draft-ietf-mmusic-rfc4566bis-14.txt   draft-ietf-mmusic-rfc4566bis-15.txt 
Network Working Group M. Handley Network Working Group M. Handley
Internet-Draft UCL Internet-Draft UCL
Obsoletes: 4566 (if approved) V. Jacobson Obsoletes: 4566 (if approved) V. Jacobson
Intended status: Standards Track PARC Intended status: Standards Track PARC
Expires: July 25, 2015 C.S. Perkins Expires: November 6, 2015 C. Perkins
University of Glasgow University of Glasgow
A. Begen A. Begen
Cisco Cisco
January 21, 2015 May 5, 2015
SDP: Session Description Protocol SDP: Session Description Protocol
draft-ietf-mmusic-rfc4566bis-14 draft-ietf-mmusic-rfc4566bis-15
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
multimedia session initiation. This document obsoletes RFC 4566. multimedia session initiation. This document obsoletes RFC 4566.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 25, 2015. This Internet-Draft will expire on November 6, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . 4 2. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . 4
3. Examples of SDP Usage . . . . . . . . . . . . . . . . . . . . 4 3. Examples of SDP Usage . . . . . . . . . . . . . . . . . . . . 4
3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 4 3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 4
3.2. Streaming Media . . . . . . . . . . . . . . . . . . . . . 5 3.2. Streaming Media . . . . . . . . . . . . . . . . . . . . . 5
3.3. Email and the World Wide Web . . . . . . . . . . . . . . 5 3.3. Email and the World Wide Web . . . . . . . . . . . . . . 5
3.4. Multicast Session Announcement . . . . . . . . . . . . . 5 3.4. Multicast Session Announcement . . . . . . . . . . . . . 5
4. Requirements and Recommendations . . . . . . . . . . . . . . 5 4. Requirements and Recommendations . . . . . . . . . . . . . . 6
4.1. Media and Transport Information . . . . . . . . . . . . . 6 4.1. Media and Transport Information . . . . . . . . . . . . . 7
4.2. Timing Information . . . . . . . . . . . . . . . . . . . 7 4.2. Timing Information . . . . . . . . . . . . . . . . . . . 7
4.3. Private Sessions . . . . . . . . . . . . . . . . . . . . 7 4.3. Private Sessions . . . . . . . . . . . . . . . . . . . . 8
4.4. Obtaining Further Information about a Session . . . . . . 8 4.4. Obtaining Further Information about a Session . . . . . . 8
4.5. Categorisation . . . . . . . . . . . . . . . . . . . . . 8 4.5. Categorisation . . . . . . . . . . . . . . . . . . . . . 8
4.6. Internationalisation . . . . . . . . . . . . . . . . . . 8 4.6. Internationalisation . . . . . . . . . . . . . . . . . . 8
5. SDP Specification . . . . . . . . . . . . . . . . . . . . . . 8 5. SDP Specification . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Protocol Version ("v=") . . . . . . . . . . . . . . . . . 11 5.1. Protocol Version ("v=") . . . . . . . . . . . . . . . . . 11
5.2. Origin ("o=") . . . . . . . . . . . . . . . . . . . . . . 11 5.2. Origin ("o=") . . . . . . . . . . . . . . . . . . . . . . 12
5.3. Session Name ("s=") . . . . . . . . . . . . . . . . . . . 13 5.3. Session Name ("s=") . . . . . . . . . . . . . . . . . . . 13
5.4. Session Information ("i=") . . . . . . . . . . . . . . . 13 5.4. Session Information ("i=") . . . . . . . . . . . . . . . 13
5.5. URI ("u=") . . . . . . . . . . . . . . . . . . . . . . . 13 5.5. URI ("u=") . . . . . . . . . . . . . . . . . . . . . . . 14
5.6. Email Address and Phone Number ("e=" and "p=") . . . . . 14 5.6. Email Address and Phone Number ("e=" and "p=") . . . . . 14
5.7. Connection Data ("c=") . . . . . . . . . . . . . . . . . 15 5.7. Connection Data ("c=") . . . . . . . . . . . . . . . . . 15
5.8. Bandwidth ("b=") . . . . . . . . . . . . . . . . . . . . 17 5.8. Bandwidth ("b=") . . . . . . . . . . . . . . . . . . . . 17
5.9. Timing ("t=") . . . . . . . . . . . . . . . . . . . . . . 18 5.9. Timing ("t=") . . . . . . . . . . . . . . . . . . . . . . 18
5.10. Repeat Times ("r=") . . . . . . . . . . . . . . . . . . . 19 5.10. Repeat Times ("r=") . . . . . . . . . . . . . . . . . . . 19
5.11. Time Zones ("z=") . . . . . . . . . . . . . . . . . . . . 20 5.11. Time Zones ("z=") . . . . . . . . . . . . . . . . . . . . 19
5.12. Encryption Keys ("k=") . . . . . . . . . . . . . . . . . 20 5.12. Encryption Keys ("k=") . . . . . . . . . . . . . . . . . 20
5.13. Attributes ("a=") . . . . . . . . . . . . . . . . . . . . 22 5.13. Attributes ("a=") . . . . . . . . . . . . . . . . . . . . 22
5.14. Media Descriptions ("m=") . . . . . . . . . . . . . . . . 23 5.14. Media Descriptions ("m=") . . . . . . . . . . . . . . . . 23
6. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . . 26 6. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . . 25
6.1. cat (category) . . . . . . . . . . . . . . . . . . . . . 26 6.1. cat (category) . . . . . . . . . . . . . . . . . . . . . 26
6.2. keywds (keywords) . . . . . . . . . . . . . . . . . . . . 26 6.2. keywds (keywords) . . . . . . . . . . . . . . . . . . . . 26
6.3. tool . . . . . . . . . . . . . . . . . . . . . . . . . . 27 6.3. tool . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.4. ptime (packet time) . . . . . . . . . . . . . . . . . . . 28 6.4. ptime (packet time) . . . . . . . . . . . . . . . . . . . 27
6.5. maxptime (maximum packet time) . . . . . . . . . . . . . 28 6.5. maxptime (maximum packet time) . . . . . . . . . . . . . 28
6.6. rtpmap . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.6. rtpmap . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.7. Media Direction Attributes . . . . . . . . . . . . . . . 31 6.7. Media Direction Attributes . . . . . . . . . . . . . . . 30
6.7.1. recvonly (receive-only) . . . . . . . . . . . . . . . 31 6.7.1. recvonly (receive-only) . . . . . . . . . . . . . . . 31
6.7.2. sendrecv (send-receive) . . . . . . . . . . . . . . . 32 6.7.2. sendrecv (send-receive) . . . . . . . . . . . . . . . 31
6.7.3. sendonly (send-only) . . . . . . . . . . . . . . . . 32 6.7.3. sendonly (send-only) . . . . . . . . . . . . . . . . 32
6.7.4. inactive . . . . . . . . . . . . . . . . . . . . . . 33 6.7.4. inactive . . . . . . . . . . . . . . . . . . . . . . 32
6.8. orient (orientation) . . . . . . . . . . . . . . . . . . 33 6.8. orient (orientation) . . . . . . . . . . . . . . . . . . 33
6.9. type (conference type) . . . . . . . . . . . . . . . . . 34 6.9. type (conference type) . . . . . . . . . . . . . . . . . 33
6.10. charset (character set) . . . . . . . . . . . . . . . . . 35 6.10. charset (character set) . . . . . . . . . . . . . . . . . 34
6.11. sdplang (SDP language) . . . . . . . . . . . . . . . . . 36 6.11. sdplang (SDP language) . . . . . . . . . . . . . . . . . 35
6.12. lang (language) . . . . . . . . . . . . . . . . . . . . . 37 6.12. lang (language) . . . . . . . . . . . . . . . . . . . . . 36
6.13. framerate (frame rate) . . . . . . . . . . . . . . . . . 37 6.13. framerate (frame rate) . . . . . . . . . . . . . . . . . 37
6.14. quality . . . . . . . . . . . . . . . . . . . . . . . . . 38 6.14. quality . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.15. fmtp (format parameters) . . . . . . . . . . . . . . . . 39 6.15. fmtp (format parameters) . . . . . . . . . . . . . . . . 38
7. Security Considerations . . . . . . . . . . . . . . . . . . . 39 7. Security Considerations . . . . . . . . . . . . . . . . . . . 39
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40
8.1. The "application/sdp" Media Type . . . . . . . . . . . . 42 8.1. The "application/sdp" Media Type . . . . . . . . . . . . 40
8.2. Registration of Parameters . . . . . . . . . . . . . . . 43 8.2. Registration of Parameters . . . . . . . . . . . . . . . 42
8.2.1. Media Types ("media") . . . . . . . . . . . . . . . . 43 8.2.1. Media Types ("media") . . . . . . . . . . . . . . . . 42
8.2.2. Transport Protocols ("proto") . . . . . . . . . . . . 44 8.2.2. Transport Protocols ("proto") . . . . . . . . . . . . 42
8.2.3. Media Formats ("fmt") . . . . . . . . . . . . . . . . 44 8.2.3. Media Formats ("fmt") . . . . . . . . . . . . . . . . 43
8.2.4. Attribute Names ("att-field") . . . . . . . . . . . . 45 8.2.4. Attribute Names ("att-field") . . . . . . . . . . . . 43
8.2.5. Bandwidth Specifiers ("bwtype") . . . . . . . . . . . 46 8.2.5. Bandwidth Specifiers ("bwtype") . . . . . . . . . . . 45
8.2.6. Network Types ("nettype") . . . . . . . . . . . . . . 46 8.2.6. Network Types ("nettype") . . . . . . . . . . . . . . 45
8.2.7. Address Types ("addrtype") . . . . . . . . . . . . . 47 8.2.7. Address Types ("addrtype") . . . . . . . . . . . . . 45
8.2.8. Registration Procedure . . . . . . . . . . . . . . . 47 8.2.8. Registration Procedure . . . . . . . . . . . . . . . 46
8.3. Encryption Key Access Methods . . . . . . . . . . . . . . 48 8.3. Encryption Key Access Methods . . . . . . . . . . . . . . 46
9. SDP Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 48 8.4. Reorganization of the nettype Registry . . . . . . . . . 47
8.5. Reorganization of the att-field Registries . . . . . . . 47
9. SDP Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 47
10. Summary of Changes from RFC 4566 . . . . . . . . . . . . . . 53 10. Summary of Changes from RFC 4566 . . . . . . . . . . . . . . 53
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 53 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 53
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 54 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 53
12.1. Normative References . . . . . . . . . . . . . . . . . . 54 12.1. Normative References . . . . . . . . . . . . . . . . . . 53
12.2. Informative References . . . . . . . . . . . . . . . . . 55 12.2. Informative References . . . . . . . . . . . . . . . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 57 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 57
1. Introduction 1. Introduction
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.
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attribute it doesn't understand. attribute it doesn't understand.
An SDP session description may contain URIs that reference external An SDP session description may contain URIs that reference external
content in the "u=", "k=", and "a=" lines. These URIs may be content in the "u=", "k=", and "a=" lines. These URIs may be
dereferenced in some cases, making the session description non-self- dereferenced in some cases, making the session description non-self-
contained. contained.
The connection ("c=") information in the session-level section The connection ("c=") information in the session-level section
applies to all the media of that session unless overridden by applies to all the media of that session unless overridden by
connection information in the media description. For instance, in connection information in the media description. For instance, in
the example below, each audio media behaves as if it were given a the example below, each audio media description behaves as if it were
"c=IN IP4 233.252.0.2". given a "c=IN IP4 233.252.0.2".
An example SDP description is: An example SDP description is:
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP4 198.51.100.1 o=jdoe 2890844526 2890842807 IN IP4 198.51.100.1
s=SDP Seminar s=SDP Seminar
i=A Seminar on the session description protocol i=A Seminar on the session description protocol
u=http://www.example.com/seminars/sdp.pdf u=http://www.example.com/seminars/sdp.pdf
e=j.doe@example.com (Jane Doe) e=j.doe@example.com (Jane Doe)
c=IN IP4 233.252.0.2 c=IN IP4 233.252.0.2
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strings MUST be interpreted as containing ISO-10646 characters in strings MUST be interpreted as containing ISO-10646 characters in
UTF-8 encoding (the presence of the "a=charset" attribute may force UTF-8 encoding (the presence of the "a=charset" attribute may force
some fields to be interpreted differently). some fields to be interpreted differently).
A session description can contain domain names in the "o=", "u=", A session description can contain domain names in the "o=", "u=",
"e=", "c=", and "a=" lines. Any domain name used in SDP MUST comply "e=", "c=", and "a=" lines. Any domain name used in SDP MUST comply
with [RFC1034], [RFC1035]. Internationalised domain names (IDNs) with [RFC1034], [RFC1035]. Internationalised domain names (IDNs)
MUST be represented using the ASCII Compatible Encoding (ACE) form MUST be represented using the ASCII Compatible Encoding (ACE) form
defined in [RFC5890] and MUST NOT be directly represented in UTF-8 or defined in [RFC5890] and MUST NOT be directly represented in UTF-8 or
any other encoding (this requirement is for compatibility with any other encoding (this requirement is for compatibility with
[RFC4566] and other early SDP-related standards, which predate the [RFC2327] and other early SDP-related standards, which predate the
development of internationalised domain names). development of internationalised domain names).
5.1. Protocol Version ("v=") 5.1. Protocol Version ("v=")
v=0 v=0
The "v=" field gives the version of the Session Description Protocol. The "v=" line gives the version of the Session Description Protocol.
This memo defines version 0. There is no minor version number. This memo defines version 0. There is no minor version number.
5.2. Origin ("o=") 5.2. Origin ("o=")
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=" line 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> forms a <sess-id>, <nettype>, <addrtype>, and <unicast-address> forms a
globally unique identifier for the session. The method of <sess- globally unique identifier for the session. The method of <sess-
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version 6 address of the machine. For both IP4 and IP6, the fully version 6 address of the machine. For both IP4 and IP6, the fully
qualified domain name is the form that SHOULD be given unless this qualified domain name is the form that SHOULD be given unless this
is unavailable, in which case a globally unique address MAY be is unavailable, in which case a globally unique address MAY be
substituted. Unless an SDP extension for NAT traversal is used substituted. Unless an SDP extension for NAT traversal is used
(e.g., ICE [RFC5245], ICE TCP [RFC6544]), a local IP address MUST (e.g., ICE [RFC5245], ICE TCP [RFC6544]), a local IP address MUST
NOT be used in any context where the SDP description might leave NOT be used in any context where the SDP description might leave
the scope in which the address is meaningful (for example, a local the scope in which the address is meaningful (for example, a local
address MUST NOT be included in an application-level referral that address MUST NOT be included in an application-level referral that
might leave the scope). might leave the scope).
In general, the "o=" field serves as a globally unique identifier for In general, the "o=" line serves as a globally unique identifier for
this version of this session description, and the subfields excepting this version of this session description, and the subfields excepting
the version taken together identify the session irrespective of any the version taken together identify the session irrespective of any
modifications. modifications.
For privacy reasons, it is sometimes desirable to obfuscate the For privacy reasons, it is sometimes desirable to obfuscate the
username and IP address of the session originator. If this is a username and IP address of the session originator. If this is a
concern, an arbitrary <username> and private <unicast-address> MAY be concern, an arbitrary <username> and private <unicast-address> MAY be
chosen to populate the "o=" field, provided that these are selected chosen to populate the "o=" line, provided that these are selected in
in a manner that does not affect the global uniqueness of the field. a manner that does not affect the global uniqueness of the field.
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=" line 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=" line per session description. The "s=" line 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 value "s= " SHOULD be used (i.e., a single space as the session
name). 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=" line provides textual information about the session. There
MUST be at most one session-level "i=" field per session description, MUST be at most one session-level "i=" line per session description,
and at most one "i=" field per media. If the "a=charset" attribute and at most one "i=" line per media. If the "a=charset" attribute is
is present, it specifies the character set used in the "i=" field. present, it specifies the character set used in the "i=" line. If
If the "a=charset" attribute is not present, the "i=" field MUST the "a=charset" attribute is not present, the "i=" line MUST contain
contain ISO 10646 characters in UTF-8 encoding. ISO 10646 characters in UTF-8 encoding.
A single "i=" field MAY also be used for each media definition. In A single "i=" line MAY also be used for each media definition. In
media definitions, "i=" fields are primarily intended for labelling media definitions, "i=" lines are primarily intended for labelling
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 The "i=" line is intended to provide a free-form human-readable
description of the session or the purpose of a media stream. It is description of the session or the purpose of a media stream. It is
not suitable for parsing by automata. not suitable for parsing by automata.
5.5. URI ("u=") 5.5. URI ("u=")
u=<uri> u=<uri>
A URI is a Uniform Resource Identifier as used by WWW clients A URI is a Uniform Resource Identifier as used by WWW clients
[RFC3986]. The URI should be a pointer to additional information [RFC3986]. The URI should be a pointer to additional information
about the session. This field is OPTIONAL, but if it is present it about the session. This line is OPTIONAL, but if it is present it
MUST be specified before the first media field. No more than one URI MUST be specified before the first media field. No more than one URI
field is allowed per session description. line 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 session. This is not necessarily the same person responsible for the session. This is not necessarily the same person
that created the session description. that created the session description.
Inclusion of an email address or phone number is OPTIONAL. Note that Inclusion of an email address or phone number is OPTIONAL. Note that
the previous version of SDP specified that either an email field or a the previous version of SDP specified that either an email line or a
phone field MUST be specified, but this was widely ignored. The phone line MUST be specified, but this was widely ignored. The
change brings the specification into line with common usage. change brings the specification into line with common usage.
If an email address or phone number is present, it MUST be specified If an email address or phone number is present, it MUST be specified
before the first media field. More than one email or phone field can before the first media field. More than one email or phone line can
be given for a session description. 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=+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
skipping to change at page 14, line 44 skipping to change at page 15, line 4
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 parentheses if it is who may be contacted. This MUST be enclosed in parentheses 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 [RFC5322] name quoting convention is also allowed for The alternative [RFC5322] name quoting convention is also allowed for
both email addresses and phone numbers. For example: both email addresses and phone numbers. For example:
e=Jane Doe <j.doe@example.com> e=Jane Doe <j.doe@example.com>
The free text string SHOULD be in the ISO-10646 character set with The free text string SHOULD be in the ISO-10646 character set with
UTF-8 encoding, or alternatively in ISO-8859-1 or other encodings if UTF-8 encoding, or alternatively in ISO-8859-1 or other encodings if
the appropriate session-level "a=charset" attribute is set. the appropriate session-level "a=charset" attribute is set.
5.7. Connection Data ("c=") 5.7. Connection Data ("c=")
c=<nettype> <addrtype> <connection-address> c=<nettype> <addrtype> <connection-address>
The "c=" field contains connection data. The "c=" line contains connection data.
A session description MUST contain either at least one "c=" field in A session description MUST contain either at least one "c=" line in
each media description or a single "c=" field at the session level. each media description or a single "c=" line at the session level.
It MAY contain a single session-level "c=" field and additional "c=" It MAY contain a single session-level "c=" line and additional "c="
field(s) per media description, in which case the per-media values line(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 text string giving the type of network. Initially, "IN" is defined
to have the meaning "Internet", but other values MAY be registered in to have the meaning "Internet", but other values MAY be registered in
the future (see Section 8). the future (see Section 8).
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. This memo only SDP to be used for sessions that are not IP based. This memo only
defines IP4 and IP6, but other values MAY be registered in the future defines IP4 and IP6, but other values MAY be registered in the future
skipping to change at page 17, line 5 skipping to change at page 17, line 4
Similarly, an IP6 example would be: Similarly, an IP6 example would be:
c=IN IP6 FF15::101/3 c=IN IP6 FF15::101/3
which is semantically equivalent to: which is semantically equivalent to:
c=IN IP6 FF15::101 c=IN IP6 FF15::101
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 IP6 multicast). (remembering that the TTL field is not present in IP6 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=" line.
The slash notation for multiple addresses described above MUST NOT be The slash notation for multiple addresses described above MUST NOT be
used for IP unicast 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 line 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 defined in the meaning of the <bandwidth> figure. Two values are defined in
this specification, but other values MAY be registered in the future this specification, but other values MAY be registered in the future
(see Section 8 and [RFC3556], [RFC3890]): (see Section 8 and [RFC3556], [RFC3890]):
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 "multimedia conference total" to the bandwidth used (the "conference total" bandwidth). The
bandwidth). The primary purpose of this is to give an approximate primary purpose of this is to give an approximate idea as to
idea as to whether two or more sessions can coexist whether two or more sessions can coexist simultaneously.
simultaneously. When using the CT modifier with RTP, if several
RTP sessions are part of the multimedia conference, the multimedia
conference total 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, be the application's concept of maximum bandwidth). Normally,
this will coincide with what is set on the application's "maximum this 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
[RFC3550]. [RFC3550].
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
skipping to change at page 19, line 21 skipping to change at page 19, line 13
session should really end. session should really end.
Permanent sessions may be shown to the user as never being active Permanent sessions may be shown to the user as never being active
unless there are associated repeat times that state precisely when unless there are associated repeat times that state precisely when
the session will be active. the session will be active.
5.10. Repeat Times ("r=") 5.10. Repeat Times ("r=")
r=<repeat interval> <active duration> <offsets from start-time> r=<repeat interval> <active duration> <offsets from start-time>
"r=" fields specify repeat times for a session. For example, if a "r=" line specifies repeat times for a session. For example, if a
session is active at 10am on Monday and 11am on Tuesday for one hour session is active at 10am on Monday and 11am on Tuesday for one hour
each week for three months, then the <start-time> in the each week for three months, then the <start-time> in the
corresponding "t=" field would be the NTP representation of 10am on corresponding "t=" line 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=" line 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=" lines might
be the following: be the following:
t=3034423619 3042462419 t=3034423619 3042462419
r=604800 3600 0 90000 r=604800 3600 0 90000
To make the description more compact, times may also be given in To make the description more compact, times may also be given in
units of days, hours, or minutes. The syntax for these is a number units of days, hours, or minutes. The syntax for these is a number
immediately followed by a single case-sensitive character. immediately followed by a single case-sensitive character.
Fractional units are not allowed -- a smaller unit should be used Fractional units are not allowed -- a smaller unit should be used
instead. The following unit specification characters are allowed: instead. The following unit specification characters are allowed:
skipping to change at page 20, line 4 skipping to change at page 19, line 41
instead. The following unit specification characters are allowed: instead. The following 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) s - seconds (allowed for completeness)
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=" lines 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 that spans a change from daylight To schedule a repeated session that 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 saving time on different dates, countries change to or from daylight saving time on different dates,
and some countries do not have daylight saving time at all. and 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
zone adjustment happens and the offset from the time when the session zone adjustment happens and the offset from the time when the session
was first scheduled. The "z=" field allows the sender to specify a was first scheduled. The "z=" line allows the sender to specify a
list of these adjustment times and offsets from the base time. list of these adjustment times and offsets from the base time.
An example might be the following: An example might be the following:
z=2882844526 -1h 2898848070 0 z=2882844526 -1h 2898848070 0
This specifies that at time 2882844526, the time base by which the 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 session's repeat times are calculated is shifted back by 1 hour, and
that at time 2898848070, the session's original time base is that at time 2898848070, the session's original time base is
restored. Adjustments are always relative to the specified start restored. Adjustments are always relative to the specified start
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If a session is likely to last several years, it is expected that the If a session is likely to last several years, it is expected that the
session description will be modified periodically rather than session description will be modified periodically rather than
transmit several years' worth of adjustments in one session transmit several years' worth of adjustments in one session
description. description.
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 line ("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 [RFC4567] to define new key exchange mechanisms for use with SDP [RFC4567]
[RFC4568], and it is expected that new applications will use those [RFC4568], and it is expected that new applications will use those
mechanisms. mechanisms.
A key field is permitted before the first media entry (in which case A key line 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 are outside the scope required. The format of keys and their usage are outside the scope
of this document, and the key field provides no way to indicate the of 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, another for protocols require two keys: one for confidentiality, another for
integrity. This specification does not support transfer of two keys. integrity. This specification does not support transfer of two 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 line.
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 encryption key the SDP is conveyed over a secure channel. The encryption key
is interpreted as text according to the charset attribute; use is interpreted as text according to the charset attribute; use
the "k=base64:" method to convey characters that are otherwise the "k=base64:" method to convey characters that are otherwise
prohibited in SDP. 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 line but has been
base64 encoded [RFC4648] because it includes characters that base64 encoded [RFC4648] because it includes characters that
are prohibited in SDP. This method MUST NOT be used unless it are prohibited in SDP. This method MUST NOT be used unless it
can be guaranteed that the SDP is conveyed over a secure can be guaranteed that the SDP is conveyed over a secure
channel. channel.
k=uri:<URI to obtain key> k=uri:<URI to obtain key>
A Uniform Resource Identifier is included in the key field. A Uniform Resource Identifier is included in the key line. The
The URI refers to the data containing the key, and may require 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 an Secure Socket the encoding for the key. The URI is often an Secure Socket
Layer/Transport Layer Security (SSL/TLS)-protected HTTP URI Layer/Transport Layer Security (SSL/TLS)-protected HTTP URI
("https:"), although this is not required. ("https:"), although this is not required.
k=prompt k=prompt
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 line 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 line MUST NOT be used unless it can be guaranteed that the
SDP is conveyed over a secure and trusted channel. An example of SDP is conveyed over a secure and trusted channel. An example of
such a channel might be SDP embedded inside an S/MIME message or a such a channel might be SDP embedded inside an S/MIME message or a
TLS-protected HTTP session. It is important to ensure that the TLS-protected HTTP session. It is important to ensure that the
secure channel is with the party that is authorised to join the secure channel is with the party that is authorised 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. access the 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=" lines)
that are media specific. These are referred to as "media-level" that 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 lines can also be added before the first media field; these "session-
"session-level" attributes convey additional information that applies level" attributes convey additional information that applies to the
to the session as a whole rather than to individual media. session as a whole rather than to individual media.
Attribute fields may be of two forms: Attribute lines may be of two forms:
o A property attribute is simply of the form "a=<flag>". These are o A property attribute is simply of the form "a=<flag>". These are
binary attributes, and the presence of the attribute conveys that binary attributes, and the presence of the attribute conveys that
the attribute is a property of the session. An example might be the attribute is a property of the session. An example might be
"a=recvonly". "a=recvonly".
o A value attribute is of the form "a=<attribute>:<value>". For o A value attribute is of the form "a=<attribute>:<value>". For
example, a whiteboard could have the value attribute example, a whiteboard could have the value attribute
"a=orient:landscape" "a=orient:landscape"
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Attributes MUST be registered with IANA (see Section 8). If an Attributes MUST be registered with IANA (see Section 8). 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 by Each media description starts with an "m=" line and is terminated by
either the next "m=" field or by the end of the session description. either the next "m=" line or by the end of the session description.
A media field has several sub-fields: A media field has several sub-fields:
<media> is the media type. Currently defined media are "audio", <media> is the media type. Currently defined media are "audio",
"video", "text", "application", and "message", although this list "video", "text", "application", and "message", although this list
may be extended in the future (see Section 8). may be extended in the future (see Section 8).
<port> is the transport port to which the media stream is sent. The <port> is the transport port to which the media stream is sent. The
meaning of the transport port depends on the network being used as meaning of the transport port depends on the network being used as
specified in the relevant "c=" field, and on the transport specified in the relevant "c=" line, and on the transport protocol
protocol defined in the <proto> sub-field of the media field. defined in the <proto> sub-field of the media field. Other ports
Other ports used by the media application (such as the RTP Control used by the media application (such as the RTP Control Protocol
Protocol (RTCP) port [RFC3550]) MAY be derived algorithmically (RTCP) port [RFC3550]) MAY be derived algorithmically from the
from the base media port or MAY be specified in a separate base media port or MAY be specified in a separate attribute (for
attribute (for example, "a=rtcp:" as defined in [RFC3605]). example, "a=rtcp:" as defined in [RFC3605]).
If non-contiguous ports are used or if they don't follow the If non-contiguous ports are used or if they don't follow the
parity rule of even RTP ports and odd RTCP ports, the "a=rtcp:" parity rule of even RTP ports and odd RTCP ports, the "a=rtcp:"
attribute MUST be used. Applications that are requested to send attribute MUST be used. Applications that are requested to send
media to a <port> that is odd and where the "a=rtcp:" is present media to a <port> that is odd and where the "a=rtcp:" is present
MUST NOT subtract 1 from the RTP port: that is, they MUST send the MUST NOT subtract 1 from the RTP port: that is, they MUST send the
RTP to the port indicated in <port> and send the RTCP to the port RTP to the port indicated in <port> and send the RTCP to the port
indicated in the "a=rtcp" attribute. indicated in the "a=rtcp" attribute.
For applications where hierarchically encoded streams are being For applications where hierarchically encoded streams are being
sent 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 transport ports. This is done using a similar notation to that
used for IP multicast addresses in the "c=" field: used for IP multicast addresses in the "c=" line:
m=<media> <port>/<number of ports> <proto> <fmt> ... m=<media> <port>/<number of ports> <proto> <fmt> ...
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 RTP, the default is that only the even-numbered ports are used For RTP, the default is that only the even-numbered ports are used
for data with the corresponding one-higher odd ports used for the for data with the corresponding one-higher odd ports used for the
RTCP belonging to the RTP session, and the <number of ports> RTCP belonging to the RTP session, and the <number of ports>
denoting the 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 would specify that ports 49170 and 49171 form one RTP/RTCP pair
and 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 non-
contiguous ports are required, they must be signalled using a contiguous ports are required, they must be signalled using a
separate attribute (for example, "a=rtcp:" as defined in separate attribute (for example, "a=rtcp:" as defined in
[RFC3605]). [RFC3605]).
If multiple addresses are specified in the "c=" field and multiple If multiple addresses are specified in the "c=" line and multiple
ports are specified in the "m=" field, a one-to-one mapping from ports are specified in the "m=" line, a one-to-one mapping from
port to the corresponding address is implied. For example: port to the corresponding address is implied. For example:
c=IN IP4 233.252.0.1/127/2 c=IN IP4 233.252.0.1/127/2
m=video 49170/2 RTP/AVP 31 m=video 49170/2 RTP/AVP 31
would imply that address 233.252.0.1 is used with ports 49170 and would imply that address 233.252.0.1 is used with ports 49170 and
49171, and address 233.252.0.2 is used with ports 49172 and 49173. 49171, and address 233.252.0.2 is used with ports 49172 and 49173.
The semantics of multiple "m=" lines using the same transport The semantics of multiple "m=" lines using the same transport
address are undefined. This implies that, unlike limited past address are undefined. This implies that, unlike limited past
practice, there is no implicit grouping defined by such means and practice, there is no implicit grouping defined by such means and
an explicit grouping framework (for example, [RFC5888]) should an explicit grouping framework (for example, [RFC5888]) should
instead be used to express the intended semantics. instead be used to express the intended semantics.
<proto> is the transport protocol. The meaning of the transport <proto> is the transport protocol. The meaning of the transport
protocol is dependent on the address type field in the relevant protocol is dependent on the address type field in the relevant
"c=" field. Thus a "c=" field of IP4 indicates that the transport "c=" line. Thus a "c=" field of IP4 indicates that the transport
protocol runs over IP4. The following transport protocols are protocol runs over IP4. The following transport protocols are
defined, but may be extended through registration of new protocols defined, but may be extended through registration of new protocols
with IANA (see Section 8): with IANA (see Section 8):
* udp: denotes an unspecified protocol running over UDP. * udp: denotes an unspecified protocol running over UDP.
* RTP/AVP: denotes RTP [RFC3550] used under the RTP Profile for * RTP/AVP: denotes RTP [RFC3550] used under the RTP Profile for
Audio and Video Conferences with Minimal Control [RFC3551] Audio and Video Conferences with Minimal Control [RFC3551]
running over UDP. running over UDP.
skipping to change at page 28, line 19 skipping to change at page 27, line 41
Name: ptime Name: ptime
Value: ptime-value Value: ptime-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
Syntax: Syntax:
ptime-value = packet-time ptime-value = non-zero-int-or-real
packet-time = integer
; do we want to define a limited range for this?
Example: Example:
a=ptime:20 a=ptime:20
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,
but may be used with other media types if it makes sense. It should but may be used with other media types if it makes sense. It should
not be necessary to know ptime to decode RTP or vat audio, and it is not be necessary to know ptime to decode RTP or vat audio, and it is
intended as a recommendation for the encoding/packetisation of audio. intended as a recommendation for the encoding/packetisation of audio.
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Name: maxptime Name: maxptime
Value: maxptime-value Value: maxptime-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
Syntax: Syntax:
maxptime-value = packet-time maxptime-value = non-zero-int-or-real
Example: Example:
a=maxptime:20 a=maxptime:20
This gives the maximum amount of media that can be encapsulated in This gives the maximum amount of media that can be encapsulated in
each packet, expressed as time in milliseconds. The time SHALL be each packet, expressed as time in milliseconds. The time SHALL be
calculated as the sum of the time the media present in the packet calculated as the sum of the time the media present in the packet
represents. For frame-based codecs, the time SHOULD be an integer represents. For frame-based codecs, the time SHOULD be an integer
multiple of the frame size. This attribute is probably only multiple of the frame size. This attribute is probably only
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Name: charset Name: charset
Value: charset-value Value: charset-value
Usage Level: session Usage Level: session
Charset Dependent: no Charset Dependent: no
Syntax: Syntax:
charset-value = mime-charset (as defined in <xref charset-value = mime-charset
target="I-D.iana-charset-reg-procedure"/>) (as defined in I-D.iana-charset-reg-procedure)
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, the ISO-10646 character set name and information data. By default, the ISO-10646 character set
in UTF-8 encoding is used. If a more compact representation is in UTF-8 encoding is used. If a more compact representation is
required, other character sets may be used. For example, the ISO required, other character sets may be used. For example, the ISO
8859-1 is specified with the following SDP attribute: 8859-1 is specified with the following SDP attribute:
a=charset:ISO-8859-1 a=charset:ISO-8859-1
The charset specified MUST be one of those registered in the IANA The charset specified MUST be one of those registered in the IANA
Character Sets registry (http://www.iana.org/assignments/character- Character Sets registry (http://www.iana.org/assignments/character-
skipping to change at page 38, line 4 skipping to change at page 37, line 14
The "lang" attribute value must be a single [RFC5646] language tag in The "lang" attribute value must be a single [RFC5646] language tag in
US-ASCII. A "lang" attribute SHOULD be specified when a session is US-ASCII. A "lang" attribute SHOULD be specified when a session is
of sufficient scope to cross geographic boundaries where the language of sufficient scope to cross geographic boundaries where the language
of recipients cannot be assumed, or where the session is in a of recipients cannot be assumed, or where the session is in a
different language from the locally assumed norm. different language from the locally assumed norm.
6.13. framerate (frame rate) 6.13. framerate (frame rate)
Name: framerate Name: framerate
Value: framerate-value Value: framerate-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
Syntax: Syntax:
framerate-value = positive-real-number framerate-value = non-zero-int-or-real
positive-real-number = (integer / "0") [ "." integer ]
; Notes:
; - this permits a zero value. OK?
; - do we want to restrict the range or precision?
Example: Example:
a=framerate:60 a=framerate:60
This gives the maximum video frame rate in frames/sec. It is This gives the maximum video frame rate in frames/sec. It is
intended as a recommendation for the encoding of video data. Decimal intended as a recommendation for the encoding of video data. Decimal
representations of fractional values are allowed. It is defined only representations of fractional values are allowed. It is defined only
for video media. for video media.
skipping to change at page 38, line 39 skipping to change at page 37, line 46
Name: quality Name: quality
Value: quality-value Value: quality-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
Syntax: Syntax:
quality-value = integer quality-value = zero-based-integer
; Do we want to restrict the range?
; The definition above limits the range to [0-10]
; *for video*, but seems to leave usage open for other media.
Example: Example:
a=quality:10 a=quality:10
This gives a suggestion for the quality of the encoding as an integer This gives a suggestion for the quality of the encoding as an integer
value. The intention of the quality attribute for video is to value. The intention of the quality attribute for video is to
specify a non-default trade-off between frame-rate and still-image specify a non-default trade-off between frame-rate and still-image
quality. For video, the value is in the range 0 to 10, with the quality. For video, the value is in the range 0 to 10, with the
following suggested meaning: following suggested meaning:
10 - the best still-image quality the compression scheme 10 - the best still-image quality the compression scheme
can give. can give.
5 - the default behaviour given no quality suggestion. 5 - the default behaviour given no quality suggestion.
0 - the worst still-image quality the codec designer 0 - the worst still-image quality the codec designer
thinks is still usable. thinks is still usable.
Editor's note: The usage should be checked with the SIP Forum to see
whether anybody is using this. Otherwise, the recommendation will be
not to use this attribute and the receiver ignores it upon reception.
6.15. fmtp (format parameters) 6.15. fmtp (format parameters)
Name: fmtp Name: fmtp
Value: fmtp-value Value: fmtp-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
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session description, for example, to have the contents of the session session description, for example, to have the contents of the session
description match NAT bindings dynamically created. These behaviours description match NAT bindings dynamically created. These behaviours
are NOT RECOMMENDED unless the session description is conveyed in are NOT RECOMMENDED unless the session description is conveyed in
such a manner that allows the intermediary system to conduct proper such a manner that allows the intermediary system to conduct proper
checks to establish the authenticity of the session description, and checks to establish the authenticity of the session description, and
the authority of its source to establish such communication sessions. the authority of its source to establish such communication sessions.
SDP by itself does not include sufficient information to enable these SDP by itself does not include sufficient information to enable these
checks: they depend on the encapsulating protocol (e.g., SIP or checks: they depend on the encapsulating protocol (e.g., SIP or
RTSP). RTSP).
Use of the "k=" field poses a significant security risk, since it Use of the "k=" line 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.
Moreover, the "k=" line provides no way to indicate or negotiate Moreover, the "k=" line provides no way to indicate or negotiate
cryptographic key algorithms. As it provides for only a single cryptographic key algorithms. As it provides for only a single
symmetric key, rather than separate keys for confidentiality and symmetric key, rather than separate keys for confidentiality and
integrity, its utility is severely limited. The use of the "k=" line integrity, its utility is severely limited. The use of the "k=" line
is NOT RECOMMENDED, as discussed in Section 5.12. is NOT RECOMMENDED, as discussed in Section 5.12.
8. IANA Considerations 8. IANA Considerations
8.1. The "application/sdp" Media Type 8.1. The "application/sdp" Media Type
skipping to change at page 44, line 29 skipping to change at page 43, line 7
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 [RFC3550] used under the RTP values: "RTP/AVP" is a reference to [RFC3550] used under the RTP
Profile for Audio and Video Conferences with Minimal Control Profile for Audio and Video Conferences with Minimal Control
[RFC3551] running over UDP/IP, "RTP/SAVP" is a reference to the [RFC3551] running over UDP/IP, "RTP/SAVP" is a reference to the
Secure Real-time Transport Protocol [RFC3711], and "udp" indicates an Secure Real-time Transport Protocol [RFC3711], and "udp" indicates an
unspecified protocol over UDP. unspecified protocol over UDP.
If other RTP profiles are defined in the future, their "proto" name If other RTP profiles are defined in the future, their "proto" name
SHOULD be specified in the same manner. For example, an RTP profile SHOULD be specified in the same manner. For example, an RTP profile
whose short name is "XYZ" would be denoted by a "proto" field of "RTP whose short name is "XYZ" would be denoted by a "proto" field of
/XYZ". "RTP/XYZ".
New transport protocols SHOULD be registered with IANA. New transport protocols SHOULD be registered with IANA.
Registrations MUST reference an RFC describing the protocol. Such an Registrations MUST reference an RFC describing the protocol. Such an
RFC MAY be Experimental or Informational, although it is preferable RFC MAY be Experimental or Informational, although it is preferable
that it be Standards Track. Registrations MUST also define the rules that it be Standards Track. Registrations MUST also define the rules
by which their "fmt" namespace is managed (see below). by which their "fmt" namespace is managed (see below).
8.2.3. Media Formats ("fmt") 8.2.3. Media Formats ("fmt")
Each transport protocol, defined by the "proto" field, has an Each transport protocol, defined by the "proto" field, has an
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attribute takes no value. Enclosing the rule name in "[" and "]" attribute takes no value. Enclosing the rule name in "[" and "]"
indicates that a value is optional. indicates that a value is optional.
o Usage level of the attribute. (One or more of: session, media, o Usage level of the attribute. (One or more of: session, media,
source). source).
o Whether the attribute value is subject to the charset attribute. o Whether the attribute value is subject to the charset attribute.
o An ABNF definition of the attribute value rule. The rule MUST NOT o An ABNF definition of the attribute value rule. The rule MUST NOT
match anything that is not also matched by <att-value>. The rule match anything that is not also matched by <att-value>. The rule
name SHOULD [MUST?] NOT be defined as an Incremental Alternative name MUST NOT be defined as an Incremental Alternative to <att-
to <att-value>. value>.
o An explanation of the purpose and usage of the attribute. o An explanation of the purpose and usage of the attribute.
o A specification of appropriate attribute values for this attribute o A specification of appropriate attribute values for this attribute
(If not included in syntax). (If not included in syntax).
o Offer/Answer procedures as explained in [RFC3264]. o Offer/Answer procedures as explained in [RFC3264].
o Indication of which "category" o Indication of which "category"
[I-D.ietf-mmusic-sdp-mux-attributes] an attribute is associated [I-D.ietf-mmusic-sdp-mux-attributes] an attribute is associated
skipping to change at page 47, line 4 skipping to change at page 45, line 28
IANA. The submission MUST reference a standards-track RFC specifying IANA. The submission MUST reference a standards-track RFC specifying
the semantics of the bandwidth specifier precisely, and indicating the semantics of the bandwidth specifier precisely, and indicating
when it should be used, and why the existing registered bandwidth when it should be used, and why the existing registered bandwidth
specifiers do not suffice. specifiers do not suffice.
IANA has registered the bandwidth specifiers "CT" and "AS" with IANA has registered the bandwidth specifiers "CT" and "AS" with
definitions as in Section 5.8 of this memo (these definitions update definitions as in Section 5.8 of this memo (these definitions update
those in [RFC4566]). those in [RFC4566]).
8.2.6. Network Types ("nettype") 8.2.6. Network Types ("nettype")
New network types (the "nettype" field) may be registered with IANA
New network types (the "nettype" field) MUST 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.
Although these are not normally the preserve of IANA, there may be The registration is subject to the RFC Required - RFC publication
circumstances when an Internet application needs to interoperate with policy of [RFC5226]. Although these are not normally the preserve of
a non-Internet application, such as when gatewaying an Internet IANA, there may be circumstances when an Internet application needs
telephone call into the Public Switched Telephone Network (PSTN). to interoperate with a non-Internet application, such as when
The number of network types should be small and should be rarely gatewaying an Internet telephone call into the Public Switched
extended. A new network type cannot be registered without Telephone Network (PSTN). The number of network types should be
registering at least one address type to be used with that network small and should be rarely extended. A new network type cannot be
type. A new network type registration MUST reference an RFC that registered without registering at least one address type to be used
gives details of the network type and address type and specifies how with that network type. A new network type registration MUST
and when they would be used. reference an RFC that gives details of the network type and address
type(s) and specifies how and when they would be used.
IANA has registered the network type "IN" to represent the Internet, IANA has registered the network type "IN" to represent the Internet,
with definition as in Sections 5.2 and 5.7 of this memo (these with definition as in Sections 5.2 and 5.7 of this memo (these
definitions update those in [RFC4566]). definitions update those in [RFC4566]).
8.2.7. Address Types ("addrtype") 8.2.7. Address Types ("addrtype")
New address types ("addrtype") may be registered with IANA. An New address types ("addrtype") MUST be registered with IANA. The
address type is only meaningful in the context of a network type, and registration is subject to the RFC Required - RFC publication policy
any registration of an address type MUST specify a registered network of [RFC5226]. An address type is only meaningful in the context of a
type or be submitted along with a network type registration. A new network type, and any registration of an address type MUST specify a
address type registration MUST reference an RFC giving details of the registered network type or be submitted along with a network type
syntax of the address type. Address types are not expected to be registration. A new address type registration MUST reference an RFC
registered frequently. giving details of the syntax of the address type. Address types are
not expected to be registered frequently.
IANA has registered the address types "IP4" and "IP6" with IANA has registered 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 [RFC4566]). definitions update those in [RFC4566]).
8.2.8. Registration Procedure 8.2.8. 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 48, line 4 skipping to change at page 46, line 31
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 for the registered name (this o a reference to the specification for the registered name (this
will typically be an RFC number) will typically be an RFC number)
In the case of a new addrtype registration, the author has to check
whether the new address type is usable with the existing network
types. If yes, the "nettype" registry MUST be updated accordingly.
In the case of a new nettype registration, the author MUST specify
the usable address type(s).
IANA may refer any registration to the IESG for review, and may IANA may refer any registration to the IESG for review, and may
request revisions to be made before a registration will be made. request revisions to be made before a registration will be made.
8.3. Encryption Key Access Methods 8.3. Encryption Key Access Methods
The IANA previously maintained a table of SDP encryption key access The IANA previously maintained a table of SDP encryption key access
method ("enckey") names. This table is obsolete, since the "k=" line method ("enckey") names. This table is obsolete, since the "k=" line
is not extensible. New registrations MUST NOT be accepted. is not extensible. New registrations MUST NOT be accepted.
8.4. Reorganization of the nettype Registry
This document adds a new column in the "nettype" registry with the
title "Usable addrtype Values" and updates the "nettype" registry as
follows:
--------------------------------------------------------------------
|Type | SDP Name | Usable addrtype Values | Reference |
--------------------------------------------------------------------
|nettype | IN | IP4, IP6 | [RFC4566] |
|nettype | TN | RFC2543 | [RFC2848] |
|nettype | ATM | NSAP, GWID, E164 | [RFC3108] |
|nettype | PSTN | E164 | [RFC7195] |
--------------------------------------------------------------------
Note that both [RFC7195] and [RFC3108] registered "E164" as an
address type, although [RFC7195] mentions that the "E164" address
type has a different context for ATM and PSTN networks.
8.5. Reorganization of the att-field Registries
This document combines all the five "att-field" registries into one
registry called "att-field" registry, and update the columns to
reflect the name, usage level(s), charset dependency and reference.
That is, the new registry uses the following columns:
Name | Usage Level | Dependent on charset? | Reference
The "Name" column reflects the attribute name (as it will appear in
the SDP). The "Usage Level" column MUST indicate one or more of the
following: session, media, source. The "Dependent on charset?"
column MUST indicate "Yes" or "No" depending on whether the attribute
value is subject to the charset attribute. Finally, the "Reference"
column indicates the specification(s) where the attribute is defined.
Editor's note: Will IANA reorganize this table based on what is in
the registry now or should we provide the updated table in this
document?
Editor's note: [I-D.ietf-mmusic-sdp-mux-attributes] adds another
column (muxing category) to this table. Should we add it here?
9. SDP Grammar 9. SDP Grammar
This section provides an Augmented BNF grammar for SDP. ABNF is This section provides an Augmented BNF grammar for SDP. ABNF is
defined in [RFC5234] and [RFC7405]. defined in [RFC5234] and [RFC7405].
; SDP Syntax ; SDP Syntax
session-description = proto-version session-description = proto-version
origin-field origin-field
session-name-field session-name-field
information-field information-field
skipping to change at page 53, line 4 skipping to change at page 52, line 34
;string of visible characters ;string of visible characters
token-char = ALPHA / DIGIT token-char = ALPHA / DIGIT
/ "!" / "#" / "$" / "%" / "&" / / "!" / "#" / "$" / "%" / "&" /
/ "'" ; (single quote) / "'" ; (single quote)
/ "*" / "+" / "-" / "." / "^" / "_" / "*" / "+" / "-" / "." / "^" / "_"
/ "`" ; (Grave accent) / "`" ; (Grave accent)
/ "{" / "|" / "}" / "~" / "{" / "|" / "}" / "~"
zero-based-integer = "0" / integer zero-based-integer = "0" / integer
token = 1*(token-char) token = 1*(token-char)
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
non-zero-int-or-real = integer / non-zero-real
non-zero-real = (integer / "0") "." *DIGIT POS-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 5234 ; ALPHA, DIGIT, CRLF, SP, VCHAR: from RFC 5234
; URI-reference: from RFC 3986 ; URI-reference: from RFC 3986
; addr-spec: from RFC 5322 ; addr-spec: from RFC 5322
skipping to change at page 55, line 7 skipping to change at page 54, line 39
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006. Encodings", RFC 4648, October 2006.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 2006.
[I-D.ietf-avtext-rtp-grouping-taxonomy] [I-D.ietf-avtext-rtp-grouping-taxonomy]
Lennox, J., Gross, K., Nandakumar, S., and G. Salgueiro, Lennox, J., Gross, K., Nandakumar, S., and G. Salgueiro,
"A Taxonomy of Grouping Semantics and Mechanisms for Real- "A Taxonomy of Grouping Semantics and Mechanisms for Real-
Time Transport Protocol (RTP) Sources", draft-ietf-avtext- Time Transport Protocol (RTP) Sources", draft-ietf-avtext-
rtp-grouping-taxonomy-02 (work in progress), June 2014. rtp-grouping-taxonomy-06 (work in progress), March 2015.
[I-D.iana-charset-reg-procedure] [I-D.iana-charset-reg-procedure]
McFadden, M. and A. Melnikov, "IANA Charset Registration McFadden, M. and A. Melnikov, "IANA Charset Registration
Procedures", draft-iana-charset-reg-procedure-00 (work in Procedures", draft-iana-charset-reg-procedure-01 (work in
progress), October 2014. progress), April 2015.
[I-D.ietf-mmusic-sdp-mux-attributes] [I-D.ietf-mmusic-sdp-mux-attributes]
Nandakumar, S., "A Framework for SDP Attributes when Nandakumar, S., "A Framework for SDP Attributes when
Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-08 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-08
(work in progress), January 2015. (work in progress), January 2015.
12.2. Informative References 12.2. Informative References
[RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description [RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998. Protocol", RFC 2327, April 1998.
skipping to change at page 56, line 34 skipping to change at page 56, line 18
[RFC3890] Westerlund, M., "A Transport Independent Bandwidth [RFC3890] Westerlund, M., "A Transport Independent Bandwidth
Modifier for the Session Description Protocol (SDP)", RFC Modifier for the Session Description Protocol (SDP)", RFC
3890, September 2004. 3890, September 2004.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT) (ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, April Traversal for Offer/Answer Protocols", RFC 5245, April
2010. 2010.
[RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B.B., and A.B. [RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach,
Roach, "TCP Candidates with Interactive Connectivity "TCP Candidates with Interactive Connectivity
Establishment (ICE)", RFC 6544, March 2012. Establishment (ICE)", RFC 6544, March 2012.
[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF", RFC [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF", RFC
7405, December 2014. 7405, December 2014.
[ITU.H332.1998] [ITU.H332.1998]
International Telecommunication Union, "H.323 extended for International Telecommunication Union, "H.323 extended for
loosely coupled conferences", ITU Recommendation H.332, loosely coupled conferences", ITU Recommendation H.332,
September 1998. September 1998.
skipping to change at page 57, line 19 skipping to change at page 57, line 5
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008. October 2008.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, RFC Specifications and Registration Procedures", BCP 13, RFC
6838, January 2013. 6838, January 2013.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload [RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, February 2007. Formats", RFC 4855, February 2007.
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
RFC 2365, July 1998.
Authors' Addresses Authors' Addresses
Mark Handley Mark Handley
University College London University College London
Department of Computer Science Department of Computer Science
London WC1E 6BT London WC1E 6BT
UK UK
EMail: M.Handley@cs.ucl.ac.uk EMail: M.Handley@cs.ucl.ac.uk
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