draft-ietf-mmusic-data-channel-sdpneg-00.txt   draft-ietf-mmusic-data-channel-sdpneg-01.txt 
MMUSIC K. Drage, Ed. MMUSIC K. Drage, Ed.
Internet-Draft M. Makaraju Internet-Draft M. Makaraju
Intended status: Standards Track J. Stoetzer-Bradler Intended status: Standards Track J. Stoetzer-Bradler
Expires: July 31, 2015 Alcatel-Lucent Expires: September 10, 2015 Alcatel-Lucent
R. Ejzak R. Ejzak
J. Marcon J. Marcon
Unaffiliated Unaffiliated
January 27, 2015 March 9, 2015
SDP-based "SCTP over DTLS" data channel negotiation SDP-based Data Channel Negotiation
draft-ietf-mmusic-data-channel-sdpneg-00 draft-ietf-mmusic-data-channel-sdpneg-01
Abstract Abstract
The Real-Time Communication in WEB-browsers (RTCWeb) working group is The Real-Time Communication in WEB-browsers (RTCWeb) working group is
charged to provide protocols to support direct interactive rich charged to provide protocols to support direct interactive rich
communications using audio, video, and data between two peers' web- communications using audio, video, and data between two peers' web-
browsers. For the support of data communication, the RTCWeb working browsers. For the support of data communication, the RTCWeb working
group has in particular defined the concept of bi-directional data group has in particular defined the concept of bi-directional data
channels over SCTP, where each data channel might be used to channels over SCTP, where each data channel might be used to
transport other protocols, called sub-protocols. Data channel setup transport other protocols, called sub-protocols. Data channel setup
can be done using either the internal in-band band (also referred to can be done using either the internal in-band band (also referred to
as 'internal' for the rest of the document) WebRTC Data Channel as 'internal' for the rest of the document) Data Channel
Establishment Protocol or some external out-of-band simply referred Establishment Protocol or some external out-of-band simply referred
to as 'external negotiation' in the rest of the document . This to as 'external negotiation' in the rest of the document . This
document specifies how the SDP offer/answer exchange can be used to document specifies how the SDP offer/answer exchange can be used to
achieve such an external negotiation. Even though data channels are achieve such an external negotiation. Even though data channels are
designed for RTCWeb use initially they may be used by other protocols designed for RTCWeb use initially they may be used by other protocols
like, but not limited to, the CLUE protocol. This document is like, but not limited to, the CLUE protocol. This document is
intended to be used wherever data channels are used. intended to be used wherever data channels are used.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 31, 2015. This Internet-Draft will expire on September 10, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Data Channels . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Data Channels . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Stream identifier numbering . . . . . . . . . . . . . . . 5 4.1. Stream Identifier Numbering . . . . . . . . . . . . . . . 5
4.2. Generic external negotiation . . . . . . . . . . . . . . 6 4.2. Generic External Negotiation . . . . . . . . . . . . . . 6
4.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 6 4.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 6
4.2.2. Opening a data channel . . . . . . . . . . . . . . . 6 4.2.2. Opening a Data Channel . . . . . . . . . . . . . . . 6
4.2.3. Closing a data channel . . . . . . . . . . . . . . . 7 4.2.3. Closing a Data Channel . . . . . . . . . . . . . . . 7
5. SDP-based external negotiation . . . . . . . . . . . . . . . 7 5. SDP-based External Negotiation . . . . . . . . . . . . . . . 7
5.1. SDP syntax . . . . . . . . . . . . . . . . . . . . . . . 8 5.1. SDP Syntax . . . . . . . . . . . . . . . . . . . . . . . 8
5.1.1. SDP attribute for data channel parameter negotiation 8 5.1.1. SDP Attribute for Data Channel Parameter Negotiation 8
5.1.1.1. dcmap attribute . . . . . . . . . . . . . . . . . 9 5.1.1.1. dcmap Attribute . . . . . . . . . . . . . . . . . 8
5.1.1.2. label parameter . . . . . . . . . . . . . . . . . 10 5.1.1.2. dcmap-stream-id Parameter . . . . . . . . . . . . 10
5.1.1.3. subprotocol parameter . . . . . . . . . . . . . . 11 5.1.1.3. label Parameter . . . . . . . . . . . . . . . . . 10
5.1.1.4. max-retr parameter . . . . . . . . . . . . . . . 11 5.1.1.4. subprotocol Parameter . . . . . . . . . . . . . . 10
5.1.1.5. max-time parameter . . . . . . . . . . . . . . . 11 5.1.1.5. max-retr Parameter . . . . . . . . . . . . . . . 10
5.1.1.6. ordered parameter . . . . . . . . . . . . . . . . 11 5.1.1.6. max-time Parameter . . . . . . . . . . . . . . . 10
5.1.2. Sub-protocol specific attributes . . . . . . . . . . 12 5.1.1.7. ordered Parameter . . . . . . . . . . . . . . . . 11
5.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . 13 5.1.2. Sub-Protocol Specific Attributes . . . . . . . . . . 11
5.2.1. Managing stream identifiers . . . . . . . . . . . . . 13 5.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . 12
5.2.2. Opening a data channel . . . . . . . . . . . . . . . 13 5.2.1. Managing Stream Identifiers . . . . . . . . . . . . . 12
5.2.3. Closing a data channel . . . . . . . . . . . . . . . 15 5.2.2. Negotiating Data Channel Parameters . . . . . . . . . 13
5.2.4. Various SDP offer/answer scenarios and considerations 16 5.2.3. Opening a Data Channel . . . . . . . . . . . . . . . 14
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.2.4. Closing a Data Channel . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19 5.2.5. Various SDP Offer/Answer Scenarios and Considerations 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 18
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. CHANGE LOG . . . . . . . . . . . . . . . . . . . . . . . . . 20 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
10.1. Changes against 'draft-ejzak-mmusic-data-channel- 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 20 10. CHANGE LOG . . . . . . . . . . . . . . . . . . . . . . . . . 21
10.1. Changes against 'draft-ietf-mmusic-data-channel-
10.2. Changes against '-01' . . . . . . . . . . . . . . . . . 21 sdpneg-00' . . . . . . . . . . . . . . . . . . . . . . . 21
10.3. Changes against '-00' . . . . . . . . . . . . . . . . . 21 10.2. Changes against 'draft-ejzak-mmusic-data-channel-
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 24
11.1. Normative References . . . . . . . . . . . . . . . . . . 22 10.3. Changes against '-01' . . . . . . . . . . . . . . . . . 25
11.2. Informative References . . . . . . . . . . . . . . . . . 22 10.4. Changes against '-00' . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.1. Normative References . . . . . . . . . . . . . . . . . . 25
11.2. Informative References . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction 1. Introduction
The RTCWeb working group has defined the concept of bi-directional The RTCWeb working group has defined the concept of bi-directional
data channels running on top of SCTP/DTLS. RTCWeb leaves it open for data channels running on top of SCTP/DTLS. RTCWeb leaves it open for
other applications to use data channels and its in-band or out-of- other applications to use data channels and its in-band or out-of-
band protocol for creating them. Each data channel consists of band protocol for creating them. Each data channel consists of
paired SCTP streams sharing the same SCTP Stream Identifier. Data paired SCTP streams sharing the same SCTP Stream Identifier. Data
channels are created by endpoint applications through the WebRTC API, channels are created by endpoint applications through the WebRTC API,
or other users of data channel like CLUE, and can be used to or other users of data channel like CLUE, and can be used to
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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", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Terminology 3. Terminology
This document uses the following terms: This document uses the following terms:
Data channel: A bidirectional channel consisting of paired SCTP Data channel: A WebRTC data channel as specified in
outbound and inbound streams. [I-D.ietf-rtcweb-data-channel].
Data channel stack: An entity which, upon application request, Data channel stack: An entity which, upon application request,
runs data channel protocol to keep track of states, sending and runs data channel protocol to keep track of states, sending and
receive data. If the application is browser based Javascript receive data. If the application is browser based JavaScript
application then this stack resides in the browser. If the application then this stack resides in the browser. If the
application is a native application then this stack resides in application is a native application then this stack resides in
application and accessible to it via some sort of APIs. application and accessible to it via some sort of APIs.
Data channel properties: fixed properties assigned to a data Data channel properties: fixed properties assigned to a data
channel at the time of its creation. Some of these properties channel at the time of its creation. Some of these properties
determine the way the data channel stack transmits data on this determine the way the data channel stack transmits data on this
channel (e.g., stream identifier, reliability, order of channel (e.g., stream identifier, reliability, order of
delivery...) delivery...).
DCEP - Data Channel Establishment Protocol defined in DCEP - Data Channel Establishment Protocol defined in
[I-D.ietf-rtcweb-data-protocol]. [I-D.ietf-rtcweb-data-protocol].
External negotiation: Data channel negotiation based on SDP offer/ External negotiation: Data channel negotiation based on SDP offer/
answer outlined in this specification. answer outlined in this specification.
Internal negotiation: Data channel negotiation based on Data Internal negotiation: Data channel negotiation based on the Data
Channel Establishment Protocol defined in Channel Establishment Protocol defined in
[I-D.ietf-rtcweb-data-protocol]. [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.
In-band negotiation: data channel negotiation based Data Channel In-band negotiation: data channel negotiation based on the Data
Establishment Protocol defined in [I-D.ietf-rtcweb-data-protocol]. Channel Establishment Protocol defined in
[I-D.ietf-rtcweb-data-protocol].
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.
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. Data Channels 4. Data Channels
This section summarizes how data channels work in general. Note that This section summarizes how data channels work in general. Note that
the references to 'browser' here is intentional as in this specific the references to 'browser' here is intentional as in this specific
example the data channel user is a webrtc enabled browser. example the data channel user is a Webrtc enabled browser.
A WebRTC application creates a data channel via the Data Channel API, A WebRTC application creates a data channel via the data channel API,
by providing a number of setup parameters (sub-protocol, label, by providing a number of setup parameters (sub-protocol, label,
reliability, order of delivery, priority). The application also reliability, order of delivery, priority). The application also
specifies if it wants to make use of the in-band negotiation using specifies if it wants to make use of the in-band negotiation using
the DCEP [I-D.ietf-rtcweb-data-protocol], or if the application the DCEP [I-D.ietf-rtcweb-data-protocol], or if the application
intends to perform an "external negotiation" using some other in-band intends to perform an "external negotiation" using some other in-band
or out-of-band mechanism. or out-of-band mechanism.
In any case, the SDP offer generated by the browser is per In any case, the SDP offer generated by the browser is per
[I-D.ietf-mmusic-sctp-sdp]. In brief, it contains one m-line for the [I-D.ietf-mmusic-sctp-sdp]. In brief, it contains one "m" line for
SCTP association on top of which data channels will run, and one the SCTP association on top of which data channels will run, and one
attribute per protocol assigned to the SCTP ports: attribute per protocol assigned to the SCTP ports:
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.
m=application 54111 UDP/DTLS/SCTP webrtc-datachannel m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 79.97.215.79 c=IN IP4 79.97.215.79
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=connection:new a=connection:new
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 browser will only use m-line format "webrtc- Note: A WebRTC browser will only use "m" line format "webrtc-
datachannel", and will not use other formats in the m-line for other datachannel", and will not use other formats in the "m" line for
protocols such as t38. [I-D.ietf-mmusic-sctp-sdp] supports only one other protocols such as t38. [I-D.ietf-mmusic-sctp-sdp] supports
SCTP association to be established on top of a DTLS session. only one SCTP association to be established on top of a DTLS session.
Note: This SDP syntax does not contain any channel-specific Note: This SDP syntax does not contain any channel-specific
information. information.
4.1. Stream identifier numbering 4.1. 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 to the browser the stream creating a data channel can either pass to the browser the stream
identifier to assign to the data channel or else let the browser pick identifier to assign to the data channel or else let the browser pick
one identifier from the ones unused. one identifier from the ones unused.
To avoid glare situations, each endpoint can moreover own an To avoid glare situations, each endpoint can moreover own an
exclusive set of stream identifiers, in which case an endpoint can 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.
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determined by convention or other means. determined by convention or other means.
For data channels negotiated in-band, one endpoint owns by For data channels negotiated in-band, one endpoint owns by
convention the even stream identifiers, whereas the other owns the convention the even stream identifiers, whereas the other owns the
odd stream identifiers, as defined in odd stream identifiers, as defined in
[I-D.ietf-rtcweb-data-protocol]. [I-D.ietf-rtcweb-data-protocol].
For data channels externally negotiated, no convention is defined For data channels externally negotiated, no convention is defined
by default. by default.
4.2. Generic external negotiation 4.2. Generic External Negotiation
4.2.1. Overview 4.2.1. Overview
In-band negotiation only provides for negotiation of data channel In-band negotiation only provides for negotiation of data channel
transport parameters and does not provide for negotiation of sub- transport parameters and does not provide for negotiation of sub-
protocol specific parameters. External negotiation can be defined to protocol specific parameters. External negotiation can be defined to
allow negotiation of parameters beyond those handled by in-band allow negotiation of parameters beyond those handled by in-band
negotiation, e.g., parameters specific to the sub-protocol negotiation, e.g., parameters specific to the sub-protocol
instantiated on a particular data channel. See Section 5.1.2 for an instantiated on a particular data channel. See Section 5.1.2 for an
example of such a parameter. example of such a parameter.
The following procedures are common to all methods of external The following procedures are common to all methods of external
negotiation, whether in-band (communicated using proprietary means on negotiation, whether in-band (communicated using proprietary means on
an already established data channel) or out-of-band (using SDP or an already established data channel) or out-of-band (using SDP or
some other protocol associated with the signaling channel). some other protocol associated with the signaling channel).
4.2.2. Opening a data channel 4.2.2. Opening a Data Channel
In the case of external negotiation, the endpoint application has the In the case of external negotiation, the endpoint application has the
option to fully control the stream identifier assignments. However option to fully control the stream identifier assignments. However
these assignments have to coexist with the assignments controlled by these assignments have to coexist with the assignments controlled by
the data channel stack for the in-band negotiated data channels (if the data channel stack for the in-band negotiated data channels (if
any). It is the responsibility of the application to ensure any). It is the responsibility of the application to 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 the creation of a new data channel to
be set up via external negotiation, the data channel stack creates be set up via external 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, and sets the data channel state to Connecting if the message in-band, and sets the data channel state to Connecting if the
SCTP association is not yet established, or sets the data channel SCTP association is not yet established, or sets the data channel
state to Open if the SCTP association is already established. The state to Open if the SCTP association is already established. The
side which starts external negotiation creates data channel using side which starts external negotiation creates data channel using
underlying data channel stack API and the data channel is put into underlying data channel stack API and the data channel is put into
open state immediately (assuming ICE, SCTP procedures were already open state immediately (assuming ICE, SCTP procedures were already
done). However, the application can't send data on this data channel done). However, the application can't send data on this data channel
until external negotiation is complete with the peer. This is until external negotiation is complete with the peer. This is
because peer needs to be aware and accept the data channel via because peer needs to be aware and accept the data channel via
external negotiation. The peer after accepting the data channel external negotiation. The peer after accepting the data channel
offer can start sending data immediately. This implies that offerer offer can start sending data immediately. This implies that the
may get data channel message before external negotiation is complete offerer may get data channel message before external negotiation is
and the application should be ready to handle it. complete and the 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 using
the stack. The offerer on the other hand needs to close the data the stack. The offerer on the other hand needs to close the data
channel that was opened by invoking relevant data channel stack API channel that was opened by invoking relevant data channel stack API
procedures. 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 API to create and close data channels; instead the
data channels are used on the fly as needed just by communicating via data channels are used on the fly as needed just by communicating via
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same stream identifier. same stream identifier.
In case the external negotiation is correlated with an SDP offer/ In case the external negotiation is correlated with an SDP offer/
answer exchange that establishes the SCTP association, the SCTP answer exchange that establishes the SCTP association, the SCTP
initialization completion triggers a callback from the data channel initialization completion triggers a callback from the data channel
stack to an application on both the ends to change the data channel stack to an application on both the ends to change the data channel
state from Connecting to Open. The details of this interface is state from Connecting to Open. The details of this interface is
specific to the data channel user application. Browser based specific to the data channel user application. Browser based
applications (could include hybrid apps) will use [WebRtcAPI], while applications (could include hybrid apps) will use [WebRtcAPI], while
native applications use a compatible API, which is yet to be native applications use a compatible API, which is yet to be
specified. See Section 5.2.2 for details on when the data channel specified. See Section 5.2.3 for details on when the data channel
stack can assume the data channel is open, and on when the stack can assume the data channel is open, and on when the
application can assume the data channel is open. application can assume the data channel is open.
4.2.3. Closing a data channel 4.2.3. Closing a Data Channel
When the application requests the closing of an externally negotiated When the application requests the closing of an externally negotiated
data channel, the data channel stack always performs an in-band SSN data channel, the data channel stack always performs an in-band SSN
reset for this channel. reset for this channel.
Depending upon the method used for external negotiation and the sub- Depending upon the method used for external negotiation and the sub-
protocol associated with the data channel, the closing might in protocol associated with the data channel, the closing might in
addition be signaled to the peer via external negotiation. addition be signaled to the peer via external negotiation.
5. SDP-based external negotiation 5. SDP-based External Negotiation
This section defines a method of external negotiation by which two This section defines a method of external negotiation by which two
clients can negotiate data channel-specific and sub-protocol-specific clients can negotiate data channel-specific and sub-protocol-specific
parameters, using the out-of-band SDP offer/answer exchange. This parameters, using the out-of-band SDP offer/answer exchange. This
SDP extension can only be used with SDP offer/answer model. SDP extension can only be used with SDP offer/answer model.
5.1. SDP syntax 5.1. SDP Syntax
Two new SDP attributes are defined to support external negotiation of Two new SDP attributes are defined to support external negotiation of
data channels. The first attribute provides for negotiation of data channels. The first attribute provides for negotiation of
channel-specific parameters. The second attribute provides for channel-specific parameters. The second attribute provides for
negotiation of sub-protocol-specific parameters. negotiation of sub-protocol-specific parameters.
5.1.1. SDP attribute for data channel parameter negotiation 5.1.1. SDP Attribute for Data Channel Parameter Negotiation
Associated with the SDP "m" line that defines the SCTP association Associated with the SDP "m" line that defines the SCTP association
for data channels (defined in Section 4), each SDP offer and answer for data channels (defined in Section 4), each SDP offer and answer
includes an attribute line that defines the data channel parameters includes one "a=dcmap:" attribute that defines the data channel
for each data channel to be negotiated. Each attribute line parameters for each data channel to be negotiated. Each such
specifies the following parameters for a data channel: Stream attribute line specifies the following parameters for a data channel:
Identifier, sub-protocol, label, reliability, order of delivery, and SCTP stream identifier, sub-protocol, label, reliability, order of
priority. Conveying a reliable data channel is achieved by including delivery, and priority.
neither 'max-retr' nor 'max-time'. Conveying a partially reliable
data channel is achieved by including only one of 'max-retr' or 'max-
time'. By definition max-retr and max-time are mutually exclusive,
so only one of them can be present in a=dcmap. If an SDP offer
contains both of these parameters then such an SDP offer will be
rejected. If an SDP answer contains both of these parameters then
the offerer may treat it as an error and may assume the associated
SDP offer/answer failed and may take appropriate recovery actions.
These recovery options are outside the scope of this specification.
Following is an example of the attribute line for sub-protocol "BFCP"
and stream id "2":
a=dcmap:2 subprotocol="BFCP";label="channel 2"
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.
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.
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].
Note: This document does not provide a complete specification of
how to negotiate the use of a data channel to transport BFCP.
Procedures specific to each sub-protocol 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
sub-protocol.
The intention of exchanging these attributes is to create data The intention of exchanging these attributes is to create data
channels on both the peers with the same set of attributes without channels on both the peers with the same set of attributes without
actually using [I-D.ietf-rtcweb-data-protocol]. It is assumed that actually using [I-D.ietf-rtcweb-data-protocol]. It is assumed that
the data channel properties (reliable/partially reliable, ordered/ the data channel properties (reliable/partially reliable, ordered/
unordered) are suitable per the sub-protocol transport requirements. unordered) are suitable per the sub-protocol transport requirements.
Data channel types defined in [I-D.ietf-rtcweb-data-protocol] are
mapped to SDP in the following manner:
DATA_CHANNEL_RELIABLE
a=dcmap:2 subprotocol="BFCP";label="channel 2"
DATA_CHANNEL_RELIABLE_UNORDERED
a=dcmap:2 subprotocol="BFCP";label="channel 2";\
ordered=0
DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT
a=dcmap:2 subprotocol="BFCP";label="channel 2";\
max-retr=3
DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED
a=dcmap:2 subprotocol="BFCP";label="channel 2";\
max-retr=3;ordered=0;
DATA_CHANNEL_PARTIAL_RELIABLE_TIMED
a=dcmap:2 subprotocol="BFCP";label="channel 2";\
max-time=10000;
DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED
a=dcmap:2 subprotocol="BFCP";label="channel 2";\
max-time=10000; ordered=0
5.1.1.1. dcmap attribute 5.1.1.1. dcmap Attribute
The 'stream' parameter indicates the actual stream identifier within "a=dcmap:" is a media level attribute having following ABNF syntax.
the association used to form the channel. Stream is a mandatory
parameter and is noted directly after the "a=dcmap:" attribute's
colon.
Formal Syntax: Formal Syntax:
TBD: Should this be moved to SDP grammar section?
Name: dcmap Name: dcmap
Value: dcmap-value Value: dcmap-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
Syntax: 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 / maxretr-opt / maxtime-opt
skipping to change at page 10, line 20 skipping to change at page 9, line 27
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 / maxretr-opt / maxtime-opt
; Either only maxretr-opt or maxtime-opt ; Either only maxretr-opt or maxtime-opt
; is present. ; is present.
; Both MUST not be present. ; Both MUST not be present.
dcmap-stream-id = 1*DIGIT dcmap-stream-id = 1*DIGIT
ordering-opt = "ordered=" ordering-value ordering-opt = "ordered=" ordering-value
ordering-value = "0"/"1" 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 = <from-Reliability-Parameter of maxretr-value = <from-Reliability-Parameter of
I-D.ietf-rtcweb-data-protocol> I-D.ietf-rtcweb-data-protocol>
; number of retransmissions ; number of retransmissions
maxtime-opt = "max-time=" maxtime-value maxtime-opt = "max-time=" maxtime-value
maxtime-value = <from-Reliability-Parameter of maxtime-value = <from-Reliability-Parameter of
I-D.ietf-rtcweb-data-protocol> I-D.ietf-rtcweb-data-protocol>
; milliseconds ; milliseconds
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 = %21 / %23-24 / %26-7E ; VCHAR without " or % quoted-visible = %21 / %23-24 / %26-7E ; VCHAR without " or %
escaped = "%" HEXDIG HEXDIG escaped-char = "%" HEXDIG HEXDIG
DQUOTE = <from-RFC5234> DQUOTE = <from-RFC5234>
integer = <from-RFC5234> integer = <from-RFC5234>
Examples: Examples:
a=dcmap:0 a=dcmap:0
a=dcmap:1 subprotocol="BFCP";max-time=60000 a=dcmap:1 subprotocol="BFCP";max-time=60000
a=dcmap:2 subprotocol="MSRP";ordered;label="MSRP" a=dcmap:2 subprotocol="MSRP";ordered=true;label="MSRP"
a=dcmap:3 label="Label 1";unordered;max-retr=5 a=dcmap:3 label="Label 1";ordered=false;max-retr=5
a=dcmap:4 label="foo%09bar";ordered;max-time=15000;max-retr=3 a=dcmap:4 label="foo%09bar";ordered=true;max-time=15000;max-retr=3
Note: The last example (a=dcmap:4) shows a 'label' parameter value
which contains one non-printable 'escaped-char' character (the
tabulator character).
5.1.1.2. label parameter 5.1.1.2. dcmap-stream-id Parameter
The 'dcmap-stream-id' parameter indicates the SCTP stream identifier
within the SCTP association used to form the data channel.
5.1.1.3. 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, an RTCDataChannel object from other RTCDataChannel the WebRTC API, an RTCDataChannel object from other RTCDataChannel
objects. This parameter maps to the 'Label' parameter defined in objects. This parameter maps to the 'Label' parameter defined in
[I-D.ietf-rtcweb-data-protocol]. The 'label' parameter is optional. [I-D.ietf-rtcweb-data-protocol]. The 'label' parameter is optional.
If it is not present, then its value defaults to the empty string. 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, Note: The empty string may also be explicitly used as 'label' value,
such that 'label=""' is equivalent to the 'label' parameter not being such that 'label=""' is equivalent to the 'label' parameter not being
present at all. [I-D.ietf-rtcweb-data-protocol] allows the present at all. [I-D.ietf-rtcweb-data-protocol] 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.
5.1.1.3. subprotocol parameter 5.1.1.4. subprotocol Parameter
The 'subprotocol' parameter indicates which protocol the client The 'subprotocol' parameter indicates which protocol the client
expects to exchange via the channel. 'Subprotocol' is an optional expects to exchange via the channel. 'Subprotocol' is an optional
parameter. If the 'subprotocol' parameter is not present, then its parameter. If the 'subprotocol' parameter is not present, then its
value defaults to the empty string. value defaults to the empty string.
5.1.1.4. max-retr parameter 5.1.1.5. 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 max times a user message will The 'max-retr' parameter indicates the max times a user message will
be retransmitted. The max-retr parameter is optional. If the max- be retransmitted. The max-retr parameter is optional. If the max-
retr parameter is not present, then the maximal number of retr parameter is not present, then the maximal number of
retransmissions is determined as per the generic SCTP retransmission retransmissions is determined as per the generic SCTP retransmission
rules as specified in [RFC4960]. This parameter maps to the 'Number rules as specified in [RFC4960]. This parameter maps to the 'Number
of RTX' parameter defined in [I-D.ietf-rtcweb-data-protocol]. of RTX' parameter defined in [I-D.ietf-rtcweb-data-protocol].
5.1.1.5. max-time parameter 5.1.1.6. 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 messages will no longer be transmitted or retransmitted after A user message will no longer be transmitted or retransmitted after a
a specified life-time given in milliseconds in the 'max-time' specified life-time given in milliseconds in the 'max-time'
parameter. The max-time parameter is optional. If the max-time parameter. The max-time parameter is optional. If the max-time
parameter is not present, then the generic SCTP retransmission timing parameter is not present, then the generic SCTP retransmission timing
rules apply as specified in [RFC4960]. This parameter maps to the rules apply as specified in [RFC4960]. This parameter maps to the
'Lifetime in ms' parameter defined in 'Lifetime in ms' parameter defined in
[I-D.ietf-rtcweb-data-protocol]. [I-D.ietf-rtcweb-data-protocol].
5.1.1.6. ordered parameter 5.1.1.7. ordered Parameter
The ordered' parameter indicates that DATA chunks in the channel MUST The 'ordered' parameter with value "true" indicates that DATA chunks
be dispatched to the upper layer by the receiver while preserving the in the channel MUST be dispatched to the upper layer by the receiver
order. The ordered parameter is optional and takes two values: "0" while preserving the order. The ordered parameter is optional and
for ordered and "1" for ordered delivery with "1" as the default takes two values: "true" for ordered and "false" for unordered
value. Any other value is ignored and default ordered is assumed. delivery with "true" as the default value. Any other value is
If the ordered parameter is absent, the receiver is required to ignored and default "ordered=true" is assumed. In the absence of
deliver DATA chunks to the upper layer in proper order. This this parameter "ordered=true" is assumed. This parameter maps to the
parameter maps to the ordered or unorderd data channel types as ordered or unordered data channel types as defined in
defined in [I-D.ietf-rtcweb-data-protocol]. [I-D.ietf-rtcweb-data-protocol].
5.1.2. Sub-protocol specific attributes 5.1.2. Sub-Protocol Specific Attributes
In the SDP, each data channel declaration MAY also be followed by In the SDP, each data channel declaration MAY also be followed by
other SDP attributes specific to the sub-protocol in use. Each of other SDP attributes specific to the sub-protocol in use. Each of
these attributes is represented by one new attribute line, and it these attributes is represented by one new attribute line, and it
includes the contents of a media-level SDP attribute already defined includes the contents of a media-level SDP attribute already defined
for use with this (sub)protocol in another IETF specification. Sub- for use with this (sub)protocol in another IETF specification. Sub-
protocol-specific attributes might also be defined for exclusive use protocol-specific attributes might also be defined for exclusive use
with data channel transport, but should use the same syntax described with data channel transport, but should use the same syntax described
here for other sub-protocol-specific attributes. here for other sub-protocol-specific attributes.
Each sub-protocol specific SDP attribute that would normally be used Each sub-protocol specific SDP attribute that would normally be used
to negotiate the subprotocol using SDP is replaced with an attribute to negotiate the subprotocol using SDP is replaced with an attribute
of the form "a=dcsa: stream-id original-attribute", where dcsa stands of the form "a=dcsa:stream-id original-attribute", where dcsa stands
for "data channel sub-protocol attribute", stream-id is the sctp for "data channel sub-protocol attribute", stream-id is the SCTP
stream identifier assigned to this sub-protocol instance, and stream identifier assigned to this sub-protocol instance, and
original-attribute represents the contents of the sub-protocol original-attribute represents the contents of the sub-protocol
related attribute to be included. related attribute to be included.
Formal Syntax: Formal Syntax:
Name: dcsa Name: dcsa
Value: dcsa-value Value: dcsa-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
Syntax: Syntax:
dcsa-value = stream-id SP attribute dcsa-value = stream-id SP attribute
attribute = <from-RFC4566> attribute = <from-RFC4566>
Examples: Example:
a=dcsa:2 accept-types:text/plain a=dcsa:2 accept-types:text/plain
Thus in the example above, the original attribute line "a=accept- Thus in the example above, the original attribute line "a=accept-
types:text/plain" is represented by the attribute line "a=dcsa:2 types:text/plain" is represented by the attribute line "a=dcsa:2
accept-types:text/plain", which specifies that this instance of MSRP accept-types:text/plain", which specifies that this instance of MSRP
being transported on the sctp association using the data channel with being transported on the sctp association using the data channel with
stream id 2 accepts plain text files. The above example creates a stream id 2 accepts plain text files.
reliable, ordered data channel.
As opposed to the data channel setup parameters, these parameters are As opposed to the data channel "a=dcmap:" attribute parameters, these
subject to offer/answer negotiation following the procedures defined parameters are subject to offer/answer negotiation following the
in the sub-protocol specific documents. procedures defined in the sub-protocol specific documents.
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 sub-protocol. negotiation of this instance of the sub-protocol.
Note: This document does not provide a complete specification of how Note: This document does not provide a complete specification of how
to negotiate the use of a data channel to transport MSRP. Procedures to negotiate the use of a data channel to transport MSRP. Procedures
specific to each sub-protocol such as MSRP will be documented specific to each sub-protocol such as MSRP will be documented
elsewhere. The use of MSRP is only an example of how the generic elsewhere. The use of MSRP is only an example of how the generic
procedures described herein might apply to a specific sub-protocol. procedures described herein might apply to a specific sub-protocol.
5.2. Procedures 5.2. Procedures
5.2.1. Managing stream identifiers 5.2.1. Managing Stream Identifiers
For the SDP-based external negotiation described in this document, If an SDP offer / answer exchange (could be the initial or a
the initial offerer based "SCTP over DTLS" owns by convention the subsequent one) results in a UDP/DTLS/SCTP or TCP/DTLS/SCTP based
even stream identifiers whereas the initial answerer owns the odd media description being accepted, and if this SDP offer / answer
stream identifiers. This ownership is invariant for the whole exchange results in the establishment of a new SCTP association, then
lifetime of the signaling session, e.g. it does not change if the the SDP offerer owns the even SCTP stream ids of this new SCTP
initial answerer sends a new offer to the initial offerer. 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.
This specification allows simultaneous use of external and internal This specification allows simultaneous use of external and internal
negotiation. However, a single stream is managed using one method at negotiation. However, a single stream is managed using one method at
a time. Stream ids that are not currently used in SDP can be used a time. Stream ids that are not currently used in SDP can be used
for internal negotiation. Stream id allocation per SDP based for internal negotiation. Stream id allocation per SDP based
external negotiation may not align with DTLS role based allocation. external negotiation may not align with DTLS role based allocation.
This could cause glare conditions when one side trying to do external This could cause glare conditions when one side trying to do external
negotiation on a stream id while the other end trying to open data negotiation on a stream id while the other end trying to open a data
channel on the same stream id using internal negotiation. To avoid channel on the same stream id using internal negotiation. To avoid
these glare conditions this specification recommends that the data these glare conditions this specification recommends that the data
channel stack user always selects stream ids per SDP offer/answer channel stack user always selects stream ids per above described SDP
rule even when internal negotiation is used. To avoid glare offer / answer rule even when internal negotiation is used. To avoid
conditions, it is possible to come up with a different stream id glare conditions, it is possible to come up with a different stream
allocation scheme, but such schemes are outside the scope of this id allocation scheme, but such schemes are outside the scope of this
specification. specification.
5.2.2. Opening a data channel 5.2.2. Negotiating Data Channel Parameters
Conveying a reliable data channel is achieved by including neither
'max-retr' nor 'max-time' in corresponding SDP offer's or answer's
a=dcmap attribute line. Conveying a partially reliable data channel
is achieved by including only one of 'max-retr' or 'max-time'. By
definition max-retr and max-time are mutually exclusive, so only one
of them can be present in a=dcmap. If an SDP offer contains both of
these parameters then such an SDP offer will be rejected. If an SDP
answer contains both of these parameters then the offerer may treat
it as an error and may assume the associated SDP offer/answer failed
and may take appropriate recovery actions. These recovery options
are outside the scope of this specification.
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.
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.
Data channel types defined in [I-D.ietf-rtcweb-data-protocol] are
mapped to SDP in the following manner:
DATA_CHANNEL_RELIABLE
a=dcmap:2 subprotocol="BFCP";label="channel 2"
DATA_CHANNEL_RELIABLE_UNORDERED
a=dcmap:2 subprotocol="BFCP";label="channel 2";\
ordered=0
DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT
a=dcmap:2 subprotocol="BFCP";label="channel 2";\
max-retr=3
DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED
a=dcmap:2 subprotocol="BFCP";label="channel 2";\
max-retr=3;ordered=0;
DATA_CHANNEL_PARTIAL_RELIABLE_TIMED
a=dcmap:2 subprotocol="BFCP";label="channel 2";\
max-time=10000;
DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED
a=dcmap:2 subprotocol="BFCP";label="channel 2";\
max-time=10000; ordered=0
5.2.3. Opening a Data Channel
The procedure for opening a data channel using external negotiation The procedure for opening a data channel using external negotiation
starts with the agent preparing to send an SDP offer. If a peer starts with the agent preparing to send an SDP offer. If a peer
receives an SDP offer before getting to send a new SDP offer with receives an SDP offer before getting to send a new SDP offer with
data channels that are to be externally negotiated, or loses an SDP data channels that are to be externally negotiated, or loses an SDP
offer glare resolution procedure in this case, it must wait until the offer glare resolution procedure in this case, it must wait until the
ongoing SDP offer/answer completes before resuming the external ongoing SDP offer/answer completes before resuming the external
negotiation procedure. negotiation procedure.
The agent that intends to send an SDP offer to create data channels The agent that intends to send an SDP offer to create data channels
skipping to change at page 14, line 23 skipping to change at page 15, line 10
o Generates a new SDP offer. In the case of the browser based o Generates a new SDP offer. In the case of the browser based
applications the browser generates the offer via the createOffer() applications the browser generates the offer via the createOffer()
API call [I-D.ietf-rtcweb-jsep]. API call [I-D.ietf-rtcweb-jsep].
o Determines the list of stream identifiers assigned to data o Determines the list of stream identifiers assigned to data
channels opened through external negotiation. channels opened through external negotiation.
o Completes the SDP offer with the dcmap and dcsa attributes needed, o Completes the SDP offer with the dcmap and dcsa attributes needed,
if any, for each externally-negotiated data channel, as described if any, for each externally-negotiated data channel, as described
in Section 5.1. in Section 5.1 and in Section 5.2.2.
o Sends the SDP offer. o Sends the SDP offer.
The peer receiving such an SDP offer performs the following: The peer receiving such an SDP offer performs the following:
o Applies the SDP offer. Note that the browser ignores data channel o Parses and applies the SDP offer. Note that the typical parser
specific attributes in the SDP. normally ignores unknown SDP attributes, which includes data
channel related attributes.
o Analyzes the channel parameters and sub-protocol attributes to o Analyzes the channel parameters and sub-protocol attributes to
determine whether to accept each offered data channel. determine whether to accept each offered data channel.
o For accepted data channels, creates peer instances for the data o For accepted data channels, it creates peer instances for the data
channels with the browser using the channel parameters described channels with the agent using the channel parameters described in
in the SDP offer. Note that the browser is asked to create data the SDP offer. Note that the agent is asked to create data
channels with stream identifiers not "owned" by the agent. channels with SCTP stream identifiers contained in the SDP offer
if the SDP offer is accepted.
o As described in Section 4.2.2, if the SCTP association is not yet o As described in Section 4.2.2, if the SCTP association is not yet
established, then the newly created data channels are in the established, then the newly created data channels are in the
Connecting state, else if the SCTP association is already Connecting state, else if the SCTP association is already
established, then the newly created data channels are in the Open established, then the newly created data channels are in the Open
state. state.
o Generates an SDP answer. o Generates an SDP answer.
o Completes the SDP answer with the dcmap and optional dcsa o Completes the SDP answer with the dcmap and optional dcsa
attributes needed for each externally-negotiated data channel, as attributes needed for each externally-negotiated data channel, as
described in Section 5.1. described in Section 5.1 and in Section 5.2.2.
o Sends the SDP answer. o Sends the SDP answer.
The agent receiving such an SDP answer performs the following: The agent receiving such an SDP answer performs the following:
o Closes any created data channels (whether in Connecting or Open o Closes any created data channels (whether in Connecting or Open
state) for which the expected dcmap and dcsa attributes are not state) for which the expected dcmap and dcsa attributes are not
present in the SDP answer. present in the SDP answer.
o Applies the SDP answer. o Applies the SDP answer.
Any data channels in Connecting state are transitioned to the Open Any data channels in Connecting state are transitioned to the Open
state when the SCTP association is established. state when the SCTP association is established.
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 in the Open state. confirmation that the data channel at the peer is in the Open state.
For webrtc, this is when both data channel stacks have channel For WebRTC, this is when both data channel stacks have channel
parameters instantiated. This occurs: parameters instantiated. This occurs:
o At both peers when a data channel is created without an o At both peers when a data channel is created without an
established SCTP association, as soon as the data channel stacks established SCTP association, as soon as the data channel stacks
report that the data channel transitions to the Open state from report that the data channel transitions to the Open state from
the Connecting state. the Connecting state.
o At the agent receiving an SDP offer for which there is an o At the agent receiving an SDP offer for which there is an
established SCTP association, as soon as it creates an externally established SCTP association, as soon as it creates an externally
negotiated data channel in the Open state based on information negotiated data channel in the Open state based on information
signaled in the SDP offer. signaled in the SDP offer.
o At the agent sending an SDP offer to create a new externally o At the agent sending an SDP offer to create a new externally
negotiated data channel for which there is an established SCTP negotiated data channel for which there is an established SCTP
association, when it receives the SDP answer confirming acceptance association, when it receives the SDP answer confirming acceptance
of the data channel or when it begins to receive data on the data of the data channel or when it begins to receive data on the data
channel from the peer, whichever occurs first. channel from the peer, whichever occurs first.
5.2.3. Closing a data channel 5.2.4. Closing a Data Channel
When the application requests the closing of a data channel that was When the application requests the closing of a data channel that was
externally negotiated, the data channel stack always performs an in- externally negotiated, the data channel stack always performs an in-
band SSN reset for this channel. band SSN reset for this channel.
It is specific to the sub-protocol whether this closing must in It is specific to the sub-protocol whether this closing must in
addition be signaled to the peer via a new SDP offer/answer exchange. addition be signaled to the peer via a new SDP offer/answer exchange.
A data channel can be closed by sending a new SDP offer which The intention to close a data channel can be signaled by sending a
excludes the dcmap and dcsa attributes lines for the data channel. new SDP offer which excludes the "a=dcmap:" and "a=dcsa:" attribute
The port value for the m line should not be changed (e.g., to zero) lines for the data channel. The port value for the "m" line SHOULD
when closing a data channel (unless all data channels are being not be changed (e.g., to zero) when closing a data channel (unless
closed and the SCTP association is no longer needed), since this all data channels are being closed and the SCTP association is no
would close the SCTP association and impact all of the data channels. longer needed), since this would close the SCTP association and
If answerer accepts the SDP offer then it MUST also exclude the impact all of the data channels. If the answerer accepts the SDP
corresponding attribute lines in the answer. In addition to that, offer then it MUST close those data channels whose "a=dcmap:" and
SDP answerer may exclude other data channels which were closed but "a=dcsa:" attribute lines were excluded from the received SDP offer,
not yet communicated to the peer. So, offerer MUST inspect the unless those data channels were already closed, and it MUST also
answer to see if it has to close other data channels which are now exclude the corresponding attribute lines in the answer. In addition
not included in the answer to that, the SDP answerer MAY exclude other data channels which were
closed but not yet communicated to the peer. So, the offerer MUST
inspect the answer to see if it has to close other data channels
which are now not included in the answer.
If a new SDP offer/answer is used to close data channels then the If a new SDP offer/answer is used to close data channels then the
data channel(s) should only be closed by the answerer/offerer after data channel(s) SHOULD only be closed by the answerer/offerer after a
successful SDP answer is sent/received. successful SDP answer is sent/received.
This delayed close is to handle cases where a successful SDP This delayed closure is RECOMMENDED in order to handle cases where
answer is not received, in which case the state of session should a successful SDP answer is not received, in which case the state
be kept per the last successful SDP offer/answer. of the session SHOULD be kept per the last successful SDP offer/
answer.
If a client receives a data channel close indication (due to inband If a client receives a data channel close indication (due to inband
SSN reset or some other reason) without associated SDP offer then an SSN reset or some other reason) without associated SDP offer then an
SDP offer which excludes this closed data channel SHOULD be SDP offer which excludes this closed data channel SHOULD be
generated. generated.
The application must also close any data channel that was externally The application must also close any data channel that was externally
negotiated, for which the stream identifiers are not listed in an negotiated, for which the stream identifiers are not listed in an
incoming SDP offer. incoming SDP offer.
A closed data channel using local close (SCTP reset), without an A closed data channel using local close (SCTP reset), without an
additional SDP offer/answer to close it, may be reused for a new data additional SDP offer/answer to close it, may be reused for a new data
channel. This can only be done via new SDP offer/answer, describing channel. This can only be done via new SDP offer/answer, describing
the new sub-protocol and its attributes, only after the corresponding the new sub-protocol and its attributes, only after the corresponding
data channel close acknowledgement is received from the peer (i.e. data channel close acknowledgement is received from the peer (i.e.
SCTP reset of both incoming and outgoing streams is completed). This SCTP reset of both incoming and outgoing streams is completed). This
restriction is to avoid the race conditions between arrival of "SDP restriction is to avoid the race conditions between arrival of "SDP
offer which reuses stream" with "SCTP reset which closes outgoing offer which reuses stream" with "SCTP reset which closes outgoing
stream" at the peer stream" at the peer
5.2.4. Various SDP offer/answer scenarios and considerations 5.2.5. Various SDP Offer/Answer Scenarios and Considerations
SDP offer has no a=dcmap attributes SDP offer has no a=dcmap attributes
* Initial SDP offer: No data channel negotiated yet. * Initial SDP offer: No data channel negotiated yet.
* Subsequent SDP offer: All the externally negotiated data * Subsequent SDP offer: All the externally negotiated data
channels must be closed now. The DTLS/SCTP association remains channels must be closed now. The DTLS/SCTP association remains
open for external or internal negotiation of data channels. open for external or internal negotiation of data channels.
SDP answer has no a=dcmap attributes SDP answer has no a=dcmap attributes
skipping to change at page 18, line 5 skipping to change at page 18, line 48
a=connection:new a=connection:new
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
Figure 1: Example 1 Figure 1: Example 1
In the above example the SDP answerer rejected the data channel with In the above example the SDP answerer rejected the data channel with
stream id 0 either for explicit reasons or because it does not stream id 0 either for explicit reasons or because it does not
understand the a=dcmap attribute. As a result the offerer will close understand the a=dcmap attribute. As a result the offerer will close
the data channel created with the external negotiation option. The the data channel created with the external negotiation option. The
SCTP association will still be setup over DTLS. At this point SCTP association will still be setup over DTLS. At this point the
offerer or answerer may use internal negotiation to open data offerer or the answerer may use internal negotiation to open data
channels. channels.
SDP offer: SDP offer:
m=application 10001 UDP/DTLS/SCTP webrtc-datachannel m=application 10001 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 10.10.10.1 c=IN IP4 10.10.10.1
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=connection:new a=connection:new
a=fingerprint:SHA-1 \ a=fingerprint:SHA-1 \
skipping to change at page 20, line 9 skipping to change at page 21, line 9
8. IANA Considerations 8. IANA Considerations
To be completed. As [I-D.ietf-rtcweb-data-protocol] this document To be completed. As [I-D.ietf-rtcweb-data-protocol] this document
should refer to IANA's WebSocket Subprotocol Name Registry defined in should refer to IANA's WebSocket Subprotocol Name Registry defined in
[RFC6455]. [RFC6455].
9. Acknowledgments 9. Acknowledgments
The authors wish to acknowledge the borrowing of ideas from other The authors wish to acknowledge the borrowing of ideas from other
internet drafts by Salvatore Loreto, Gonzalo Camarillo, Peter Dunkley internet drafts by Salvatore Loreto, Gonzalo Camarillo, Peter Dunkley
and Gavin Llewellyn, and to thank Paul Kyzivat, Jonathan Lennox, and Gavin Llewellyn, and to thank Christian Groves, Christer
Christian Groves and Uwe Rauschenbach for their invaluable comments. Holmberg, Paul Kyzivat, Jonathan Lennox, and Uwe Rauschenbach for
their invaluable comments.
10. CHANGE LOG 10. CHANGE LOG
10.1. Changes against 'draft-ejzak-mmusic-data-channel-sdpneg-02' 10.1. 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 4 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 5.1.1 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 5.1.1.1. 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 sub-protocol 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 sub-protocol."
o In Section 5.1.1 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 5.1.1.1: "dcmap is a media level attribute having
following ABNF syntax:"
o Insertion of new Section 5.1.1.2 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 5.1.1.1 modification of the 'ordering-value' values
from "0" or "1" to "true" or "false". Corresponding text
modifications in Section 5.1.1.7.
o In Section 5.1.1.1 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 5.1.1.1 regarding the non-printable
"escaped-char" character within the "label" value.
o In Section 5.1.2's second paragraph replacement of "sctp stream
identifier" with "SCTP stream identifier".
o In first paragraph of Section 5.2.1 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 5.2.3 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 5.2.3 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 5.2.4 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 5.2.4 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 5.1.1 contained already procedural descriptions related to
data channel reliability negotiation. Creation of new
Section 5.2.2 and moval of reliability negotiation related text to
this new section.
10.2. Changes against 'draft-ejzak-mmusic-data-channel-sdpneg-02'
o Removal of note "[ACTION ITEM]" from section "subprotocol o Removal of note "[ACTION ITEM]" from section "subprotocol
parameter". As [I-D.ietf-rtcweb-data-protocol] this document parameter". As [I-D.ietf-rtcweb-data-protocol] this document
should refer to IANA's WebSocket Subprotocol Name Registry defined should refer to IANA's WebSocket Subprotocol Name Registry defined
in [RFC6455]. in [RFC6455].
o In whole document, replacement of "unreliable" with "partially o In whole document, replacement of "unreliable" with "partially
reliable", which is used in [I-D.ietf-rtcweb-data-channel] and in reliable", which is used in [I-D.ietf-rtcweb-data-channel] and in
[I-D.ietf-rtcweb-data-protocol] in most places. [I-D.ietf-rtcweb-data-protocol] in most places.
skipping to change at page 21, line 11 skipping to change at page 24, line 50
o In section "subprotocol parameter" the sentence "Subprotocol is a o In section "subprotocol parameter" the sentence "Subprotocol is a
mandatory parameter." was replaced with "'Subprotocol' is an mandatory parameter." was replaced with "'Subprotocol' is an
optional parameter. If the 'subprotocol' parameter is not optional parameter. If the 'subprotocol' parameter is not
present, then its value defaults to the empty string." present, then its value defaults to the empty string."
o In the "Examples" section, in the first two SDP offer examples in o In the "Examples" section, in the first two SDP offer examples in
the a=dcmap attribute lines 'label="BGCP"' was replaced with the a=dcmap attribute lines 'label="BGCP"' was replaced with
'label="BFCP"'. 'label="BFCP"'.
o In all examples, the m-line proto value "DTLS/SCTP" was replaced o In all examples, the "m" line proto value "DTLS/SCTP" was replaced
with "UDP/DTLS/SCTP" and the "a=fmtp" attribute lines were with "UDP/DTLS/SCTP" and the "a=fmtp" attribute lines were
replaced with "a=max-message-size" attribute lines, as per draft- replaced with "a=max-message-size" attribute lines, as per draft-
ietf-mmusic-sctp-sdp-12. ietf-mmusic-sctp-sdp-12.
10.2. Changes against '-01' 10.3. Changes against '-01'
o Formal syntax for dcmap and dcsa attribute lines. o Formal syntax for dcmap and dcsa attribute lines.
o Making subprotocol as an optional parameter in dcmap. o Making subprotocol as an optional parameter in dcmap.
o Specifying disallowed parameter combinations for max-time and max- o Specifying disallowed parameter combinations for max-time and max-
retr. retr.
o Clarifications on data channel close procedures. o Clarifications on WebRTC data channel close procedures.
10.3. Changes against '-00' 10.4. Changes against '-00'
o Revisions to identify difference between internal and external o Revisions to identify difference between internal and external
negotiation and their usage. negotiation and their usage.
o Introduction of more generic terminology, e.g. "application" o Introduction of more generic terminology, e.g. "application"
instead of "browser". instead of "browser".
o Clarification of how "max-retr and max-time affect the usage of o Clarification of how "max-retr and max-time affect the usage of
unreliable and reliable data channels. unreliable and reliable WebRTC data channels.
o Updates of examples to take into account the SDP syntax changes o Updates of examples to take into account the SDP syntax changes
introduced with draft-ietf-mmusic-sctp-sdp-07. introduced with draft-ietf-mmusic-sctp-sdp-07.
o Removal of the SCTP port number from the a=dcmap and a=dcsa 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, attributes as this is now contained in the a=sctp-port attribute,
and as draft-ietf-mmusic-sctp-sdp-07 supports only one SCTP and as draft-ietf-mmusic-sctp-sdp-07 supports only one SCTP
association on top of the DTLS connection. association on top of the DTLS connection.
11. References 11. References
skipping to change at page 22, line 33 skipping to change at page 26, line 22
[I-D.ietf-rtcweb-data-channel] [I-D.ietf-rtcweb-data-channel]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data
Channels", draft-ietf-rtcweb-data-channel-13 (work in Channels", draft-ietf-rtcweb-data-channel-13 (work in
progress), January 2015. progress), January 2015.
[I-D.ietf-mmusic-sctp-sdp] [I-D.ietf-mmusic-sctp-sdp]
Holmberg, C., Loreto, S., and G. Camarillo, "Stream Holmberg, C., Loreto, S., and G. Camarillo, "Stream
Control Transmission Protocol (SCTP)-Based Media Transport Control Transmission Protocol (SCTP)-Based Media Transport
in the Session Description Protocol (SDP)", draft-ietf- in the Session Description Protocol (SDP)", draft-ietf-
mmusic-sctp-sdp-12 (work in progress), January 2015. mmusic-sctp-sdp-14 (work in progress), March 2015.
[WebRtcAPI] [WebRtcAPI]
Bergkvist, A., Burnett, D., Jennings, C., and A. Bergkvist, A., Burnett, D., Jennings, C., and A.
Narayanan, "WebRTC 1.0: Real-time Communication Between Narayanan, "WebRTC 1.0: Real-time Communication Between
Browsers", World Wide Web Consortium WD-webrtc-20130910, Browsers", World Wide Web Consortium WD-webrtc-20130910,
September 2013, September 2013,
<http://www.w3.org/TR/2013/WD-webrtc-20130910/>. <http://www.w3.org/TR/2013/WD-webrtc-20130910/>.
11.2. Informative References 11.2. Informative References
skipping to change at page 23, line 38 skipping to change at page 27, line 26
Authors' Addresses Authors' Addresses
Keith Drage (editor) Keith Drage (editor)
Alcatel-Lucent Alcatel-Lucent
Quadrant, Stonehill Green, Westlea Quadrant, Stonehill Green, Westlea
Swindon Swindon
UK UK
Email: keith.drage@alcatel-lucent.com Email: keith.drage@alcatel-lucent.com
Raju Makaraju Maridi R. Makaraju (Raju)
Alcatel-Lucent Alcatel-Lucent
2000 Lucent Lane 2000 Lucent Lane
Naperville, Illinois Naperville, Illinois
US US
Email: Raju.Makaraju@alcatel-lucent.com Email: Raju.Makaraju@alcatel-lucent.com
Juergen Stoetzer-Bradler Juergen Stoetzer-Bradler
Alcatel-Lucent Alcatel-Lucent
Lorenzstrasse 10 Lorenzstrasse 10
D-70435 Stuttgart D-70435 Stuttgart
Germany Germany
Email: Juergen.Stoetzer-Bradler@alcatel-lucent.com Email: Juergen.Stoetzer-Bradler@alcatel-lucent.com
Richard Ejzak Richard Ejzak
Unaffiliated Unaffiliated
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