draft-ietf-mmusic-data-channel-sdpneg-28.txt   rfc8864.txt 
MMUSIC K. Drage Internet Engineering Task Force (IETF) K. Drage
Internet-Draft Unaffiliated Request for Comments: 8864 M. Makaraju
Intended status: Standards Track M. Makaraju Category: Standards Track R. Ejzak
Expires: November 12, 2019 Nokia ISSN: 2070-1721 J. Marcon
R. Ejzak
J. Marcon
Unaffiliated Unaffiliated
R. Even, Ed. R. Even, Ed.
Huawei January 2021
May 11, 2019
SDP-based Data Channel Negotiation Negotiation Data Channels Using the Session Description Protocol (SDP)
draft-ietf-mmusic-data-channel-sdpneg-28
Abstract Abstract
Data channel setup can be done using either the in-band Data Channel Data channel setup can be done using either the in-band Data Channel
Establishment Protocol (DCEP) or using some out-of-band non-DCEP Establishment Protocol (DCEP) or some out-of-band non-DCEP protocol.
protocol. This document specifies how the SDP (Session Description This document specifies how the SDP (Session Description Protocol)
Protocol) offer/answer exchange can be used to achieve an out-of-band offer/answer exchange can be used to achieve an out-of-band non-DCEP
non-DCEP negotiation for establishing a data channel. negotiation for establishing a data channel.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on November 12, 2019. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8864.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2021 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
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Terminology
4. Applicability Statement . . . . . . . . . . . . . . . . . . . 6 4. Applicability Statement
5. SDP Data Channel Attributes . . . . . . . . . . . . . . . . . 6 5. SDP Data Channel Attributes
5.1. SDP DCMAP Attribute . . . . . . . . . . . . . . . . . . . 6 5.1. SDP DCMAP Attribute
5.1.1. DCMAP Attribute Syntax . . . . . . . . . . . . . . . 6 5.1.1. DCMAP Attribute Syntax
5.1.2. Dcmap-stream-id Parameter . . . . . . . . . . . . . . 8 5.1.2. 'dcmap-stream-id' Parameter
5.1.3. Label Parameter . . . . . . . . . . . . . . . . . . . 8 5.1.3. 'label' Parameter
5.1.4. Subprotocol Parameter . . . . . . . . . . . . . . . . 8 5.1.4. 'subprotocol' Parameter
5.1.5. Max-retr Parameter . . . . . . . . . . . . . . . . . 9 5.1.5. 'max-retr' Parameter
5.1.6. Max-time Parameter . . . . . . . . . . . . . . . . . 9 5.1.6. 'max-time' Parameter
5.1.7. Ordered Parameter . . . . . . . . . . . . . . . . . . 9 5.1.7. 'ordered' Parameter
5.1.8. Priority Parameter . . . . . . . . . . . . . . . . . 10 5.1.8. 'priority' Parameter
5.1.9. DCMAP Multiplexing Category . . . . . . . . . . . . . 10 5.1.9. DCMAP Multiplexing Category
5.2. SDP DCSA Attribute . . . . . . . . . . . . . . . . . . . 10 5.2. SDP DCSA Attribute
5.2.1. DCSA Syntax . . . . . . . . . . . . . . . . . . . . . 11 5.2.1. DCSA Attribute Syntax
5.2.2. DCSA Multiplexing Category . . . . . . . . . . . . . 12 5.2.2. DCSA Multiplexing Category
6. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 13 6. SDP Offer/Answer Procedures
6.1. Managing Stream Identifiers . . . . . . . . . . . . . . . 13 6.1. Managing Stream Identifiers
6.2. Negotiating Data Channel Parameters . . . . . . . . . . . 13 6.2. Negotiating Data Channel Parameters
6.3. Generating the Initial Offer for A Data Channel . . . . . 14 6.3. Generating the Initial Offer for a Data Channel
6.4. Generating SDP Answer . . . . . . . . . . . . . . . . . . 14 6.4. Generating the SDP Answer
6.5. Offerer Processing of the SDP Answer . . . . . . . . . . 15 6.5. Offerer Processing of the SDP Answer
6.6. Modifying the Session . . . . . . . . . . . . . . . . . . 15 6.6. Modifying the Session
6.6.1. Closing a Data Channel . . . . . . . . . . . . . . . 16 6.6.1. Closing a Data Channel
6.7. Various SDP Offer/Answer Considerations . . . . . . . . . 16 6.7. Various SDP Offer/Answer Considerations
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7. Examples
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19 8. Security Considerations
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 9. IANA Considerations
9.1. Subprotocol Identifiers . . . . . . . . . . . . . . . . . 20 9.1. Subprotocol Identifiers
9.2. New SDP Attributes . . . . . . . . . . . . . . . . . . . 20 9.2. New SDP Attributes
9.2.1. dcmap . . . . . . . . . . . . . . . . . . . . . . . . 20 9.2.1. dcmap
9.2.2. dcsa . . . . . . . . . . . . . . . . . . . . . . . . 21 9.2.2. dcsa
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 21 9.3. Registering Attributes for Use with Data Channels
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 10. References
12. CHANGE LOG . . . . . . . . . . . . . . . . . . . . . . . . . 22 10.1. Normative References
12.1. Changes against 'draft-ietf-mmusic-data-channel- 10.2. Informative References
sdpneg-15' . . . . . . . . . . . . . . . . . . . . . . . 22 Appendix A. Generic Data Channel Negotiation Aspects when Not
Using DCEP
12.2. Changes against 'draft-ietf-mmusic-data-channel- A.1. Stream Identifier Numbering
sdpneg-14' . . . . . . . . . . . . . . . . . . . . . . . 22 A.2. Generic Data Channel Negotiation Not Using DCEP
12.3. Changes against 'draft-ietf-mmusic-data-channel- A.2.1. Overview
sdpneg-12' . . . . . . . . . . . . . . . . . . . . . . . 22 A.2.2. Opening a Data Channel
12.4. Changes against 'draft-ietf-mmusic-data-channel- A.2.3. Closing a Data Channel
sdpneg-11' . . . . . . . . . . . . . . . . . . . . . . . 22 Acknowledgements
12.5. Changes against 'draft-ietf-mmusic-data-channel- Contributors
sdpneg-10' . . . . . . . . . . . . . . . . . . . . . . . 22 Authors' Addresses
12.6. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-09' . . . . . . . . . . . . . . . . . . . . . . . 22
12.7. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-08' . . . . . . . . . . . . . . . . . . . . . . . 23
12.8. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-07' . . . . . . . . . . . . . . . . . . . . . . . 24
12.9. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-06' . . . . . . . . . . . . . . . . . . . . . . . 24
12.10. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-05' . . . . . . . . . . . . . . . . . . . . . . . 24
12.11. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-04' . . . . . . . . . . . . . . . . . . . . . . . 25
12.12. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-03' . . . . . . . . . . . . . . . . . . . . . . . 26
12.13. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 27
12.14. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-01' . . . . . . . . . . . . . . . . . . . . . . . 28
12.15. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-00' . . . . . . . . . . . . . . . . . . . . . . . 30
12.16. Changes against 'draft-ejzak-mmusic-data-channel-
sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 33
12.17. Changes against '-01' . . . . . . . . . . . . . . . . . 34
12.18. Changes against '-00' . . . . . . . . . . . . . . . . . 34
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
13.1. Normative References . . . . . . . . . . . . . . . . . . 34
13.2. Informative References . . . . . . . . . . . . . . . . . 36
Appendix A. Generic Data Channel Negotiation Aspects When Not
Using DCEP . . . . . . . . . . . . . . . . . . . . . 36
A.1. Stream Identifier Numbering . . . . . . . . . . . . . . . 37
A.2. Generic Data Channel Negotiation Not Using DCEP . . . . . 38
A.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 38
A.2.2. Opening a Data Channel . . . . . . . . . . . . . . . 38
A.2.3. Closing a Data Channel . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 39
1. Introduction 1. Introduction
The concept of establishing a bi-directional data channel running on The concept of establishing a bidirectional data channel running on
top of the Stream Control Transmission Protocol (SCTP) is in top of the Stream Control Transmission Protocol (SCTP) is discussed
[I-D.ietf-rtcweb-data-channel] allowing applications to use data in [RFC8831], allowing applications to use data channels. An in-band
channels. An in-band Data Channel Establishment Protocol (DCEP) is Data Channel Establishment Protocol (DCEP) is described in [RFC8832];
in [I-D.ietf-rtcweb-data-protocol], however other in-band or out-of- however, other in-band or out-of-band protocols may be used for
band protocols may be used for establishing data channels. Each data establishing data channels. Each data channel consists of paired
channel consists of paired SCTP streams sharing the same SCTP Stream SCTP streams sharing the same SCTP Stream Identifier. Data channels
Identifier. Data channels are created by endpoint applications using are created by endpoint applications using (1) the WebRTC API
the WebRTC API (Application Programming Interface), or other (Application Programming Interface) [WebRtcAPI] or (2) other
protocols like CLUE [I-D.ietf-clue-datachannel]. The protocols can protocols (e.g., Controlling Multiple Streams for Telepresence (CLUE)
be signaled by the data channel "subprotocol" parameter, conceptually [RFC8850]). The protocols can be signaled by the data channel
similar to the WebSocket [RFC5234] "subprotocol". However, apart 'subprotocol' parameter, conceptually similar to a WebSocket
from the "subprotocol" value transmitted to the peer, an endpoint subprotocol as described in [RFC6455]. However, apart from the
application can agree on how to instantiate a given subprotocol on a "subprotocol" value transmitted to the peer, an endpoint application
data channel, and whether it is signaled in-band using DCEP or out- can agree on how to instantiate a given subprotocol on a data
of-band using a non-DCEP protocol (or both). channel, and whether it is signaled in-band using DCEP or out-of-band
using a non-DCEP protocol (or both).
This document defines SDP offer/answer [RFC3264] procedures that This document defines Session Description Protocol (SDP) offer/answer
enable out-of-band negotiation for establishing data channels for procedures [RFC3264] that enable out-of-band negotiation for
transport of well-defined subprotocols. These procedures are based establishing data channels for transport of well-defined
on generic SDP offer/answer negotiation rules for SCTP based media subprotocols. These procedures are based on generic SDP offer/answer
transport as specified in [I-D.ietf-mmusic-sctp-sdp] for the SDP "m" negotiation rules for SCTP-based media transport as specified in
line proto values UDP/DTLS/SCTP and TCP/DTLS/SCTP. [RFC8841] for the SDP "m=" line proto values UDP/DTLS/SCTP and
TCP/DTLS/SCTP.
This document uses MSRP (Message Session Relay Protocol) [RFC4975] This document uses MSRP (the Message Session Relay Protocol)
and BFCP (Binary Floor Control Protocol) [RFC4582] in many of the [RFC4975] and BFCP (the Binary Floor Control Protocol) [RFC8855] in
examples. It does not provide a complete specification of how to several examples. It does not provide a complete specification of
negotiate the use of a data channel to transport MSRP. Procedures how to negotiate the use of a data channel to transport MSRP.
specific to each subprotocol would have to be documented elsewhere. Procedures specific to each subprotocol would have to be documented
For MSRP they are documented in elsewhere. For MSRP, they are documented in [RFC8873]. The use of
[I-D.ietf-mmusic-msrp-usage-data-channel] . The use of MSRP in some MSRP in some examples is only to show how the generic procedures
examples is only to show how the generic procedures described herein described herein might apply to a specific subprotocol.
might apply to a specific subprotocol.
2. Conventions 2. Conventions
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
BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Terminology 3. Terminology
This document uses the following terms: This document uses the following terms:
Data channel: A WebRTC data channel as specified in Data channel: A WebRTC data channel as specified in [RFC8831].
[I-D.ietf-rtcweb-data-channel].
Data channel stack: An entity which, upon application request, Data channel stack: An entity that, upon application request, runs
runs the data channel protocol to keep track of states, sending the data channel protocol to keep track of states as well as the
and receiving data. If the application is a browser based sending and receiving of data. If the application is a browser-
JavaScript application then this stack resides in the browser. If based JavaScript application, then this stack resides in the
the application is a native application then this stack resides in browser. If the application is a native application, then this
the application and is accessible via some sort of APIs. stack resides in the application and is accessible via some sort
of API or APIs.
Data channel properties: Fixed properties assigned to a data Data channel properties: Fixed properties assigned to a data channel
channel at the time of its creation. Some of these properties at the time of its creation. Some of these properties determine
determine the way the data channel stack transmits data on this the way the data channel stack transmits data on this channel
channel (e.g., stream identifier, reliability, order of delivery, (e.g., stream identifier, reliability, order of delivery).
etc.).
Data channel subprotocol: The application protocol which is Data channel subprotocol: The application protocol that is
transported over a single data channel. Data channel subprotocol transported over a single data channel. Data channel subprotocol
messages are sent as data channel payload over an established data messages are sent as data channel payload over an established data
channel. SDP offer/answer exchange can be used as specified in channel. An SDP offer/answer exchange can be used as specified in
this document to negotiate the establishment of data channels, this document to negotiate the establishment of data channels,
corresponding data channel properties, associated data channel corresponding data channel properties, associated data channel
subprotocols and data channel subprotocol properties. In this subprotocols, and data channel subprotocol properties. In this
case the data channel subprotocols may be identified by the values case, the data channel subprotocols may be identified by the
of the "subprotocol" parameters of the SDP "a=dcmap" attribute as values of the 'subprotocol' parameters of the SDP "a=dcmap:"
described in Section 5.1.4. Within this document the term "data attribute as described in Section 5.1.4. Within this document,
channel subprotocol" is often abbreviated as just "subprotocol". the term "data channel subprotocol" is often abbreviated as just
"subprotocol".
DCEP: Data Channel Establishment Protocol defined in DCEP: Data Channel Establishment Protocol, as defined in [RFC8832].
[I-D.ietf-rtcweb-data-protocol].
In-band: Transmission through the peer-to-peer SCTP association. In-band: Transmission through the peer-to-peer SCTP association.
Out-of-band: Transmission through the application signaling path. Out-of-band: Transmission through the application signaling path.
Peer: From the perspective of one of the agents in a session, its Peer: From the perspective of one of the agents in a session, its
peer is the other agent. Specifically, from the perspective of peer is the other agent. Specifically, from the perspective of
the SDP offerer, the peer is the SDP answerer. From the the SDP offerer, the peer is the SDP answerer. From the
perspective of the SDP answerer, the peer is the SDP offerer. perspective of the SDP answerer, the peer is the SDP offerer.
SCTP Stream Sequence Number (SSN): the SCTP stream sequence number SCTP Stream Sequence Number (SSN): The SCTP Stream Sequence Number,
as specified in [RFC4960]. as specified in [RFC4960].
Stream identifier: The identifier of the outbound and inbound SCTP Stream identifier: The identifier of the outbound and inbound SCTP
streams composing a data channel. streams composing a data channel.
4. Applicability Statement 4. Applicability Statement
The mechanism in this document only applies to the Session The mechanism described in this document only applies to SDP
Description Protocol (SDP) [I-D.ietf-mmusic-rfc4566bis] when used [RFC8866] when used together with the SDP offer/answer mechanism
together with the SDP offer/answer mechanism [RFC3264]. Declarative [RFC3264]. Declarative usage of SDP is out of scope for this
usage of SDP is out of scope for this document, and is thus document and is thus undefined.
undefined.
5. SDP Data Channel Attributes 5. SDP Data Channel Attributes
This section defines two new SDP media-level attributes that can be This section defines two new SDP media-level attributes that can be
used together with the SDP Offer/Answer mechanism to negotiate data used together with the SDP Offer/Answer mechanism to negotiate data-
channel-specific and subprotocol-specific parameters without the channel-specific and subprotocol-specific parameters without the
usage of DCEP [I-D.ietf-rtcweb-data-protocol]. The first attribute usage of DCEP [RFC8832]. The first attribute (Section 5.1) provides
provides for negotiation of channel-specific parameters. The second for negotiation of channel-specific parameters. The second attribute
attribute provides for negotiation of subprotocol-specific (Section 5.2) provides for negotiation of subprotocol-specific
parameters. parameters.
Note: Appendix A provides information how data channels work in | Note: Appendix A provides information regarding how data
general and especially summarizes some key aspects, which should be | channels work in general. In particular, it summarizes some
considered for the negotiation of data channels if DCEP is not used. | key aspects that should be considered for the negotiation of
| data channels if DCEP is not used.
5.1. SDP DCMAP Attribute 5.1. SDP DCMAP Attribute
This section defines a new media level attribute "a=dcmap:" that This section defines a new media-level attribute, "a=dcmap:", that
defines the data channel parameters for each data channel to be defines the data channel parameters for each data channel to be
negotiated. negotiated.
The attribute is used to create bi-directional SCTP data channels This attribute is used to create bidirectional SCTP data channels
having the same set of attributes. The data channel properties having the same set of attributes. The data channel properties
(reliable/partially reliable, ordered/unordered) need to be suitable (reliable / partially reliable, ordered/unordered) need to be
per the subprotocol transport requirements. suitable per the subprotocol transport requirements.
5.1.1. DCMAP Attribute Syntax 5.1.1. DCMAP Attribute Syntax
"a=dcmap:" is a media level attribute having the following ABNF "a=dcmap:" is a media-level attribute having the following definition
(Augmented Backus-Naur Form, [RFC5234]) syntax. and ABNF (Augmented Backus-Naur Form) syntax [RFC5234].
Formal Syntax:
Name: dcmap
Value: dcmap-value +=================================+
| "a=dcmap:" Attribute |
+===================+=============+
| Name | dcmap |
+-------------------+-------------+
| Value | dcmap-value |
+-------------------+-------------+
| Usage Level | media |
+-------------------+-------------+
| Charset Dependent | No |
+-------------------+-------------+
Usage Level: media Table 1: "a=dcmap:" Attribute
Charset Dependent: no Definition
Syntax: Formal syntax:
dcmap-value = dcmap-stream-id dcmap-value = dcmap-stream-id
[ SP dcmap-opt *(";" dcmap-opt) ] [ SP dcmap-opt *(";" dcmap-opt) ]
dcmap-opt = ordering-opt / subprotocol-opt / label-opt dcmap-opt = ordering-opt / subprotocol-opt / label-opt
/ maxretr-opt / maxtime-opt / priority-opt / maxretr-opt / maxtime-opt / priority-opt
; maxretr-opt and maxtime-opt are mutually exclusive ; maxretr-opt and maxtime-opt are
; ; mutually exclusive
dcmap-stream-id = 1*5DIGIT dcmap-stream-id = 1*5DIGIT
ordering-opt = "ordered=" ordering-value ordering-opt = "ordered=" ordering-value
ordering-value = "true" / "false" ordering-value = "true" / "false"
subprotocol-opt = "subprotocol=" quoted-string subprotocol-opt = "subprotocol=" quoted-string
label-opt = "label=" quoted-string label-opt = "label=" quoted-string
maxretr-opt = "max-retr=" maxretr-value maxretr-opt = "max-retr=" maxretr-value
maxretr-value = "0" / integer maxretr-value = "0" / integer
; number of retransmissions, ; number of retransmissions,
; less than 2^32, ; less than 2^32,
; derived from 'Reliability Parameter' of ; derived from 'Reliability Parameter' [RFC8832]
; [I-D.ietf-rtcweb-data-protocol] maxtime-opt = "max-time=" maxtime-value
maxtime-opt = "max-time=" maxtime-value maxtime-value = "0" / integer
maxtime-value = "0" / integer ; milliseconds,
; milliseconds, ; less than 2^32,
; less than 2^32, ; derived from 'Reliability Parameter' [RFC8832]
; derived from 'Reliability Parameter' of priority-opt = "priority=" priority-value
; [I-D.ietf-rtcweb-data-protocol] priority-value = "0" / integer
priority-opt = "priority=" priority-value ; unsigned integer value indicating the priority of
priority-value = "0" / integer ; the data channel,
; unsigned integer value indicating the priority of ; less than 2^16,
; the data channel, ; derived from 'Priority' [RFC8832]
; less than 2^16,
; derived from 'Priority' of
; [I-D.ietf-rtcweb-data-protocol]
quoted-string = DQUOTE *(quoted-char / escaped-char) DQUOTE quoted-string = DQUOTE *(quoted-char / escaped-char) DQUOTE
quoted-char = SP / quoted-visible quoted-char = SP / quoted-visible
quoted-visible = %x21 / %x23-24 / %x26-7E ; VCHAR without " or % quoted-visible = %x21 / %x23-24 / %x26-7E ; VCHAR without " or %
escaped-char = "%" HEXDIG HEXDIG escaped-char = "%" HEXDIG HEXDIG
DQUOTE = <from-RFC5234> DQUOTE = <from RFC 5234>
integer = <from-RFC4566> integer = <from RFC 8866>
Examples: Examples:
a=dcmap:0 a=dcmap:0
a=dcmap:1 subprotocol="bfcp";max-time=60000;priority=512 a=dcmap:1 subprotocol="bfcp";max-time=60000;priority=512
a=dcmap:2 subprotocol="msrp";ordered=true;label="msrp" a=dcmap:2 subprotocol="msrp";ordered=true;label="msrp"
a=dcmap:3 label="Label 1";ordered=false;max-retr=5;priority=128 a=dcmap:3 label="Label 1";ordered=false;max-retr=5;priority=128
a=dcmap:4 label="foo%09bar";ordered=true;max-time=15000 a=dcmap:4 label="foo%09bar";ordered=true;max-time=15000
Note: The last example (a=dcmap:4) shows a 'label' parameter value | Note: The last example (a=dcmap:4) shows a 'label' parameter
which contains one non-printable 'escaped-char' character (the | value that contains one nonprintable 'escaped-char' character
tabulator character). | (the tabulator character).
Within an 'a=dcmap:' attribute line's 'dcmap-opt' value only one Within an "a=dcmap:" attribute line's 'dcmap-opt' value, only one
'maxretr-opt' parameter or one 'maxtime-opt' parameter may be 'maxretr-opt' parameter or one 'maxtime-opt' parameter may be
present. Both MUST NOT be present. present. Both parameters MUST NOT be present.
5.1.2. Dcmap-stream-id Parameter 5.1.2. 'dcmap-stream-id' Parameter
The 'dcmap-stream-id' parameter indicates the SCTP stream identifier The 'dcmap-stream-id' parameter indicates the SCTP stream identifier
within the SCTP association used to form the data channel. within the SCTP association used to form the data channel.
5.1.3. Label Parameter 5.1.3. 'label' Parameter
The 'label' parameter indicates the name of the channel. It The 'label' parameter indicates the name of the channel. It
represents a label that can be used to distinguish, in the context of represents a label that can be used to distinguish, in the context of
the WebRTC API [WebRtcAPI], an RTCDataChannel object from other the WebRTC API [WebRtcAPI], an RTCDataChannel object from other
RTCDataChannel objects. This parameter maps to the 'Label' parameter RTCDataChannel objects. This parameter maps to the 'Label' parameter
defined in [I-D.ietf-rtcweb-data-protocol]. The 'label' parameter is defined in [RFC8832]. The 'label' parameter is optional. If it is
optional. If it is not present, then its value defaults to the empty not present, then its value defaults to the empty string.
string.
In order to communicate with WEbRTC API the label attribute should: In order to communicate with the WebRTC API, the 'label' parameter
should
o Serialize the WebRTC label as a UTF-8 string [RFC3629]. * Serialize the WebRTC label as a UTF-8 string [RFC3629].
o Treat the UTF-8 serialization as a series of bytes * Treat the UTF-8 serialization as a series of bytes.
o For each byte in the serialization: * For each byte in the serialization,
* If the byte can be expressed as a `quoted-char`, do so - If the byte can be expressed as a 'quoted-char', do so.
* Otherwise, express the byte as an `escaped-char`. - Otherwise, express the byte as an 'escaped-char'.
Note: The empty string MAY also be explicitly used as a 'label' | Note: The empty string can also be explicitly used as a 'label'
value, such that 'label=""' is equivalent to the 'label' parameter | value, such that 'label=""' is equivalent to the 'label'
not being present at all. [I-D.ietf-rtcweb-data-protocol] allows the | parameter not being present at all. [RFC8832] allows the
DATA_CHANNEL_OPEN message's 'Label' value to be an empty string. | DATA_CHANNEL_OPEN message's 'Label' value to be an empty
| string.
5.1.4. Subprotocol Parameter 5.1.4. 'subprotocol' Parameter
The 'subprotocol' parameter indicates which protocol the client The 'subprotocol' parameter indicates which protocol the client
expects to exchange via the channel. This parameter maps to the expects to exchange via the channel. This parameter maps to the
'Protocol' parameter defined in [I-D.ietf-rtcweb-data-protocol]. 'Protocol' parameter defined in [RFC8832]. Section 9.1 specifies how
values for new subprotocol parameters are registered. 'subprotocol'
Section 9.1 specifies how new subprotocol parameter values are is an optional parameter. If the 'subprotocol' parameter is not
registered. 'subprotocol' is an optional parameter. If the present, then its value defaults to an empty string.
'subprotocol' parameter is not present, then its value defaults to an
empty string.
Note: The empty string MAY also be explicitly used as 'subprotocol' | Note: The empty string can also be explicitly used as a
value, such that 'subprotocol=""' is equivalent to the 'subprotocol' | 'subprotocol' value, such that 'subprotocol=""' is equivalent
parameter not being present at all. [I-D.ietf-rtcweb-data-protocol] | to the 'subprotocol' parameter not being present at all.
allows the DATA_CHANNEL_OPEN message's 'Subprotocol' value to be an | [RFC8832] allows the DATA_CHANNEL_OPEN message's 'Protocol'
empty string. | value to be an empty string.
5.1.5. Max-retr Parameter 5.1.5. 'max-retr' Parameter
This parameter indicates that the data channel is partially reliable. This parameter indicates that the data channel is partially reliable.
The 'max-retr' parameter indicates the maximal number of times a user The 'max-retr' parameter indicates the maximal number of times a user
message will be retransmitted. The max-retr parameter is optional. message will be retransmitted. The 'max-retr' parameter is optional.
If the max-retr parameter and the max-time parameter are not present, If the 'max-retr' parameter and the 'max-time' parameter are not
then reliable transmission is performed as specified in [RFC4960]. present, then reliable transmission is performed as specified in
This parameter maps to the 'Number of RTX' parameter defined in [RFC4960]. This parameter maps to the 'Number of RTX' parameter
[I-D.ietf-rtcweb-data-protocol]. defined in [RFC8832].
5.1.6. Max-time Parameter 5.1.6. 'max-time' Parameter
This parameter indicates that the data channel is partially reliable. This parameter indicates that the data channel is partially reliable.
A user message will no longer be transmitted or retransmitted after a A user message will no longer be transmitted or retransmitted after a
specified life-time given in milliseconds in the 'max-time' specified lifetime, given in milliseconds, in the 'max-time'
parameter. The life-time starts when providing the user message to parameter. The lifetime starts when providing the user message to
the protocol stack. The max-time parameter is optional. If the max- the protocol stack. The 'max-time' parameter is optional. If the
retr parameter and the max-time parameter are not present, then 'max-retr' parameter and the 'max-time' parameter are not present,
reliable transmission is performed as specified in [RFC4960]. This then reliable transmission is performed as specified in [RFC4960].
parameter maps to the 'Lifetime in ms' parameter defined in This parameter maps to the 'Lifetime in ms' parameter defined in
[I-D.ietf-rtcweb-data-protocol]. [RFC8832].
5.1.7. Ordered Parameter 5.1.7. 'ordered' Parameter
The 'ordered' parameter with value "true" indicates that the receiver The 'ordered' parameter with value "true" indicates that the receiver
will dispatch DATA chunks in the data channel to the upper layer will dispatch DATA chunks in the data channel to the upper layer
while preserving the order. The ordered parameter is optional and while preserving the order. The 'ordered' parameter is optional and
takes two values: "true" for ordered and "false" for unordered takes two values -- "true" for ordered delivery and "false" for
delivery with "true" as the default value. Any other value is unordered delivery -- with "true" as the default value. Any other
ignored and default "ordered=true" is assumed. In the absence of value is ignored, and the default "ordered=true" is assumed. In the
this parameter "ordered=true" is assumed. This parameter maps to the absence of this parameter, "ordered=true" is assumed. This parameter
ordered or unordered data channel types as defined in maps to the ordered or unordered data channel types as defined in
[I-D.ietf-rtcweb-data-protocol]. [RFC8832].
5.1.8. Priority Parameter 5.1.8. 'priority' Parameter
The 'priority' parameter indicates the data channel's priority The 'priority' parameter indicates the data channel's priority
relative to the priorities of other data channels, which may relative to the priorities of other data channels, which may
additionally exist over the same SCTP association. The 'priority' additionally exist over the same SCTP association. The 'priority'
parameter maps to the 'Priority' parameter defined in parameter maps to the 'Priority' parameter defined in [RFC8832]. The
[I-D.ietf-rtcweb-data-protocol]. The 'priority' parameter is 'priority' parameter is optional. In the absence of this parameter,
optional. In the absence of this parameter "priority=256" is "priority=256" is assumed.
assumed.
5.1.9. DCMAP Multiplexing Category 5.1.9. DCMAP Multiplexing Category
The multiplexing category [I-D.ietf-mmusic-sdp-mux-attributes] of the The multiplexing category [RFC8859] of the "a=dcmap:" attribute is
"a=dcmap:" attribute is SPECIAL. SPECIAL.
As the usage of multiple SCTP associations on top of a single DTLS As the usage of multiple SCTP associations on top of a single DTLS
association is outside the scope of [I-D.ietf-mmusic-sctp-sdp], no association is outside the scope of [RFC8841], no "a=dcmap:"
"a=dcmap:" attribute multiplexing rules are specified for the attribute multiplexing rules are specified for the UDP/DTLS/SCTP and
UDP/DTLS/SCTP and TCP/DTLS/SCTP proto values. If future extensions TCP/DTLS/SCTP proto values. If future extensions of [RFC8841] define
of [I-D.ietf-mmusic-sctp-sdp] define how to negotiate multiplexing of how to negotiate multiplexing of multiple SCTP associations on top of
multiple SCTP associations on top of a single DTLS association, or a single DTLS association or how to add multiple SCTP associations to
how to add multiple SCTP associations to one BUNDLE group, then one BUNDLE group, then multiplexing rules for the "a=dcmap:"
multiplexing rules for the "a=dcmap:" attribute need to be defined as attribute need to be defined as well -- for instance, in an extension
well, for instance in an extension of this SDP offer/answer based of this specification.
data channel negotiation specification.
5.2. SDP DCSA Attribute 5.2. SDP DCSA Attribute
In the SDP media description, each data channel declaration MAY also In the SDP media description, each data channel declaration MAY also
be followed by other media level SDP attributes, which are either be followed by other SDP attributes, which apply to the corresponding
specifically defined for or applied to the subprotocol in use. Each data channel and its subprotocol. Each of these attributes is
of these attributes is represented by one new attribute line, and it represented by one new "a=dcsa:" attribute line that references
includes the contents of a media-level SDP attribute already defined another SDP attribute defined for use with this data channel's
for use with this (sub)protocol in another IETF document. subprotocol. Instructions for registering attributes for use with a
Subprotocol specific attributes MAY also be defined for exclusive use data channel are given in Section 9.3.
with data channel transport, but MUST use the same syntax described
here for other subprotocol related attributes.
Each SDP attribute, related to the subprotocol, that would normally Each SDP attribute that is related to the subprotocol and that would
be used to negotiate the subprotocol using SDP offer/answer is normally be used to negotiate the subprotocol using the SDP offer/
replaced with an attribute of the form "a=dcsa:stream-id original- answer mechanism is replaced with an attribute of the form
attribute", where dcsa stands for "data channel subprotocol "a=dcsa:stream-id original-attribute", where "dcsa" stands for "data
attribute", stream-id is the SCTP stream identifier assigned to this channel subprotocol attribute", "stream-id" is the SCTP stream
subprotocol instance, and original-attribute represents the contents identifier assigned to this subprotocol instance, and "original-
of the subprotocol related attribute to be included. attribute" represents the contents of the subprotocol-related
attribute to be included.
The same syntax applies to any other SDP attribute required for The same syntax applies to any other SDP attribute required for
negotiation of this instance of the subprotocol. negotiation of this instance of the subprotocol.
The detailed offer/answer procedures for the dcsa attribute are The detailed offer/answer procedures for the dcsa attribute are
dependent on the associated sub-protocol. If no offer/answer dependent on the associated subprotocol. If no offer/answer
procedures exist for the sub-protocol when used outside of the dcsa procedures exist for the subprotocol when used outside of the dcsa
attribute, no specification is needed for use with dcsa. The IANA attribute, no specification is needed for use with dcsa. The IANA
registration procedures for the WebSocket Subprotocol Name Registry (Internet Assigned Numbers Authority) registration procedures for the
(Section 9.1) do not strictly require a specification of the offer/ "WebSocket Subprotocol Name Registry" (Section 9.1) do not strictly
answer procedures for the sub-protocol when used with dcsa. If the require a specification of the offer/answer procedures for the
sub-protocol has defined offer/answer procedures when used outside of subprotocol when used with dcsa. If the subprotocol has defined
dcsa, such a specification is encouraged to ensure interoperability. offer/answer procedures when used outside of dcsa, such a
If the sub-protocol has defined offer/answer procedures when used specification is encouraged to ensure interoperability. If the
outside of dcsa, but no specification exists for the offer/answer subprotocol has defined offer/answer procedures when used outside of
procedures for the sub-protocol when used with dcsa, implementations dcsa but no specification exists for the offer/answer procedures for
SHOULD assume the use of the default values for all otherwise- the subprotocol when used with dcsa, implementations SHOULD assume
negotiable and applicable sub-protocol parameters. the use of the default values for all otherwise-negotiable and
applicable subprotocol parameters.
5.2.1. DCSA Syntax
Formal Syntax:
Name: dcsa 5.2.1. DCSA Attribute Syntax
Value: dcsa-value "a=dcsa:" is a media-level attribute having the following definition
and ABNF (Augmented Backus-Naur Form) syntax [RFC5234].
Usage Level: media +================================+
| "a=dcsa:" Attribute |
+===================+============+
| Name | dcsa |
+-------------------+------------+
| Value | dcsa-value |
+-------------------+------------+
| Usage Level | media |
+-------------------+------------+
| Charset Dependent | No |
+-------------------+------------+
Charset Dependent: no Table 2: "a=dcsa:" Attribute
Definition
Syntax: Formal syntax:
dcsa-value = stream-id SP attribute dcsa-value = stream-id SP attribute
stream-id = 1*5DIGIT stream-id = 1*5DIGIT
attribute = <from-RFC4566> attribute = <from RFC 8866>
Example: Example:
a=dcmap:2 subprotocol="msrp";ordered=true;label="msrp" a=dcmap:2 subprotocol="msrp";ordered=true;label="msrp"
a=dcsa:2 accept-types:text/plain a=dcsa:2 accept-types:text/plain
Note that the reference to [I-D.ietf-mmusic-rfc4566bis] defines where The reference to [RFC8866] defines where the attribute definition can
the attribute definition can be found; it does not provide any be found; it does not provide any limitations on support of
limitation on support of attributes defined in other documents in attributes defined in other documents in accordance with this
accordance with this attribute definition. Note however that not all attribute definition. However, not all SDP attributes are suitable
SDP attributes are suitable as a "a=dcsa:" parameter. IANA SDP as an "a=dcsa:" parameter. The registry of IANA SDP parameters
parameters contains the lists of IANA (Internet Assigned Numbers contains the lists of IANA-registered session-level and media-level
Authority) registered session and media level or media level only SDP or media-level-only SDP attributes.
attributes.
Thus in the example above, the original attribute line "a=accept- Thus, in the example above, the original attribute line
types:text/plain" is represented by the attribute line "a=dcsa:2 "a=accept-types:text/plain" is represented by the attribute line
accept-types:text/plain", which specifies that this instance of the "a=dcsa:2 accept-types:text/plain", which specifies that this
MSRP subprotocol being transported on the SCTP association using the instance of the MSRP subprotocol being transported on the SCTP
data channel with stream id 2 accepts plain text files. association using the data channel with stream id 2 accepts plaintext
files.
As opposed to the data channel "a=dcmap:" attribute parameters, these As opposed to the data channel "a=dcmap:" attribute parameters, these
parameters are subject to offer/answer negotiation following the parameters are subject to offer/answer negotiation, following the
procedures defined in the subprotocol specific documents. procedures defined in the subprotocol-specific documents.
It is assumed that in general the usages of subprotocol related media It is assumed that in general the usages of subprotocol-related
level attributes are independent from the subprotocol's transport media-level attributes are independent from the subprotocol's
protocol. Such transport protocol independent subprotocol related transport protocol. Such transport-protocol-independent subprotocol-
attributes are used in the same way as defined in the original related attributes are used in the same way as defined in the
subprotocol specification, also if the subprotocol is transported original subprotocol specification, also if the subprotocol is
over a data channel and if the attribute is correspondingly embedded transported over a data channel and if the attribute is
in a "a=dcsa" attribute. correspondingly embedded in an "a=dcsa:" attribute.
There may be cases, where the usage of a subprotocol related media There may be cases where the usage of a subprotocol-related media-
level attribute depends on the subprotocol's transport protocol. In level attribute depends on the subprotocol's transport protocol. In
such cases the subprotocol related usage of the attribute is expected such cases, the subprotocol-related usage of the attribute is
to be described for the data channel transport. A data channel expected to be described for the data channel transport. A data-
specific usage of a subprotocol attribute is expected to be specified channel-specific usage of a subprotocol attribute is expected to be
in the same document that registers the subprotocol's identifier for specified in the same document that registers the subprotocol's
data channel usage as described in Section 9.1. identifier for data channel usage as described in Section 9.1.
SDP attributes that are only defined for use at the dcsa usage level,
SHALL use the dcsa usage level when registering the attribute. If
existing media attributes are used in a datachannel subprotocol
specific way, then a new dcsa usage level MUST be defined for the
existing media attribute. Where the SDP attribute is applicable to a
particular subprotocol/s this SHALL also be registered by indicating
the applicable subprotocol identifiers (see
/[I-D.ietf-mmusic-rfc4566bis] section-8.5) along with the dcsa usage
level.
5.2.2. DCSA Multiplexing Category 5.2.2. DCSA Multiplexing Category
The multiplexing category of the "a=dcsa:" attribute is SPECIAL. The multiplexing category of the "a=dcsa:" attribute is SPECIAL.
As the usage of multiple SCTP associations on top of a single DTLS As the usage of multiple SCTP associations on top of a single DTLS
association is outside the scope of [I-D.ietf-mmusic-sctp-sdp], no association is outside the scope of [RFC8841], no "a=dcsa:" attribute
"a=dcsa:" attribute multiplexing rules are specified for the multiplexing rules are specified for the UDP/DTLS/SCTP and
UDP/DTLS/SCTP and TCP/DTLS/SCTP proto values. If future extensions TCP/DTLS/SCTP proto values. If future extensions of [RFC8841] define
of [I-D.ietf-mmusic-sctp-sdp] define how to negotiate multiplexing of how to negotiate multiplexing of multiple SCTP associations on top of
multiple SCTP associations on top of a single DTLS association, or a single DTLS association or how to add multiple SCTP associations to
how to add multiple SCTP associations to one BUNDLE group, then one BUNDLE group, then multiplexing rules for the "a=dcsa:" attribute
multiplexing rules for the "a=dcsa:" attribute need to be defined as need to be defined as well -- for instance, in an extension of this
well, for instance in an extension of this SDP based data channel specification.
negotiation specification.
6. SDP Offer/Answer Procedures 6. SDP Offer/Answer Procedures
This section defines how data channels can be negotiated using the This section defines how data channels can be negotiated using the
SDP offer/answer mechanism. A given media description can describe SDP offer/answer mechanism. A given media description can describe
multiple data channels (each represented by a separate SDP dcmap multiple data channels (each represented by a separate SDP dcmap
attribute) that can be created, modified and closed using different attribute) that can be created, modified, and closed using different
offer/answer exchanges. The procedures in this section apply for a offer/answer exchanges. The procedures in this section apply for a
given data channel. given data channel.
The generic offer/answer procedures for negotiating the SCTP The generic offer/answer procedures for negotiating the SCTP
association used to realize data channels are defined in association used to realize data channels are defined in [RFC8841].
[I-D.ietf-mmusic-sctp-sdp]. This section only defines the data This section only defines the data-channel-specific procedures.
channel specific procedures.
"Initial offer" refers to the offer in which a data channel is "Initial offer" refers to the offer in which a data channel is
opened. It can be the initial offer, or a subsequent offer, of the opened. It can be either the initial offer or a subsequent offer of
associated SDP session. the associated SDP session.
The detailed offer/answer procedures for the dcsa attribute are The detailed offer/answer procedures for the dcsa attribute are
dependent on the associated sub-protocol see Section 5.2. dependent on the associated subprotocol; see Section 5.2.
6.1. Managing Stream Identifiers 6.1. Managing Stream Identifiers
In order to avoid SCTP Stream identifier collisions, in alignment In order to avoid SCTP Stream identifier collisions, in alignment
with [I-D.ietf-rtcweb-data-protocol], the endpoint acting as DTLS with [RFC8832], the endpoint acting as a DTLS client (for the SCTP
client (for the SCTP association used to realize data channels) MUST association used to realize data channels) MUST use even identifier
use even identifier values, and the endpoint acting as DTLS server values, and the endpoint acting as a DTLS server MUST use odd
MUST use odd identifier values. identifier values.
SCTP stream identifiers associated with data channels that have been SCTP stream identifiers associated with data channels that have been
negotiated using DCEP MUST NOT be included in SDP offers and answers. negotiated using DCEP MUST NOT be included in SDP offers and answers.
6.2. Negotiating Data Channel Parameters 6.2. Negotiating Data Channel Parameters
The data channel types defined in [I-D.ietf-rtcweb-data-protocol] are The data channel types defined in [RFC8832] are mapped to the dcmap
mapped to the dcmap SDP attribute parameters in the following manner SDP attribute parameters in the following manner, where
where "ordered=true" is the default and may be omitted: "ordered=true" is the default and may be omitted:
DATA_CHANNEL_RELIABLE DATA_CHANNEL_RELIABLE
ordered=true ordered=true
DATA_CHANNEL_RELIABLE_UNORDERED DATA_CHANNEL_RELIABLE_UNORDERED
ordered=false ordered=false
DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT
ordered=true;max-retr=<number of retransmissions> ordered=true;max-retr=<number of retransmissions>
DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED
ordered=false;max-retr=<number of retransmissions> ordered=false;max-retr=<number of retransmissions>
DATA_CHANNEL_PARTIAL_RELIABLE_TIMED DATA_CHANNEL_PARTIAL_RELIABLE_TIMED
ordered=true;max-time=<lifetime in milliseconds> ordered=true;max-time=<lifetime in milliseconds>
DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED
ordered=false;max-time=<lifetime in milliseconds> ordered=false;max-time=<lifetime in milliseconds>
By definition max-retr and max-time are mutually exclusive, so both By definition, 'max-retr' and 'max-time' are mutually exclusive, so
MUST NOT be present in the "a=dcmap:" attribute line. If an SDP both MUST NOT be present in the "a=dcmap:" attribute line. If an SDP
offer contains both of these parameters then the receiver of such an offer contains both of these parameters, then the receiver of such an
SDP offer MUST reject the SDP offer. If an SDP answer contains both SDP offer MUST reject the SDP offer. If an SDP answer contains both
of these parameters then the offerer MUST treat the associated SDP of these parameters, then the offerer MUST treat the associated SDP
offer/answer as failed. offer/answer as failed.
6.3. Generating the Initial Offer for A Data Channel 6.3. Generating the Initial Offer for a Data Channel
When an offerer sends an initial offer, in order to negotiate an SCTP When an offerer sends an initial offer, in order to negotiate an SCTP
stream for a data channel, the offerer: stream for a data channel, the offerer
o SHALL include an SDP dcmap attribute (Section 5 and Section 6.2) * SHALL include an SDP dcmap attribute (Sections 5.1 and 6.2)
associated with the data channel in the "m=" section representing associated with the data channel in the "m=" section representing
the SCTP association used to realize the data channel; and the SCTP association used to realize the data channel, and
o MAY include one or more SDP dcsa attributes (Section 5.2) * MAY include one or more SDP dcsa attributes (Section 5.2)
associated with the data channel. The value of the stream-id part associated with the data channel. The value of the 'stream-id'
of each attribute SHALL match the dcmap-stream-id value of the part of each attribute SHALL match the 'dcmap-stream-id' value of
dcmap attribute. the dcmap attribute.
6.4. Generating SDP Answer 6.4. Generating the SDP Answer
When an answerer receives an offer that includes an "m=" section for When an answerer receives an offer that includes an "m=" section for
an SCTP association, that describes an SCTP stream for a data an SCTP association, the offer describes an SCTP stream for a data
channel, if the answerer accepts the data channel it: channel, if the answerer accepts the data channel, it
o SHALL include an SDP dcmap attribute (Section 5 and Section 6.2) * SHALL include an SDP dcmap attribute (Sections 5.1 and 6.2)
associated with the data channel in the "m=" section representing associated with the data channel in the "m=" section representing
the SCTP association used to realize the data channel. The value the SCTP association used to realize the data channel. The value
of the dcmap-stream-id, max-retr and max-time values of the dcmap of the 'dcmap-stream-id', 'max-retr', and 'max-time' values of the
attribute SHALL be identical to the value used for the data dcmap attribute SHALL be identical to the value used for the data
channel in the offer; and channel in the offer, and
o MAY include one or more SDP dcsa attributes (Section 5.2) * MAY include one or more SDP dcsa attributes (Section 5.2)
associated with the data channel. associated with the data channel.
6.5. Offerer Processing of the SDP Answer 6.5. Offerer Processing of the SDP Answer
An offerer receiving an SDP answer performs the following: An offerer receiving an SDP answer performs the following:
o SHALL close any created data channels as described in * It SHALL close any created data channels as described in
Section 6.6.1 for which the expected "a=dcmap:" attributes are not Section 6.6.1 for which the expected "a=dcmap:" attributes are not
present in the SDP answer. If the SDP answer has no "a=dcmap" present in the SDP answer. If the SDP answer has no "a=dcmap:"
attribute either the peer does not support "a=dcmap:" attributes attributes, either the peer does not support "a=dcmap:" attributes
or it rejected all the data channels. In either case the offerer or it rejected all the data channels. In either case, the offerer
closes all the SDP offered data channels that were open at the closes all the data channels offered by SDP that were open at the
time of offer. The DTLS association and SCTP association will time of the offer. The DTLS association and SCTP association will
still be setup. At this point the offerer may use DCEP still be set up. At this point, the offerer may use DCEP
negotiation [I-D.ietf-rtcweb-data-protocol] to open data channels negotiation [RFC8832] to open data channels.
Each agent application MUST wait to send data until it has Each agent application MUST wait to send data until it has
confirmation that the data channel at the peer is instantiated. For confirmation that the data channel at the peer is instantiated. For
WebRTC, this is when both data channel stacks have channel parameters WebRTC, this is when both data channel stacks have channel parameters
instantiated. This occurs: instantiated and occurs as follows:
o At both peers when a data channel is created without a previously * At both peers when a data channel is created without a previously
established SCTP association, as soon as the SCTP association is established SCTP association, as soon as the SCTP association is
successfully established. successfully established.
o At the agent receiving an SDP offer for which there is an * At the agent receiving an SDP offer for which there is an
established SCTP association, as soon as it creates the negotiated established SCTP association, as soon as it creates the negotiated
data channel based on information signaled in the SDP offer. data channel based on information signaled in the SDP offer.
o At the agent sending an SDP offer to create a new data channel for * At the agent sending an SDP offer to create a new data channel for
which there is an established SCTP association, when it receives which there is an established SCTP association, when it receives
the SDP answer confirming acceptance of the data channel or when the SDP answer confirming acceptance of the data channel or when
it begins to receive data on the data channel from the peer, it begins to receive data on the data channel from the peer,
whichever occurs first. whichever occurs first.
6.6. Modifying the Session 6.6. Modifying the Session
When an offer sends a subsequent offer, that includes information for When an offerer sends a subsequent offer that includes information
a previously negotiated data channel, unless the offerer intends to for a previously negotiated data channel, unless the offerer intends
close the data channel (Section 6.6.1), the offerer SHALL include the to close the data channel (Section 6.6.1), the offerer SHALL include
previously negotiated SDP attributes and attribute values associated the previously negotiated SDP attributes and attribute values
with the data channel. The answerer may reject the offer. The means associated with the data channel. The answerer may reject the offer.
for rejecting an offer are dependent on the higher layer protocol. The means for rejecting an offer are dependent on the higher-layer
protocol. The offer/answer exchange is atomic; if the answer is
The offer/answer exchange is atomic; if the answer is rejected, the rejected, the session reverts to the state prior to the offer
session reverts to the state prior to the offer [RFC3264]. [RFC3264].
6.6.1. Closing a Data Channel 6.6.1. Closing a Data Channel
In order to close a data channel, the endpoint that wants to close In order to close a data channel, the endpoint that wants to close
SHALL send the SCTP SSN reset message [RFC6525], following the the data channel SHALL send an SCTP SSN Reset message [RFC6525],
procedures in section 6.7 of [I-D.ietf-rtcweb-data-channel]. In following the procedure in Section 6.7 of [RFC8831]. In addition, if
addition, if the closed data channel was negotiated using the offer/ the closed data channel was negotiated using the offer/answer
answer mechanism Section 6.3, the endpoint that closed the data mechanism (Section 6.3), the endpoint that closed the data channel
channel SHALL send a subsequent offer in which it either: SHALL send a subsequent offer in which it does one of the following:
o removes the SDP dcmap attribute and SDP dcsa attributes associated * Removes the SDP dcmap attribute and SDP dcsa attributes associated
with the closed data channel. Once the endpoint receives a with the closed data channel. Once the endpoint receives a
successful answer, the SCTP stream identifier value can later be successful answer, the SCTP stream identifier value can later be
used for a new data channel (negotiated using DCTP or using the used for a new data channel (negotiated using either SCTP or the
offer/answer mechanism); or offer/answer mechanism), or
o after a reset has been performed re-uses the SCTP stream used for * After a reset has been performed, reuses the SCTP stream used for
the closed data channel for a new data channel, using the the closed data channel for a new data channel, following the
procedures in Section 6.3. The offerer SHALL use a different SDP procedure in Section 6.3. The offerer SHALL use a different SDP
dcmap attribute value for the data channel using the same SCTP dcmap attribute value for the data channel using the same SCTP
stream. stream.
6.7. Various SDP Offer/Answer Considerations 6.7. Various SDP Offer/Answer Considerations
An SDP offer or answer has no "a=dcmap:" attributes but has An SDP offer or answer has no "a=dcmap:" attributes but has "a=dcsa:"
"a=dcsa:" attributes. attributes:
* This is considered an error case. In this case the receiver of * This is considered an error case. In this case, the receiver of
such an SDP offer or answer MUST discard this "a=dcsa:" such an SDP offer or answer MUST discard the "a=dcsa:" attributes.
attributes.
SDP offer or answer has an "a=dcsa" attribute, whose subprotocol An SDP offer or answer has an "a=dcsa:" attribute whose subprotocol
attribute is unknown. attribute is unknown:
* The receiver of such an SDP offer or answer SHOULD ignore this * The receiver of such an SDP offer or answer SHOULD ignore this
entire "a=dcsa" attribute line. entire "a=dcsa:" attribute line.
SDP offer or answer has an "a=dcsa" attribute, whose subprotocol An SDP offer or answer has an "a=dcsa:" attribute whose subprotocol
attribute is known, but whose subprotocol attribute semantic is attribute is known but whose subprotocol attribute semantic is not
not known for the data channel transport case. known for the data channel transport case:
* The receiver of such an SDP offer or answer SHOULD ignore this * The receiver of such an SDP offer or answer SHOULD ignore this
entire "a=dcsa" attribute line. entire "a=dcsa:" attribute line.
7. Examples 7. Examples
SDP offer: Figure 1 shows an example of an SDP offer and answer where the SDP
answerer rejects the data channel with stream id 0 either for
explicit reasons or because it does not understand the "a=dcmap:"
attribute. As a result, the offerer will close the data channel
created with the SDP offer/answer negotiation option. The SCTP
association will still be set up over DTLS. At this point, the
offerer or the answerer may use DCEP negotiation to open data
channels.
m=application 10001 UDP/DTLS/SCTP webrtc-datachannel m=application 10001 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP6 2001:db8::3 c=IN IP6 2001:db8::3
a=max-message-size:100000 a=max-message-size:100000
a=sctp-port:5000 a=sctp-port:5000
a=setup:actpass a=setup:actpass
a=fingerprint:SHA-1 \ a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=tls-id:abc3de65cddef001be82 a=tls-id:abc3de65cddef001be82
a=dcmap:0 subprotocol="bfcp";label="bfcp" a=dcmap:0 subprotocol="bfcp";label="bfcp"
SDP answer:
m=application 10002 UDP/DTLS/SCTP webrtc-datachannel m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP6 2001:db8::1 c=IN IP6 2001:db8::1
a=max-message-size:100000 a=max-message-size:100000
a=sctp-port:5002 a=sctp-port:5002
a=setup:passive a=setup:passive
a=fingerprint:SHA-1 \ a=fingerprint:SHA-1 \
5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA
a=tls-id:dcb3ae65cddef0532d42 a=tls-id:dcb3ae65cddef0532d42
Figure 1: Example 1 Figure 1: Example 1
In the example in Figure 1 the SDP answerer rejected the data channel Figure 2 shows an example of an SDP offer and answer where the SDP
with stream id 0 either for explicit reasons or because it does not offer contains data channels for BFCP and MSRP subprotocols. The SDP
understand the "a=dcmap:" attribute. As a result the offerer will answer rejects BFCP and accepts MSRP. So, the offerer closes the
close the data channel created with the SDP offer/answer negotiation data channel for BFCP, and both the offerer and the answerer may
option. The SCTP association will still be setup over DTLS. At this start using the MSRP data channel (after the SCTP association is
point the offerer or the answerer may use DCEP negotiation to open set up). The data channel with stream id 0 is free and can be used
data channels. for future DCEP or SDP offer/answer negotiation.
SDP offer:
m=application 10001 UDP/DTLS/SCTP webrtc-datachannel m=application 10001 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.1 c=IN IP4 192.0.2.1
a=max-message-size:100000 a=max-message-size:100000
a=sctp-port:5000 a=sctp-port:5000
a=setup:actpass a=setup:actpass
a=fingerprint:SHA-1 \ a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=tls-id:abc3de65cddef001be82 a=tls-id:abc3de65cddef001be82
a=dcmap:0 subprotocol="bfcp";label="bfcp" a=dcmap:0 subprotocol="bfcp";label="bfcp"
a=dcmap:2 subprotocol="msrp";label="msrp" a=dcmap:2 subprotocol="msrp";label="msrp"
a=dcsa:2 accept-types:message/cpim text/plain a=dcsa:2 accept-types:message/cpim text/plain
a=dcsa:2 path:msrp://alice.example.com:10001/2s93i93idj;dc a=dcsa:2 path:msrp://alice.example.com:10001/2s93i93idj;dc
SDP answer:
m=application 10002 UDP/DTLS/SCTP webrtc-datachannel m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.2 c=IN IP4 192.0.2.2
a=max-message-size:100000 a=max-message-size:100000
a=sctp-port:5002 a=sctp-port:5002
a=setup:passive a=setup:passive
a=fingerprint:SHA-1 \ a=fingerprint:SHA-1 \
5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA
a=tls-id:dcb3ae65cddef0532d42 a=tls-id:dcb3ae65cddef0532d42
a=dcmap:2 subprotocol="msrp";label="msrp" a=dcmap:2 subprotocol="msrp";label="msrp"
a=dcsa:2 accept-types:message/cpim text/plain a=dcsa:2 accept-types:message/cpim text/plain
a=dcsa:2 path:msrp://bob.example.com:10002/si438dsaodes;dc a=dcsa:2 path:msrp://bob.example.com:10002/si438dsaodes;dc
Figure 2: Example 2 Figure 2: Example 2
In the example in Figure 2 the SDP offer contains data channels for The example in Figure 3 is a continuation of the example in Figure 2.
BFCP (Binary Floor Control Protocol) and MSRP subprotocols. The SDP The SDP offerer now removes the MSRP data channel with stream id 2
answer rejected BFCP and accepted MSRP. So, the offerer closes the but opens a new MSRP data channel with stream id 4. The answerer
data channel for BFCP and both offerer and answerer may start using accepts the entire offer. As a result, the offerer closes the
the MSRP data channel (after the SCTP association is set up). The previously negotiated MSRP-related data channel, and both the offerer
data channel with stream id 0 is free and can be used for future DCEP and the answerer may start using the new MSRP-related data channel.
or SDP offer/answer negotiation.
Continuing the example in Figure 2.
Subsequent SDP offer:
m=application 10001 UDP/DTLS/SCTP webrtc-datachannel m=application 10001 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.1 c=IN IP4 192.0.2.1
a=max-message-size:100000 a=max-message-size:100000
a=sctp-port:5000 a=sctp-port:5000
a=setup:actpass a=setup:actpass
a=fingerprint:SHA-1 \ a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=tls-id:abc3de65cddef001be82 a=tls-id:abc3de65cddef001be82
a=dcmap:4 subprotocol="msrp";label="msrp" a=dcmap:4 subprotocol="msrp";label="msrp"
a=dcsa:4 accept-types:message/cpim text/plain a=dcsa:4 accept-types:message/cpim text/plain
a=dcsa:4 path:msrp://alice.example.com:10001/2s93i93idj;dc a=dcsa:4 path:msrp://alice.example.com:10001/2s93i93idj;dc
Subsequent SDP answer:
m=application 10002 UDP/DTLS/SCTP webrtc-datachannel m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.2 c=IN IP4 192.0.2.2
a=max-message-size:100000 a=max-message-size:100000
a=sctp-port:5002 a=sctp-port:5002
a=setup:passive a=setup:passive
a=fingerprint:SHA-1 \ a=fingerprint:SHA-1 \
5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA 5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA
a=tls-id:dcb3ae65cddef0532d42 a=tls-id:dcb3ae65cddef0532d42
a=dcmap:4 subprotocol="msrp";label="msrp" a=dcmap:4 subprotocol="msrp";label="msrp"
a=dcsa:4 accept-types:message/cpim text/plain a=dcsa:4 accept-types:message/cpim text/plain
a=dcsa:4 path:msrp://bob.example.com:10002/si438dsaodes;dc a=dcsa:4 path:msrp://bob.example.com:10002/si438dsaodes;dc
Figure 3: Example 3 Figure 3: Example 3
The example in Figure 3 is a continuation of the example in Figure 2.
The SDP offerer now removes the MSRP data channel with stream id 2,
but opens a new MSRP data channel with stream id 4. The answerer
accepts the entire offer. As a result the offerer closes the earlier
negotiated MSRP related data channel and both offerer and answerer
may start using new the MSRP related data channel.
8. Security Considerations 8. Security Considerations
This document specifies new SDP attributes used in the negotiation of This document specifies new SDP attributes used in the negotiation of
the DATA channel parameters. data channel parameters.
These parameter are negotiated as part of opening a SCTP channel over These parameters are negotiated as part of opening an SCTP channel
DTLS as specified in [I-D.ietf-mmusic-sctp-sdp]. Each subprotocol over DTLS as specified in [RFC8841]. Each subprotocol may come with
may come with it's own security considerations that need to be its own security considerations that need to be documented as part of
documented as part of the subprotocol definition. Otherwise this the subprotocol definition. Otherwise, this document does not add
document does not add any security considerations to the ones any security considerations to those specified in [RFC8841].
specified in [I-D.ietf-mmusic-sctp-sdp]
Error cases like the use of unknown parameter values or violation the Error cases such as the use of unknown parameter values or violations
odd/even rule MUST be handled by closing the corresponding Data of the odd/even rule (Section 6.1) MUST be handled by closing the
Channel. corresponding data channel.
9. IANA Considerations 9. IANA Considerations
9.1. Subprotocol Identifiers 9.1. Subprotocol Identifiers
Registration of new subprotocol identifiers is performed using the Registration of new subprotocol identifiers is performed using the
existing IANA "WebSocket Subprotocol Name Registry" table. existing IANA "WebSocket Subprotocol Name Registry" table.
The following text should be added following the title of the table. The following text has been added below the title of the table.
"This table also includes subprotocol identifiers specified for usage "This table also includes subprotocol identifiers specified for usage
within a WebRTC data channel." within a WebRTC data channel."
The following reference should be added to under the heading This document (RFC 8864) has been added to the "Reference" list for
reference: "RFC XXXX". the registry.
This document assigns no new values to this table. This document assigns no new values to this table.
A subprotocol may simultaneously be defined for data channel A subprotocol may simultaneously be defined for data channel
transport and for Websocket transport. In such a case the transport and for WebSocket transport. In such a case, the
"Subprotocol Definition" and "Reference" cells in the subprotocol's "Subprotocol Definition" and "Reference" cells in the subprotocol's
row of the IANA "WebSocket Subprotocol Name Registry" table should row of the IANA "WebSocket Subprotocol Name Registry" table should
contain two entries. One entry in each of these cells should refer contain two entries. One entry in each of these cells should refer
to the Websocket related subprotocol specification, and the other to the WebSocket-related subprotocol specification, and the other
entry should refer to the data channel related subprotocol entry should refer to the data-channel-related subprotocol
specification. specification.
NOTE to RFC Editor: Please replace "XXXX" with the number of this
RFC.
9.2. New SDP Attributes 9.2. New SDP Attributes
9.2.1. dcmap 9.2.1. dcmap
NOTE to RFC Editor: Please replace "XXXX" with the number of this This document defines a new SDP media-level attribute, "a=dcmap:", as
RFC.
This document defines a new SDP media-level attribute "a=dcmap:" as
follows: follows:
+-----------------------+-------------------------------------------+ +==================================================================+
| Contact name: | IESG | | "a=dcmap:" |
| Contact email: | iesg@ietf.org | +=====================+============================================+
| Attribute name: | dcmap | | Contact name | IESG |
| Attribute syntax: | As per Section 5.1.1 | +---------------------+--------------------------------------------+
| Attribute semantics: | As per Section 5.1.1 | | Contact email | iesg@ietf.org |
| Usage level: | media | +---------------------+--------------------------------------------+
| Charset dependent: | No | | Attribute name | dcmap |
| Purpose: | Define data channel specific parameters | +---------------------+--------------------------------------------+
| Appropriate values: | As per Section 5.1.1 | | Attribute syntax | As per Section 5.1.1 |
| O/A procedures: | As per Section 6 | +---------------------+--------------------------------------------+
| Mux category: | SPECIAL. See Section 5.1.9 | | Attribute semantics | As per Section 5.1.1 |
| Reference: | RFCXXXX | +---------------------+--------------------------------------------+
+-----------------------+-------------------------------------------+ | Usage level | media |
+---------------------+--------------------------------------------+
| Charset dependent | No |
+---------------------+--------------------------------------------+
| Purpose | To define data-channel-specific parameters |
+---------------------+--------------------------------------------+
| Appropriate values | As per Section 5.1.1 |
+---------------------+--------------------------------------------+
| O/A procedures | SDP offer/answer procedures as per |
| | Section 6 |
+---------------------+--------------------------------------------+
| Mux category | SPECIAL. See Section 5.1.9 |
+---------------------+--------------------------------------------+
| Reference | RFC 8864 |
+---------------------+--------------------------------------------+
9.2.2. dcsa Table 3: New "a=dcmap:" Attribute
NOTE to RFC Editor: Please replace "XXXX" with the number of this 9.2.2. dcsa
RFC.
This document defines a new SDP media-level attribute "a=dcsa:" as This document defines a new SDP media-level attribute, "a=dcsa:", as
follows: follows:
+-----------------------+-------------------------------------------+ +=============================================================+
| Contact name: | IESG | | "a=dcsa:" |
| Contact email: | iesg@ietf.org | +=====================+=======================================+
| Attribute name: | dcsa | | Contact name | IESG |
| Attribute syntax: | As per Section 5.2.1 | +---------------------+---------------------------------------+
| Attribute semantics: | As per Section 5.2.1 | | Contact email | iesg@ietf.org |
| Usage level: | media | +---------------------+---------------------------------------+
| Charset dependent: | No | | Attribute name | dcsa |
| Purpose: | Define data channel subprotocol specific | +---------------------+---------------------------------------+
| | attributes | | Attribute syntax | As per Section 5.2.1 |
| Appropriate values: | As per Section 5.2.1 | +---------------------+---------------------------------------+
| O/A procedures: | As per Section 6 | | Attribute semantics | As per Section 5.2.1 |
| Mux category: | SPECIAL. See Section 5.2.2 | +---------------------+---------------------------------------+
| Reference: | RFCXXXX | | Usage level | media |
+-----------------------+-------------------------------------------+ +---------------------+---------------------------------------+
| Charset dependent | No |
10. Contributors +---------------------+---------------------------------------+
| Purpose | To define attributes that are |
Juergen Stoetzer-Bradler co-authored this document. | | specific to data channel subprotocols |
+---------------------+---------------------------------------+
11. Acknowledgments | Appropriate values | As per Section 5.2.1 |
+---------------------+---------------------------------------+
The authors wish to acknowledge the borrowing of ideas from other | O/A procedures | SDP offer/answer procedures as per |
internet drafts by Salvatore Loreto, Gonzalo Camarillo, Peter Dunkley | | Section 6 |
and Gavin Llewellyn, and to thank Flemming Andreasen, Christian +---------------------+---------------------------------------+
Groves, Gunnar Hellstrom, Paul Kyzivat, Jonathan Lennox, Uwe | Mux category | SPECIAL. See Section 5.2.2 |
Rauschenbach and Roman Shpount for their invaluable comments. +---------------------+---------------------------------------+
| Reference | RFC 8864 |
Special thanks to Christer Holmberg for helping finish the document +---------------------+---------------------------------------+
and cleaning the SDP offer/answer section.
12. CHANGE LOG
12.1. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-15'
o Editorial changes separate sections for offer/answer procedures.
o Update security section.
12.2. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-14'
o Change "dtls-id" to "tls-id" and assign 20 octet long values
o Remove of RFC4566bis draft from list of normative references.
12.3. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-12'
o Modification of Keith's address information.
12.4. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-11'
o dcmap-stream-id syntax change to limit size to 5 digits.
o Add missing 'x' prefix to quoted-visible syntax.
o Align SDP offerer and answerer handling when both max-retr and
max-time are present.
o Use of TEST-NET-1 ip addresses in examples.
o Add missing a=dtls-id in one example.
12.5. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-10'
o Removal of the "a=connection" attribute lines from all SDP
examples.
12.6. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-09'
o In the introduction:
* Replacement of the sentence "The RTCWeb working group has
defined the concept of bi-directional data channels running on
top of SCTP/DTLS (SCTP over the Datagram Transport Layer
Security protocol)" with "The RTCWeb working group has defined
the concept of bi-directional data channels running on top of
the Stream Control Transmission Protocol (SCTP)".
* Addition of following sentences to the second paragraph: "These
procedures are based on generic SDP offer/answer negotiation
rules for SCTP based media transport as specified in
[I-D.ietf-mmusic-sctp-sdp] for the SDP "m" line proto values
UDP/DTLS/SCTP and TCP/DTLS/SCTP. In the future, data channels
could be defined over other SCTP based protocols, such as SCTP
over IP. However, corresponding potential other "m" line proto
values are not considered in this document."
o Replacement of "DTLS connection" with "DTLS association"
throughout the document.
o In sections Section 5.1.9 and Section 5.2.2 removal of the
sentences "This document also does not specify multiplexing rules
for this attribute for SCTP or SCTP/DTLS proto values".
o In the text related to "Subsequent SDP answer" in section
Section 6.7 replacement of "The DTLS/SCTP association remains open
..." with "The SCTP association remains open ...".
o In the text after the second SDP answer in section Section 7
replacement of "... (after SCTP/DTLS association is setup)" with
"... (after the SCTP association is set up)".
o Addition of draft-ietf-mmusic-dtls-sdp to the list of informative
references.
o Addition of "a=dtls-id" attribute lines to the SDP offer/answer
examples in Section 7.
12.7. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-08'
o Addition of definition of "data channel subprotocol" to Section 3
as proposed on the MMUSIC list, https://www.ietf.org/mail-
archive/web/mmusic/current/msg15827.html.
o Addition of RFC4566bis draft to list of normative references.
o Updates of tables in Section 9.2.1 and Section 9.2.2 as per
section 8.2.4 of RFC4566bis draft.
o Addition of new "new-usage-level">.
12.8. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-07'
o Addition of two new paragraphs to Section 5.2.1 regarding
subprotocol attribute relationship with transport protocol.
o Addition of a note to Section 9.1 regarding subprotocols
simultaneously defined for data channel and Websocket usage.
o Addition of two further SDP offer/answer considerations to
Section 6.7 regarding unknown subprotocol attributes and known
subprotocol attributes with unknown data channel transport related
semantic.
12.9. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-06'
o Changes addressing Christian Groves's WGLC review comments raised
in http://www.ietf.org/mail-archive/web/mmusic/current/
msg15357.html and http://www.ietf.org/mail-
archive/web/mmusic/current/msg15359.html.
12.10. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-05'
o In IANA registration Section 9.2.1 and Section 9.2.2 replacement
of contact name and e-mail address with "MMUSIC Chairs" and
"mmusic-chairs@ietf.org".
o In Section 5.2.1 replacement of "Thus in the example above, the
original attribute line "a=accept- types:text/plain" is
represented by the attribute line "a=dcsa:2 accept-types:text/
plain", which specifies that this instance of MSRP being
transported on the SCTP association using the data channel with
stream id 2 accepts plain text files." with "... which specifies
that this instance of the MSRP subprotocol being transported ...".
o The last paragraph of Section 5.2.1 started with "Note: This
document does not provide a complete specification ...". Removal
of "Note:" and move of this paragraph to the introduction in
Section 1 as last paragraph.
o Section 5.2's headline was "Subprotocol Specific Attributes".
Change of this headline to "Other Media Level Attributes" and
adaptations of the first paragraph of this section and the first
paragraph of Section 5.2.1 in order to clarify that not only those
attributes may be encapsulated in a "dcsa" attribute, which are
specifically defined for the subprotocol, but that also other
attributes may be encapsulated if they are related to the specific
subprotocol instance.
o Move of the last but one paragraph of Section 5.2.1 starting with
"The same syntax applies to ..." right in front of the formal
syntax definition of the "dcsa" attribute.
o Modifications of the text in Section 5.1.9 and Section 5.2.2 in
order not to explicitly restrict usage of the "a=dcmap:" and
"a=dcsa:" attributes to "m" lines with proto values "UDP/DTLS/
SCTP" or "TCP/DTLS/SCTP".
12.11. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-04'
o In Section 5.1.4 the first (and only) paragraph was "The
'subprotocol' parameter indicates which protocol the client
expects to exchange via the channel. 'subprotocol' is an optional
parameter. If the 'subprotocol' parameter is not present, then
its value defaults to the empty string." Replacement of this
paragraph with following two paragraphs:
* The 'subprotocol' parameter indicates which protocol the client
expects to exchange via the channel. This parameter maps to
the 'Protocol' parameter defined in
[I-D.ietf-rtcweb-data-protocol]. Section 9.1 specifies how new
subprotocol parameter values are registered. 'subprotocol' is
an optional parameter. If the 'subprotocol' parameter is not
present, then its value defaults to the empty string.
* Note: The empty string MAY also be explicitly used as
'subprotocol' value, such that 'subprotocol=""' is equivalent
to the 'subprotocol' parameter not being present at all.
[I-D.ietf-rtcweb-data-protocol] allows the DATA_CHANNEL_OPEN
message's 'subprotocol' value to be an empty string.
o Addition of [I-D.ietf-mmusic-sdp-mux-attributes] to list the of
normative references.
o Addition of dcmap attribute specific IANA registration
Section 9.2.1.
o Addition of dcsa attribute specific IANA registration
Section 9.2.2.
o Addition of new Section 5.1.9 describing the mux category of the
dcmap SDP attribute. This section and the new "a=dcsa:" attribute
related mux category section are similar to the "Mux Category"
sections of the "a=sctp-port:" and "a=max-message-size:"
attributes in [I-D.ietf-mmusic-sctp-sdp].
o Addition of new Section 5.2.2 describing the mux category of the
dcsa SDP attribute.
12.12. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-03'
o In Section 1 replacement of "RTCWeb leaves it open for other
applications to use data channels and its in-band DCEP or out-of-
band non-DCEP protocols for creating them" with "... to use data
channels and its in-band DCEP or other in-band or out-of-band
protocols for creating them". Additionally replacement of "In
particular, the SDP offer generated by the application includes no
channel-specific information" with "... generated by the RTCweb
data channel stack includes no channel-specific information".
o Move of former section 5 ("Data Channels") to new Appendix A and
removal of JavaScript API specific discussions from this moved
text (like mentioning of data channel stack specific states).
Therefore former section 6 ("SDP Offer/Answer Negotiation") is now
Section 5.
o In Section 5:
* Relacement of Section 5's first paragraph "This section defines
a method of non-DCEP negotiation by which two clients can
negotiate data channel-specific and subprotocol-specific
parameters, using the out-of-band SDP offer/answer exchange.
This SDP extension can only be used with the SDP offer/answer
model." with "This section defines an SDP extension by which
two clients can negotiate data channel-specific and
subprotocol-specific parameters without using DCEP
[I-D.ietf-rtcweb-data-protocol]. This SDP extension only
defines usage in the context of SDP offer/answer."
* Addition of new paragraph: "Appendix A provides information how
data channels work in general and especially summarizes some
key aspects, which should be considered for the negotiation of
data channels if DCEP is not used."
o In Section 5.1 replacement of "The intention of exchanging these
attributes is to create data channels on both the peers with the
same set of attributes without actually using the DCEP
[I-D.ietf-rtcweb-data-protocol]" with "The intention in exchanging
these attributes is to create, on two peers, without use of DCEP
[I-D.ietf-rtcweb-data-protocol], matched pairs of oppositely
directed data channels having the same set of attributes".
o In Section 5.1.5 replacement of "The 'max-retr' parameter
indicates the maximal number a user message will be retransmitted"
with "The 'max-retr' parameter indicates the maximal number of
times a user message will be retransmitted".
o In Section 6.1 replacement of "However, an SDP offer/answer
exchange MUST NOT be initiated if the associated SCTP stream is
already negotiated via DCEP" with "However, an SCTP stream MUST
NOT be referenced in a dcmap or dcsa attribute of an SDP offer/
answer exchange if the associated SCTP stream has already been
negotiated via DCEP".
o In the examples in Section 7 addition of the previously missing
colons to the "a=sctp-port" attribute lines.
12.13. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-02'
o Move of reference draft-ietf-rtcweb-jsep from the list of
normative references to the list of informative references.
Remover in -07 since not referenced
o Addition of IANA SDP parameters to the list of informative
references and addition of following two sentences to the first
paragraph after the ABNF definition: "Note however that not all
SDP attributes are suitable as "a=dcsa:" parameter. IANA SDP
parameters contains the lists of IANA registered session and media
level or media level only SDP attributes."
o In the introduction replacement of last sentence "This document
defines SDP-based out-of-band negotiation procedures to establish
data channels for transport of well-defined subprotocols" with
"This document defines SDP offer/answer negotiation procedures to
establish data channels for transport of well-defined
subprotocols, to enable out-of-band negotiation".
o Throughout the document replacement of "external negotiation" with
"SDP offer/answer negotiation" and removal of term "external
negotiation" from the terminology list in Section 3.
o Throughout the document replacement of "internal negotiation" with
"DCEP" and removal of terms "internal negotiation" and "in-band
negotiation" from the terminology list in Section 3.
o Addition of "SCTP Stream Sequence Number (SSN)" to the list of
terms.
o In Section 6.1 replacement of sentence "However, a single stream
is managed using one method at a time." with "However, an SDP
offer/answer exchange MUST NOT be initiated if the associated SCTP
stream is already negotiated via DCEP".
o In Section 6.2 replacement of sentence "By definition max-retr and
max-time are mutually exclusive, so only one of them can be
present in a=dcmap" with "By definition max-retr and max-time are
mutually exclusive, so aBoth MUST NOT be present in a=dcmap".
o Move of reference [WebRtcAPI] from list of normative references to
list of informative references.
o Removal of almost all text parts, which discussed JavaScript or
other API specific aspects. Such API specific aspects were mainly
discussed in sub-sections of Section 5 and Section 5 of draft-
ietf-mmusic-data-channel-sdpneg-02.
12.14. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-01'
o New Section 4 regarding applicability to SDP offer/answer only.
o Addition of new Section 9.1 "Subprotocol identifiers" as
subsection of the "IANA Considerations" related Section 9. Also
removal of the temporary note "To be completed. As [I-D.ietf-
rtcweb-data-protocol] this document should refer to IANA's
WebSocket Subprotocol Name Registry defined in [RFC6455]"
o In Section 6.2:
* In the first paragraph replacement of the sentence "If an SDP
offer contains both of these parameters then such an SDP offer
will be rejected." with "If an SDP offer contains both of these
parameters then the receiver of such an SDP offer MUST reject
the SDP offer."
* In the second paragraph capitalization of "shall" and "may"
such that both sentences now read: "The SDP answer SHALL echo
the same subprotocol, max-retr, max-time, ordered parameters,
if those were present in the offer, and MAY include a label
parameter. They MAY appear in any order, which could be
different from the SDP offer, in the SDP answer."
* In the third paragraph replacement of the sentence "The same
information MUST be replicated without changes in any
subsequent offer or answer, as long as the data channel is
still opened at the time of offer or answer generation." with
"When sending a subsequent offer or an answer, and for as long
as the data channel is still open, the sender MUST replicate
the same information.".
o In Section 6.2 the mapping of data channel types defined in
[I-D.ietf-rtcweb-data-protocol] to the SDP "a=dcmap" attribute
parameters were illustrated using example "a=dcmap" attribute
lines. Replacement of these example "a=dcmap" attribute lines
with just the "a=dcmap" attribute parameters being relevant for
the channel type.
o In Section 6.7 the description of bullet point "SDP offer has no
a=dcmap attributes - Initial SDP offer:" was "Initial SDP offer:
No data channel negotiated yet." Replacement of this description
with "Initial SDP offer: No data channel is negotiated yet. The
DTLS connection and SCTP association is negotiated and, if agreed,
established as per [I-D.ietf-mmusic-sctp-sdp]."
o In Section 6.7 in both bullet points related to "Subsequent SDP
offer" and "Subsequent SDP answer" replacement of "All the
externally negotiated data channels must be closed now." with "All
the externally negotiated data channels are expected to be closed
now.".
o In Appendix A.2.2's sixth paragraph replacement of the two
occurrences of "must" with "MUST".
o In Section 5.1.1 in the definition of the ABNF rule "dcmap-opt"
there was a comment saying that "Only maxretr-opt or maxtime-opt
is present. Both MUST NOT be present." Removal of the second
normative sentence and instead addition of following new paragraph
to the end of this section: "Within an 'a=dcmap' attribute line's
'dcmap-opt' value only one 'maxretr-opt' parameter or one
'maxtime-opt' parameter is present. Both MUST NOT be present."
o In Section 5.1.7 replacement of the first sentence "The 'ordered'
parameter with value "true" indicates that DATA chunks in the
channel MUST be dispatched to the upper layer by the receiver
while preserving the order." with "The 'ordered' parameter with
value "true" indicates that the receiver MUST dispatch DATA chunks
in the data channel to the upper layer while preserving the
order.".
o In Section 6.3's first paragraph replacement of the one occurrence
of "must" with "..., it MUST wait until ...".
o In Section 6.6.1:
* In the second paragraph replacement of "must" with "... whether
this closing MUST in addition ..."
* In the third paragraph replacement of the sentence "The port
value for the "m" line SHOULD NOT be changed (e.g., to zero)
when closing a data channel ..." with "The offerer SHOULD NOT
change the port value for the "m" line (e.g., to zero) when
closing a data channel ...".
* In the last but two paragraph replacement of the sentence "...
then an SDP offer which excludes this closed data channel
SHOULD be generated." with "... then the client SHOULD generate
an SDP offer which excludes this closed data channel.".
* In the last but one paragraph replacement of "must" with "The
application MUST also close...".
o In Section 5.2 addition of following note after the formal
definition of the 'a=dcsa' attribute: "Note that the above
reference to RFC 4566 defines were the attribute definition can be
found; it does not provide any limitation on support of attributes
defined in other documents in accordance with this attribute
definition."
12.15. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-00'
o In Section 3 "WebRTC data channel" was defined as "A bidirectional
channel consisting of paired SCTP outbound and inbound streams."
Replacement of this definition with "Data channel: A WebRTC data
channel as specified in [I-D.ietf-rtcweb-data-channel]", and
consistent usage of "data channel" in the remainder of the
document including the document's headline."
o In Section 5 removal of following note: 'OPEN ISSUE: The syntax in
[I-D.ietf-mmusic-sctp-sdp] may change as that document progresses.
In particular we expect "webrtc-datachannel" to become a more
general term.'
o Consistent usage of '"m" line' in whole document as per RFC4566.
o In Section 5.1 removal of the example dcmap attribute line
'a=dcmap:2 subprotocol="bfcp";label="channel 2' as there are
already four examples right after the ABNF rules in Section 5.1.1.
Corresponding removal of following related note: "Note: This
document does not provide a complete specification of how to
negotiate the use of a WebRTC data channel to transport BFCP.
Procedures specific to each subprotocol such as BFCP will be
documented elsewhere. The use of BFCP is only an example of how
the generic procedures described herein might apply to a specific
subprotocol."
o In Section 5.1 removal of following note: "Note: This attribute is
derived from attribute "webrtc-DataChannel", which was defined in
old version 03 of the following draft, but which was removed along
with any support for SDP external negotiation in subsequent
versions: [I-D.ietf-mmusic-sctp-sdp]."
o Insertion of following new sentence to the beginning of
Section 5.1.1: "dcmap is a media level attribute having following
ABNF syntax:"
o Insertion of new Section 5.1.2 containing the dcmap-stream-id
specifying sentence, which previously was placed right before the
formal ABNF rules. Removal of the sentence 'Stream is a mandatory
parameter and is noted directly after the "a=dcmap:" attribute's
colon' as this information is part of the ABNF specification.
o In Section 5.1.1 modification of the 'ordering-value' values from
"0" or "1" to "true" or "false". Corresponding text modifications
in Section 5.1.7.
o In Section 5.1.1 the ABNF definition of "quoted-string" referred
to rule name "escaped-char", which was not defined. Instead a
rule with name "escaped" was defined. Renamed that rule's name to
"escaped-char".
o Insertion of a dedicated note right after the "a=dcmap:4"
attribute example in Section 5.1.1 regarding the non-printable
"escaped-char" character within the "label" value.
o In Section 5.2's second paragraph replacement of "sctp stream
identifier" with "SCTP stream identifier".
o In first paragraph of Section 6.1 replacement of first two
sentences 'For the SDP-based external negotiation described in
this document, the initial offerer based "SCTP over DTLS" owns by
convention the even stream identifiers whereas the initial
answerer owns the odd stream identifiers. This ownership is
invariant for the whole lifetime of the signaling session, e.g. it
does not change if the initial answerer sends a new offer to the
initial offerer.' with 'If an SDP offer/answer exchange (could be
the initial or a subsequent one) results in a UDP/DTLS/SCTP or
TCP/DTLS/SCTP based media description being accepted, and if this
SDP offer/answer exchange results in the establishment of a new
SCTP association, then the SDP offerer owns the even SCTP stream
ids of this new SCTP association and the answerer owns the odd
SCTP stream identifiers. If this "m" line is removed from the
signaling session (its port number set to zero), and if usage of
this or of a new UDP/DTLS/SCTP or TCP/DTLS/SCTP based "m" line is
renegotiated later on, then the even and odd SCTP stream
identifier ownership is redetermined as well as described above.'
o In Section 6.3 the first action of an SDP answerer, when receiving
an SDP offer, was described as "Applies the SDP offer. Note that
the browser ignores data channel specific attributes in the SDP."
Replacement of these two sentences with "Parses and applies the
SDP offer. Note that the typical parser normally ignores unknown
SDP attributes, which includes data channel related attributes."
o In Section 6.3 the second sentence of the third SDP answerer
action was "Note that the browser is asked to create data channels
with stream identifiers not "owned" by the agent.". Replacement
of this sentence with "Note that the agent is asked to create data
channels with SCTP stream identifiers contained in the SDP offer
if the SDP offer is accepted."
o In Section 6.6.1 the third paragraph began with "A data channel
can be closed by sending a new SDP offer which excludes the dcmap
and dcsa attribute lines for the data channel. The port value for
the m line SHOULD NOT be changed (e.g., to zero) when closing a
data channel (unless all data channels are being closed and the
SCTP association is no longer needed), since this would close the
SCTP association and impact all of the data channels. If the
answerer accepts the SDP offer then it MUST also exclude the
corresponding attribute lines in the answer. ..." Replacement of
this part with "The intention to close a data channel can be
signaled by sending a new SDP offer which excludes the "a=dcmap:"
and "a=dcsa:" attribute lines for the data channel. The port
value for the "m" line SHOULD NOT be changed (e.g., to zero) when
closing a data channel (unless all data channels are being closed
and the SCTP association is no longer needed), since this would
close the SCTP association and impact all of the data channels.
If the answerer accepts the SDP offer then it MUST close those
data channels whose "a=dcmap:" and "a=dcsa:" attribute lines were
excluded from the received SDP offer, unless those data channels
were already closed, and it MUST also exclude the corresponding
attribute lines in the answer."
o In Section 6.6.1 the hanging text after the third paragraph was
"This delayed close is to handle cases where a successful SDP
answer is not received, in which case the state of session should
be kept per the last successful SDP offer/answer." Replacement of
this sentence with "This delayed closure is RECOMMENDED in order
to handle cases where a successful SDP answer is not received, in
which case the state of the session SHOULD be kept per the last
successful SDP offer/answer."
o Although dedicated to "a=dcmap" and "a=dcsa" SDP syntax aspects
Section 5.1 contained already procedural descriptions related to
data channel reliability negotiation. Creation of new Section 6.2
and moval of reliability negotiation related text to this new
section.
12.16. Changes against 'draft-ejzak-mmusic-data-channel-sdpneg-02'
o Removal of note "ACTION ITEM" from section "subprotocol
parameter". As [I-D.ietf-rtcweb-data-protocol] this document
should refer to IANA's WebSocket Subprotocol Name Registry defined
in [RFC6455]
o In whole document, replacement of "unreliable" with "partially
reliable", which is used in [I-D.ietf-rtcweb-data-channel] and in
[I-D.ietf-rtcweb-data-protocol] in most places.
o Clarification of the semantic if the "max-retr" parameter is not
present in an "a=dcmap" attribute line. In section "max-retr
parameter" the sentence "The max-retr parameter is optional with
default value unbounded" was replaced with "The max-retr parameter
is optional. If the max-retr parameter is not present, then the
maximal number of retransmissions is determined as per the generic
SCTP retransmission rules as specified in [RFC4960]".
o Clarification of the semantic if the "max-time" parameter is not
present in an "a=dcmap" attribute line. In section "max-time
parameter" the sentence "The max-time parameter is optional with
default value unbounded" was replaced with "The max-time parameter
is optional. If the max-time parameter is not present, then the
generic SCTP retransmission timing rules apply as specified in
[RFC4960]".
o In section "label parameter" the sentence "Label is a mandatory
parameter." was removed and following new sentences (including the
note) were added: "The 'label' parameter is optional. If it is
not present, then its value defaults to the empty string. Note:
The empty string may also be explicitly used as 'label' value,
such that 'label=""' is equivalent to the 'label' parameter not
being present at all. [I-D.ietf-rtcweb-data-protocol] allows the
DATA_CHANNEL_OPEN message's 'Label' value to be an empty string."
o In section "subprotocol parameter" the sentence "subprotocol is a
mandatory parameter." was replaced with "'subprotocol' is an
optional parameter. If the 'subprotocol' parameter is not
present, then its value defaults to the empty string."
o In the "Examples" section, in the first two SDP offer examples in
the "a=dcmap" attribute lines 'label="BGCP"' was replaced with
'label="bfcp"'.
o In all examples, the "m" line proto value "DTLS/SCTP" was replaced
with "UDP/DTLS/SCTP" and the "a=fmtp" attribute lines were
replaced with "a=max-message-size" attribute lines, as per draft-
ietf-mmusic-sctp-sdp-12.
12.17. Changes against '-01'
o Formal syntax for dcmap and dcsa attribute lines.
o Making subprotocol as an optional parameter in dcmap.
o Specifying disallowed parameter combinations for max-time and max-
retr.
o Clarifications on WebRTC data channel close procedures.
12.18. Changes against '-00'
o Revisions to identify difference between internal and external
negotiation and their usage.
o Introduction of more generic terminology, e.g. "application"
instead of "browser".
o Clarification of how "max-retr and max-time affect the usage of
unreliable and reliable WebRTC data channels.
o Updates of examples to take into account the SDP syntax changes
introduced with draft-ietf-mmusic-sctp-sdp-07.
o Removal of the SCTP port number from the "a=dcmap" and "a=dcsa"
attributes as this is now contained in the a=sctp-port attribute,
and as draft-ietf-mmusic-sctp-sdp-07 supports only one SCTP
association on top of the DTLS connection.
13. References
13.1. Normative References Table 4: New "a=dcsa:" Attribute
[I-D.ietf-mmusic-rfc4566bis] 9.3. Registering Attributes for Use with Data Channels
Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
Session Description Protocol", draft-ietf-mmusic-
rfc4566bis-32 (work in progress), December 2018.
[I-D.ietf-mmusic-sctp-sdp] When a subprotocol is defined for use over data channels with the SDP
Holmberg, C., Shpount, R., Loreto, S., and G. Camarillo, offer/answer mechanism, any SDP attributes that may be negotiated
"Session Description Protocol (SDP) Offer/Answer using the "a=dcsa:" attribute MUST be added to the IANA "attribute-
Procedures For Stream Control Transmission Protocol (SCTP) name registry (formerly "att-field")", as specified in [RFC8866],
over Datagram Transport Layer Security (DTLS) Transport.", Section 8.2.4. This document specifies that new Usage Levels of the
draft-ietf-mmusic-sctp-sdp-26 (work in progress), April form "dcsa (foo)" (where "foo" is a placeholder for the subprotocol
2017. name) should be registered by documents that specify negotiation of
particular subprotocols.
[I-D.ietf-mmusic-sdp-mux-attributes] IANA has updated the "attribute-name (formerly "att-field")" registry
Nandakumar, S., "A Framework for SDP Attributes when to point to this document.
Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-17
(work in progress), February 2018.
[I-D.ietf-rtcweb-data-channel] 10. References
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data
Channels", draft-ietf-rtcweb-data-channel-13 (work in
progress), January 2015.
[I-D.ietf-rtcweb-data-protocol] 10.1. Normative References
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel
Establishment Protocol", draft-ietf-rtcweb-data-
protocol-09 (work in progress), January 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002, DOI 10.17487/RFC3264, June 2002,
<https://www.rfc-editor.org/info/rfc3264>. <https://www.rfc-editor.org/info/rfc3264>.
skipping to change at page 36, line 14 skipping to change at line 968
[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control [RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control
Transmission Protocol (SCTP) Stream Reconfiguration", Transmission Protocol (SCTP) Stream Reconfiguration",
RFC 6525, DOI 10.17487/RFC6525, February 2012, RFC 6525, DOI 10.17487/RFC6525, February 2012,
<https://www.rfc-editor.org/info/rfc6525>. <https://www.rfc-editor.org/info/rfc6525>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
13.2. Informative References [RFC8831] Jesup, R., Loreto, S., and M. Tüxen, "WebRTC Data
Channels", RFC 8831, DOI 10.17487/RFC8831, January 2021,
<https://www.rfc-editor.org/info/rfc8831>.
[I-D.ietf-clue-datachannel] [RFC8832] Jesup, R., Loreto, S., and M. Tüxen, "WebRTC Data Channel
Holmberg, C., "CLUE Protocol data channel", draft-ietf- Establishment Protocol", RFC 8832, DOI 10.17487/RFC8832,
clue-datachannel-18 (work in progress), April 2019. January 2021, <https://www.rfc-editor.org/info/rfc8832>.
[I-D.ietf-mmusic-msrp-usage-data-channel] [RFC8841] Holmberg, C., Shpount, R., Loreto, S., and G. Camarillo,
Drage, K., Makaraju, M., Stoetzer-Bradler, J., Ejzak, R., "Session Description Protocol (SDP) Offer/Answer
Marcon, J., and J. Recio, "MSRP over Data Channels", Procedures for Stream Control Transmission Protocol (SCTP)
draft-ietf-mmusic-msrp-usage-data-channel-10 (work in over Datagram Transport Layer Security (DTLS) Transport",
progress), April 2019. RFC 8841, DOI 10.17487/RFC8841, January 2021,
<https://www.rfc-editor.org/info/rfc8841>.
[RFC4582] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor [RFC8859] Nandakumar, S., "A Framework for Session Description
Control Protocol (BFCP)", RFC 4582, DOI 10.17487/RFC4582, Protocol (SDP) Attributes When Multiplexing", RFC 8859,
November 2006, <https://www.rfc-editor.org/info/rfc4582>. DOI 10.17487/RFC8859, January 2021,
<https://www.rfc-editor.org/info/rfc8859>.
[RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
Session Description Protocol", RFC 8866,
DOI 10.17487/RFC8866, January 2021,
<https://www.rfc-editor.org/info/rfc8866>.
10.2. Informative References
[RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed., [RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed.,
"The Message Session Relay Protocol (MSRP)", RFC 4975, "The Message Session Relay Protocol (MSRP)", RFC 4975,
DOI 10.17487/RFC4975, September 2007, DOI 10.17487/RFC4975, September 2007,
<https://www.rfc-editor.org/info/rfc4975>. <https://www.rfc-editor.org/info/rfc4975>.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", [RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011, RFC 6455, DOI 10.17487/RFC6455, December 2011,
<https://www.rfc-editor.org/info/rfc6455>. <https://www.rfc-editor.org/info/rfc6455>.
[RFC8850] Holmberg, C., "Controlling Multiple Streams for
Telepresence (CLUE) Protocol Data Channel", RFC 8850,
DOI 10.17487/RFC8850, January 2021,
<https://www.rfc-editor.org/info/rfc8850>.
[RFC8855] Camarillo, G., Drage, K., Kristensen, T., Ott, J., and C.
Eckel, "The Binary Floor Control Protocol (BFCP)",
RFC 8855, DOI 10.17487/RFC8855, January 2021,
<https://www.rfc-editor.org/info/rfc8855>.
[RFC8873] Recio, JM., Ed. and C. Holmberg, "Message Session Relay
Protocol (MSRP) over Data Channels", RFC 8873,
DOI 10.17487/RFC8873, January 2021,
<https://www.rfc-editor.org/info/rfc8873>.
[T38] International Telecommunication Union, "Procedures for
real-time Group 3 facsimile communication over IP
networks", ITU-T Recommendation T.38, November 2015,
<https://www.itu.int/rec/T-REC-T.38-201511-I/en>.
[WebRtcAPI] [WebRtcAPI]
Bergkvist, A., Burnett, D., Jennings, C., Narayanan, A., Jennings, C., Boström, H., and J-I. Bruaroey, "WebRTC 1.0:
Aboba, B., Brandstetter, T., and J. Bruaroey, "WebRTC 1.0: Real-time Communication Between Browsers", W3C Proposed
Real-time Communication Between Browsers", World Wide Web Recommendation, <https://www.w3.org/TR/webrtc/>.
Consortium CR CR-webrtc-20180927, September 2018,
<https://www.w3.org/TR/2018/CR-webrtc-20180927/>.
Appendix A. Generic Data Channel Negotiation Aspects When Not Using Appendix A. Generic Data Channel Negotiation Aspects when Not Using
DCEP DCEP
This appendix summarizes how data channels work in general and This appendix summarizes how data channels work in general and
discusses some key aspects, which should be considered for the out- discusses some key aspects that should be considered for the out-of-
of-band negotiation of data channels if DCEP is not used. band negotiation of data channels if DCEP is not used.
A WebRTC application creates a data channel by providing a number of A WebRTC application creates a data channel by providing a number of
setup parameters (subprotocol, label, maximal number of setup parameters (subprotocol, label, maximal number of
retransmissions, maximal retransmission time, order of delivery, retransmissions, maximal retransmission time, order of delivery,
priority). The application also specifies if it wants to make use of priority). The application also specifies whether it wants to make
the negotiation using the DCEP [I-D.ietf-rtcweb-data-protocol], or if use of the negotiation using DCEP [RFC8832] or intends to negotiate
the application intends to negotiate data channels using the SDP data channels using the SDP offer/answer protocol.
offer/answer protocol.
In any case, the SDP offer generated by the application is per In any case, the SDP offer generated by the application is per
[I-D.ietf-mmusic-sctp-sdp]. In brief, it contains one "m" line for [RFC8841]. In brief, it contains one "m=" line for the SCTP
the SCTP association on top of which data channels will run: association on top of which the data channels will run:
m=application 54111 UDP/DTLS/SCTP webrtc-datachannel m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.1 c=IN IP4 192.0.2.1
a=max-message-size:100000 a=max-message-size:100000
a=sctp-port:5000 a=sctp-port:5000
a=tls-id:abc3de65cddef001be82 a=tls-id:abc3de65cddef001be82
a=setup:actpass a=setup:actpass
a=fingerprint:SHA-1 \ a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
Note: A WebRTC application will only use "m" line format "webrtc- | Note: A WebRTC application will only use the "m=" line format
datachannel", and will not use other formats in the "m" line for | "webrtc-datachannel" and will not use other formats in the "m="
other protocols such as t38. [I-D.ietf-mmusic-sctp-sdp] supports | line for other protocols such as T.38 [T38]. [RFC8841]
only one SCTP association to be established on top of a DTLS | supports only one SCTP association to be established on top of
association. | a DTLS association.
Note: The above SDP media description does not contain any channel- | Note: The above SDP media description does not contain any
specific information. | channel-specific information.
A.1. Stream Identifier Numbering A.1. Stream Identifier Numbering
Independently from the requested type of negotiation, the application Independently from the requested type of negotiation, the application
creating a data channel can either pass the stream identifier to the creating a data channel can either (1) pass the stream identifier to
data channel stack to assign to the data channel or else let the data the data channel stack to assign to the data channel or (2) let the
channel stack pick one identifier from the unused ones. data channel stack pick one identifier from the unused ones.
To avoid glare situations [RFC3264], each endpoint can moreover own Moreover, to avoid glare situations [RFC3264], each endpoint can own
an exclusive set of stream identifiers, in which case an endpoint can an exclusive set of stream identifiers, in which case an endpoint can
only create a data channel with a stream identifier it owns. only create a data channel with a stream identifier it owns.
Which set of stream identifiers is owned by which endpoint is Which set of stream identifiers is owned by which endpoint is
determined by convention or other means. determined by convention or other means.
Note:For data channels negotiated with the DCEP, one endpoint owns | Note: For data channels negotiated with DCEP, one endpoint owns
by convention the even stream identifiers, whereas the other owns | by convention the even stream identifiers, whereas the other
the odd stream identifiers, as defined in | owns the odd stream identifiers, as defined in [RFC8832].
[I-D.ietf-rtcweb-data-protocol].
Note:For data channels negotiated via different protocol from | Note: For data channels negotiated via a protocol other than
DCEP, no convention is defined by default. | DCEP, no convention is defined by default.
A.2. Generic Data Channel Negotiation Not Using DCEP A.2. Generic Data Channel Negotiation Not Using DCEP
A.2.1. Overview A.2.1. Overview
DCEP negotiation only provides for negotiation of data channel DCEP negotiation only provides for negotiation of data channel
transport parameters and does not provide for negotiation of transport parameters and does not provide for negotiation of
subprotocol specific parameters. DCEP-less data channel negotiation subprotocol-specific parameters. Non-DCEP data channel negotiation
can be defined to allow negotiation of parameters beyond those can be defined to allow negotiation of parameters beyond those
handled by DCEP, e.g., parameters specific to the subprotocol handled by DCEP, e.g., parameters specific to the subprotocol
instantiated on a particular data channel. instantiated on a particular data channel.
The following procedures are common to all methods of data channel The following procedures are common to all methods of data channel
negotiation not using DCEP, whether in-band (communicated using negotiation not using DCEP, whether in-band (communicated using
proprietary means on an already established data channel) or out-of- proprietary means on an already-established data channel) or out-of-
band (using SDP offer/answer or some other protocol associated with band (using the SDP offer/answer mechanism or some other protocol
the signaling channel). associated with the signaling channel).
A.2.2. Opening a Data Channel A.2.2. Opening a Data Channel
In the case of DCEP-less negotiation, the endpoint application has In the case of non-DCEP negotiation, the endpoint application has the
the option to fully control the stream identifier assignments. option to fully control the stream identifier assignments. However,
However these assignments have to coexist with the assignments these assignments have to coexist with the assignments controlled by
controlled by the data channel stack for the DCEP negotiated data the data channel stack for data channels negotiated using DCEP (if
channels (if any). It is the responsibility of the application to any). It is the responsibility of the application to ensure
ensure consistent assignment of stream identifiers. consistent assignment of stream identifiers.
When the application requests the creation of a new data channel to When the application requests that the creation of a new data channel
be set up via DCEP-less negotiation, the data channel stack creates be set up via non-DCEP negotiation, the data channel stack creates
the data channel locally without sending any DATA_CHANNEL_OPEN the data channel locally without sending any DATA_CHANNEL_OPEN
message in-band. However, even if the ICE (Interactive Connectivity messages in-band. However, even if the ICE (Interactive Connectivity
Establishment), DTLS and SCTP procedures were already successfully Establishment), DTLS, and SCTP procedures were already successfully
completed, the application can't send data on this data channel until completed, the application can't send data on this data channel until
the negotiation is complete with the peer. This is because the peer the negotiation with the peer is complete. This is because the peer
needs to be aware of and accept the usage of this data channel. The needs to be aware of and accept the usage of this data channel. The
peer, after accepting the data channel offer, can start sending data peer, after accepting the data channel offer, can start sending data
immediately. This implies that the offerer may receive data channel immediately. This implies that the offerer may receive data channel
subprotocol messages before the negotiation is complete and the subprotocol messages before the negotiation is complete, and the
application should be ready to handle it. application should be ready to handle it.
If the peer rejects the data channel part of the offer then it If the peer rejects the data channel part of the offer, then it
doesn't have to do anything as the data channel was not created using doesn't have to do anything, as the data channel was not created
the stack. The offerer on the other hand needs to close the data using the stack. The offerer, on the other hand, needs to close the
channel that was opened by invoking relevant data channel stack API data channel that was opened by invoking relevant data channel stack
procedures. API procedures.
It is also worth noting that a data channel stack implementation may It is also worth noting that a data channel stack implementation may
not provide any API to create and close data channels; instead the not provide any APIs to create and close data channels; instead, the
data channels may be used on the fly as needed just by communicating data channels may be used on the fly as needed, just by communicating
via non-DCEP means or by even having some local configuration/ via non-DCEP means or even by having some local configuration/
assumptions on both the peers. assumptions on both of the peers.
The application then negotiates the data channel properties and The application then negotiates the data channel properties and
subprotocol properties with the peer's application using a mechanism subprotocol properties with the peer's application using a mechanism
different from DCEP. different from DCEP.
The peer then symmetrically creates a data channel with these The peer then symmetrically creates a data channel with these
negotiated data channel properties. This is the only way for the negotiated data channel properties. This is the only way for the
peer's data channel stack to know which properties to apply when peer's data channel stack to know which properties to apply when
transmitting data on this channel. The data channel stack must allow transmitting data on this channel. The data channel stack must allow
data channel creation with any non-conflicting stream identifier so data channel creation with any nonconflicting stream identifier so
that both peers can create the data channel with the same stream that both peers can create the data channel with the same stream
identifier. identifier.
A.2.3. Closing a Data Channel A.2.3. Closing a Data Channel
When the application requests the closing of a data channel When the application requests the closing of a data channel
negotiated without DCEP, the data channel stack always performs an negotiated without DCEP, the data channel stack always performs an
SCTP SSN reset for this channel. SCTP SSN Reset for this channel.
Depending upon the method used for DCEP-less negotiation and the Depending upon the method used for non-DCEP negotiation and the
subprotocol associated with the data channel, the closing might in subprotocol associated with the data channel, the closing of the data
addition be signaled to the peer via SDP offer/answer negotiation. channel might also be signaled to the peer via SDP offer/answer
negotiation.
Acknowledgements
The authors wish to acknowledge the borrowing of ideas from other
draft documents by Salvatore Loreto, Gonzalo Camarillo, Peter
Dunkley, and Gavin Llewellyn. The authors also wish to thank
Flemming Andreasen, Christian Groves, Gunnar Hellström, Paul Kyzivat,
Jonathan Lennox, Uwe Rauschenbach, and Roman Shpount for their
invaluable comments.
Special thanks to Christer Holmberg for helping finish the document
and cleaning up Section 6.
Contributors
Juergen Stoetzer-Bradler made significant contributions to this
document and should be considered a coauthor.
Authors' Addresses Authors' Addresses
Keith Drage Keith Drage
Unaffiliated Unaffiliated
Email: drageke@ntlworld.com Email: drageke@ntlworld.com
Maridi R. Makaraju (Raju) Maridi R. Makaraju (Raju)
Nokia Unaffiliated
2000 Lucent Lane
Naperville, Illinois Email: mmraju@gmail.com
US
Email: Raju.Makaraju@nokia.com
Richard Ejzak Richard Ejzak
Unaffiliated Unaffiliated
Email: richard.ejzak@gmail.com Email: richard.ejzak@gmail.com
Jerome Marcon Jerome Marcon
Unaffiliated Unaffiliated
Email: jeromee.marcon@free.fr Email: jeromee.marcon@free.fr
Roni Even (editor) Roni Even (editor)
Huawei
Email: roni.even@huawei.com Email: ron.even.tlv@gmail.com
 End of changes. 184 change blocks. 
1297 lines changed or deleted 665 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/