draft-ietf-mmusic-sdp-01.txt   draft-ietf-mmusic-sdp-02.txt 
Internet Engineering Task Force MMUSIC WG Internet Engineering Task Force MMUSIC WG
INTERNET-DRAFT Mark Handley/Van Jacobson INTERNET-DRAFT Mark Handley/Van Jacobson
draft-ietf-mmusic-sdp-01.ps UCL/LBL draft-ietf-mmusic-sdp-02.txt ISI/LBNL
22nd Nov 1995 21st Nov 1996
Expires: 22nd May 1995 Expires: 21st May 1997
SDP: Session Description Protocol SDP: Session Description Protocol
Status of this Memo Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working docu- This document is an Internet-Draft. Internet-Drafts are working docu-
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working groups. Note that other groups may also distribute working working groups. Note that other groups may also distribute working
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Distribution of this document is unlimited. Distribution of this document is unlimited.
Abstract Abstract
The sd session directory tool has been in use for some time on This document defined the Session Description Protocol, SDP.
the Mbone for announcing multicast sessions. This document SDP is intended for describing multimedia sessions for the
describes an enhanced version of the sd protocol (SDP v2), and purposes of session announcement, session invitation, and
explains the extensions to the protocol that have become other forms of session initiation.
desirable.
This document is a product of the Multiparty Multimedia Session Control This document is a product of the Multiparty Multimedia Session Control
(MMUSIC) working group of the Internet Engineering Task Force. Comments (MMUSIC) working group of the Internet Engineering Task Force. Comments
are solicited and should be addressed to the working group's mailing are solicited and should be addressed to the working group's mailing
list at confctrl@isi.edu and/or the authors. list at confctrl@isi.edu and/or the authors.
1. Introduction 1. Introduction
The LBL session directory tool (sd) has been in use on the Mbone for On the Internet multicast backbone (Mbone), a session directory tool is
some time to advertise multimedia conferences and communicate the used to advertise multimedia conferences and communicate the conference
conference addresses and conference tool specific information necessary addresses and conference tool-specific information necessary for parti-
cipation. This document defines a session description protocol for this
for participation. This document defines an extended version of the purpose, and for general real-time multimedia session description pur-
session directory protocol and some extensions to the protocol that have poses. This draft does not describe multicast address allocation or the
become desirable. In the body of the paper, we describe a proposed Ses- distribution of SDP messages in detail. These are described in accom-
sion Description Protocol (SDP v2). In Appendix A, we describe how this panying drafts.
differs from the protocol currently used by sd (SDP v1). This draft
does not describe multicast address allocation or the distribution of
SDP messages in detail - these are left to accompanying drafts.
2. Background 2. Background
The Multicast Backbone (Mbone) is an experimental overlay network on the The Mbone is the part of the internet that supports IP multicast, and
internet that permits efficient many to many communication. For the thus permits efficient many-to-many communication. It is used exten-
past few years it has been used extensively for multimedia conferencing. sively for multimedia conferencing. Such conferences usually have the
Such multimedia conferences usually have the property that tight coordi- property that tight coordination of conference membership is not neces-
nation of conference membership is not necessary; in order to receive a sary; to receive a conference, a user at an Mbone site only has to know
conference, a user at an Mbone site has to know only the correct multi- the conference's multicast group address and the UDP ports for the
cast group address for the conference and the UDP ports the conferencing conference data streams.
applications will use to receive the conference data streams.
In order to assist the advertisement of conference sessions and to com- Session directories assist the advertisement of conference sessions and
municate the relevant conference setup information to prospective parti- communicate the relevant conference setup information to prospective
cipants, the session directory (sd) tool was written. Sd has now been participants.
in wide scale use for close to 2 years, during which time Mbone usage
has greatly increased and diversified. The Mbone has now reached the
stage where assistance with coordination of resource usage is required,
and where compatible session announcement tools are starting to emerge.
This document is an attempt to prevent diversification of the sd proto- This document defines a session description protocol that is used to
col as tool writers each add their own modifications. It is also an define multimedia sessions. It is also an attempt to provide guidelines
attempt to provide guidelines to the writers of such announcement tools to the writers of such announcement tools to protect the Mbone from
in order to protect the Mbone from misuse and to preserve the inherent misuse and to preserve the inherent scalability of the original LBNL sd
scalability of the original sd program whilst enhancing its functional- session directory program whilst enhancing its functionality.
ity.
In defining SDP v2, we also aim to enhance to generality of SDP so that We have also attempted to enhance the generality of SDP so that it can
it can be used for a wider range of network environments and applica- be used for a wider range of network environments and applications than
tions. just multicast session directories.
3. The Use of SDP (background) 3. Glossary of Terms
3.1. Multicast Announcement The following terms are used in this document, and have specific meaning
within the context of this document.
SDP is a session description protocol for multimedia sessions. It is Conference
normally used by an SDP client which announces a conference session by A multimedia conference is a set of two or more communicating users
along with the software they are using to communicate.
Session
A multimedia session is a set a multimedia senders and receivers and
the data streams flowing from senders to receivers. A multimedia
conference is an example of a multimedia session.
Session Advertisement
See session announcement.
Session Announcement
A session announcement is a mechanism by which a session description
is conveyed to users is a pro-active fashion, i.e., the session
description was not explicitly requested by the user.
Session Description
A well defined format for conveying sufficient information to dis-
cover and participate in a multimedia session.
4. SDP Usage
4.1. Multicast Announcements
SDP is a session description protocol for multimedia sessions. Normally
it is used by an SDP client that announces a conference session by
periodically multicasting an announcement packet on a well known multi- periodically multicasting an announcement packet on a well known multi-
cast address and port. With the advent of administrative scoping in the cast address and port. With the advent of administrative scoping in the
Mbone, it is likely that sd clients will need to be able to listen for Mbone, it is likely that session directory clients will need to be able
such announcements on multiple addresses. The Session Directory to listen for such announcements on multiple addresses. This multicast-
Announcement Protocol is described in more detail in a companion draft. ing of announcements is performed by the Session Announcement Protocol
(SAP).
Sd packets are UDP packets of the following format: SAP packets are UDP packets with the following format:
0 31 0 31
|____________________| |--------------------|
| SDAP header | | SAP header |
|____________________| |--------------------|
| text payload | | text payload |
|/\/\/\/\/\/\/\/\/\/\| |/\/\/\/\/\/\/\/\/\/\|
The first four bytes are Session Directory Announcement Protocol (SDAP) The header is the Session Announcement Protocol header. SAP is
header. described in more detail in a companion draft [4]
The text payload is an SDP session description, as described in this The text payload is an SDP session description, as described in this
draft. The text payload should be no greater than 1 Kbyte in length. draft. The text payload should be no greater than 1 Kbyte in length.
If announced by SDAP, only one session annoucement is permitted in a If announced by SAP, only one session announcement is permitted in a
single packet. single packet.
3.2. SDP announcement by email and WWW 4.2. Email and WWW Announcements
It should be noted that announcements of multicast sessions made only
via email or the World Wide Web (WWW) do not have property that the
receiver of a session announcement can receive the session, nor do they
provide Mbone booking feedback or allow scalable dynamic multicast
address allocation, and so should normally be used to supplement
periodic multicast announcements.
For both email and WWW distribution, the use of the MIME content type For both email and WWW distribution, the use of the MIME content type
``application/x-sd'' is suggested. This enables the automatic launching ``application/x-sdp'' is currently suggested. This enables the
of applications from the WWW client or mail reader in a standard manner. automatic launching of applications from the WWW client or mail reader
in a standard manner.
4. Requirements Note that announcements of multicast sessions made only via email or the
World Wide Web (WWW) do not have the property that the receiver of a
session announcement can necessarily receive the session, nor do they
allow scalable dynamic multicast address allocation.
5. Requirements and Recommendations
The purpose of SDP is to convey information about media streams in mul- The purpose of SDP is to convey information about media streams in mul-
timedia sessions to allow the recipients of a session description to timedia sessions to allow the recipients of a session description to
participate in the session. SDP is primarily intended for use in an participate in the session. SDP is primarily intended for use in an
internetwork, although it is sufficiently general that it can describe internetwork, although it is sufficiently general that it can describe
conferences in other network environments. conferences in other network environments.
A multimedia session, for these purposes, is defined as a set of media A multimedia session, for these purposes, is defined as a set of media
streams that exist for a duration of time. Media streams can be many- streams that exist for some duration of time. Media streams can be
to-many. The times during which the session is active need not be con- many-to-many. The times during which the session is active need not be
tinuous. continuous.
Multicast based sessions on the internet differ from many other forms of Thus far, multicast based sessions on the internet have differed from
conferencing in that anyone receiving the traffic can join the session many other forms of conferencing in that anyone receiving the traffic
(unless the session traffic is encrypted). In such an environment, SDP can join the session (unless the session traffic is encrypted). In such
serves two primary purposes - as a means to communicate the existence of an environment, SDP serves two primary purposes. It is a means to com-
a session, and as a means to convey sufficient information to enable municate the existence of a session, and is a means to convey sufficient
joining and participating in the session. In a unicast environment, information to enable joining and participating in the session. In a
only the latter purpose is likely to be relevant. unicast environment, only the latter purpose is likely to be relevant.
Thus the information SDP must convey includes: Thus SDP includes:
o Name and purpose of session + Session name and purpose
o Time(s) the session is active + Time(s) the session is active
o The media comprising the session + The media comprising the session
o Information to receive those media + Information to receive those media (addresses, ports, formats and so
on)
As resources (such as bandwidth) necessary to participate in a session As resources necessary to participate in a session may be limited, some
may be limited, some additional information is also desirable: additional information may also be desirable:
o Contact information for the person responsible for the session + Information about the bandwidth to be used by the conference
o Information about the bandwidth to be used by the conference + Contact information for the person responsible for the session
In general, SDP must convey sufficient information to be able to join a In general, SDP must convey sufficient information to be able to join a
session (with the possible exception of encryption keys) and to announce session (with the possible exception of encryption keys) and to announce
the resources to be used to non-participants that may need to know. the resources to be used to non-participants that may need to know.
4.1. Media Information 5.1. Media Information
The information that must be conveyed is: SDP includes:
o The type of media (video, audio, etc) + The type of media (video, audio, etc)
o The transport protocol (RTP/UDP/IP, H.320, etc) + The transport protocol (RTP/UDP/IP, H.320, etc)
o The format of the media (H.261 video, MPEG video, etc) + The format of the media (H.261 video, MPEG video, etc)
In an IP multicast session, the following must also be conveyed: For an IP multicast session, the following are also conveyed:
o Multicast address for media + Multicast address for media
o Transport Port for media + Transport Port for media
In an IP unicast session, the following must be conveyed: For an IP unicast session, the following are conveyed:
o Contact address for media + Contact address for media
o Transport port for contact address + Transport port for contact address
This may or may not be be the source and destination of the media This may or may not be be the source and destination of the media
stream. stream.
Sessions being conveyed over other networks will have their own specific Sessions being conveyed over other types of network will have their own
requirements - SDP must be extensible for these. specific requirements - SDP must be extensible for these.
4.2. Timing Information
Sessions may either be bounded in time, or they may be unbounded. 5.2. Timing Information
Whether or not they are bounded, they may be only active at specific Sessions may either be bounded or unbounded in time. Whether or not
times. they are bounded, they may be only active at specific times.
SDP must be able to convey: SDP can convey:
o An arbitrary list of start and stop times bounding the session + An arbitrary list of start and stop times bounding the session
o For each bound, repeat times such as "every Wednesday at 10am for + For each bound, repeat times such as "every Wednesday at 10am for
one hour" one hour"
o These times must be 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 5.3. Private Sessions
It should be possible to create both public sessions and private ses- It is possible to create both public sessions and private sessions.
sions. However, private sessions on the existing Mbone infrastructure Private sessions will typically be conveyed by encrypting the session
rapidly use up the available bandwidth. It should be possible to create description to distribute it. The details of how encryption is per-
private sessions along with contact information if those sessions become formed are dependent on the mechanism used to convey SDP - see [4] for
a problem. how this is done for session announcements.
If a session announcement is private (encrypted) it should be possible If a session announcement is private it is possible to use that private
to use that private announcement to convey encryption keys necessary to announcement to convey encryption keys necessary to decode each of the
decode each of the media in a conference, including enough information media in a conference, including enough information to know which
to know which encryption scheme is used for each media. encryption scheme is used for each media.
4.4. Further Information 5.4. Further Information
SDP should convey enough information to decide whether a session is the SDP should convey enough information to decide whether or not to parti-
session a user wishes to participate in. It should also convey where to cipate in a session. It should include additional pointers in the form
go to find more information about the session. This extra information of Universal Resources Identifiers (URIs) for
should be in the form of Universal Resources Identifiers (URIs). more information about the session.
4.5. Categorisation 5.5. Categorisation
When many session descriptions are being conveyed by SDAP or any other When many session descriptions are being distributed by SAP or any other
advertisement mechanism, it is important to be able to filter session advertisement mechanism, it may be desirable to filter announcements
announcements that are of interest from those that are not. SDP should that are of interest from those that are not. SDP should support a
support a categorisation mechanism for sessions that can be automated. categorisation mechanism for sessions that is capable of being
automated.
4.6. Internationalization 5.6. Internationalization
The SDP specification recommends the use of 8 bit ISO 8859-1 character The SDP specification recommends the use of 8-bit ISO 8859-1 character
sets to allow the extended ASCII characters used by many western and sets to allow the extended ASCII characters used by many western and
northern European languages to be represented. However, there are many northern European languages to be represented. However, there are many
languages that cannot be represented in an ISO 8859-1 character set. languages that cannot be represented in an ISO 8859-1 character set.
SDP should also allow extensions to allow other font types to be used SDP should also allow extensions to allow other font types to be used
when required. when required.
5. SDP Specification 6. SDP Specification
SDP session descriptions are entirely textual. The textual form, as SDP session descriptions are entirely textual. The textual form, as
opposed to a binary encoding such as ASN/1 or XDR, was chosen to enhance opposed to a binary encoding such as ASN/1 or XDR, was chosen to enhance
portability, to enable a variety of transports to be used (e.g, session portability, to enable a variety of transports to be used (e.g, session
description in a MIME email message) and to allow flexible, text-based description in a MIME email message) and to allow flexible, text-based
toolkits (e.g., Tcl/Tk ) to be used to generate and process session toolkits (e.g., Tcl/Tk ) to be used to generate and to process session
descriptions. However, since the total bandwidth allocated to all SDAP descriptions. However, since the total bandwidth allocated to all SAP
announcements is strictly limited, the encoding is deliberately compact. announcements is strictly limited, the encoding is deliberately compact.
Also, since announcements may be transported via very unreliable means Also, since announcements may be transported via very unreliable means
(e.g., email) or damaged by an intermediate caching server, the encoding (e.g., email) or damaged by an intermediate caching server, the encoding
was designed with strict order and formatting rules so that likely was designed with strict order and formatting rules so that most errors
errors would result in malformed announcements which could be detected would result in malformed announcements which could be detected easily
easily and discarded. This also allows rapid discarding of encrypted and discarded. This also allows rapid discarding of encrypted announce-
announcements for which a receiver does not have the correct key. ments for which a receiver does not have the correct key.
An SDP session description takes the form of a number of lines of text An SDP session description consists of a number of lines of text of the
of the form form
<type>=<value> <type>=<value>
<type> is always exactly one character and case is significant. <value> <type> is always exactly one character and is case-significant. <value>
is a structured text string whose format depends on <type>. Whitespace is a structured text string whose format depends on <type>. Whitespace
is not permitted either side of the `=' sign. In general <value> is is not permitted either side of the `=' sign. In general <value> is
either a number of fields delimited by a single space character or free either a number of fields delimited by a single space character or a
format string. free format string.
Each announcement consists of a session description section followed by Each announcement consists of a session description section followed by
zero or more `media' description sections. The session description zero or more `media' description sections. The session description
starts with an `v=' line and continues to the first media description or starts with a `v=' line and continues to the first media description or
the next session description. The media description starts with an `m=' the next session description. The media description starts with an `m='
line and continues to the next media description or session description. line and continues to the next media description or session description.
When SDP is conveyed by SDAP, only one session description is allowed in When SDP is conveyed by SAP, only one session description is allowed per
each packet. When SDP is conveyed by other means, many SDP session packet. When SDP is conveyed by other means, many SDP session descrip-
descriptions may be carried together. Some lines in each description tions may be concatenated together. Some lines in each description are
are required and some are optional but all must appear in exactly the required and some are optional but all must appear in exactly the order
order given here (the fixed order greatly enhances error detection and given here (the fixed order greatly enhances error detection and allows
allows for a simple parser). (Optional items are marked with a `*'.) for a simple parser). Optional items are marked with a `*'.
Session description Session description
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=* (URL of description) u=* (URI of description)
e=* (email address) e=* (email address)
p=* (phone number) p=* (phone number)
c= (connection information) c=* (connection information - not required if included in all media)
b=* (bandwidth information) b=* (bandwidth information)
t=* (zero or more times) One or more time descriptions
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
Time description
t= (time the session is active)
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) c=* (connection information - optional if included at session-level)
b=* (bandwidth information) b=* (bandwidth information)
k=* (encryption key) k=* (encryption key)
a=* (zero or more media attribute lines) a=* (zero or more media attribute lines)
The set of `type' letters is deliberately small and not intended to be The set of `type' letters is deliberately small and not intended to be
extensible -- SDP parsers must completely ignore any announcement that extensible -- SDP parsers must completely ignore any announcement that
contains a `type' letter that it does not understand. The `attribute' contains a `type' letter that it does not understand. The `attribute'
mechanism (described below) is the primary means for extending sd and mechanism (described below) is the primary means for extending SDP and
tailoring it to particular applications or media. Some attributes (the tailoring it to particular applications or media. Some attributes (the
ones listed in this document) have a defined meaning but others may be ones listed in this document) have a defined meaning but others may be
added on an application-, media- or session-specific basis. A session added on an application-, media- or session-specific basis. A session
directory must ignore any attribute it doesn't understand. directory must ignore any attribute it doesn't understand.
The connection (`c=') and attribute (`a=') information in the session The connection (`c=') and attribute (`a=') information in the session
section applies to all the media of that session unless overridden by section applies to all the media of that session unless overridden by
connection information or an attribute of the same name in the media connection information or an attribute of the same name in the media
description. In the example below, each media behaves as if it were description. For instance, in the example below, each media behaves as
given a `recvonly' attribute. if it were given a `recvonly' attribute.
An example SDP v2 description is: An example SDP description is:
v=0 v=0
o=mhandley 2890844526 2890842807 IN IP4 126.16.64.4 o=mhandley 2890844526 2890842807 IN IP4 126.16.64.4
s=Sd Seminar s=SDP Seminar
i=A Seminar on the session description protocol i=A Seminar on the session description protocol
u=http://www.cs.ucl.ac.uk/staff/M.Handley/sdp.01.ps u=http://www.cs.ucl.ac.uk/staff/M.Handley/sdp.03.ps
e=M.Handley@cs.ucl.ac.uk (Mark Handley) e=mjh@isi.edu (Mark Handley)
c=IN IP4 224.2.17.12/127 c=IN IP4 224.2.17.12/127
t=2873397496 2873404696 t=2873397496 2873404696
a=recvonly a=recvonly
m=audio 3456 VAT PCMU m=audio 3456 RTP/AVP 0
m=video 2232 RTP H261 m=video 2232 RTP/AVP 31
m=whiteboard 32416 UDP WB m=whiteboard 32416 UDP WB
a=orient:portrait a=orient:portrait
Text records such as the session name and information may contain any Text records such as the session name and information may contain any
printable 8 bit ISO 8859-1 character with the exceptions of 0x0a (new- printable 8 bit ISO 8859-1 character with the exceptions of 0x0a (new-
line) and 0x0d (carriage return). Carriage Return is prohibited, and line) and 0x0d (carriage return). Carriage Return is prohibited, and
Newline is used to end a record. Newline is used to end a record.
SDP version 1 is not compatible with SDP version 2 described below,
although it is similar. The differences between SDP v1 and SDP v2 are
described in Appendix A.
Protocol Version Protocol Version
v=0 v=0
The ``v'' field gives the version of the Session Description Protocol. The ``v'' field gives the version of the Session Description Protocol.
As SDP v1 had no version number, we begin numbering with SDP v2 as pro- There is no minor version number.
tocol version 0. There is no minor version number.
Origin Origin
o=<username> <session id> <version> <network type> <address type> o=<username> <session id> <version> <network type> <address type>
<address> <address>
The ``o'' field gives the originator of the session (their username and The ``o'' field gives the originator of the session (their username and
the address of their host) plus a session id and session version number. the address of the user's host) plus a session id and session version
username is the user's login on the originating host, or it is ``-'' if number. <username> is the user's login on the originating host, or it
the originating host does not support the concept of user ids. <session is ``-'' if the originating host does not support the concept of user
id> is a numeric string such that the triple of <username>, <session id> ids. <username> must not contain spaces. <session id> is a numeric
and <address> form a globally unique identifier for the session. Its string such that the triple of <username>, <session id> and <address>
method of allocation is up to the creating tool, but it has been sug- form a globally unique identifier for the session. The method of ses-
gested that a Network Time Protocol (NTP, [1]) timestamp be used to sion id allocation is up to the creating tool, but it has been suggested
ensure uniqueness. <version> is a version number for this announcement. that a Network Time Protocol (NTP) timestamp be used to ensure unique-
It is needed for proxy announcements to detect which of several ness [1]. <version> is a version number for this announcement. It is
announcements for the same session is the most recent. Again its usage needed for proxy announcements to detect which of several announcements
is up to the creating tool, so long as <version> is increased when a for the same session is the most recent. Again its usage is up to the
modification is made to the session data. Again, it has been suggested creating tool, so long as <version> is increased when a modification is
(but not mandatory) that an NTP timestamp is used. <network type> is a made to the session data. Again, it is recommended (but not mandatory)
text string giving the type of network. Initially ``IN'' is defined to
have the meaning ``Internet''. <address type> is a text string giving that an NTP timestamp is used. <network type> is a text string giving
the type of the address that follows. Initially ``IP4'' and ``IP6'' are the type of network. Initially ``IN'' is defined to have the meaning
defined. Address is the globally unique address of the machine that the ``Internet''. <address type> is a text string giving the type of the
session was created from. For an address type of IP4, this is the address that follows. Initially ``IP4'' and ``IP6'' are defined.
dotted-decimal representation of the IP version 4 address of the <address> is the globally unique address of the machine from which the
machine. session was created. For an address type of IP4, this is the dotted-
decimal representation of the IP version 4 address of the machine.
Session Name Session Name
s=<session name> s=<session name>
The ``s'' field is the session name. There must be one and only one The ``s'' field is the session name. There must be one and only one
``s'' field per announcement, and it must contain printable ISO 8859-1 ``s'' field per announcement, and it must contain printable ISO 8859-1
characters (but see also the `charset' attribute below). characters (but see also the `charset' attribute below).
Information Session and Media Information
i=<session description> i=<session description>
The ``i'' field is information about the session. There must be no more The ``i'' field is information about the session. There must be no more
than one ``i'' field per session announcement. Although it may be omit- than one session-level ``i'' field per session announcement. Although it
ted, this is discouraged, and user interfaces for composing sessions may be omitted, this is discouraged, and user interfaces for composing
should require text to be entered. If it is present it must contain sessions should require text to be entered. If it is present it must
printable ISO 8859-1 characters (but see also the `charset' attribute contain printable ISO 8859-1 characters (but see also the `charset'
below). attribute below).
A single ``i'' field can also be used for each media definition. In A single ``i'' field can 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 single 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 media type. session has more than one distinct media stream of the same media type.
An example would be two different whiteboards, one for slides and one An example would be two different whiteboards, one for slides and one
for feedback and questions. for feedback and questions.
URI URI
u=<URI> u=<URI>
o A URI is a Universal Resource Identifier as used by WWW clients + A URI is a Universal Resource Identifier as used by WWW clients
o The URI should be a pointer to additional information about the + The URI should be a pointer to additional information about the
conference conference
o This field is optional, but if it is present it should be specified + This field is optional, but if it is present it should be specified
before the first media field before the first media field
o No more than one URI field is allowed per session description + No more than one URI field is allowed per session description
Email Address and Phone Number Email Address and Phone Number
e=<email address> e=<email address>
p=<phone number> p=<phone number>
o These specify contact information for the person responsible for + These specify contact information for the person responsible for the
the conference. This is not necessarily the same person that conference. This is not necessarily the same person that created
created the conference announcement. the conference announcement.
o Either an email field or a phone field must be specified. Addi- + Either an email field or a phone field must be specified. Addi-
tional email and phone fields are allowed. tional email and phone fields are allowed.
o If these are present, they should be specified before the first + If these are present, they should be specified before the first
media field. media field.
o More than one email or phone field can be given for a session + More than one email or phone field can be given for a session
description. description.
o Phone numbers should be given in the conventional international + Phone numbers should be given in the conventional international for-
format - preceded by a ``+'' and the international country code. mat - preceded by a ``+'' and the international country code. There
There must be a space or a hyphen (``-'') between the country code must be a space or a hyphen (``-'') between the country code and the
and the rest of the phone number. Spaces and hyphens may be used to rest of the phone number. Spaces and hyphens may be used to split
split up a phone field to aid readability if desired. For example: up a phone field to aid readability if desired. For example:
p=+44-171-380-7777 p=+44-171-380-7777 or p=+1 617 253 6011
o Both email addresses and phone numbers can have an optional free + Both email addresses and phone numbers can have an optional free
text string associated with them, normally giving the name of the text string associated with them, normally giving the name of the
person who may be contacted. This should be enclosed in parenthesis person who may be contacted. This should be enclosed in parenthesis
if it is present. For example: if it is present. For example:
e=M.Handley@cs.ucl.ac.uk (Mark Handley) e=mjh@isi.edu (Mark Handley)
The alternative RFC822 name quoting convention is also allowed for The alternative RFC822 name quoting convention is also allowed for
both email addresses and phone numbers. For example, both email addresses and phone numbers. For example,
e=Mark Handley <M.Handley@cs.ucl.ac.uk> e=Mark Handley <mjh@isi.edu>
The free text string should be in an IS0-8859-1 character set, or The free text string should be in an IS0-8859-1 character set, or
alternatively in unicode UTF-7 encoding if the appropriate charset alternatively in unicode UTF-7 encoding if the appropriate charset
conference attribute is set. session-level attribute is set.
Connection Data Connection Data
c=<network type> <address type> <connection address> c=<network type> <address type> <connection address>
The ``c'' field contains connection data. The ``c'' field contains connection data.
The first sub-field is the network type, which is a text string giving The first sub-field is the network type, which is a text string giving
the type of network. Initially ``IN'' is defined to have the meaning the type of network. Initially ``IN'' is defined to have the meaning
``Internet'' ``Internet''
The second sub-field is the address type. This allows SDP to be used The second sub-field is the address type. This allows SDP to be used
for sessions that are not IP based. Currently only IP4 is defined. for sessions that are not IP based. Currently only IP4 is defined.
The third sub-field is the connection address. Optional extra sub- The third sub-field is the connection address. Optional extra sub-
fields may be added after the connection address depending on the value fields may be added after the connection address depending on the value
of the address type field. of the <address type> field.
For IP4 addresses, the connection address is defined as follows: For IP4 addresses, the connection address is defined as follows:
o Typically the connection address will be a class-D IP multicast + Typically the connection address will be a class-D IP multicast
group address. If the conference is not multicast, then the connec- group address. If the conference is not multicast, then the connec-
tion address contains the unicast IP address of the expected data tion address contains the unicast IP address of the expected data
source or data relay or data sink as determined by additional attri- source or data relay or data sink as determined by additional attri-
bute fields. It is not expected that unicast addresses will be bute fields. It is not expected that unicast addresses will be
given in a session description that is communicated by a multicast given in a session description that is communicated by a multicast
announcement. announcement, though this is not prohibited.
Conferences using a IP multicast connection address must also have a + Conferences using an IP multicast connection address must also have
TTL (time to live) value present in addition to the multicast a time to live (TTL) value present in addition to the multicast
address. The TTL defines the scope with which multicast packets address. The TTL defines the scope with which multicast packets
sent in this conference should be sent. TTL values must be in the sent in this conference should be sent. TTL values must be in the
range 0-255. The Mbone usage guidelines (currently available at range 0-255. The Mbone usage guidelines (currently available at
ftp://ftp.isi.edu/mbone/faq.txt) define several standard settings ftp://ftp.isi.edu/mbone/faq.txt) define several standard settings
for ttl: for TTL:
local net: 1 local net: 1
site: 15 site: 15
region: 63 region: 63
world: 127 world: 127
Other settings may have local meaning (e.g., 47 for all sites within Other settings may have local meaning (e.g., 31 for all sites within
an organization). an organization).
The TTL to be used for the session must be appended to the address The TTL for the session is appended to the address using a slash as
using a slash as a separator. An example is: a separator. An example is:
c=IN IP4 224.2.1.1/127 c=IN IP4 224.2.1.1/127
Hierarchical or layered encoding schemes are data streams where the
The RSVP WG of the IETF has defined that hierarchical encoding encoding from a single media source is split into a number of
schemes should be transmitted in multiple multicast groups to allow layers. The receiver can choose the desired quality (and hence
multicast pruning to keep unwanted traffic from sites only requiring bandwidth) by only subscribing to a subset of these layers. Such
some levels of the hierarchy. For applications which require multi- layered encodings are normally transmitted in multiple multicast
ple multicast groups, we allow the following notation to be used for groups to allow multicast pruning. This technique keeps unwanted
the connection address: traffic from sites only requiring certain levels of the hierarchy.
For applications requiring multiple multicast groups, we allow the
following notation to be used for the connection address:
<base multicast address>/<ttl>/<number of addresses> <base multicast address>/<ttl>/<number of addresses>
If the number of addresses is not given it is assumed to be one. If the number of addresses is not given it is assumed to be one.
Multicast addresses so assigned are contiguously allocated above the Multicast addresses so assigned are contiguously allocated above the
base address, so that, for example: base address, so that, for example:
c=IN IP4 224.2.1.1/127/3 c=IN IP4 224.2.1.1/127/3
would state that addresses 224.2.1.1, 224.2.1.2 and 224.2.1.3 are to would state that addresses 224.2.1.1, 224.2.1.2 and 224.2.1.3 are to
be used at a ttl of 127. be used at a ttl of 127.
It is illegal for the slash notation described above for either ttl It is illegal for the slash notation described above to be used for
or number of addresses to be used for IP unicast addresses. IP unicast addresses.
A session announcement must contain at least one ``c'' field. It A session announcement must contain one ``c'' field in each media
may contain one additional ``c'' field per media field (see below), description (see below) or a ``c'' field at the session-level. It
in which case the per-media values override the conference-wide set- may contain a session-level ``c'' field and one additional ``c''
tings for the relevant media. field per media description, in which case the per-media values
override the session-level settings for the relevant media.
Bandwidth Bandwidth
b=<modifier>:<bandwidth-value> b=<modifier>:<bandwidth-value>
o This specifies the proposed bandwidth to be used by the session or + This specifies the proposed bandwidth to be used by the session or
media, and is optional. media, and is optional.
o bandwidth is in kilobits per second + <bandwidth-value> is in kilobits per second
o modifier is an single alphanumeric word giving the meaning of the + <modifier> is an single alphanumeric word giving the meaning of the
bandwidth figure. bandwidth figure.
o Two modifiers are initially defined: + Two modifiers are initially defined:
CT Conference Total: An implicit maximum bandwidth is associated with CT Conference Total: An implicit maximum bandwidth is associated with
each ttl on the Mbone or within a particular multicast administra- each TTL on the Mbone or within a particular multicast
tive scope region (the Mbone bandwidth vs. ttl limits are given in administrative scope region (the Mbone bandwidth vs. TTL limits
the mbone faq). If the bandwidth of a session or media in a ses- are given in the MBone FAQ). If the bandwidth of a session or
sion is different from the bandwidth implicit in the ttl, A media in a session is different from the bandwidth implicit from
`b=CT:...' line should be supplied for the session giving the pro- the scope, a `b=CT:...' line should be supplied for the session
posed upper limit to the bandwidth used. The primary purpose of giving the proposed upper limit to the bandwidth used. The pri-
this is to give an approximate idea as to whether two or more mary purpose of this is to give an approximate idea as to whether
conferences can co-exist simultaneously. two or more conferences can co-exist simultaneously.
AS Application Specific: The bandwidth is interpreted to be applica- AS Application Specific Maximum: The bandwidth is interpreted to be
tion specific, i.e., will be the application's concept of maximum application specific, i.e., will be the application's concept of
bandwidth. Normally this will coincide with what is set on the maximum bandwidth. Normally this will coincide with what is set
applications ``maximum bandwidth'' control if applicable. on the application's ``maximum bandwidth'' control if applicable.
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.
o Extension Mechanism: Tool writers can define experimental bandwidth + Extension Mechanism: Tool writers can define experimental bandwidth
modifiers by prefixing their modifier with ``X-''. For example: modifiers by prefixing their modifier with ``X-''. For example:
b=X-YZ:128 b=X-YZ:128
SDP parsers should ignore bandwidth fields with unknown modifiers. SDP parsers should ignore bandwidth fields with unknown modifiers.
Modifiers should be alpha-numeric and, although no length limit is Modifiers should be alpha-numeric and, although no length limit is
___________________________________________________________________________ given, they are recommended to be short.
| It is unclear who (if anyone) should be the registry for bandwidth |
|_________________________________________________________________________|
Times, Repeat Times and Time Zones Times, Repeat Times and Time Zones
t=<start time> <stop time> t=<start time> <stop time>
o ``t'' fields specify the start and stop times for a conference ses- + ``t'' fields specify the start and stop times for a conference ses-
sion. Multiple ``t'' fields may be used if a session is active at sion. Multiple ``t'' fields may be used if a session is active at
multiple irregularly spaced times; each additional ``t'' field multiple irregularly spaced times; each additional ``t'' field
specifies an addition period of time that the session will be active specifies an additional period of time for which the session will be
for. If the session is active at regular times, an ``r'' field active. If the session is active at regular times, an ``r'' field
should be used in addition to a ``t'' field - in which case the (see below) should be used in addition to and following a ``t''
``t'' field specifies the start and stop times of the repeat field - in which case the ``t'' field specifies the start and stop
sequence. times of the repeat sequence.
o The first and second sub-fields give the start and stop times for + The first and second sub-fields give the start and stop times for
the conference respectively. These values are the decimal represen- the conference respectively. These values are the decimal represen-
tation of Network Time Protocol (NTP, [1]) time values in seconds. tation of Network Time Protocol (NTP) time values in seconds [1].
To convert these values to UNIX time, subtract decimal 2208988800. To convert these values to UNIX time, subtract decimal 2208988800.
If these values are both set to zero, then the conference is not
bounded. User interfaces should prohibit or strongly discourage the + If the stop-time is set to zero, then the session is not bounded,
creation of unbounded conferences as they give no information about though it will not become active until after the start-time. If the
when the session is actually going to be active. It is prohibited start-time is also zero, the session is regarded as permanent.
for the start time to be after the stop time.
User interfaces should strongly discourage the creation of unbounded
and permanent sessions as they give no information about when the
session is actually going to terminate, and so make scheduling dif-
ficult.
The general assumption may be made, when displaying unbounded ses-
sions that have not timed out to the user, that an unbounded session
will only be active until half an hour from the current time or the
session start time, whichever is the later. If behaviour other than
this is required, an end-time should be given and modified as
appropriate when new information becomes available about when the
session should really end.
Permanent sessions may be shown to the user as never being active
unless there are associated repeat times which state precisely when
the session will be active. In general, permanent sessions should
not be created for any session expected to have a duration of less
than 2 months, and should be discouraged for sessions expected to
have a duration of less than 6 months.
+ It is prohibited for the start time to be after the stop time.
r=<repeat interval> <active duration> <list of offsets from start-time> r=<repeat interval> <active duration> <list of offsets from start-time>
o ``r'' fields specify repeat times for a session. For example, if + ``r'' fields specify repeat times for a session. For example, if a
a session is active at 10am on Monday and 11am on Tuesday for one session is active at 10am on Monday and 11am on Tuesday for one hour
hour each week for three months, then the <start time> in the each week for three months, then the <start time> in the correspond-
corresponding ``t'' field would be the NTP representation of 10am on ing ``t'' field would be the NTP representation of 10am on the first
the first Monday, the <repeat interval> would be 1 week, the <active Monday, the <repeat interval> would be 1 week, the <active duration>
duration> would be 1 hour, and the offsets would be zero and 25 would be 1 hour, and the offsets would be zero and 25 hours. The
hours. The corresponding ``t'' field stop time would be the NTP corresponding ``t'' field stop time would be the NTP representation
representation of the end of the last session three months later. By of the end of the last session three months later. By default all
default all fields are in seconds, so the ``r'' field would be: fields are in seconds, so the ``r'' and ``t'' fields might be:
t=3034423619 3042462419
r=604800 3600 0 90000 r=604800 3600 0 90000
To make announcements more compact, times may also be given in units To make announcements more compact, times may also be given in
of days, hours or minutes. To allow yearly or monthly announcements units of days, hours or minutes. The syntax for these is a number
(same day each year or month), units of years and months are also immediately followed by a single case-sensitive character. Frac-
allowed. The syntax for these is a number immediately followed by a tional units are not allowed - a smaller unit should be used
single case-sensitive character. Fractional units are not allowed - instead. The following unit specification characters are allowed:
a smaller unit should be used instead. The following unit specifica-
tion characters are allowed:
Y - years (same day of same month each repeated year)
M - months (same day of the month each repeated month)
d - days (86400 seconds) d - days (86400 seconds)
h - minutes (3600 seconds) h - minutes (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 announcement could also have been written:
Thus, the above announcement could have been written:
r=1d 1h 0 25h r=1d 1h 0 25h
Monthly and yearly repeats cannot currently be directly specified
with a single SDP repeat time - instead separate "t" fields should
be used to explicitly list the session times.
z=<adjustment time> <offset> <adjustment time> <offset> .... z=<adjustment time> <offset> <adjustment time> <offset> ....
Should it be necessary to schedule a repeated session which spans a + Should it be necessary to schedule a repeated session which spans a
change from daylight time to standard time or vice-versa, it is change from daylight-saving time to standard time or vice-versa, it
necessary to specify offsets from the base repeat times. This is is necessary to specify offsets from the base repeat times. This is
necessary because different time zones change time at different necessary because different time zones change time at different
times of day, because different countries change to or from day- times of day, different countries change to or from daylight time on
light time on different dates, and because some countries to not different dates, and some countries to not have daylight saving time
have daylight saving time at all. 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
zone adjustment happens and the offset from the time when the ses- zone adjustment happens and the offset from the time when the ses-
sion was first scheduled. The ``z'' field allows the sender to sion was first scheduled. The ``z'' field allows the sender to
specify a list of these adjustment times and offsets from the base specify a list of these adjustment times and offsets from the base
time. time.
An example might be: An example might be:
z=2882844526 -1h 2898848070 0 z=2882844526 -1h 2898848070 0
If a session is likely to last several years, it is expected that This specifies that at time 2882844526 the time base by which the
session's repeat times are calculated is shifted back by 1 hour, and
that at time 2898848070 the session's original time base is
restored. Adjustments are always relative to the specified start
time - they are not cumulative.
+ If a session is likely to last several years, it is expected that
the session announcement will be modified periodically rather than the session announcement will be modified periodically rather than
transmit several years worth of adjustments in one announcement. transmit several years worth of adjustments in one announcement.
Encryption Keys Encryption Keys
k=<encryption key> k=<method>
k=<method>:<encryption key>
o In countries where encrypted sessions are not prohibited by law, + In countries where encrypted sessions are not prohibited by law, the
the session description protocol may be use to convey encryption session description protocol may be used to convey encryption keys.
keys.
o A key field is permitted before the first media entry, or for each + A key field is permitted before the first media entry (in which case
media entry as required. it applies to all media in the session), or for each media entry as
required.
o The format of keys and their usage is outside the scope of this + The format of keys and their usage is outside the scope of this
document, but see [4] document, but see [3].
+ The method indicates the mechanism to be used to obtain a usable key
by external means, or from the encoded encryption key given. The
following methods are defined:
k=clear:<encryption key>
The encryption key (as described in [3] for RTP media streams
under the AV profile) is included untransformed in this key
field.
k=base64:<encoded encryption key>
The encryption key (as described in [3] for RTP media streams
under the AV profile) is included in this key field but has been
base64 encoded because it includes characters that are prohi-
bited in SDP.
k=uri:<URI to obtain key>
A Universal Resource Identifier as used by WWW clients is
included in this key field. The URI refers to the data contain-
ing the key, and may require additional authentication before
the key can be returned. The key should not be obtained until
the user wishes to join the session to reduce synchronisation of
requests to the WWW server(s).
k=prompt
No key is included in this SDP description, but the session or
media stream referred to by this key field is encrypted. The
user should be prompted for the key when attempting to join the
session, and this user-supplied key should then used to decrypt
the media streams.
Attributes Attributes
a=<flag> a=<flag>
a=<attribute>:<value> a=<attribute>:<value>
A media field may also have any number of attributes (``a'' fields) A media field may also have any number of attributes (``a'' fields)
which are media specific. Attribute fields may be of two forms: which are media specific. Attribute fields may be of two forms:
o flag attributes. A flag attribute is simply of the form + flag attributes. A flag attribute is simply of the form
``a=<flag>''. These are binary attributes, and the presence of the ``a=<flag>''. These are binary attributes, and the presence of the
attribute conveys that the attribute is ``true''. attribute conveys that the attribute is ``true''. An example might
be ``a=recvonly''.
o value attributes. A value attribute is of the form + value attributes. A value attribute is of the form
``a=<attribute>:<value>''. An example might be that a whiteboard ``a=<attribute>:<value>''. An example might be that a whiteboard
could have the value attribute ``a=orient:landscape'' could have the value attribute ``a=orient:landscape''
Attribute interpretation depends on the media tool being invoked. Thus Attribute interpretation depends on the media tool being invoked. Thus
receivers of sd session descriptions should be configurable in their receivers of session descriptions should be configurable in their
interpretation of announcements in general and of attributes in particu- interpretation of announcements in general and of attributes in particu-
lar. lar.
Attribute fields (``a'' fields) can also be added before the first media Attribute fields (``a'' fields) can also be added before the first media
field. These attributes would convey additional information that field. These attributes would convey additional information that
applies to the conference as a whole rather than to individual media. applies to the conference as a whole rather than to individual media.
An example might be the conference's floor control policy. An example might be the conference's floor control policy.
Media Announcements Media Announcements
m=<media> <port> <transport> <fmt> m=<media> <port> <transport> <fmt list>
A session announcement may contain a number of media announcements. A session announcement may contain a number of media announcements.
Each media announcement starts with an ``m'' field, and is terminated by Each media announcement starts with an ``m'' field, and is terminated by
either the next ``m'' field or by the end of the session announcement. either the next ``m'' field or by the end of the session announcement.
A media field also has several sub-fields: A media field also has several sub-fields:
o The first sub-field is the media type. Currently defined media are + The first sub-field is the media type. Currently defined media are
``audio'', ``video'', ``whiteboard'' and ``text'', though this list ``audio'', ``video'', ``whiteboard'', ``text'' and ``data'', though
may be extended as new communication modalities emerge (e.g., this list may be extended as new communication modalities emerge
telepresense or conference control). (e.g., telepresense or conference control).
o The second sub-field is the transport port to which the media + The second sub-field is the transport port to which the media stream
stream will be sent. The meaning of the transport port depends on will be sent. The meaning of the transport port depends on the net-
the network being used as specified in the relevant ``c'' field and work being used as specified in the relevant ``c'' field and on the
on the transport protocol defined in the third sub-field. Other transport protocol defined in the third sub-field. Other ports used
ports used by the media application (such as the RTCP port, see [2]) by the media application (such as the RTCP port, see [2]) should be
should be derived algorithmically from the base media port. derived algorithmically from the base media port.
For transports based on UDP, the value should be in the range 1024 For transports based on UDP, the value should be in the range 1024
to 65535 inclusive. For RTPv2 compliance it should be an even to 65535 inclusive. For RTP compliance it should be an even number.
number. If the port is allocated randomly by the creating applica- If the port is allocated randomly by the creating application, it is
tion, it is recommended that ports above 5000 are chosen as, on Unix recommended that ports above 5000 are chosen as, on Unix systems,
systems, ports below 5000 may be allocated automatically by the ports below 5000 may be allocated automatically by the operating
operating system. system.
For applications where hierarchically encoded streams are being send For applications where hierarchically encoded streams are being sent
to a unicast address, it may be necessary to specify multiple tran- to a unicast address, it may be necessary to specify multiple tran-
sport ports. This is done using a similar notation to that used for sport ports. This is done using a similar notation to that used for
IP multicast addresses in the ``c'' field: IP multicast addresses in the ``c'' field:
m=<media> <port>/<number of ports> <transport> <fmt> m=<media> <port>/<number of ports> <transport> <fmt list>
In such a case, the ports used depend on the transport protocol. In such a case, the ports used depend on the transport protocol.
For RTPv2, only the even ports are used for data and the correspond- For RTP, only the even ports are used for data and the corresponding
ing one-higher odd port is used for RTCP. For example: one-higher odd port is used for RTCP. For example:
m=video 3456/2 RTP H261 m=video 3456/2 RTP/AVP 31
would specify that ports 3456 and 3457 form one RTP/RTCP pair and would specify that ports 3456 and 3457 form one RTP/RTCP pair and
3458 and 3459 form the second RTP/RTCP pair. 3458 and 3459 form the second RTP/RTCP pair. RTP/AVP is the tran-
sport protocol and 31 is the format (see below).
It is illegal for both multiple addresses to be specified in the It is illegal for both multiple addresses to be specified in the
``c'' field and for multiple ports to be specified in the ``m'' ``c'' field and for multiple ports to be specified in the ``m''
field in the same session announcement. field in the same session announcement.
o The third sub-field is the transport protocol. The transport pro- + The third sub-field is the transport protocol. The transport proto-
tocol values are dependent on the address-type field in the ``c'' col values are dependent on the address-type field in the ``c''
fields. Thus a ``c'' field of IP4 defines that the transport proto- fields. Thus a ``c'' field of IP4 defines that the transport proto-
col runs over IP4. For IP4, it is normally expected that most col runs over IP4. For IP4, it is normally expected that most
media traffic will be carried as RTP over UDP. However, some com- media traffic will be carried as RTP over UDP. However, some com-
monly used applications such as vat [5] do not use RTP. Thus the monly used applications such as vat [5] do not use RTP. Thus the
following transport protocols are defined: following transport protocols are defined:
- RTP - the IETF's Realtime Transport Protocol carried over UDP. - RTP/AVP - the IETF's Realtime Transport Protocol using the
Audio/Video profile carried over UDP.
- VAT - LBL's Visual Audio Tool packet format carried over UDP. - VAT - LBL's Visual Audio Tool packet format carried over UDP.
- UDP - User Datagram Protocol - UDP - User Datagram Protocol
If an application uses a propriety media format and transport proto- If an application uses a single combined propriety media format and
col over UDP, then simply specifying the transport protocol as UDP transport protocol over UDP, then simply specifying the transport
is recommended. protocol as UDP and using the format field to distinguish the com-
bined 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. VAT and RTP are
examples of transport protocols that carry 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 The main reason to specify the transport protocol in addition to the
media format is that the same standard media formats may be carried media format is that the same standard media formats may be carried
over different transport protocols even when the network protocol is over different transport protocols even when the network protocol is
the same - for example vat PCM audio and RTP PCM audio. the same - for example vat PCM audio and RTP PCM audio. In addi-
tion, relays and monitoring tools that are transport protocol
o The fourth sub-field is the media format. For audio and video, specific but format independent are possible.
this will normally be a media format string as defined in the RTP
Audio/Video Profile.
Predefined formats are as below. For more details on audio and video
formats, see [3].
o Audio Formats:
PCMU: 8-bit mu-law encoded 8kHz PCM
PCMA: 8-bit A-law encoded 8kHz PCM
IDVI: Intel DVI ADPCM
GSM: GSM (Group Speciale Mobile)
LPC: An experimental Linear Predictive Coder written by Ron
Frederick
1016: CELP encoding as specified in FED-STD 1016
G721: ITU recommendation G721 For RTP media streams operating under the RTP Audio/Video Profile
[3], 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''.
G723: ITU recommendation G723 + The fourth and subsequent sub-fields are media formats. For audio
and video, these will normally be a media payload type as defined in
the RTP Audio/Video Profile.
L8: 8 bit linear audio When a list of payload formats is given, this implies that all of
L16: 16 bit linear audio these formats may be used in the session, but the first of these
formats is the default format for the session.
MPA: MPEG audio 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.
VDVI: A variable rate version of IDVI For media whose transport protocol is RTP, SDP can be used to pro-
vide a dynamic binding of media encoding to RTP payload type. The
payload 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 pay-
load types.
TSP0: TrueSpeech proprietary encoding An example of a static payload type is u-law PCM coded single chan-
nel 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 3456 is:
VSC: Vocaltec Software Compression proprietary encoding. m=video 3456 RTP/AVP 0
An example of a dynamic payload type is 16 bit linear encoded stereo
audio sampled at 16KHz. If we wish to use dynamic RTP/AVP payload
type 98 for such a stream, additional information is required to
decode it:
o Video Formats: m=video 3456 RTP/AVP 98
a=rtpmap:98 L16/16000/2
JPEG: Motion JPEG The general form of an rtpmap attribute is:
MPV: MPEG encoding a=rtpmap:<payload type> <encoding name>/<clock rate>[/<encoding parameters>]
MP2T: MPEG II transport stream For audio streams, <encoding parameters> optionally specifies number
of audio channels. For video streams, no encoding parameters are
currently specified.
CelB: Sun Cell-B encoding Up to one rtpmap attribute can be define for each media format
specified. Thus we might have:
H261: CCITT/ITU-T recommendation H.261 m=audio 12345 RTP/AVP 96 97 98
a=rtpmap:96 L8/8000
a=rtpmap:97 L16/8000
a=rtpmap:98 L16/11025/2
nv: Xerox Parc Network Video Experimental encoding formats can also be specified in this way.
RTP formats that are not registered with IANA as standard format
names must be preceded by ``X-''. Thus a new experimental redundant
audio stream called GSMLPC using dynamic payload type 99 could be
specified as:
CPV: Compressed Packet Video (proprietary encoding) m=video 3456 RTP/AVP 99
a=rtpmap:99 X-GSMLPC/8000
HDCC: HDCC proprietary encoding from Silicon Graphics Such an experimental encoding requires that any site wishing to
receive the media stream has relevant configured state in its ses-
sion directory to know which tools are appropriate.
CUSM: CU-SeeMe video encoding Note that 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.
PicW: PictureWindow encoding from BBN For more details on RTP audio and video formats, see [3].
RGB: 8 bit encoding of RGB values + Predefined formats for UDP protocol non-RTP media are as below.
o Whiteboard Formats: Whiteboard Formats:
WB: LBL Whiteboard (transport: UDP) WB: LBL Whiteboard (transport: UDP)
o Text Formats: Text Formats:
NT: UCL Network Text Editor (transport: UDP) NT: UCL Network Text Editor (transport: UDP)
MMBL: mumble text chat tool (transport: UDP)
o Note that audio formats do not include packetisation information.
If a non-default (as defined in the RTP Audio/Video Profile)
packetisation is required, the ``ptime'' attribute is used as given
below.
Suggested Attributes Suggested Attributes
The following attributes are suggested. Since application writers may The following attributes are suggested. 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.
a=cat:<category> a=cat:<category>
This attribute gives the dot-separated hierarchical category of the This attribute gives the dot-separated hierarchical category of the
session. This is to enable a receiver to filter unwanted sessions session. This is to enable a receiver to filter unwanted sessions
by category. It would probably have been a compulsory separate by category. It would probably have been a compulsory separate
field, except for its experimental nature at this time. It is a field, except for its experimental nature at this time. It is a
session attribute. session attribute.
a=keywds:<keywords> a=keywds:<keywords>
Like the cat attribute, this is to assist identifying wanted ses- Like the cat attribute, this is to assist identifying wanted ses-
sions at the receiver. It is a session attribute. sions at the receiver. It is a session attribute.
a=ptime:<packet time> a=ptime:<packet time>
This gives the length of time in milliseconds represented by the This gives the length of time in milliseconds represented by the
media in a packet. This is probably only meaningful for audio data. media in a packet. This is probably only meaningful for audio data.
It should not be necessary to know ptime to decode RTP or vat audio It should not be necessary to know ptime to decode RTP or vat audio,
- it is intended as a recommendation for the encoding/packetisation and it is intended as a recommendation for the
of audio. It is a media attribute. encoding/packetisation of audio. It is a media attribute.
a=recvonly a=recvonly
This specifies that the tools should be started in receive only mode This specifies that the tools should be started in receive-only mode
where applicable. It can be either a session or media attribute. where applicable. It can be either a session or media attribute.
a=sendrecv a=sendrecv
This specifies that the tools should be started in send and receive This specifies that the tools should be started in send and receive
mode. This is necessary for interactive conferences with tools such mode. This is necessary for interactive conferences with tools such
as wb which defaults to receive only mode. It can be either a ses- as wb which defaults to receive only mode. It can be either a ses-
sion or media attribute. sion or media attribute.
a=sendonly a=sendonly
This specifies that the tools should be started in send-only mode. This specifies that the tools should be started in send-only mode.
Typically this may be used where a different unicast address is to Typically this may be used where a different unicast address is to
be used for a traffic destination that for a traffic source. It can be used for a traffic destination than for a traffic source. It can
be either a session or media attribute, but would normally only be be either a session or media attribute, but would normally only be
used as a media attribute. used as a media attribute.
a=orient:<whiteboard orientation> a=orient:<whiteboard orientation>
Normally only used in a whiteboard media specification, this speci- Normally this is only used in a whiteboard media specification. It
fies the orientation of a the whiteboard on the screen. It is a specifies the orientation of a the whiteboard on the screen. It is
media attribute. Permitted values are `portrait', `landscape' and a media attribute. Permitted values are `portrait', `landscape' and
`seascape' (upside down landscape). `seascape' (upside down landscape).
a=type:<conference type> a=type:<conference type>
This specifies the type of the conference. Suggested values are This specifies the type of the conference. Suggested values are
`broadcast', `meeting', and `moderated'. `recvonly' should be the `broadcast', `meeting', and `moderated'. `recvonly' should be the
default for `type:broadcast' sessions, `type:meeting' should imply default for `type:broadcast' sessions, `type:meeting' should imply
`sendrecv' and `type:moderated' should imply the use of a floor con- `sendrecv' and `type:moderated' should imply the use of a floor con-
trol tool and that the media tools are started so as to ``mute'' new trol tool and that the media tools are started so as to ``mute'' new
sites joining the conference. It is a session attribute. sites joining the conference.
Specifying the attribute type:test is also suggested as a hint that,
unless explicitly requested otherwise, receivers can safely avoid
displaying this session description to users.
type is a session attribute.
a=charset:<character set> a=charset:<character set>
This specifies the character set to be used to display the session This specifies the character set to be used to display the session
name and information data. By default, an ISO 8859-1 character set name and information data. By default, an ISO 8859-1 character set
is used. If an ISO 8859-1 character set is not suitable, the use of is used. If an ISO 8859-1 character set is not suitable, the use of
unicode (ISO 10646, [6],[7]), as specified in RFC1641 [8] is sug- unicode (ISO 10646) [6],[7], as specified in RFC1641 [8] is sug-
gested. In particular, the UTF-7 (RFC1642, [9]) encoding is sug- gested. In particular, the UTF-7 (RFC1642) [9] encoding is sug-
gested with the following SDP attribute: gested with the following SDP attribute:
a=charset:unicode-1-1-utf-7 a=charset:unicode-1-1-utf-7
This is a session attribute; if this attribute is present, it must This is a session attribute; if this attribute is present, it must
be before the first media field. be before the first media field.
5.1. Communicating Conference Control Policy a=framerate:<frame rate>
This gives the maximum video frame rate in frames/sec. It is
intended as a recommendation for the encoding of video data.
Decimal representations of fractional values using the notation
"<integer>.<fraction>" are allowed. It is a media attribute, and is
only defined for video media.
a=quality:<quality>
This gives a suggestion for the quality of the encoding as an
integer value.
The intention of the quality attribute for video is to specify a
non-default trade-off between frame-rate and still-image quality.
For video, the value in the range 0 to 10, with the following sug-
gested meaning:
10 - the best still-image quality the compression scheme can give.
5 - the default behaviour given no quality suggestion.
0 - the worst still-image quality the codec designer thinks is
still usable.
6.1. Communicating Conference Control Policy
There is some debate over the way conference control policy should be There is some debate over the way conference control policy should be
communicated. In general, the authors believe that an implicit declara- communicated. In general, the authors believe that an implicit declara-
tive style of specifying conference control is desirable where possible. tive style of specifying conference control is desirable where possible.
A simple declarative style uses a single conference attribute field A simple declarative style uses a single conference attribute field
before the first media field, possibly supplemented by flags such as before the first media field, possibly supplemented by flags such as
`recvonly' for some of the media tools. This conference attribute con- `recvonly' for some of the media tools. This conference attribute con-
veys the conference control policy. An example might be: veys the conference control policy. An example might be:
skipping to change at page 19, line 44 skipping to change at page 24, line 39
In some cases, however, it is possible that this may be insufficient to In some cases, however, it is possible that this may be insufficient to
communicate the details of an unusual conference control policy. If communicate the details of an unusual conference control policy. If
this is the case, then a conference attribute specifying external con- this is the case, then a conference attribute specifying external con-
trol might be set, and then one or more ``media'' fields might be used trol might be set, and then one or more ``media'' fields might be used
to specify the conference control tools and configuration data for those to specify the conference control tools and configuration data for those
tools. A fictional example might be: tools. A fictional example might be:
... ...
a=type:external-control a=type:external-control
m=audio 12345 VAT PCMU m=audio 12345 RTP/AVP 0
m=video 12347 RTP H261 m=video 12347 RTP/AVP 31
m=whiteboard 12349 UDP WB m=whiteboard 12349 UDP WB
m=control 12341 UDP CCCP m=control 12341 UDP SCCP
a=mode:chaired a=mode:chaired
a=chair:128.16.64.2 a=chair:128.16.64.2
a=video:follows-audio a=video:follows-audio
a=audio:on-demand a=audio:on-demand
a=audio:chair-mutes-mike a=audio:chair-mutes-mike
a=whiteboard:chaired a=whiteboard:chaired
In this fictional example (i.e., this is not implemented anywhere), a In this fictional example (i.e., this is not implemented anywhere), a
general conference attribute is specified stating that conference
general conference attribute is specified stating that conference con- control will be provided by an external tool, and specific attributes
trol will be provided by an external tool, and specific attributes are are given to specify the control policy that tool should use.
given to specify the control policy that tool should use.
In this document, only the former style of conference control declara- In this document, only the former style of conference control declara-
tion is specified, though we recognise that some variant on the latter tion is specified, though we recognise that some variant on the latter
may also be used eventually. may also be used eventually.
Appendix A: SDP Grammar Appendix A: SDP Grammar
announcement ::= proto-version announcement ::= proto-version
origin-field origin-field
session-name-field session-name-field
skipping to change at page 21, line 39 skipping to change at page 26, line 39
session-name-field ::= "s=" text session-name-field ::= "s=" text
information-field ::= ["i=" text newline] information-field ::= ["i=" text newline]
uri-field ::= ["u=" uri newline] uri-field ::= ["u=" uri newline]
email-fields ::= ("e=" email-address newline)* email-fields ::= ("e=" email-address newline)*
phone-fields ::= ("p=" phone-number newline)* phone-fields ::= ("p=" phone-number newline)*
connection-field ::= "c=" nettype space addrtype space connection-field ::= ["c=" nettype space addrtype space
connection-address newline connection-address newline]
;a connection field must be present
;in every media description or at the
;session-level
bandwidth-fields ::= ("b=" bwtype ":" bandwidth newline)* bandwidth-fields ::= ("b=" bwtype ":" bandwidth newline)*
time-fields ::= ( "t=" start-time space stop-time time-fields ::= ( "t=" start-time space stop-time
(newline repeat-fields)* newline)* (newline repeat-fields)* newline)+
[zone-adjustments newline] [zone-adjustments newline]
repeat-fields ::= repeat-interval space typed-time (space typed-time)+ repeat-fields ::= "r=" repeat-interval space typed-time
(space typed-time)+
zone-adjustments ::= time space [``-''] typed-time zone-adjustments ::= time space [``-''] typed-time
(space time space [``-''] typed-time)* (space time space [``-''] typed-time)*
key-field ::= ["k=" (printable-ascii)+ newline] key-field ::= ["k=" key-type newline]
key-type ::= "prompt" |
"clear:" key-data |
"base64:" key-data |
"uri:" uri
key-data ::= printable-ascii
attribute-fields ::= ("a=" attribute newline)* attribute-fields ::= ("a=" attribute newline)*
media-descriptions ::= ( media-field media-descriptions ::= ( media-field
information-field information-field
connection-field connection-field
bandwidth-fields bandwidth-fields
key-field key-field
attribute-fields )* attribute-fields )*
media-field ::= "m=" media space port ["/" integer] media-field ::= "m=" media space port ["/" integer]
space proto space fmt newline space proto (space fmt)+ newline
media ::= (alpha-numeric)+ media ::= (alpha-numeric)+
;typically "audio", "video", "whiteboard" ;typically "audio", "video", "whiteboard"
;or "text" ;or "text"
fmt ::= (alpha-numeric)+ fmt ::= (alpha-numeric)+
;typically an RTP media type for audio ;typically an RTP payload type for audio
;and video media ;and video media
proto ::= (alpha-numeric)+ proto ::= (alpha-numeric)+
;typically "RTP", "VAT", or "UDP" for IP4 ;typically "RTP/AVP", "VAT", or "UDP" for IP4
port ::= (DIGIT)+ port ::= (DIGIT)+
;should in the range "1024" to "65535" inclusive ;should in the range "1024" to "65535" inclusive
;for UDP based media ;random allocation should ;for UDP based media ;random allocation should
;only assign above UDP port "5000". ;only assign above UDP port "5000".
attribute ::= att-field ":" att-value | att-field attribute ::= att-field ":" att-value | att-field
att-field ::= (ALPHA)+ att-field ::= (ALPHA)+
skipping to change at page 23, line 38 skipping to change at page 29, line 28
interval-time ::= (DIGIT)+ variable-len-time-unit interval-time ::= (DIGIT)+ variable-len-time-unit
fixed-len-time-unit ::= ``d'' | ``h'' | ``m'' | ``s'' fixed-len-time-unit ::= ``d'' | ``h'' | ``m'' | ``s''
variable-len-time-unit ::= ``Y'' | ``M'' variable-len-time-unit ::= ``Y'' | ``M''
bwtype ::= (alpha-numeric)+ bwtype ::= (alpha-numeric)+
bandwidth ::= (DIGIT)+ bandwidth ::= (DIGIT)+
username ::= ;not defined here username ::= alpha-numeric
;perhaps this is too restrictive...
email-address ::= email | email "(" text ")" | text "<" email ">" email-address ::= email | email "(" text ")" | text "<" email ">"
email ::= ;defined in RFC822 email ::= ;defined in RFC822
uri::= ;defined in RFC1630 uri::= ;defined in RFC1630
phone-number ::= phone | phone "(" text ")" | phone-number ::= phone | phone "(" text ")" |
text "<" phone ">" text "<" phone ">"
skipping to change at page 25, line 7 skipping to change at page 31, line 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))
integer ::= POS-DIGIT (DIGIT)* integer ::= POS-DIGIT (DIGIT)*
alpha-numeric ::= ALPHA | DIGIT alpha-numeric ::= ALPHA | DIGIT
printable-ascii ::= unicode-safe | "~" | "\" printable-ascii ::= unicode-safe | "~" | "
DIGIT ::= 0 | POS-DIGIT DIGIT ::= 0 | POS-DIGIT
POS-DIGIT ::= 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 POS-DIGIT ::= 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
ALPHA ::= a | b | c | d | e | f | g | h | i | j | k | ALPHA ::= a | b | c | d | e | f | g | h | i | j | k |
l | m | n | o | p | q | r | s | t | u | v | l | m | n | o | p | q | r | s | t | u | v |
w | x | y | z | A | B | C | D | E | F | G | w | x | y | z | A | B | C | D | E | F | G |
H | I | J | K | L | M | N | O | P | Q | R | H | I | J | K | L | M | N | O | P | Q | R |
S | T | U | V | W | X | Y | Z S | T | U | V | W | X | Y | Z
skipping to change at page 26, line 5 skipping to change at page 32, line 5
"?" | """ | "#" | "$" | "&" | "*" | ";" | "<" | "?" | """ | "#" | "$" | "&" | "*" | ";" | "<" |
"=" | ">" | "@" | "[" | "]" | "^" | "_" | "`" | "=" | ">" | "@" | "[" | "]" | "^" | "_" | "`" |
"{" | "|" | "}" | "+" | space | tab "{" | "|" | "}" | "+" | space | tab
;although unicode allows newline and carriage ;although unicode allows newline and carriage
;return, we don't here. ;return, we don't here.
space ::= ;ascii code 32 space ::= ;ascii code 32
tab ::= ;ascii code 9 tab ::= ;ascii code 9
newline ::= ;ascii code 10 newline ::= ;ascii code 10
Appendix B: Summary of differences between SDPv1 and SDPv2
For this purpose SDPv1 is defined as the protocol in use by version 1.14
of the sd session description tool. SDPv2 is the proposed protocol
described in the document.
SDPv1 allows the use of only the following SDP fields:
s= session name - no change
i= session information - SDP v2 allows ``i'' fields to be used in
the media descriptions as media labels.
o= originator - in SDP v1, originator is of the form
username@hostname, and the sd packet headers contain a binary
representation of the IP 4 address of the originating host.
This essentially contains duplicate information and cannot cope
with non-IP4 addresses. Thus in SDP v2 we add an address type
field and put the address of the originating machine in the ori-
ginator field. In SDP v2 we also add two more sub-fields - a
session id and a session version - to the origin field. This
means that all the information to identify a session and whether
that session has changed is in one field. To make this field
easier to find, we move to to the beginning of the announcement
after the new protocol version field.
c= conference data - only one conference data field is allowed
before the first media field in SDPv1. In SDP v1 the conference
start and stop times are the third and fourth fields of the
conference data field. In SDP v2 they have moved to the t= time
field. To convert from SDPv1 time-stamps to UNIX time, subtract
decimal 2085978496. To convert from SDPv2 time-stamps to UNIX
time, subtract decimal 2208988800 (SDPv1 uses NTP time-stamps
incorrectly).
In SDPv1 no network type or address type subfields are present,
and the ttl is a separate subfield following the multicast
address. Multiple multicast addresses are not allowed in SDPv1.
m= media - In SDP v1, the third subfield is the RTP v1 ID. This is
now obsolete. In SDP v1, the media format allowed a default
format if none was specific, but non-default values were speci-
fied using the fmt attribute. In SDP v2, allow default attri-
butes and not allowed, and the fourth subfield in a media field
gives the media format. In SDPv1, there is no way to distin-
guish between the same media format carried by different tran-
sport protocols. In SDP v2 the third subfield in a media field
gives the transport protocol.
In SDPv1 multiple ports are not allowed for hierarchical encod-
ings on a unicast address.
a= attributes - attributes are allowed only after the first media
field in SDPv1.
SDPv2 additionally defines the following fields which are defined above:
v= Protocol Version
b= Bandwidth
e= Email Address
p= Phone Number
u= URL
t= Time
r= Repeat Time
z= Time Zone info
k= Encryption Key
Appendix C: Authors' Addresses Appendix C: Authors' Addresses
Mark Handley Mark Handley
Department of Computer Science Information Sciences Institute
University College London c/o MIT Laboratory for Computer Science
London WC1E 6BT 545 Technology Square
United Kingdom Cambridge, MA 02139
electronic mail: M.Handley@cs.ucl.ac.uk United States
electronic mail: mjh@isi.edu
Van Jacobson Van Jacobson
MS 46a-1121 MS 46a-1121
Lawrence Berkeley Laboratory Lawrence Berkeley Laboratory
Berkeley, CA 94720 Berkeley, CA 94720
United States United States
electronic mail: van@ee.lbl.gov electronic mail: van@ee.lbl.gov
Acknowledgments
Many people in the IETF MMUSIC working group have made comments and
suggestions contributing to this document. In particular, we would like
to thank Eve Schooler, Steve Casner, Bill Fenner, Allison Mankin and
Ross Finlayson.
References References
[1] D. Mills, ``Network Time Protocol version 2 specification and imple- [1] D. Mills, ``Network Time Protocol version 2 specification and imple-
mentation", RFC1119, 1st Sept 1989. mentation", RFC1119, 1st Sept 1989.
[2] H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson, ``RTP: A Tran- [2] H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson, ``RTP: A Tran-
sport Protocol for Real-Time Applications'', INTERNET-DRAFT, draft- sport Protocol for Real-Time Applications'', RFC 1889
ietf-avt-rtp-07.txt, 21st March 1995.
[3] H. Schulzrinne, ``RTP Profile for Audio and Video Conferences with [3] H. Schulzrinne, ``RTP Profile for Audio and Video Conferences with
Minimal Control'', INTERNET-DRAFT, draft-ietf-avt-profile-04.txt, 21st Minimal Control'', RFC 1890
March 1995.
[4] M. Handley (editor), ``The Use of Plain Text Keys for Multimedia [4] M. Handley, ``SAP - Session Announcement Protocol'', INTERNET-DRAFT,
Conferences'', Research Note RN-95-19, Department of Computer Science, November 25th 1996.
University College London, Feb 1995.
http://www.cs.ucl.ac.uk/rns/RN9519.ps
[5] V. Jacobson, S. McCanne, ``vat - X11-based audio teleconferencing [5] V. Jacobson, S. McCanne, ``vat - X11-based audio teleconferencing
tool'' vat manual page, Lawrence Berkeley Laboratory, 1994. tool'' vat manual page, Lawrence Berkeley Laboratory, 1994.
[6] ``The Unicode Standard, Version 1.1'': Version 1.0, Volume 1 (ISBN [6] ``The Unicode Standard, Version 1.1'': Version 1.0, Volume 1 (ISBN
0-201-56788-1), Version 1.0, Volume 2 (ISBN 0-201-60845-6), and "Unicode 0-201-56788-1), Version 1.0, Volume 2 (ISBN 0-201-60845-6), and "Unicode
Technical Report #4, The Unicode Standard, Version 1.1" (available from Technical Report #4, The Unicode Standard, Version 1.1" (available from
The Unicode Consortium, and soon to be published by Addison- Wesley). The Unicode Consortium, and soon to be published by Addison- Wesley).
[7] ISO/IEC 10646-1:1993(E) Information Technology--Universal Multiple- [7] ISO/IEC 10646-1:1993(E) Information Technology--Universal Multiple-
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