draft-ietf-mmusic-rfc4566bis-24.txt   draft-ietf-mmusic-rfc4566bis-25.txt 
Network Working Group M. Handley Network Working Group A. Begen
Internet-Draft UCL Internet-Draft Networked Media
Obsoletes: 4566 (if approved) C. Perkins Obsoletes: 4566 (if approved) P. Kyzivat
Intended status: Standards Track University of Glasgow Intended status: Standards Track
Expires: April 10, 2018 A. Begen Expires: August 23, 2018 C. Perkins
Networked Media University of Glasgow
October 7, 2017 M. Handley
UCL
February 19, 2018
SDP: Session Description Protocol SDP: Session Description Protocol
draft-ietf-mmusic-rfc4566bis-24 draft-ietf-mmusic-rfc4566bis-25
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 https://datatracker.ietf.org/drafts/current/. Drafts is at https://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 April 10, 2018. This Internet-Draft will expire on August 23, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 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
(https://trustee.ietf.org/license-info) in effect on the date of (https://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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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2. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . 4 2. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . 4
3. Examples of SDP Usage . . . . . . . . . . . . . . . . . . . . 5 3. Examples of SDP Usage . . . . . . . . . . . . . . . . . . . . 5
3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 5 3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . 6 4. Requirements and Recommendations . . . . . . . . . . . . . . 6
4.1. Media and Transport Information . . . . . . . . . . . . . 7 4.1. Media and Transport Information . . . . . . . . . . . . . 7
4.2. Timing Information . . . . . . . . . . . . . . . . . . . 7 4.2. Timing Information . . . . . . . . . . . . . . . . . . . 7
4.3. Obtaining Further Information about a Session . . . . . . 8 4.3. Obtaining Further Information about a Session . . . . . . 8
4.4. Categorisation . . . . . . . . . . . . . . . . . . . . . 8 4.4. Categorization . . . . . . . . . . . . . . . . . . . . . 8
4.5. Internationalisation . . . . . . . . . . . . . . . . . . 8 4.5. Internationalization . . . . . . . . . . . . . . . . . . 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=") . . . . . . . . . . . . . . . . . . . . . . 12 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=") . . . . . . . . . . . . . . . . . . . . . . . 14 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 Information ("c=") . . . . . . . . . . . . . . 15
5.8. Bandwidth ("b=") . . . . . . . . . . . . . . . . . . . . 17 5.8. Bandwidth Information ("b=") . . . . . . . . . . . . . . 17
5.9. Timing ("t=") . . . . . . . . . . . . . . . . . . . . . . 18 5.9. Time Active ("t=") . . . . . . . . . . . . . . . . . . . 18
5.10. Repeat Times ("r=") . . . . . . . . . . . . . . . . . . . 19 5.10. Repeat Times ("r=") . . . . . . . . . . . . . . . . . . . 19
5.11. Time Zones ("z=") . . . . . . . . . . . . . . . . . . . . 19 5.11. Time Zones ("z=") . . . . . . . . . . . . . . . . . . . . 19
5.12. Encryption Keys ("k=") . . . . . . . . . . . . . . . . . 20 5.12. Encryption Keys ("k=") . . . . . . . . . . . . . . . . . 20
5.13. Attributes ("a=") . . . . . . . . . . . . . . . . . . . . 20 5.13. Attributes ("a=") . . . . . . . . . . . . . . . . . . . . 20
5.14. Media Descriptions ("m=") . . . . . . . . . . . . . . . . 21 5.14. Media Descriptions ("m=") . . . . . . . . . . . . . . . . 21
6. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . . 24 6. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . . 24
6.1. cat (category) . . . . . . . . . . . . . . . . . . . . . 24 6.1. cat (category) . . . . . . . . . . . . . . . . . . . . . 24
6.2. keywds (keywords) . . . . . . . . . . . . . . . . . . . . 25 6.2. keywds (keywords) . . . . . . . . . . . . . . . . . . . . 25
6.3. tool . . . . . . . . . . . . . . . . . . . . . . . . . . 25 6.3. tool . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.4. ptime (packet time) . . . . . . . . . . . . . . . . . . . 26 6.4. ptime (packet time) . . . . . . . . . . . . . . . . . . . 26
6.5. maxptime (maximum packet time) . . . . . . . . . . . . . 26 6.5. maxptime (maximum packet time) . . . . . . . . . . . . . 26
6.6. rtpmap . . . . . . . . . . . . . . . . . . . . . . . . . 27 6.6. rtpmap . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.7. Media Direction Attributes . . . . . . . . . . . . . . . 28 6.7. Media Direction Attributes . . . . . . . . . . . . . . . 29
6.7.1. recvonly (receive-only) . . . . . . . . . . . . . . . 29 6.7.1. recvonly (receive-only) . . . . . . . . . . . . . . . 29
6.7.2. sendrecv (send-receive) . . . . . . . . . . . . . . . 30 6.7.2. sendrecv (send-receive) . . . . . . . . . . . . . . . 30
6.7.3. sendonly (send-only) . . . . . . . . . . . . . . . . 30 6.7.3. sendonly (send-only) . . . . . . . . . . . . . . . . 30
6.7.4. inactive . . . . . . . . . . . . . . . . . . . . . . 30 6.7.4. inactive . . . . . . . . . . . . . . . . . . . . . . 30
6.8. orient (orientation) . . . . . . . . . . . . . . . . . . 31 6.8. orient (orientation) . . . . . . . . . . . . . . . . . . 31
6.9. type (conference type) . . . . . . . . . . . . . . . . . 31 6.9. type (conference type) . . . . . . . . . . . . . . . . . 31
6.10. charset (character set) . . . . . . . . . . . . . . . . . 32 6.10. charset (character set) . . . . . . . . . . . . . . . . . 32
6.11. sdplang (SDP language) . . . . . . . . . . . . . . . . . 33 6.11. sdplang (SDP language) . . . . . . . . . . . . . . . . . 33
6.12. lang (language) . . . . . . . . . . . . . . . . . . . . . 34 6.12. lang (language) . . . . . . . . . . . . . . . . . . . . . 34
6.13. framerate (frame rate) . . . . . . . . . . . . . . . . . 35 6.13. framerate (frame rate) . . . . . . . . . . . . . . . . . 35
6.14. quality . . . . . . . . . . . . . . . . . . . . . . . . . 36 6.14. quality . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.15. fmtp (format parameters) . . . . . . . . . . . . . . . . 36 6.15. fmtp (format parameters) . . . . . . . . . . . . . . . . 36
7. Security Considerations . . . . . . . . . . . . . . . . . . . 37 7. Security Considerations . . . . . . . . . . . . . . . . . . . 37
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
8.1. The "application/sdp" Media Type . . . . . . . . . . . . 39 8.1. The "application/sdp" Media Type . . . . . . . . . . . . 39
8.2. Registration of Parameters . . . . . . . . . . . . . . . 41 8.2. Registration of Parameters . . . . . . . . . . . . . . . 40
8.2.1. Media Types ("media") . . . . . . . . . . . . . . . . 41 8.2.1. Media Types ("media") . . . . . . . . . . . . . . . . 40
8.2.2. Transport Protocols ("proto") . . . . . . . . . . . . 41 8.2.2. Transport Protocols ("proto") . . . . . . . . . . . . 41
8.2.3. Media Formats ("fmt") . . . . . . . . . . . . . . . . 42 8.2.3. Media Formats ("fmt") . . . . . . . . . . . . . . . . 41
8.2.4. Attribute Names ("att-field") . . . . . . . . . . . . 42 8.2.4. Attribute Names ("att-field") . . . . . . . . . . . . 42
8.2.5. Bandwidth Specifiers ("bwtype") . . . . . . . . . . . 45 8.2.5. Bandwidth Specifiers ("bwtype") . . . . . . . . . . . 44
8.2.6. Network Types ("nettype") . . . . . . . . . . . . . . 45 8.2.6. Network Types ("nettype") . . . . . . . . . . . . . . 45
8.2.7. Address Types ("addrtype") . . . . . . . . . . . . . 46 8.2.7. Address Types ("addrtype") . . . . . . . . . . . . . 45
8.2.8. Registration Procedure . . . . . . . . . . . . . . . 46 8.2.8. Registration Procedure . . . . . . . . . . . . . . . 45
8.3. Encryption Key Access Methods . . . . . . . . . . . . . . 47 8.3. Encryption Key Access Methods . . . . . . . . . . . . . . 46
8.4. Reorganization of the nettype Registry . . . . . . . . . 47 8.4. Reorganization of the nettype Registry . . . . . . . . . 46
8.5. Reorganization of the att-field Registries . . . . . . . 47 8.5. Reorganization of the att-field Registries . . . . . . . 47
9. SDP Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 48 9. SDP Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 47
10. Summary of Changes from RFC 4566 . . . . . . . . . . . . . . 53 10. Summary of Changes from RFC 4566 . . . . . . . . . . . . . . 53
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 54 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 . . . . . . . . . . . . . . . . . . . . . . . 58 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.
SDP provides a standard representation for such information, SDP provides a standard representation for such information,
irrespective of how that information is transported. SDP is purely a irrespective of how that information is transported. SDP is purely a
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not intended to support negotiation of session content or media not intended to support negotiation of session content or media
encodings: this is viewed as outside the scope of session encodings: this is viewed as outside the scope of session
description. description.
This memo obsoletes [RFC4566]. The changes relative to [RFC4566] are This memo obsoletes [RFC4566]. The changes relative to [RFC4566] are
limited to essential corrections, and are outlined in Section 10 of limited to essential corrections, and are outlined in Section 10 of
this memo. this memo.
2. Glossary of Terms 2. Glossary of Terms
The following terms are used in this document and has specific The following terms are used in this document and have specific
meaning within the context of this document. meaning within the context of this document.
Session Description: A well-defined format for conveying sufficient Session Description: A well-defined format for conveying sufficient
information to discover and participate in a multimedia session. information to discover and participate in a multimedia session.
Media Description: A media description starts with an "m=" line and Media Description: A media description starts with an "m=" line and
is terminated by either the next "m=" line or by the end of the is terminated by either the next "m=" line or by the end of the
session description. session description.
Session-level Section: This refers to the parts that are not media Session-level Section: This refers to the parts that are not media
descriptions, whereas the session description refers to the whole descriptions, whereas the session description refers to the whole
body that includes the session-level section and the media body that includes the session-level section and the media
description(s). description(s).
The terms "multimedia conference" and "multimedia session" are used The terms "multimedia conference" and "multimedia session" are used
in this document as defined in [RFC7656]. The terms "session" and in this document as defined in [RFC7656]. The terms "session" and
"multimedia session" are used interchangeably in this document. "multimedia session" are used interchangeably in this document.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in BCP
[RFC2119]. 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Examples of SDP Usage 3. Examples of SDP Usage
3.1. Session Initiation 3.1. Session Initiation
The Session Initiation Protocol (SIP) [RFC3261] is an application- The Session Initiation Protocol (SIP) [RFC3261] is an application-
layer control protocol for creating, modifying, and terminating layer control protocol for creating, modifying, and terminating
sessions such as Internet multimedia conferences, Internet telephone sessions such as Internet multimedia conferences, Internet telephone
calls, and multimedia distribution. The SIP messages used to create calls, and multimedia distribution. The SIP messages used to create
sessions carry session descriptions that allow participants to agree sessions carry session descriptions that allow participants to agree
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o The format of the media (H.261 video, MPEG video, etc.) o The format of the media (H.261 video, MPEG video, etc.)
In addition to media format and transport protocol, SDP conveys In addition to media format and transport protocol, SDP conveys
address and port details. For an IP multicast session, these address and port details. For an IP multicast session, these
comprise: comprise:
o The multicast group address for media o The multicast group address for media
o The transport port for media o The transport port for media
This address and port are the destination address and destination This address and port is the destination address and destination port
port of the multicast stream, whether being sent, received, or both. of the multicast stream, whether being sent, received, or both.
For unicast IP sessions, the following are conveyed: For unicast IP sessions, the following are conveyed:
o The remote address for media o The remote address for media
o The remote transport port for media o The remote transport port for media
The semantics of this address and port depend on the media and The semantics of this address and port depend on the media and
transport protocol defined. By default, this SHOULD be the remote transport protocol defined. By default, this SHOULD be the remote
address and remote port to which data is sent. Some media types may address and remote port to which data is sent. Some media types may
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This timing information is globally consistent, irrespective of local This timing information is globally consistent, irrespective of local
time zone or daylight saving time (see Section 5.9). time zone or daylight saving time (see Section 5.9).
4.3. Obtaining Further Information about a Session 4.3. Obtaining Further Information about a Session
A session description could convey enough information to decide A session description could convey enough information to decide
whether or not to participate in a session. SDP may include whether or not to participate in a session. SDP may include
additional pointers in the form of Uniform Resource Identifiers additional pointers in the form of Uniform Resource Identifiers
(URIs) for more information about the session. (URIs) for more information about the session.
4.4. Categorisation 4.4. Categorization
When many session descriptions are being distributed by SAP, or any When many session descriptions are being distributed by SAP, or any
other advertisement mechanism, it may be desirable to filter session other advertisement mechanism, it may be desirable to filter session
announcements that are of interest from those that are not. SDP announcements that are of interest from those that are not. SDP
supports a categorisation mechanism for sessions that is capable of supports a categorization mechanism for sessions that is capable of
being automated (the "a=cat:" attribute; see Section 6). being automated (the "a=cat:" attribute; see Section 6).
4.5. Internationalisation 4.5. Internationalization
The SDP specification recommends the use of the ISO 10646 character The SDP specification recommends the use of the ISO 10646 character
set in the UTF-8 encoding [RFC3629] to allow many different languages set in the UTF-8 encoding [RFC3629] to allow many different languages
to be represented. However, to assist in compact representations, to be represented. However, to assist in compact representations,
SDP also allows other character sets such as ISO 8859-1 to be used SDP also allows other character sets such as ISO 8859-1 to be used
when desired. Internationalisation only applies to free-text fields when desired. Internationalization only applies to free-text fields
(session name and background information), and not to SDP as a whole. (session name and background information), and not to SDP as a whole.
5. SDP Specification 5. SDP Specification
An SDP description is denoted by the media type "application/sdp" An SDP description is denoted by the media type "application/sdp"
(See Section 8). (See Section 8).
An SDP description is entirely textual. SDP field names and An SDP description is entirely textual. SDP field names and
attribute names use only the US-ASCII subset of UTF-8, but textual attribute names use only the US-ASCII subset of UTF-8, but textual
fields and attribute values MAY use the full ISO 10646 character set fields and attribute values MAY use the full ISO 10646 character set
in UTF-8 encoding, or some other character set defined by the in UTF-8 encoding, or some other character set defined by the
"a=charset:" attribute. Field and attribute values that use the full "a=charset:" attribute. Field and attribute values that use the full
UTF-8 character set are never directly compared, hence there is no UTF-8 character set are never directly compared, hence there is no
requirement for UTF-8 normalisation. The textual form, as opposed to requirement for UTF-8 normalization. The textual form, as opposed to
a binary encoding such as ASN.1 or XDR, was chosen to enhance a binary encoding such as ASN.1 or XDR, was chosen to enhance
portability, to enable a variety of transports to be used, and to portability, to enable a variety of transports to be used, and to
allow flexible, text-based toolkits to be used to generate and allow flexible, text-based toolkits to be used to generate and
process session descriptions. However, since SDP may be used in process session descriptions. However, since SDP may be used in
environments where the maximum permissible size of a session environments where the maximum permissible size of a session
description is limited, the encoding is deliberately compact. Also, description is limited, the encoding is deliberately compact. Also,
since announcements may be transported via very unreliable means or since announcements may be transported via very unreliable means or
damaged by an intermediate caching server, the encoding was designed damaged by an intermediate caching server, the encoding was designed
with strict order and formatting rules so that most errors would with strict order and formatting rules so that most errors would
result in malformed session announcements that could be detected result in malformed session announcements that could be detected
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An SDP description consists of a number of lines of text of the form: An SDP description consists of a number of lines of text of the form:
<type>=<value> <type>=<value>
where <type> MUST be exactly one case-significant character and where <type> MUST be exactly one case-significant character and
<value> is structured text whose format depends on <type>. In <value> is structured text whose format depends on <type>. In
general, <value> is either a number of fields delimited by a single general, <value> is either a number of fields delimited by a single
space character or a free format string, and is case-significant space character or a free format string, and is case-significant
unless a specific field defines otherwise. Whitespace separators unless a specific field defines otherwise. Whitespace separators
MUST NOT be used on either side of the "=" sign, however, if the MUST NOT be used on either side of the "=" sign, however, the value
value can contain a leading whitespace as part of its syntax, i.e., can contain a leading whitespace as part of its syntax, i.e., that
that whitespace is part of the value. whitespace is part of the value.
An SDP description consists of a session-level section followed by An SDP description consists of a session-level section followed by
zero or more media descriptions. The session-level section starts zero or more media descriptions. The session-level section starts
with a "v=" line and continues to the first media description (or the with a "v=" line and continues to the first media description (or the
end of the whole description, whichever comes first). Each media end of the whole description, whichever comes first). Each media
description starts with an "m=" line and continues to the next media description starts with an "m=" line and continues to the next media
description or the end of the whole session description - whichever description or the end of the whole session description - whichever
comes first. In general, session-level values are the default for comes first. In general, session-level values are the default for
all media unless overridden by an equivalent media-level value. all media unless overridden by an equivalent media-level value.
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description that contains a type letter that it does not understand. description that contains a type letter that it does not understand.
The attribute mechanism ("a=" described below) is the primary means The attribute mechanism ("a=" described below) is the primary means
for extending SDP and tailoring it to particular applications or for extending SDP and tailoring it to particular applications or
media. Some attributes (the ones listed in Section 6 of this memo) media. Some attributes (the ones listed in Section 6 of this memo)
have a defined meaning, but others may be added on an application-, have a defined meaning, but others may be added on an application-,
media-, or session-specific basis. An SDP parser MUST ignore any media-, or session-specific basis. An SDP parser MUST ignore any
attribute it doesn't understand. attribute it doesn't understand.
An SDP description may contain URIs that reference external content An SDP description may contain URIs that reference external content
in the "u=", "k=", and "a=" lines. These URIs may be dereferenced in in the "u=", "k=", and "a=" lines. These URIs may be dereferenced in
some cases, making the session description non-self- contained. some cases, making the session description non-self-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 descriptions of that session unless
connection information in the media description. For instance, in overridden by connection information in the media description. For
the example below, each audio media description behaves as if it were instance, in the example below, each audio media description behaves
given a "c=IN IP4 233.252.0.2". as if it were 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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0x0a (ASCII newline), and 0x0d (ASCII carriage return). The sequence 0x0a (ASCII newline), and 0x0d (ASCII carriage return). The sequence
CRLF (0x0d0a) is used to end a record, although parsers SHOULD be CRLF (0x0d0a) is used to end a record, although parsers SHOULD be
tolerant and also accept records terminated with a single newline tolerant and also accept records terminated with a single newline
character. If the "a=charset" attribute is not present, these octet character. If the "a=charset" attribute is not present, these octet
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]. Internationalized 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
[RFC2327] 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 internationalized domain names).
5.1. Protocol Version ("v=") 5.1. Protocol Version ("v=")
v=0 v=0
The "v=" line 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=")
skipping to change at page 13, line 6 skipping to change at page 13, line 6
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=" line 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 sub-fields this version of the session description, and the sub-fields excepting
excepting the version taken together identify the session the version, taken together identify the session irrespective of any
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=" line, provided that these are selected in chosen to populate the "o=" line, provided that these are selected 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=" line 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=" line per session description. The "s=" line 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 "s=
value "s= " SHOULD be used (i.e., a single space as the session " line 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 information>
The "i=" line 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=" line per session description, MUST be at most one session-level "i=" line per session description,
and at most one "i=" line per media description/definition. Unless a and at most one "i=" line in each media description. Unless a media
media level "i="" line is used, the session-level "i="" line applies level "i= line is provided, the session-level "i= line applies to
to that media description. If the "a=charset" attribute is present, that media description. If the "a=charset" attribute is present, it
it specifies the character set used in the "i=" line. If the specifies the character set used in the "i=" line. If the
"a=charset" attribute is not present, the "i=" line MUST contain ISO "a=charset" attribute is not present, the "i=" line MUST contain ISO
10646 characters in UTF-8 encoding. 10646 characters in UTF-8 encoding.
A single "i=" line can be used for each media definition. In media At most one "i=" line can be used for each media description. In
definitions, "i=" lines are primarily intended for labelling media media definitions, "i=" lines are primarily intended for labelling
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
session has more than one distinct media stream of the same media single session has more than one distinct media stream of the same
type. An example would be two different whiteboards, one for slides media type. An example would be two different whiteboards, one for
and one for feedback and questions. slides and one for feedback and questions.
The "i=" line 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
skipping to change at page 14, line 26 skipping to change at page 14, line 26
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. Inclusion of an email address or phone number is OPTIONAL.
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 line can before the first media description. More than one email or phone
be given for a session description. line can be given for a session description.
Phone numbers SHOULD be given in the form of an international public Phone numbers SHOULD be given in the form of an international public
telecommunication number (see ITU-T Recommendation E.164) preceded by telecommunication number (see ITU-T Recommendation E.164 [E164])
a "+". Spaces and hyphens may be used to split up a phone field to preceded by a "+". Spaces and hyphens may be used to split up a
aid readability if desired. For example: phone field to 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
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 Information ("c=")
c=<nettype> <addrtype> <connection-address> c=<nettype> <addrtype> <connection-address>
The "c=" line contains connection data. The "c=" line contains connection data.
A session description MUST contain either at least one "c=" line in A session description MUST contain either at least one "c=" line in
each media description or a single "c=" line at the session level. each media description or a single "c=" line at the session level.
It MAY contain a single session-level "c=" line and additional "c=" It MAY contain a single session-level "c=" line and additional "c="
line(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.
skipping to change at page 15, line 28 skipping to change at page 15, line 28
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
(see Section 8). (see Section 8).
The third sub-field ("<connection-address>") is the connection The third sub-field ("<connection-address>") is the connection
address. OPTIONAL sub-fields MAY be added after the connection address. Additional sub-fields MAY be added after the connection
address depending on the value of the <addrtype> field. address depending on the value of the <addrtype> field.
When the <addrtype> is IP4 and IP6, the connection address is defined When the <addrtype> is IP4 and IP6, the connection address is defined
as follows: as follows:
o If the session is multicast, the connection address will be an IP o If the session is multicast, the connection address will be an IP
multicast group address. If the session is not multicast, then multicast group address. If the session is not multicast, then
the connection address contains the unicast IP address of the the connection address contains the unicast IP address of the
expected data source or data relay or data sink as determined by expected data source, data relay or data sink as determined by
additional attribute fields. It is not expected that unicast additional attribute fields. It is not expected that unicast
addresses will be given in a session description that is addresses will be given in a session description that is
communicated by a multicast announcement, though this is not communicated by a multicast announcement, though this is not
prohibited. prohibited.
o Sessions using an IP4 multicast connection address MUST also have o Sessions using an IP4 multicast connection address MUST also have
a time to live (TTL) value present in addition to the multicast a time to live (TTL) value present in addition to the multicast
address. The TTL and the address together define the scope with address. The TTL and the address together define the scope with
which multicast packets sent in this session will be sent. TTL which multicast packets sent in this session will be sent. TTL
values MUST be in the range 0-255. Although the TTL MUST be values MUST be in the range 0-255. Although the TTL MUST be
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<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 233.252.0.1/127/3 c=IN IP4 233.252.0.1/127/3
would state that addresses 233.252.0.1, 233.252.0.2, and 233.252.0.3 would state that addresses 233.252.0.1, 233.252.0.2, and 233.252.0.3
are to be used at a TTL of 127. This is semantically identical to are to be used with a TTL of 127. This is semantically identical to
including multiple "c=" lines in a media description: including multiple "c=" lines in a media description:
c=IN IP4 233.252.0.1/127 c=IN IP4 233.252.0.1/127
c=IN IP4 233.252.0.2/127 c=IN IP4 233.252.0.2/127
c=IN IP4 233.252.0.3/127 c=IN IP4 233.252.0.3/127
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 description basis only if they provide multicast addresses for
in a hierarchical or layered encoding scheme. They MUST NOT be different layers in a hierarchical or layered encoding scheme. They
specified for a session-level "c=" line. MUST NOT be 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 Information ("b=")
b=<bwtype>:<bandwidth> b=<bwtype>:<bandwidth>
This OPTIONAL line 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 description. The <bwtype> is an alphanumeric
the meaning of the <bandwidth> figure. Two values are defined in modifier giving the meaning of the <bandwidth> figure. Two values
this specification, but other values MAY be registered in the future are defined in this specification, but other values MAY be registered
(see Section 8 and [RFC3556], [RFC3890]): in the future (see Section 8 and [RFC3556], [RFC3890]):
CT If the bandwidth of a session is different from the bandwidth CT If the bandwidth of a session is different from the bandwidth
implicit from the scope, a "b=CT:..." line SHOULD be supplied for implicit from the scope, a "b=CT:..." line SHOULD be supplied for
the session giving the proposed upper limit to the bandwidth used the session giving the proposed upper limit to the bandwidth used
(the "conference total" bandwidth). Similarly, if the bandwidth (the "conference total" bandwidth). Similarly, if the bandwidth
of bundled media streams in an m line is different from the of bundled media streams in an m line is different from the
implicit value from the scope, a "b=CT:..." line SHOULD be implicit value from the scope, a "b=CT:..." line SHOULD be
supplied in the media level. The primary purpose of this is to supplied in the media level. The primary purpose of this is to
give an approximate idea as to whether two or more sessions (or give an approximate idea as to whether two or more sessions (or
bundled media streams) can coexist simultaneously. Note that CT bundled media streams) can coexist simultaneously. Note that CT
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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]. Note that AS gives a bandwidth figure for a single [RFC3550]. Note that AS gives a bandwidth figure for a single
media at a single endpoint, although there may be many endpoints media at a single endpoint, although there may be many endpoints
sending simultaneously. sending simultaneously.
A prefix "X-" is defined for <bwtype> names. This is intended for A prefix "X-" is defined for <bwtype> names. This is intended for
experimental purposes only. For example: experimental purposes only. For example:
b=X-YZ:128 b=X-YZ:128
Use of the "X-" prefix is NOT RECOMMENDED: instead new modifiers Use of the "X-" prefix is NOT RECOMMENDED: instead new <bwtype> names
SHOULD be registered with IANA in the standard namespace. SDP SHOULD be registered with IANA in the standard namespace. SDP
parsers MUST ignore bandwidth fields with unknown modifiers. parsers MUST ignore bandwidth fields with unknown <bwtype> names.
Modifiers MUST be alphanumeric and, although no length limit is The <bwtype> names MUST be alphanumeric and, although no length limit
given, it is recommended that they be short. is given, it is recommended that they be short.
The <bandwidth> is interpreted as kilobits per second by default. The <bandwidth> is interpreted as kilobits per second by default.
The definition of a new <bwtype> modifier MAY specify that the The definition of a new <bwtype> modifier MAY specify that the
bandwidth is to be interpreted in some alternative unit (the "CT" and bandwidth is to be interpreted in some alternative unit (the "CT" and
"AS" modifiers defined in this memo use the default units). "AS" modifiers defined in this memo use the default units).
5.9. Timing ("t=") 5.9. Time Active ("t=")
t=<start-time> <stop-time> t=<start-time> <stop-time>
The "t=" lines specify the start and stop times for a session. The "t=" lines specify the start and stop times for a session.
Multiple "t=" lines MAY be used if a session is active at multiple Multiple "t=" lines MAY be used if a session is active at multiple
irregularly spaced times; each additional "t=" line specifies an irregularly spaced times; each additional "t=" line specifies an
additional period of time for which the session will be active. If additional period of time for which the session will be active. If
the session is active at regular times, an "r=" line (see below) the session is active at regular repeat times, an "r=" line (see
should be used in addition to, and following, a "t=" line -- in which below) should be used in addition to, and following, a "t=" line --
case the "t=" line specifies the start and stop times of the repeat in which case the "t=" line specifies the start and stop times of the
sequence. entire repeat sequence.
The first and second sub-fields give the start and stop times, The first and second sub-fields give the start and stop times,
respectively, for the session. These values are the decimal respectively, for the session. These values are the decimal
representation of Network Time Protocol (NTP) time values in seconds representation of Network Time Protocol (NTP) time values in seconds
since 1900 [RFC5905]. To convert these values to UNIX time, subtract since 1900 [RFC5905]. To convert these values to UNIX time, subtract
decimal 2208988800. decimal 2208988800.
NTP timestamps are elsewhere represented by 64-bit values, which wrap NTP timestamps are elsewhere represented by 64-bit values, which wrap
sometime in the year 2036. Since SDP uses an arbitrary length sometime in the year 2036. Since SDP uses an arbitrary length
decimal representation, this should not cause an issue (SDP decimal representation, this should not cause an issue (SDP
timestamps MUST continue counting seconds since 1900, NTP will use timestamps MUST continue counting seconds since 1900 - NTP will use
the value modulo the 64-bit limit). the value modulo the 64-bit limit).
If the <stop-time> is set to zero, then the session is not bounded, If the <stop-time> is set to zero, then the session is not bounded,
though it will not become active until after the <start-time>. If though it will not become active until after the <start-time>. If
the <start-time> is also zero, the session is regarded as permanent. the <start-time> is also zero, the session is regarded as permanent.
User interfaces SHOULD strongly discourage the creation of unbounded User interfaces SHOULD strongly discourage the creation of unbounded
and permanent sessions as they give no information about when the and permanent sessions as they give no information about when the
session is actually going to terminate, and so make scheduling session is actually going to terminate, and so make scheduling
difficult. difficult.
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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=" line specifies repeat times for a session. For example, if a An "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=" line 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=" line 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=" lines might default, all fields are in seconds, so the "r=" and "t=" lines might
be the following: be the following:
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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=" lines) 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 description specific. These are referred to as
attributes and add information about the media stream. Attribute "media-level" attributes and add information about the media
lines can also be added before the first media field; these "session- description. Attribute lines can also be added before the first
level" attributes convey additional information that applies to the media description; these "session-level" attributes convey additional
session as a whole rather than to individual media. information that applies to the session as a whole rather than to
individual media descriptions.
Attribute lines 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=<attribute>". These
binary attributes, and the presence of the attribute conveys that are binary attributes, and the presence of the attribute conveys
the attribute is a property of the session. An example might be that the attribute is a property of the session. An example might
"a=recvonly". be "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"
Attribute interpretation depends on the media tool being invoked. Attribute interpretation depends on the media tool being invoked.
Thus receivers of session descriptions should be configurable in Thus receivers of session descriptions should be configurable in
their interpretation of session descriptions in general and of their interpretation of session descriptions in general and of
attributes in particular. attributes in particular.
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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=" line and is terminated by Each media description starts with an "m=" line (media field) and is
either the next "m=" line or by the end of the session description. terminated by either the next "m=" line or by the end of the session
A media field has several sub-fields: description. A media field has several sub-fields:
<media> is the media type. This document defines the values <media> is the media type. This document defines the values
"audio", "video", "text", "application", and "message". This list "audio", "video", "text", "application", and "message". This list
is extended and may be further extended by other memos registering is extended by other memos and may be further extended by
media types in the future (see Section 8). For example, [RFC6466] additional memos registering media types in the future (see
defined the "image" media type. Section 8). For example, [RFC6466] defined the "image" media
type.
<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=" line, and on the transport protocol specified in the relevant "c=" line, and on the transport protocol
defined in the <proto> sub-field of the media field. Other ports defined in the <proto> sub-field of the media field. Other ports
used by the media application (such as the RTP Control Protocol used by the media application (such as the RTP Control Protocol
(RTCP) port [RFC3550]) MAY be derived algorithmically from the (RTCP) port [RFC3550]) MAY be derived algorithmically from the
base media port or MAY be specified in a separate attribute (for base media port or MAY be specified in a separate attribute (for
example, "a=rtcp:" as defined in [RFC3605]). example, "a=rtcp:" as defined in [RFC3605]).
skipping to change at page 23, line 11 skipping to change at page 23, line 15
If multiple addresses are specified in the "c=" line and multiple If multiple addresses are specified in the "c=" line and multiple
ports are specified in the "m=" line, 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 This document provides no semantics for using multiple "m=" lines
address are undefined. This implies that, unlike limited past using the same transport address. This implies that, unlike
practice, there is no implicit grouping defined by such means and limited past practice, there is no implicit grouping defined by
an explicit grouping framework (for example, [RFC5888]) should such means and an explicit grouping framework (for example,
instead be used to express the intended semantics. [RFC5888]) should instead be used to express the intended
semantics. Such semantics may alo be added as extensions. For
instance, see [I-D.ietf-mmusic-sdp-bundle-negotiation].
<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=" line. 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.
* RTP/SAVP: denotes the Secure Real-time Transport Protocol * RTP/SAVP: denotes the Secure Real-time Transport Protocol
[RFC3711] running over UDP. [RFC3711] running over UDP.
The main reason to specify the transport protocol in addition to The main reason to specify the transport protocol in addition to
the media format is that the same standard media formats may be the media format is that the same standard media formats may be
carried over different transport protocols even when the network carried over different transport protocols even when the network
protocol is the same -- a historical example is vat Pulse Code protocol is the same -- a historical example is VAT (MBone's
Modulation (PCM) audio and RTP PCM audio; another might be TCP/RTP popular multimedia audio tool) Pulse Code Modulation (PCM) audio
PCM audio. In addition, relays and monitoring tools that are and RTP PCM audio; another might be TCP/RTP PCM audio. In
transport-protocol-specific but format-independent are possible. addition, relays and monitoring tools that are transport-protocol-
specific but format-independent are possible.
<fmt> is a media format description. The fourth and any subsequent <fmt> is a media format description. The fourth and any subsequent
sub-fields describe the format of the media. The interpretation sub-fields describe the format of the media. The interpretation
of the media format depends on the value of the <proto> sub-field. of the media format depends on the value of the <proto> sub-field.
If the <proto> sub-field is "RTP/AVP" or "RTP/SAVP" the <fmt> sub- If the <proto> sub-field is "RTP/AVP" or "RTP/SAVP" the <fmt> sub-
fields contain RTP payload type numbers. When a list of payload fields contain RTP payload type numbers. When a list of payload
type numbers is given, this implies that all of these payload type numbers is given, this implies that all of these payload
formats MAY be used in the session, but the first of these formats formats MAY be used in the session, but the first of these formats
SHOULD be used as the default format for the session. For dynamic SHOULD be used as the default format for the session. For dynamic
skipping to change at page 24, line 31 skipping to change at page 24, line 40
also states that both of these names are case-insensitive in both also states that both of these names are case-insensitive in both
places, similar to parameter names which are case-insensitive both places, similar to parameter names which are case-insensitive both
in media type strings and in the default mapping to the SDP a=fmtp in media type strings and in the default mapping to the SDP a=fmtp
attribute. attribute.
6. SDP Attributes 6. SDP Attributes
The following attributes are defined. Since application writers may The following attributes are defined. Since application writers may
add new attributes as they are required, this list is not exhaustive. add new attributes as they are required, this list is not exhaustive.
Registration procedures for new attributes are defined in Registration procedures for new attributes are defined in
Section 8.2.4. Section 8.2.4. Syntax is provided using ABNF [RFC7405] with some of
the rules defined further in Section 9.
6.1. cat (category) 6.1. cat (category)
Name: cat Name: cat
Value: cat-value Value: cat-value
Usage Level: session Usage Level: session
Charset Dependent: no Charset Dependent: no
skipping to change at page 25, line 31 skipping to change at page 25, line 39
keywds-value = keywords keywds-value = keywords
keywords = text keywords = text
Example: Example:
a=keywds:SDP session description protocol a=keywds:SDP session description protocol
Like the cat attribute, this is to assist identifying wanted sessions Like the cat attribute, this is to assist identifying wanted sessions
at the receiver. This allows a receiver to select interesting at the receiver. This allows a receiver to select interesting
session based on keywords describing the purpose of the session; sessions based on keywords describing the purpose of the session;
there is no central registry of keywords. Its value should be there is no central registry of keywords. Its value should be
interpreted in the charset specified for the session description if interpreted in the charset specified for the session description if
one is specified, or by default in ISO 10646/UTF-8. This attribute one is specified, or by default in ISO 10646/UTF-8. This attribute
is obsoleted. is obsoleted.
6.3. tool 6.3. tool
Name: tool Name: tool
Value: tool-value Value: tool-value
skipping to change at page 26, line 34 skipping to change at page 26, line 40
ptime-value = non-zero-int-or-real ptime-value = non-zero-int-or-real
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/packetization of audio.
6.5. maxptime (maximum packet time) 6.5. maxptime (maximum packet time)
Name: maxptime Name: maxptime
Value: maxptime-value Value: maxptime-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
skipping to change at page 28, line 26 skipping to change at page 28, line 32
m=audio 49230 RTP/AVP 96 97 98 m=audio 49230 RTP/AVP 96 97 98
a=rtpmap:96 L8/8000 a=rtpmap:96 L8/8000
a=rtpmap:97 L16/8000 a=rtpmap:97 L16/8000
a=rtpmap:98 L16/11025/2 a=rtpmap:98 L16/11025/2
RTP profiles that specify the use of dynamic payload types MUST RTP profiles that specify the use of dynamic payload types MUST
define the set of valid encoding names and/or a means to register define the set of valid encoding names and/or a means to register
encoding names if that profile is to be used with SDP. The "RTP/AVP" encoding names if that profile is to be used with SDP. The "RTP/AVP"
and "RTP/SAVP" profiles use media subtypes for encoding names, under and "RTP/SAVP" profiles use media subtypes for encoding names, under
the top-level media type denoted in the "m=" line. In the example the top-level media type denoted in the "m=" line. In the example
above, the media types are "audio/l8" and "audio/l16". above, the media types are "audio/L8" and "audio/L16".
For audio streams, <encoding parameters> indicates the number of For audio streams, encoding-params indicates the number of audio
audio channels. This parameter is OPTIONAL and may be omitted if the channels. This parameter is OPTIONAL and may be omitted if the
number of channels is one, provided that no additional parameters are number of channels is one, provided that no additional parameters are
needed. needed.
For video streams, no encoding parameters are currently specified. For video streams, no encoding parameters are currently specified.
Additional encoding parameters MAY be defined in the future, but Additional encoding parameters MAY be defined in the future, but
codec-specific parameters SHOULD NOT be added. Parameters added to codec-specific parameters SHOULD NOT be added. Parameters added to
an "a=rtpmap:" attribute SHOULD only be those required for a session an "a=rtpmap:" attribute SHOULD only be those required for a session
directory to make the choice of appropriate media to participate in a directory to make the choice of appropriate media to participate in a
session. Codec-specific parameters should be added in other session. Codec-specific parameters should be added in other
attributes (for example, "a=fmtp:"). attributes (for example, "a=fmtp:").
Note: RTP audio formats typically do not include information about Note: RTP audio formats typically do not include information about
the number of samples per packet. If a non-default (as defined in the number of samples per packet. If a non-default (as defined in
the RTP Audio/Video Profile) packetisation is required, the "ptime" the RTP Audio/Video Profile [RFC3551]) packetization is required, the
attribute is used as given above. "ptime" attribute is used as given above.
6.7. Media Direction Attributes 6.7. Media Direction Attributes
At most one of recvonly/sendrecv/sendonly/inactive MAY appear at At most one of recvonly/sendrecv/sendonly/inactive MAY appear at
session level, and at most one MAY appear in each media section. session level, and at most one MAY appear in each media description.
If any one of these appears in a media section then it applies for If any one of these appears in a media description then it applies
that media section. If none appear in a media section then the one for that media description. If none appear in a media description
from session level, if any, applies to that media section. then the one from session level, if any, applies to that media
description.
If none of the media direction attributes is present at either If none of the media direction attributes is present at either
session level or media level, "sendrecv" SHOULD be assumed as the session level or media level, "sendrecv" SHOULD be assumed as the
default for sessions that are not of the multimedia conference type default for sessions that are not of the multimedia conference type
"broadcast" or "H332" (see below). "broadcast" or "H332" (see below).
Within the following SDP example, the "inactive" attribute applies to Within the following SDP example, the "inactive" attribute applies to
audio media and the "recvonly" attribute applies to video media. audio media and the "recvonly" attribute applies to video media.
v=0 v=0
skipping to change at page 31, line 50 skipping to change at page 32, line 4
values are "portrait", "landscape", and "seascape" (upside-down values are "portrait", "landscape", and "seascape" (upside-down
landscape). landscape).
6.9. type (conference type) 6.9. type (conference type)
Name: type Name: type
Value: type-value Value: type-value
Usage Level: session Usage Level: session
Charset Dependent: no Charset Dependent: no
Syntax: Syntax:
type-value = conference-type type-value = conference-type
conference-type = broadcast / meeting / moderated / test / conference-type = broadcast / meeting / moderated / test /
H332 H332
broadcast = %s"broadcast" broadcast = %s"broadcast"
meeting = %s"meeting" meeting = %s"meeting"
moderated = %s"moderated" moderated = %s"moderated"
test = %s"test" test = %s"test"
H332 = %s"H332" H332 = %s"H332"
; NOTE: These names are case-sensitive. ; NOTE: These names are case-sensitive.
Example: Example:
a=type:moderated a=type:moderated
skipping to change at page 34, line 9 skipping to change at page 34, line 9
languages. languages.
As a session-level attribute, it specifies the language for the As a session-level attribute, it specifies the language for the
session description (not the language of the media). As a media- session description (not the language of the media). As a media-
level attribute, it specifies the language for any media-level SDP level attribute, it specifies the language for any media-level SDP
information field associated with that media (again not the language information field associated with that media (again not the language
of the media), overriding any sdplang attributes specified at session of the media), overriding any sdplang attributes specified at session
level. level.
In general, sending session descriptions consisting of multiple In general, sending session descriptions consisting of multiple
languages is discouraged. Instead, multiple descriptions SHOULD be languages is discouraged. Instead, multiple sesssion descriptions
sent describing the session, one in each language. However, this is SHOULD be sent describing the session, one in each language.
not possible with all transport mechanisms, and so multiple sdplang However, this is not possible with all transport mechanisms, and so
attributes are allowed although NOT RECOMMENDED. multiple sdplang attributes are allowed although NOT RECOMMENDED.
The "sdplang" attribute value must be a single [RFC5646] language tag The "sdplang" attribute value must be a single [RFC5646] language tag
in US-ASCII. An "sdplang" attribute SHOULD be specified when a in US-ASCII. An "sdplang" attribute SHOULD be specified when a
session is distributed with sufficient scope to cross geographic session is distributed with sufficient scope to cross geographic
boundaries, where the language of recipients cannot be assumed, or boundaries, where the language of recipients cannot be assumed, or
where the session is in a different language from the locally assumed where the session is in a different language from the locally assumed
norm. norm.
6.12. lang (language) 6.12. lang (language)
skipping to change at page 35, line 11 skipping to change at page 35, line 11
for the session being described. As a media-level attribute, it for the session being described. As a media-level attribute, it
specifies a language capability for that media, overriding any specifies a language capability for that media, overriding any
session-level language(s) specified. session-level language(s) specified.
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 participants cannot be assumed, or where the session has of participants cannot be assumed, or where the session has
capabilities in languages different from the locally assumed norm. capabilities in languages different from the locally assumed norm.
The "lang" attribute is supposed to be used for settling the initial The "lang" attribute is supposed to be used for setting the initial
language(s) used in the session. Events during the session may language(s) used in the session. Events during the session may
influence which language(s) are used, and the participants are not influence which language(s) are used, and the participants are not
strictly bound to only use the declared languages. strictly bound to only use the declared languages.
Most real-time use cases start with just one language used, while Most real-time use cases start with just one language used, while
other cases involve a range of languages, e.g. an interpreted or other cases involve a range of languages, e.g. an interpreted or
subtitled session. When more than one 'lang' attribute is specified, subtitled session. When more than one 'lang' attribute is specified,
the "lang" attribute itself does not provide any information about if the "lang" attribute itself does not provide any information about
multiple languages are intended to be used during the session, or if multiple languages being intended to be used during the session, or
the intention is to only select one language. Other attributes or if the intention is to only select one of the languages. If needed,
the semantics in which the "lang" attributes are used might indicate a new attribute can be defined and used to indicate such intentions.
such conditions. Without such indications of usage intent, it is Without such semantics, it is assumed that for a negotiated session
assumed that for a negotiated session one of the declared languages one of the declared languages will be selected and used.
will be selected and used.
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
skipping to change at page 36, line 35 skipping to change at page 36, line 35
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
Syntax: Syntax:
fmtp-value = fmt SP format-specific-params fmtp-value = fmt SP format-specific-params
format-specific-params = byte-string format-specific-params = byte-string
; Notes: ; Notes:
; - The format parameters are media type parameters and ; - The format parameters are media type parameters and
need to reflect their syntax. need to reflect their syntax.
Example: Example:
skipping to change at page 37, line 34 skipping to change at page 37, line 27
7. Security Considerations 7. Security Considerations
SDP is frequently used with the Session Initiation Protocol [RFC3261] SDP is frequently used with the Session Initiation Protocol [RFC3261]
using the offer/answer model [RFC3264] to agree on parameters for using the offer/answer model [RFC3264] to agree on parameters for
unicast sessions. When used in this manner, the security unicast sessions. When used in this manner, the security
considerations of those protocols apply. considerations of those protocols apply.
SDP is a session description format that describes multimedia SDP is a session description format that describes multimedia
sessions. Entities receiving and acting upon an SDP message SHOULD sessions. Entities receiving and acting upon an SDP message SHOULD
be aware that a session description cannot be trusted unless it has be aware that a session description cannot be trusted unless it has
been obtained by an authenticated transport protocol from a known and been obtained by an authenticated and integrity-protected transport
trusted source. Many different transport protocols may be used to protocol from a known and trusted source. Many different transport
distribute session descriptions, and the nature of the authentication protocols may be used to distribute session descriptions, and the
will differ from transport to transport. For some transports, nature of the authentication and integrity-protection will differ
security features are often not deployed. In case a session from transport to transport. For some transports, security features
description has not been obtained in a trusted manner, the endpoint are often not deployed. In case a session description has not been
SHOULD exercise care because, among other attacks, the media sessions obtained in a trusted manner, the endpoint SHOULD exercise care
received may not be the intended ones, the destination where media is because, among other attacks, the media sessions received may not be
sent to may not be the expected one, any of the parameters of the the intended ones, the destination where media is sent to may not be
session may be incorrect, or the media security may be compromised. the expected one, any of the parameters of the session may be
It is up to the endpoint to make a sensible decision taking into incorrect, or the media security may be compromised. It is up to the
account the security risks of the application and the user endpoint to make a sensible decision taking into account the security
preferences and may decide to ask the user whether or not to accept risks of the application and the user preferences - the endpoint may
the session. decide to ask the user whether or not to accept the session.
One transport that can be used to distribute session descriptions is One transport that can be used to distribute session descriptions is
the SAP. SAP provides both encryption and authentication mechanisms, the SAP. SAP provides both encryption and authentication mechanisms,
but due to the nature of session announcements it is likely that but due to the nature of session announcements it is likely that
there are many occasions where the originator of a session there are many occasions where the originator of a session
announcement cannot be authenticated because the originator is announcement cannot be authenticated because the originator is
previously unknown to the receiver of the announcement and because no previously unknown to the receiver of the announcement and because no
common public key infrastructure is available. common public key infrastructure is available.
On receiving a session description over an unauthenticated transport On receiving a session description over an unauthenticated transport
mechanism or from an untrusted party, software parsing the session mechanism or from an untrusted party, software parsing the session
should take a few precautions. Session descriptions contain should take a few precautions. Similar concerns apply if integrity
information required to start software on the receiver's system. protection is not in place. Session descriptions contain information
Software that parses a session description MUST NOT be able to start required to start software on the receiver's system. Software that
other software except that which is specifically configured as parses a session description MUST NOT be able to start other software
appropriate software to participate in multimedia sessions. It is except that which is specifically configured as appropriate software
normally considered inappropriate for software parsing a session to participate in multimedia sessions. It is normally considered
description to start, on a user's system, software that is inappropriate for software parsing a session description to start, on
appropriate to participate in multimedia sessions, without the user a user's system, software that is appropriate to participate in
first being informed that such software will be started and giving multimedia sessions, without the user first being informed that such
the user's consent. Thus, a session description arriving by session software will be started and giving the user's consent. Thus, a
announcement, email, session invitation, or WWW page MUST NOT deliver session description arriving by session announcement, email, session
the user into an interactive multimedia session unless the user has invitation, or WWW page MUST NOT deliver the user into an interactive
explicitly pre-authorised such action. As it is not always simple to multimedia session unless the user has explicitly pre-authorised such
tell whether or not a session is interactive, applications that are action. As it is not always simple to tell whether or not a session
unsure should assume sessions are interactive. is interactive, applications that are unsure should assume sessions
are interactive.
In this specification, there are no attributes that would allow the In this specification, there are no attributes that would allow the
recipient of a session description to be informed to start multimedia recipient of a session description to be informed to start multimedia
tools in a mode where they default to transmitting. Under some tools in a mode where they default to transmitting. Under some
circumstances it might be appropriate to define such attributes. If circumstances it might be appropriate to define such attributes. If
this is done, an application parsing a session description containing this is done, an application parsing a session description containing
such attributes SHOULD either ignore them or inform the user that such attributes SHOULD either ignore them or inform the user that
joining this session will result in the automatic transmission of joining this session will result in the automatic transmission of
multimedia data. The default behaviour for an unknown attribute is multimedia data. The default behaviour for an unknown attribute is
to ignore it. to ignore it.
skipping to change at page 39, line 7 skipping to change at page 38, line 48
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=" line 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 keying material, unless it can be guaranteed that the
over which the SDP is delivered is both private and authenticated. channel over which the SDP is delivered is both private and
Moreover, the "k=" line provides no way to indicate or negotiate authenticated. Moreover, the "k=" line provides no way to indicate
cryptographic key algorithms. As it provides for only a single or negotiate cryptographic key algorithms. As it provides for only a
symmetric key, rather than separate keys for confidentiality and single symmetric key, rather than separate keys for confidentiality
integrity, its utility is severely limited. The use of the "k=" line and integrity, its utility is severely limited. The "k=" line MUST
is NOT RECOMMENDED, as discussed in Section 5.12. NOT be used, 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
One media type registration from [RFC4566] is to be updated, as One media type registration from [RFC4566] is to be updated, as
defined below. defined below.
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of media type "application/sdp" Subject: Registration of media type "application/sdp"
skipping to change at page 40, line 36 skipping to change at page 39, line 46
Interoperability considerations: Interoperability considerations:
See RFC XXXX. See RFC XXXX.
Published specification: Published specification:
See RFC XXXX. See RFC XXXX.
Applications which use this media type: Applications which use this media type:
Voice over IP, video teleconferencing, streaming media, instant Voice over IP, video teleconferencing, streaming media, instant
messaging, among others. See also Section 3 of RFC XXXX. messaging, among others. See also Section 3 of RFC XXXX.
Fragment identifier considerations: None
Additional information: Additional information:
Deprecated alias names for this type: N/A
Magic number(s): None. Magic number(s): None.
File extension(s): The extension ".sdp" is commonly used. File extension(s): The extension ".sdp" is commonly used.
Macintosh File Type Code(s): "sdp " Macintosh File Type Code(s): "sdp "
Person & email address to contact for further information: Person & email address to contact for further information:
IETF MMUSIC working group <mmusic@ietf.org> IETF MMUSIC working group <mmusic@ietf.org>
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: None
Author/Change controller: Author/Change controller:
Authors of RFC XXXX Authors of RFC XXXX
IETF MMUSIC working group delegated from the IESG IETF MMUSIC working group delegated from the IESG
8.2. Registration of Parameters 8.2. Registration of Parameters
There are seven field names that are registered with IANA. Using the There are seven field names that are registered with IANA. Using the
terminology in the SDP specification Backus-Naur Form (BNF), they are terminology in the SDP specification Augmented Backus-Naur Form
"media", "proto", "fmt", "att-field", "bwtype", "nettype", and (ABNF), they are "media", "proto", "fmt", "att-field", "bwtype",
"addrtype". "nettype", and "addrtype".
The contact address for all parameters registered below is: The contact address for all parameters registered below is:
IETF MMUSIC working group <mmusic@ietf.org> IETF MMUSIC working group <mmusic@ietf.org>
8.2.1. Media Types ("media") 8.2.1. Media Types ("media")
The set of media types is intended to be small and SHOULD NOT be The set of media types is intended to be small and SHOULD NOT be
extended except under rare circumstances. The same rules should extended except under rare circumstances. The same rules should
apply for media names as for top-level media types, and where apply for media names as for top-level media types, and where
possible the same name should be registered for SDP as for MIME. For possible the same name should be registered for SDP as for MIME. For
media other than existing top-level media types, a Standards Track media other than existing top-level media types, a Standards Track
RFC MUST be produced for a new top-level media type to be registered, RFC MUST be produced for a new top-level media type to be registered,
and the registration MUST provide good justification why no existing and the registration MUST provide good justification why no existing
media name is appropriate (the "Standards Action" policy of media name is appropriate (the "Standards Action" policy of
[RFC8126]. [RFC8126]).
This memo registers the media types "audio", "video", "text", This memo registers the media types "audio", "video", "text",
"application", and "message". "application", and "message".
Note: The media types "control" and "data" were listed as valid in an Note: The media types "control" and "data" were listed as valid in an
early version of this specification (RFC 2327); however, their early version of this specification (RFC 2327); however, their
semantics were never fully specified and they are not widely used. semantics were never fully specified and they are not widely used.
These media types have been removed in this specification, although These media types have been removed in this specification, although
they still remain valid media type capabilities for a SIP user agent they still remain valid media type capabilities for a SIP user agent
as defined in [RFC3840]. If these media types are considered useful as defined in [RFC3840]. If these media types are considered useful
skipping to change at page 42, line 50 skipping to change at page 42, line 16
of the associated "proto" specification. of the associated "proto" specification.
Registrations of new formats MUST specify which transport protocols Registrations of new formats MUST specify which transport protocols
they apply to. they apply to.
8.2.4. Attribute Names ("att-field") 8.2.4. Attribute Names ("att-field")
8.2.4.1. New Attributes 8.2.4.1. New Attributes
Attribute field names ("att-field") MUST be registered with IANA and Attribute field names ("att-field") MUST be registered with IANA and
documented, because of noticeable issues due to conflicting documented, to avoid any issues due to conflicting attribute
attributes under the same name. Unknown attributes in SDP are simply definitions under the same name. Unknown attributes in SDP are
ignored, but conflicting ones that fragment the protocol are a simply ignored, but conflicting ones that fragment the protocol are a
serious problem. serious problem.
New attribute registrations are accepted according to the New attribute registrations are accepted according to the
"Specification Required" policy of [RFC8126], provided that the "Specification Required" policy of [RFC8126], provided that the
specification includes the following information: specification includes the following information:
o Contact Name. o Contact Name.
o Contact Email Address. o Contact Email Address.
o Attribute Name: The name of the attribute that will appear in o Attribute Name: The name of the attribute that will appear in
SDP). This MUST conform to the definition of <att-field>. SDP). This MUST conform to the definition of <att-field>.
o Attribute Syntax: For a value attribute (see clause 5.13), an ABNF o Attribute Syntax: For a value attribute (see clause 5.13), an ABNF
definition of the attribute value <att-value> syntax (See definition of the attribute value <att-value> syntax (See
Section Section 9) MUST be provided. The syntax MUST follow the Section 9) MUST be provided. The syntax MUST follow the rule form
rule form as per Section 2.2 of [RFC5234]. This SHALL define the as per Section 2.2 of [RFC5234] and [RFC7405]. This SHALL define
allowable values that the attribute might take. It MAY also the allowable values that the attribute might take. It MAY also
define an extension method for the addition of future values. For define an extension method for the addition of future values. For
a property attribute, the ABNF definition is omitted as the a property attribute, the ABNF definition is omitted as the
property attribute takes no values. property attribute takes no values.
o Attribute Semantics: For a value attribute, a semantic description o Attribute Semantics: For a value attribute, a semantic description
of the values that the attribute might take MUST be provided. The of the values that the attribute might take MUST be provided. The
usage of a property attribute is described under purpose below. usage of a property attribute is described under purpose below.
o Attribute Value: The name of an ABNF syntax rule defining the o Attribute Value: The name of an ABNF syntax rule defining the
syntax of the value. Absence of a rule name indicates that the syntax of the value. Absence of a rule name indicates that the
skipping to change at page 44, line 24 skipping to change at page 43, line 37
in the spirit of SDP attributes, most notably that the attribute is in the spirit of SDP attributes, most notably that the attribute is
platform independent in the sense that it makes no implicit platform independent in the sense that it makes no implicit
assumptions about operating systems and does not name specific pieces assumptions about operating systems and does not name specific pieces
of software in a manner that might inhibit interoperability. of software in a manner that might inhibit interoperability.
Submitters of registrations should also carefully choose the Submitters of registrations should also carefully choose the
attribute usage level. They should not choose only "session" when attribute usage level. They should not choose only "session" when
the attribute can have different values when media is disaggregated, the attribute can have different values when media is disaggregated,
i.e., when each m= section has its own IP address on a different i.e., when each m= section has its own IP address on a different
endpoint. In that case the attribute type chosen should be "session, endpoint. In that case the attribute type chosen should be "session,
media". The default rule is that for all new SDP attributes that can media" or "media" (depending on desired semantics). The default rule
occur both in session and media level, the media level overrides the is that for all new SDP attributes that can occur both in session and
session level. When this is not the case for a new SDP attribute, it media level, the media level overrides the session level. When this
MUST be explicitly stated. is not the case for a new SDP attribute, it MUST be explicitly
stated.
IANA has registered the initial set of attribute names ("att-field" IANA has registered the initial set of attribute names ("att-field"
values), with definitions as in Section 6 of this memo (these values) with definitions as in Section 6 of this memo (these
definitions replace those in [RFC4566]). definitions replace those in [RFC4566]).
8.2.4.2. Updates to Existing Attributes 8.2.4.2. Updates to Existing Attributes
Updated attribute registrations are accepted according to the Updated attribute registrations are accepted according to the
"Specification Required" policy of [RFC8126], provided that the "Specification Required" policy of [RFC8126], provided that the
specification updating the attribute (for example, by adding a new specification updating the attribute (for example, by adding a new
value) considers the registration information items from value) considers the registration information items from
Section Section 8.2.4.1 according to the following bullets: Section 8.2.4.1 according to the following bullets:
o Contact Name: A name MUST be provided. o Contact Name: A name MUST be provided.
o Contact Email Address: An email address MUST be provided. o Contact Email Address: An email address MUST be provided.
o Attribute Name: MUST be provided and MUST NOT be changed. o Attribute Name: MUST be provided and MUST NOT be changed.
Otherwise it is a new attribute. Otherwise it is a new attribute.
o Attribute Syntax: The existing rule syntax with the syntax o Attribute Syntax: The existing rule syntax with the syntax
extensions MUST be provided if there is a change to the syntax. A extensions MUST be provided if there is a change to the syntax. A
skipping to change at page 45, line 19 skipping to change at page 44, line 33
o Usage Level: Updates MAY only add additional levels. o Usage Level: Updates MAY only add additional levels.
o Charset Dependent: MUST NOT be changed. o Charset Dependent: MUST NOT be changed.
o Purpose: MAY be extended according to the updated usage. o Purpose: MAY be extended according to the updated usage.
o O/A Procedures: MAY be updated in a backward compatible manner o O/A Procedures: MAY be updated in a backward compatible manner
and/or it applies to a new usage level only. and/or it applies to a new usage level only.
o Mux Category: No change unless from TBD to another value. It MAY o Mux Category: No change unless from "TBD" to another value (see
also change if 'media' level is being added to the definition of [I-D.ietf-mmusic-sdp-mux-attributes]. It MAY also change if
an attribute that previously did not include it. 'media' level is being added to the definition of an attribute
that previously did not include it.
o Reference: A new reference MUST be provided. o Reference: A new reference MUST be provided.
Items SHOULD be omitted if there is no impact to them as a result of Items SHOULD be omitted if there is no impact to them as a result of
the attribute update. the attribute update.
8.2.5. Bandwidth Specifiers ("bwtype") 8.2.5. Bandwidth Specifiers ("bwtype")
A proliferation of bandwidth specifiers is strongly discouraged. A proliferation of bandwidth specifiers is strongly discouraged.
skipping to change at page 45, line 46 skipping to change at page 45, line 13
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) MUST 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.
The registration is subject to the RFC Required - RFC publication The registration is subject to the "RFC Required" policy of
policy of [RFC8126]. Although these are not normally the preserve of [RFC8126]. Although these are not normally the preserve of IANA,
IANA, there may be circumstances when an Internet application needs there may be circumstances when an Internet application needs to
to interoperate with a non-Internet application, such as when interoperate with a non-Internet application, such as when gatewaying
gatewaying an Internet telephone call into the Public Switched an Internet telephone call into the Public Switched Telephone Network
Telephone Network (PSTN). The number of network types should be (PSTN). The number of network types should be small and should be
small and should be rarely extended. A new network type cannot be rarely extended. A new network type cannot be registered without
registered without registering at least one address type to be used registering at least one address type to be used with that network
with that network type. A new network type registration MUST type. A new network type registration MUST reference an RFC that
reference an RFC that gives details of the network type and address gives details of the network type and address type(s) and specifies
type(s) and specifies how and when they would be used. 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") MUST be registered with IANA. The New address types ("addrtype") MUST be registered with IANA. The
registration is subject to the RFC Required - RFC publication policy registration is subject to the "RFC Required" policy of [RFC8126].
of [RFC8126]. An address type is only meaningful in the context of a An address type is only meaningful in the context of a network type,
network type, and any registration of an address type MUST specify a and any registration of an address type MUST specify a registered
registered network type or be submitted along with a network type network type or be submitted along with a network type registration.
registration. A new address type registration MUST reference an RFC A new address type registration MUST reference an RFC giving details
giving details of the syntax of the address type. Address types are of the syntax of the address type. Address types are not expected to
not expected to be registered frequently. 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
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8.4. Reorganization of the nettype Registry 8.4. Reorganization of the nettype Registry
This document adds a new column in the "nettype" registry with the This document adds a new column in the "nettype" registry with the
title "Usable addrtype Values" and updates the "nettype" registry as title "Usable addrtype Values" and updates the "nettype" registry as
follows: follows:
-------------------------------------------------------------------- --------------------------------------------------------------------
|Type | SDP Name | Usable addrtype Values | Reference | |Type | SDP Name | Usable addrtype Values | Reference |
-------------------------------------------------------------------- --------------------------------------------------------------------
|nettype | IN | IP4, IP6 | [RFC4566] | |nettype | IN | IP4, IP6 | [RFCXXXX] |
|nettype | TN | RFC2543 | [RFC2848] | |nettype | TN | RFC2543 | [RFC2848] |
|nettype | ATM | NSAP, GWID, E164 | [RFC3108] | |nettype | ATM | NSAP, GWID, E164 | [RFC3108] |
|nettype | PSTN | E164 | [RFC7195] | |nettype | PSTN | E164 | [RFC7195] |
-------------------------------------------------------------------- --------------------------------------------------------------------
Note that both [RFC7195] and [RFC3108] registered "E164" as an Note that both [RFC7195] and [RFC3108] registered "E164" as an
address type, although [RFC7195] mentions that the "E164" address address type, although [RFC7195] mentions that the "E164" address
type has a different context for ATM and PSTN networks. type has a different context for ATM and PSTN networks.
8.5. Reorganization of the att-field Registries 8.5. Reorganization of the att-field Registries
skipping to change at page 53, line 33 skipping to change at page 52, line 48
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, HEXDIG, 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
10. Summary of Changes from RFC 4566 10. Summary of Changes from RFC 4566
The ABNF rule for IP6-address has been corrected. As a result, the The ABNF rule for IP6-address has been corrected. As a result, the
ABNF rule for IP6-multicast has changed, and the (now unused) rules ABNF rule for IP6-multicast has changed, and the (now unused) rules
for hexpart, hexseq, and hex4 have been removed. for hexpart, hexseq, and hex4 have been removed.
IP4 unicast and multicast addresses in the example SDP descriptions IP4 unicast and multicast addresses in the example SDP descriptions
skipping to change at page 54, line 21 skipping to change at page 53, line 35
11. Acknowledgements 11. Acknowledgements
Many people in the IETF Multiparty Multimedia Session Control Many people in the IETF Multiparty Multimedia Session Control
(MMUSIC) working group have made comments and suggestions (MMUSIC) working group have made comments and suggestions
contributing to this document. contributing to this document.
12. References 12. References
12.1. Normative References 12.1. Normative References
[E164] International Telecommunication Union, "E.164 : The
international public telecommunication numbering plan",
ITU Recommendation E.164, November 2010.
[I-D.ietf-mmusic-data-channel-sdpneg] [I-D.ietf-mmusic-data-channel-sdpneg]
Drage, K., Makaraju, M., Stoetzer-Bradler, J., Ejzak, R., Drage, K., Makaraju, M., Stoetzer-Bradler, J., Ejzak, R.,
and J. Marcon, "SDP-based Data Channel Negotiation", Marcon, J., and R. Even, "SDP-based Data Channel
draft-ietf-mmusic-data-channel-sdpneg-13 (work in Negotiation", draft-ietf-mmusic-data-channel-sdpneg-16
progress), September 2017. (work in progress), December 2017.
[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-16 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16
(work in progress), December 2016. (work in progress), December 2016.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>. <https://www.rfc-editor.org/info/rfc1034>.
skipping to change at page 55, line 38 skipping to change at page 55, line 10
[RFC5890] Klensin, J., "Internationalized Domain Names for [RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework", Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010, RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://www.rfc-editor.org/info/rfc5890>. <https://www.rfc-editor.org/info/rfc5890>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References 12.2. Informative References
[I-D.ietf-mmusic-sdp-bundle-negotiation]
Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
negotiation-48 (work in progress), January 2018.
[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.
[RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description [RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, DOI 10.17487/RFC2327, April 1998, Protocol", RFC 2327, DOI 10.17487/RFC2327, April 1998,
<https://www.rfc-editor.org/info/rfc2327>. <https://www.rfc-editor.org/info/rfc2327>.
[RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session [RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session
skipping to change at page 58, line 12 skipping to change at page 57, line 47
DOI 10.17487/RFC7656, November 2015, DOI 10.17487/RFC7656, November 2015,
<https://www.rfc-editor.org/info/rfc7656>. <https://www.rfc-editor.org/info/rfc7656>.
[RFC7826] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M., [RFC7826] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
and M. Stiemerling, Ed., "Real-Time Streaming Protocol and M. Stiemerling, Ed., "Real-Time Streaming Protocol
Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December
2016, <https://www.rfc-editor.org/info/rfc7826>. 2016, <https://www.rfc-editor.org/info/rfc7826>.
Authors' Addresses Authors' Addresses
Mark Handley Ali Begen
University College London Networked Media
Department of Computer Science Konya
London WC1E 6BT Turkey
UK
EMail: M.Handley@cs.ucl.ac.uk EMail: ali.begen@networked.media
Paul Kyzivat
USA
EMail: pkyzivat@alum.mit.edu
Colin Perkins Colin Perkins
University of Glasgow University of Glasgow
School of Computing Science School of Computing Science
University of Glasgow University of Glasgow
Glasgow G12 8QQ Glasgow G12 8QQ
UK UK
EMail: csp@csperkins.org EMail: csp@csperkins.org
Ali Begen Mark Handley
Networked Media University College London
Konya Department of Computer Science
Turkey London WC1E 6BT
UK
EMail: ali.begen@networked.media EMail: M.Handley@cs.ucl.ac.uk
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