing the format under the "audio",
"text" and "video" top-level MIME types. The media type
registration SHOULD define the packetization format for use with
UDP transport.
wb: LBL Whiteboard (transport: udp) For media using other transport protocols, the <fmt> field is
nt: UCL Network Text Editor (transport: udp) protocol specific. Rules for interpretation of the <fmt>
sub-field MUST be defined when registering new protocols (see
section 9.2.2).
6. Suggested Attributes 6. Suggested Attributes
The following attributes are defined. Since application writers may The following attributes are defined. Since application writers may
add new attributes as they are required, this list is not exhaustive. add new attributes as they are required, this list is not exhaustive.
Registration procedures for new attributes are defined in Section
9.2.4.
a=cat:<category> a=cat:<category>
This attribute gives the dot-separated hierarchical category This attribute gives the dot-separated hierarchical category
of the session. This is to enable a receiver to filter of the session. This is to enable a receiver to filter
unwanted sessions by category. It is a session-level unwanted sessions by category. It is a session-level
attribute, and is not dependent on charset. attribute, and is not dependent on charset.
a=keywds:<keywords> a=keywds:<keywords>
skipping to change at page 25, line 42 skipping to change at page 25, line 8
size. This attribute is probably only meaningful for audio size. This attribute is probably only meaningful for audio
data, but may be used with other media types if it makes data, but may be used with other media types if it makes
sense. It is a media attribute, and is not dependent on sense. It is a media attribute, and is not dependent on
charset. Note that this attribute was introduced after RFC charset. Note that this attribute was introduced after RFC
2327, and non updated implementations will ignore this 2327, and non updated implementations will ignore this
attribute. attribute.
a=rtpmap:<payload type> <encoding name>/<clock rate> a=rtpmap:<payload type> <encoding name>/<clock rate>
[/<encoding parameters>] [/<encoding parameters>]
See Section 5.14. This is a media level attribute that is not This attribute maps from an RTP payload type number (as used in
an "m=" line) to an encoding name denoting the payload format
to be used. It also provides information on the clock rate and
encoding parameters. It is a media level attribute that is not
dependent on charset. dependent on charset.
While an RTP profile may make static assignments of payload
type numbers to payload formats, it is more common for that
assignment to be done dynamically using "a=rtpmap:" attributes.
As an example of a static payload type, consider u-law PCM
coded single channel audio sampled at 8kHz. This is completely
defined in the RTP Audio/Video profile as payload type 0, so
there is no need for an "a=rtpmap: attribute, and the media for
such a stream sent to UDP port 49232 can be specified as:
m=audio 49232 RTP/AVP 0
An example of a dynamic payload type is 16 bit linear encoded
stereo audio sampled at 16 kHz. If we wish to use the dynamic
RTP/AVP payload type 98 for this stream, additional information
is required to decode it:
m=audio 49232 RTP/AVP 98
a=rtpmap:98 L16/16000/2
Up to one rtpmap attribute can be defined for each media format
specified. Thus we might have:
m=audio 49230 RTP/AVP 96 97 98
a=rtpmap:96 L8/8000
a=rtpmap:97 L16/8000
a=rtpmap:98 L16/11025/2
RTP profiles that specify the use of dynamic payload types MUST
define the set of valid encoding names and/or a means to
register encoding names if that profile is to be used with SDP.
The "RTP/AVP" and "RTP/SAVP" profiles use MIME sub-types for
encoding names, under the top-level media type denoted in the
"m=" line. In the example above, the media types are "audio/l8"
and "audio/l16".
For audio streams, <encoding parameters> indicates the
number of audio channels. This parameter is OPTIONAL and
may be omitted if the number of channels is one, provided
no additional parameters are needed.
For video streams, no encoding parameters are currently
specified.
Additional encoding parameters MAY be defined in the future,
but codec specific parameters SHOULD NOT be added. Parameters
added to an "a=rtpmap:" attribute SHOULD only be those required
for a session directory to make the choice of appropriate media
to participate in a session. Codec-specific parameters should
be added in other attributes (for example, "a=fmtp:").
Note: RTP audio formats typically do not include information
about the number of samples per packet. If a non-default (as
defined in the RTP Audio/Video Profile) packetisation is
required, the "ptime" attribute is used as given below.
a=recvonly a=recvonly
This specifies that the tools should be started in receive This specifies that the tools should be started in receive
only mode where applicable. It can be either a session or only mode where applicable. It can be either a session or
media attribute, and is not dependent on charset. Note that media attribute, and is not dependent on charset. Note that
recvonly applies to the media only, not to any associated recvonly applies to the media only, not to any associated
control protocol (e.g. an RTP based system in recvonly mode control protocol (e.g. an RTP based system in recvonly mode
SHOULD still send RTCP packets). SHOULD still send RTCP packets).
a=sendrecv a=sendrecv
skipping to change at page 31, line 50 skipping to change at page 32, line 25
Use of the "k=" field poses a significant security risk, since it Use of the "k=" field poses a significant security risk, since it
conveys session encryption keys in the clear. SDP MUST NOT be used conveys session encryption keys in the clear. SDP MUST NOT be used
to convey key material, unless it can be guaranteed that the channel to convey key material, unless it can be guaranteed that the channel
over which the SDP is delivered is both private and authenticated. over which the SDP is delivered is both private and authenticated.
9. IANA Considerations 9. IANA Considerations
9.1 The "application/sdp" media type 9.1 The "application/sdp" media type
One MIME type is to be registered, as defined below. This updates the One MIME type is to be registered, as defined below. This updates
previous definition from RFC 2327. the previous definition from RFC 2327.
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of MIME media type application/sdp Subject: Registration of media type "application/sdp"
MIME media type name: application MIME media type name: application
MIME subtype name: sdp MIME subtype name: sdp
Required parameters: None. Required parameters: None.
Optional parameters: None. Optional parameters: None.
Encoding considerations: Encoding considerations:
See section 5 of RFC XXXX See section 5 of RFC XXXX
Security considerations: Security considerations:
See section 8 of RFC XXXX See section 8 of RFC XXXX
Interoperability considerations: Interoperability considerations:
See RFC XXXX See RFC XXXX
Published specification: Published specification:
RFC XXXX See RFC XXXX
Applications which use this media type: Applications which use this media type:
Voice over IP, video teleconferencing, streaming media, instant Voice over IP, video teleconferencing, streaming media, instant
messaging, etc. See also section 3 of RFC XXXX. messaging, etc. See also section 3 of RFC XXXX.
Additional information: Additional information:
Magic number(s): None. Magic number(s): None.
File extension(s): The extension ".sdp" is commonly used. File extension(s): The extension ".sdp" is commonly used.
Macintosh File Type Code(s): "sdp " Macintosh File Type Code(s): "sdp "
Person & email address to contact for further information: Person & email address to contact for further information:
Colin Perkins <csp@csperkins.org> Colin Perkins <csp@csperkins.org>
IETF MMUSIC working group IETF MMUSIC working group
Intended usage: COMMON Intended usage: COMMON
Author/Change controller: Author/Change controller:
Authors of RFC XXXX Authors of RFC XXXX
IETF MMUSIC working group IETF MMUSIC working group delegated from the IESG
9.2 Registration of Parameters 9.2 Registration of Parameters
There are seven field names that may be registered with IANA. Using There are seven field names that may be registered with IANA. Using
the terminology in the SDP specification BNF, they are "media", the terminology in the SDP specification BNF, they are "media",
"proto", "fmt", "att-field", "bwtype", "nettype" and "addrtype". "proto", "fmt", "att-field", "bwtype", "nettype" and "addrtype".
9.2.1 Media types ("media") 9.2.1 Media types ("media")
The set of media types is intended to be small and SHOULD NOT be The set of media types is intended to be small and SHOULD NOT be
skipping to change at page 33, line 26 skipping to change at page 33, line 47
justification why no existing media name is appropriate (the justification why no existing media name is appropriate (the
"Standards Action" policy of RFC 2434 [5]. "Standards Action" policy of RFC 2434 [5].
This memo registers the media types "audio", "video", "text", This memo registers the media types "audio", "video", "text",
"application", "data" and "control". "application", "data" and "control".
9.2.2 Transport protocols ("proto") 9.2.2 Transport protocols ("proto")
The "proto" field describes the transport protocol used. This SHOULD The "proto" field describes the transport protocol used. This SHOULD
reference a standards-track protocol RFC. This memo registers three reference a standards-track protocol RFC. This memo registers three
values: "RTP/AVP" is a reference to RTP [12] used under the RTP values: "RTP/AVP" is a reference to RTP [14] used under the RTP
Profile for Audio and Video Conferences with Minimal Control [13] Profile for Audio and Video Conferences with Minimal Control [15]
running over UDP/IP, "RTP/SAVP" is a reference to the Secure running over UDP/IP, "RTP/SAVP" is a reference to the Secure
Real-time Transport Protocol [15], and "udp" indicates an unspecified Real-time Transport Protocol [18], and "udp" indicates an unspecified
format over UDP. protocol over UDP.
New transport protocols MAY be registered with IANA. Registrations If other RTP profiles are defined in the future, their "proto" name
MUST reference an RFC describing the protocol. Such an RFC MAY be SHOULD be specified in the same manner. For example, an RTP profile
Experimental or Informational, although it is preferable if it is whose short name is "XYZ" would be denoted by a "proto" field of
Standards-Track. Registrations MUST also define the rules by which "RTP/XYZ".
their "fmt" namespace is managed (see below).
New transport protocols SHOULD be registered with IANA.
Registrations MUST reference an RFC describing the protocol. Such an
RFC MAY be Experimental or Informational, although it is preferable
if it is Standards-Track. Registrations MUST also define the rules
by which their "fmt" namespace is managed (see below).
9.2.3 Media formats ("fmt") 9.2.3 Media formats ("fmt")
Each transport protocol, defined by the "proto" field, has an Each transport protocol, defined by the "proto" field, has an
associated "fmt" namespace that describes the media formats which may associated "fmt" namespace that describes the media formats which may
conveyed by that protocol. Formats cover all the possible encodings conveyed by that protocol. Formats cover all the possible encodings
that might want to be transported in a multimedia session. that might want to be transported in a multimedia session.
RTP payload formats under the "RTP/AVP" and "RTP/SAVP" profiles MUST RTP payload formats under the "RTP/AVP" and "RTP/SAVP" profiles MUST
use the payload type number as their "fmt" value. If the payload use the payload type number as their "fmt" value. If the payload
skipping to change at page 34, line 10 skipping to change at page 34, line 37
additional "rtpmap" attribute MUST be included to specify the format additional "rtpmap" attribute MUST be included to specify the format
name and parameters as defined by the MIME type registration for the name and parameters as defined by the MIME type registration for the
payload format. It is RECOMMENDED that other RTP profiles which are payload format. It is RECOMMENDED that other RTP profiles which are
registered (in combination with RTP) as SDP transport protocols registered (in combination with RTP) as SDP transport protocols
specify the same rules for the "fmt" namespace. specify the same rules for the "fmt" namespace.
For the "udp" protocol, new formats SHOULD be registered. Use of an For the "udp" protocol, new formats SHOULD be registered. Use of an
existing MIME subtype for the format is encouraged. If no MIME existing MIME subtype for the format is encouraged. If no MIME
subtype exists, it is RECOMMENDED that a suitable one is registered subtype exists, it is RECOMMENDED that a suitable one is registered
through the IETF process (RFC 2048) by production of, or reference through the IETF process (RFC 2048) by production of, or reference
to, a standards-track RFC. If a MIME subtype is for some reason to, a standards-track RFC that defines the transport protocol for the
inappropriate, an RFC publication describing the format MUST be format.
referenced in the registration, but it may be Informational or
Experimental if the protocol is not deemed to be of widespread
deployment.
For other protocols, formats MAY be registered according to the rules For other protocols, formats MAY be registered according to the rules
of the associated "proto" specification. of the associated "proto" specification.
Registrations of new formats MUST specify which transport protocols Registrations of new formats MUST specify which transport protocols
they apply to. they apply to.
9.2.4 Attribute names ("att-field") 9.2.4 Attribute names ("att-field")
Attribute field names ("att-field") MUST be registered with IANA and Attribute field names ("att-field") MUST be registered with IANA and
skipping to change at page 36, line 8 skipping to change at page 37, line 4
New network types (the "nettype" field) may be registered with IANA New network types (the "nettype" field) may be registered with IANA
if SDP needs to be used in the context of non-Internet environments. if SDP needs to be used in the context of non-Internet environments.
Whilst these are not normally the preserve of IANA, there may be Whilst these are not normally the preserve of IANA, there may be
circumstances when an Internet application needs to interoperate with circumstances when an Internet application needs to interoperate with
a non- Internet application, such as when gatewaying an Internet a non- Internet application, such as when gatewaying an Internet
telephony call into the PSTN. The number of network types should be telephony call into the PSTN. The number of network types should be
small and should be rarely extended. A new network type cannot be small and should be rarely extended. A new network type cannot be
registered without registering at least one address type to be used registered without registering at least one address type to be used
with that network type. A new network type registration MUST with that network type. A new network type registration MUST
reference an RFC which gives details of the network type and address reference an RFC which gives details of the network type and address
type and specifies how and when they would be used. Such an RFC MAY type and specifies how and when they would be used.
be Informational.
IANA is requested to register the network type "IN" to represent the IANA is requested to register the network type "IN" to represent the
Internet, with definition as in Sections 5.2 and 5.7 of this memo Internet, with definition as in Sections 5.2 and 5.7 of this memo
(these definitions update those in RFC 2327). (these definitions update those in RFC 2327).
9.2.7 Address types ("addrtype") 9.2.7 Address types ("addrtype")
New address types ("addrtype") may be registered with IANA. An New address types ("addrtype") may be registered with IANA. An
address type is only meaningful in the context of a network type, and address type is only meaningful in the context of a network type, and
any registration of an address type MUST specify a registered network any registration of an address type MUST specify a registered network
type, or be submitted along with a network type registration. A new type, or be submitted along with a network type registration. A new
address type registration MUST reference an RFC giving details of the address type registration MUST reference an RFC giving details of the
syntax of the address type. Such an RFC MAY be Informational. syntax of the address type. Address types are not expected to be
Address types are not expected to be registered frequently. registered frequently.
IANA is requested to register the address types "IP4" and "IP6" with IANA is requested to register the address types "IP4" and "IP6" with
definitions as in Sections 5.2 and 5.7 of this memo (these definitions as in Sections 5.2 and 5.7 of this memo (these
definitions update those in RFC 2327). definitions update those in RFC 2327).
9.2.8 Registration Procedure 9.2.8 Registration Procedure
In the RFC documentation that registers SDP "media", "proto", "fmt", In the RFC documentation that registers SDP "media", "proto", "fmt",
"bwtype", "nettype" and "addrtype" fields, the authors MUST include "bwtype", "nettype" and "addrtype" fields, the authors MUST include
the following information for IANA to place in the appropriate the following information for IANA to place in the appropriate
skipping to change at page 36, line 35 skipping to change at page 37, line 30
IANA is requested to register the address types "IP4" and "IP6" with IANA is requested to register the address types "IP4" and "IP6" with
definitions as in Sections 5.2 and 5.7 of this memo (these definitions as in Sections 5.2 and 5.7 of this memo (these
definitions update those in RFC 2327). definitions update those in RFC 2327).
9.2.8 Registration Procedure 9.2.8 Registration Procedure
In the RFC documentation that registers SDP "media", "proto", "fmt", In the RFC documentation that registers SDP "media", "proto", "fmt",
"bwtype", "nettype" and "addrtype" fields, the authors MUST include "bwtype", "nettype" and "addrtype" fields, the authors MUST include
the following information for IANA to place in the appropriate the following information for IANA to place in the appropriate
registry: registry:
o contact name, email address and telephone number o contact name, email address and telephone number
o name being registered (as it will appear in SDP) o name being registered (as it will appear in SDP)
o long-form name in English o long-form name in English
o type of name ("media", "proto", "fmt", "bwtype", "nettype", or o type of name ("media", "proto", "fmt", "bwtype", "nettype", or
"addrtype") "addrtype")
o a one paragraph explanation of the purpose of the registered name. o a one paragraph explanation of the purpose of the registered name.
o a reference to the specification (e.g. RFC number) of the
registered name. o a reference to the specification for the registered name (this
will typically be an RFC number).
IANA may refer any registration to the IESG Transport Area Directors IANA may refer any registration to the IESG Transport Area Directors
for review, and may request revisions to be made before a for review, and may request revisions to be made before a
registration will be made. registration will be made.
9.3 Encryption Key Access Methods 9.3 Encryption Key Access Methods
The IANA currently maintains a table of SDP encryption key access The IANA currently maintains a table of SDP encryption key access
method ("enckey") names. This table is obsolete and SHOULD be method ("enckey") names. This table is obsolete and SHOULD be
removed, since the "k=" line is not extensible. New registrations removed, since the "k=" line is not extensible. New registrations
skipping to change at page 38, line 45 skipping to change at page 39, line 46
sess-version = 1*DIGIT sess-version = 1*DIGIT
;0 is a new session ;0 is a new session
nettype = token nettype = token
;typically "IN" ;typically "IN"
addrtype = token addrtype = token
;typically "IP4" or "IP6" ;typically "IP4" or "IP6"
; sub-rules of 'u=' ; sub-rules of 'u='
uri = URI-reference; see RFC1630 and RFC2732 uri = URI-reference
; see RFC2396 and RFC2732
; sub-rules of 'e=' ; sub-rules of 'e='
email-address = email *SP "(" 1*email-safe ")" / email-address = email *SP "(" 1*email-safe ")" /
1*email-safe "<" email ">" / 1*email-safe "<" email ">" /
email email
email = addr-spec ; defined in RFC2822 email = addr-spec ; defined in RFC2822
; modified to remove CFWS ; modified to remove CFWS
; sub-rules of 'p=' ; sub-rules of 'p='
phone-number = phone *SP "(" 1*email-safe ")" / phone-number = phone *SP "(" 1*email-safe ")" /
1*email-safe "<" phone ">" / 1*email-safe "<" phone ">" /
phone phone
phone = "+" POS-DIGIT 1*(SP / "-" / DIGIT) phone = ["+"] DIGIT 1*(SP / "-" / DIGIT)
; sub-rules of 'c=' ; sub-rules of 'c='
connection-address = multicast-address / unicast-address connection-address = multicast-address / unicast-address
; sub-rules of 'b=' ; sub-rules of 'b='
bwtype = token bwtype = token
bandwidth = 1*DIGIT bandwidth = 1*DIGIT
; sub-rules of 't=' ; sub-rules of 't='
start-time = time / "0" start-time = time / "0"
stop-time = time / "0" stop-time = time / "0"
time = POS-DIGIT 9*DIGIT time = POS-DIGIT 9*DIGIT
; 10-digit NTP time represents times between ; Decimal representation of NTP time in
; 1931 and 5068 AD. 9* allows times after ; seconds since 1900. The representation
; that as well. ; of NTP time is an unbounded length field
; containing at least 10 digits. Unlike the
; 64-bit representation used elsewhere, time
; in SDP does not wrap in the year 2036.
; sub-rules of 'r=' and 'z=' ; sub-rules of 'r=' and 'z='
repeat-interval = POS-DIGIT *DIGIT [fixed-len-time-unit] repeat-interval = POS-DIGIT *DIGIT [fixed-len-time-unit]
typed-time = 1*DIGIT [fixed-len-time-unit] typed-time = 1*DIGIT [fixed-len-time-unit]
fixed-len-time-unit = "d" / "h" / "m" / "s" fixed-len-time-unit = "d" / "h" / "m" / "s"
; sub-rules of 'k=' ; sub-rules of 'k='
key-type = "prompt" / key-type = "prompt" /
"clear:" text / "clear:" text /
"base64:" base64 / "base64:" base64 /
"uri:" uri / "uri:" uri
key-method [ ":" text ]
base64 = *base64-unit [base64-pad] base64 = *base64-unit [base64-pad]
base64-unit = 4base64-char base64-unit = 4base64-char
base64-pad = 2base64-char "==" / 3base64-char "=" base64-pad = 2base64-char "==" / 3base64-char "="
base64-char = ALPHA / DIGIT / "+" / "/" base64-char = ALPHA / DIGIT / "+" / "/"
key-method = token
; sub-rules of 'a=' ; sub-rules of 'a='
attribute = (att-field ":" att-value) / att-field attribute = (att-field ":" att-value) / att-field
att-field = token att-field = token
att-value = byte-string att-value = byte-string
; sub-rules of 'm=' ; sub-rules of 'm='
media = token media = token
;typically "audio", "video", "text", ;typically "audio", "video", "text",
skipping to change at page 40, line 32 skipping to change at page 41, line 35
port = 1*DIGIT port = 1*DIGIT
;should be either "0" or in the range "1024" ;should be either "0" or in the range "1024"
;to "65535" inclusive for UDP based media ;to "65535" inclusive for UDP based media
;(a value of "0" is used to signal special ;(a value of "0" is used to signal special
;conditions in some uses of SDP) ;conditions in some uses of SDP)
; generic sub-rules: addressing ; generic sub-rules: addressing
unicast-address = IP4-address / IP6-address / FQDN / extn-addr unicast-address = IP4-address / IP6-address / FQDN / extn-addr
multicast-address = IP4-multicast / IP6-multicast multicast-address = IP4-multicast / IP6-multicast / extn-addr
IP4-multicast = m1 3( "." decimal-uchar ) IP4-multicast = m1 3( "." decimal-uchar )
"/" ttl [ "/" integer ] "/" ttl [ "/" integer ]
; IPv4 multicast addresses may be in the ; IPv4 multicast addresses may be in the
; range 224.0.0.0 to 239.255.255.255 ; range 224.0.0.0 to 239.255.255.255
m1 = ("22" ("4"/"5"/"6"/"7"/"8"/"9")) / m1 = ("22" ("4"/"5"/"6"/"7"/"8"/"9")) /
("23" DIGIT ) ("23" DIGIT )
IP6-multicast = hexpart [ "/" integer ] IP6-multicast = hexpart [ "/" integer ]
skipping to change at page 41, line 47 skipping to change at page 43, line 4
email-safe = %x01-09/%x0B-0C/%x0E-27/%x2A-3B/%x3D/%x3F-FF email-safe = %x01-09/%x0B-0C/%x0E-27/%x2A-3B/%x3D/%x3F-FF
;any byte except NUL, CR, LF, or the quoting ;any byte except NUL, CR, LF, or the quoting
;characters ()<> ;characters ()<>
integer = POS-DIGIT *DIGIT integer = POS-DIGIT *DIGIT
; generic sub-rules: primitives ; generic sub-rules: primitives
alpha-numeric = ALPHA / DIGIT alpha-numeric = ALPHA / DIGIT
POS-DIGIT = %x31-39 ; 1 - 9 POS-DIGIT = %x31-39 ; 1 - 9
decimal-uchar = DIGIT decimal-uchar = DIGIT
/ POS-DIGIT DIGIT / POS-DIGIT DIGIT
/ ("1" 2*(DIGIT)) / ("1" 2*(DIGIT))
/ ("2" ("0"/"1"/"2"/"3"/"4") DIGIT) / ("2" ("0"/"1"/"2"/"3"/"4") DIGIT)
/ ("2" "5" ("0"/"1"/"2"/"3"/"4"/"5")) / ("2" "5" ("0"/"1"/"2"/"3"/"4"/"5"))
; external references: ; external references:
; ALPHA, DIGIT, CRLF, SP, VCHAR: from RFC 2234 ; ALPHA, DIGIT, CRLF, SP, VCHAR: from RFC 2234
; URI-reference: from RFC1630 and RFC2732 ; URI-reference: from RFC2396 and RFC2732
; addr-spec: from RFC 2822 ; addr-spec: from RFC 2822
Appendix B. Acknowledgments Appendix B. Acknowledgments
Many people in the IETF MMUSIC working group have made comments and Many people in the IETF MMUSIC working group have made comments and
suggestions contributing to this document. In particular, we would suggestions contributing to this document. In particular, we would
like to thank Eve Schooler, Steve Casner, Bill Fenner, Allison like to thank Eve Schooler, Steve Casner, Bill Fenner, Allison
Mankin, Ross Finlayson, Peter Parnes, Joerg Ott, Carsten Bormann, Mankin, Ross Finlayson, Peter Parnes, Joerg Ott, Carsten Bormann,
Steve Hanna, Jonathan Lennox and Keith Drage. Steve Hanna, Jonathan Lennox and Keith Drage.
skipping to change at page 42, line 38 skipping to change at page 43, line 42
[3] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC [3] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998. 2279, January 1998.
[4] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource [4] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
Identifiers (URI): Generic Syntax", RFC 2396, August 1998. Identifiers (URI): Generic Syntax", RFC 2396, August 1998.
[5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA [5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[6] Alvestrand, H., "Tags for the Identification of Languages", BCP [6] Hinden, R., Carpenter, B. and L. Masinter, "Format for Literal
IPv6 Addresses in URL's", RFC 2732, December 1999.
[7] Alvestrand, H., "Tags for the Identification of Languages", BCP
47, RFC 3066, January 2001. 47, RFC 3066, January 2001.
10.2 Informative References 10.2 Informative References
[7] Mills, D., "Network Time Protocol (Version 3) Specification, [8] Mills, D., "Network Time Protocol (Version 3) Specification,
Implementation", RFC 1305, March 1992. Implementation", RFC 1305, March 1992.
[8] Handley, M., Perkins, C. and E. Whelan, "Session Announcement [9] Handley, M., Perkins, C. and E. Whelan, "Session Announcement
Protocol", RFC 2974, October 2000. Protocol", RFC 2974, October 2000.
[9] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [10] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[10] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming [11] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming
Protocol (RTSP)", RFC 2326, April 1998. Protocol (RTSP)", RFC 2326, April 1998.
[11] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with [12] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002. Session Description Protocol (SDP)", RFC 3264, June 2002.
[12] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, [13] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
"RTP: A Transport Protocol for Real-Time Applications", RFC RFC 3548, July 2003.
3550, July 2003.
[13] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video [14] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
Conferences with Minimal Control", RFC 3551, July 2003. "RTP: A Transport Protocol for Real-Time Applications", STD 64,
RFC 3550, July 2003.
[14] Huitema, C., "Real Time Control Protocol (RTCP) attribute in [15] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
Conferences with Minimal Control", STD 65, RFC 3551, July 2003.
[16] Casner, S., "Session Description Protocol (SDP) Bandwidth
Modifiers for RTP Control Protocol (RTCP) Bandwidth", RFC 3556,
July 2003.
[17] Huitema, C., "Real Time Control Protocol (RTCP) attribute in
Session Description Protocol (SDP)", RFC 3605, October 2003. Session Description Protocol (SDP)", RFC 3605, October 2003.
[15] Baugher, M., McGrew, D., Naslund, M., Carrara, E. and K. [18] Baugher, M., McGrew, D., Naslund, M., Carrara, E. and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC
3711, March 2004. 3711, March 2004.
[16] International Telecommunications Union, "H.323 extended for [19] International Telecommunications Union, "H.323 extended for
loosely coupled conferences", ITU Recommendation H.332, loosely coupled conferences", ITU Recommendation H.332,
September 1998. September 1998.
[17] Arkko, J., "Key Management Extensions for Session Description [20] Arkko, J., Carrara, E., Lindholm, F., Naslund, M. and K.
Norrman, "Key Management Extensions for Session Description
Protocol (SDP) and Real Time Streaming Protocol (RTSP)", Protocol (SDP) and Real Time Streaming Protocol (RTSP)",
draft-ietf-mmusic-kmgmt-ext-09 (work in progress), October draft-ietf-mmusic-kmgmt-ext-11 (work in progress), April 2004.
2003.
[18] Andreasen, F., Baugher, M. and D. Wing, "SDP Security [21] Andreasen, F., Baugher, M. and D. Wing, "Session Description
Descriptions for Media Streams", Protocol Security Descriptions for Media Streams",
draft-ietf-mmusic-sdescriptions-02 (work in progress), October draft-ietf-mmusic-sdescriptions-07 (work in progress), July
2003. 2004.
[22] Westerlund, M., "A Transport Independent Bandwidth Modifier for
the Session Description Protocol (SDP)",
draft-ietf-mmusic-sdp-bwparam-06 (work in progress), April
2004.
Authors' Addresses Authors' Addresses
Mark Handley Mark Handley
University College London University College London
Department of Computer Science
Gower Street Gower Street
London WC1E 6BT London WC1E 6BT
UK UK
EMail: M.Handley@cs.ucl.ac.uk EMail: M.Handley@cs.ucl.ac.uk
Van Jacobson Van Jacobson
Packet Design Packet Design
2465 Latham Street 2465 Latham Street
Mountain View, CA 94040 Mountain View, CA 94040
USA USA
EMail: van@packetdesign.com EMail: van@packetdesign.com
Colin Perkins Colin Perkins
University of Glasgow University of Glasgow
skipping to change at page 44, line 14 skipping to change at page 45, line 32
Van Jacobson Van Jacobson
Packet Design Packet Design
2465 Latham Street 2465 Latham Street
Mountain View, CA 94040 Mountain View, CA 94040
USA USA
EMail: van@packetdesign.com EMail: van@packetdesign.com
Colin Perkins Colin Perkins
University of Glasgow University of Glasgow
Department of Computing Science
17 Lilybank Gardens 17 Lilybank Gardens
Glasgow G12 8QQ Glasgow G12 8QQ
UK UK
EMail: csp@csperkins.org EMail: csp@csperkins.org
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