draft-ietf-mmusic-data-channel-sdpneg-03.txt   draft-ietf-mmusic-data-channel-sdpneg-04.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: January 22, 2016 Alcatel-Lucent Expires: February 5, 2016 Alcatel-Lucent
R. Ejzak R. Ejzak
J. Marcon J. Marcon
Unaffiliated Unaffiliated
July 21, 2015 August 4, 2015
SDP-based Data Channel Negotiation SDP-based Data Channel Negotiation
draft-ietf-mmusic-data-channel-sdpneg-03 draft-ietf-mmusic-data-channel-sdpneg-04
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
skipping to change at page 1, line 47 skipping to change at page 1, line 47
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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 January 22, 2016. This Internet-Draft will expire on February 5, 2016.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Applicability Statement . . . . . . . . . . . . . . . . . . . 4 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 5
5. Data Channels . . . . . . . . . . . . . . . . . . . . . . . . 5 5. SDP Offer/Answer Negotiation . . . . . . . . . . . . . . . . 5
5.1. Stream Identifier Numbering . . . . . . . . . . . . . . . 5 5.1. SDP Syntax . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Generic Non-DCEP Negotiation . . . . . . . . . . . . . . 6 5.1.1. SDP Attribute for Data Channel Parameter Negotiation 5
5.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 6 5.1.1.1. dcmap Attribute . . . . . . . . . . . . . . . . . 5
5.2.2. Opening a Data Channel . . . . . . . . . . . . . . . 6 5.1.1.2. dcmap-stream-id Parameter . . . . . . . . . . . . 7
5.2.3. Closing a Data Channel . . . . . . . . . . . . . . . 8 5.1.1.3. label Parameter . . . . . . . . . . . . . . . . . 7
6. SDP Offer/Answer Negotiation . . . . . . . . . . . . . . . . 8 5.1.1.4. subprotocol Parameter . . . . . . . . . . . . . . 7
6.1. SDP Syntax . . . . . . . . . . . . . . . . . . . . . . . 9 5.1.1.5. max-retr Parameter . . . . . . . . . . . . . . . 7
6.1.1. SDP Attribute for Data Channel Parameter Negotiation 9 5.1.1.6. max-time Parameter . . . . . . . . . . . . . . . 8
6.1.1.1. dcmap Attribute . . . . . . . . . . . . . . . . . 9 5.1.1.7. ordered Parameter . . . . . . . . . . . . . . . . 8
6.1.1.2. dcmap-stream-id Parameter . . . . . . . . . . . . 11 5.1.2. Sub-Protocol Specific Attributes . . . . . . . . . . 8
6.1.1.3. label Parameter . . . . . . . . . . . . . . . . . 11 5.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . 10
6.1.1.4. subprotocol Parameter . . . . . . . . . . . . . . 11 5.2.1. Managing Stream Identifiers . . . . . . . . . . . . . 10
6.1.1.5. max-retr Parameter . . . . . . . . . . . . . . . 11 5.2.2. Negotiating Data Channel Parameters . . . . . . . . . 10
6.1.1.6. max-time Parameter . . . . . . . . . . . . . . . 12 5.2.3. Opening a Data Channel . . . . . . . . . . . . . . . 11
6.1.1.7. ordered Parameter . . . . . . . . . . . . . . . . 12 5.2.4. Closing a Data Channel . . . . . . . . . . . . . . . 13
6.1.2. Sub-Protocol Specific Attributes . . . . . . . . . . 12 5.2.5. Various SDP Offer/Answer Scenarios and Considerations 14
6.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . 14 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.2.1. Managing Stream Identifiers . . . . . . . . . . . . . 14 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6.2.2. Negotiating Data Channel Parameters . . . . . . . . . 14 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
6.2.3. Opening a Data Channel . . . . . . . . . . . . . . . 15 8.1. Subprotocol Identifiers . . . . . . . . . . . . . . . . . 17
6.2.4. Closing a Data Channel . . . . . . . . . . . . . . . 17 8.2. New SDP Attributes . . . . . . . . . . . . . . . . . . . 18
6.2.5. Various SDP Offer/Answer Scenarios and Considerations 18 8.2.1. dcmap . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 19 8.2.2. dcsa . . . . . . . . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 10. CHANGE LOG . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1. Subprotocol Identifiers . . . . . . . . . . . . . . . . . 21 10.1. Changes against 'draft-ietf-mmusic-data-channel-
9.2. New SDP Attributes . . . . . . . . . . . . . . . . . . . 22 sdpneg-03' . . . . . . . . . . . . . . . . . . . . . . . 18
9.2.1. dcmap . . . . . . . . . . . . . . . . . . . . . . . . 22 10.2. Changes against 'draft-ietf-mmusic-data-channel-
9.2.2. dcsa . . . . . . . . . . . . . . . . . . . . . . . . 22 sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 19
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22 10.3. Changes against 'draft-ietf-mmusic-data-channel-
11. CHANGE LOG . . . . . . . . . . . . . . . . . . . . . . . . . 22 sdpneg-01' . . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Changes against 'draft-ietf-mmusic-data-channel- 10.4. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 22 sdpneg-00' . . . . . . . . . . . . . . . . . . . . . . . 23
11.2. Changes against 'draft-ietf-mmusic-data-channel- 10.5. Changes against 'draft-ejzak-mmusic-data-channel-
sdpneg-01' . . . . . . . . . . . . . . . . . . . . . . . 23 sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 25
11.3. Changes against 'draft-ietf-mmusic-data-channel- 10.6. Changes against '-01' . . . . . . . . . . . . . . . . . 26
sdpneg-00' . . . . . . . . . . . . . . . . . . . . . . . 25 10.7. Changes against '-00' . . . . . . . . . . . . . . . . . 27
11.4. Changes against 'draft-ejzak-mmusic-data-channel- 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 28 11.1. Normative References . . . . . . . . . . . . . . . . . . 27
11.5. Changes against '-01' . . . . . . . . . . . . . . . . . 29 11.2. Informative References . . . . . . . . . . . . . . . . . 28
11.6. Changes against '-00' . . . . . . . . . . . . . . . . . 29 Appendix A. Generic Data Channel Negotiation Aspects When Not
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 Using DCEP . . . . . . . . . . . . . . . . . . . . . 29
12.1. Normative References . . . . . . . . . . . . . . . . . . 30 A.1. Stream Identifier Numbering . . . . . . . . . . . . . . . 30
12.2. Informative References . . . . . . . . . . . . . . . . . 31 A.2. Generic Data Channel Negotiation Not Using DCEP . . . . . 30
A.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 30
A.2.2. Opening a Data Channel . . . . . . . . . . . . . . . 31
A.2.3. Closing a Data Channel . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
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 DCEP or out- other applications to use data channels and its in-band DCEP or other
of-band non-DCEP protocols for creating them. Each data channel in-band or out-of-band protocols for creating them. Each data
consists of paired SCTP streams sharing the same SCTP Stream channel consists of paired SCTP streams sharing the same SCTP Stream
Identifier. Data channels are created by endpoint applications Identifier. Data channels are created by endpoint applications
through the WebRTC API, or other users of data channel like CLUE, and through the WebRTC API, or other users of data channel like CLUE, and
can be used to transport proprietary or well-defined protocols, which can be used to transport proprietary or well-defined protocols, which
in the latter case can be signaled by the data channel "sub-protocol" in the latter case can be signaled by the data channel "sub-protocol"
parameter, conceptually similar to the WebSocket "sub-protocol". parameter, conceptually similar to the WebSocket "sub-protocol".
However, apart from the "sub-protocol" value transmitted to the peer, However, apart from the "sub-protocol" value transmitted to the peer,
RTCWeb leaves it open how endpoint applications can agree on how to RTCWeb leaves it open how endpoint applications can agree on how to
instantiate a given sub-protocol on a data channel, and whether it is instantiate a given sub-protocol on a data channel, and whether it is
signaled in-band using DCEP or out-of-band using a non-DCEP protocol signaled in-band using DCEP or out-of-band using a non-DCEP protocol
(or both). In particular, the SDP offer generated by the application (or both). In particular, the SDP offer generated by the RTCweb data
includes no channel-specific information. channel stack includes no channel-specific information.
This document defines SDP offer/answer negotiation procedures to This document defines SDP offer/answer negotiation procedures to
establish data channels for transport of well-defined sub-protocols, establish data channels for transport of well-defined sub-protocols,
to enable out-of-band negotiation. to enable out-of-band negotiation.
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].
skipping to change at page 5, line 5 skipping to change at page 5, line 12
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 specification only applies to the Session The mechanism in this specification only applies to the Session
Description Protocol (SDP) [RFC4566], when used together with the SDP Description Protocol (SDP) [RFC4566], when used together with the SDP
offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of
scope of this document, and is thus undefined. scope of this document, and is thus undefined.
5. Data Channels 5. SDP Offer/Answer Negotiation
This section summarizes how data channels work in general.
A WebRTC application creates a data channel by providing a number of
setup parameters (sub-protocol, label, reliability, order of
delivery, priority). The application also specifies if it wants to
make use of the negotiation using the DCEP
[I-D.ietf-rtcweb-data-protocol], or if the application intends to
negotiate data channels using the SDP offer/answer protocol.
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 SCTP association on top of which data channels will run:
m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 79.97.215.79
a=max-message-size:100000
a=sctp-port 5000
a=setup:actpass
a=connection:new
a=fingerprint:SHA-1 \
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-
datachannel", and will not use other formats in the "m" line for
other protocols such as t38. [I-D.ietf-mmusic-sctp-sdp] supports
only one SCTP association to be established on top of a DTLS session.
Note: This SDP syntax does not contain any channel-specific
information.
5.1. Stream Identifier Numbering
[Editor's note: This entire Section 5.1 could possibly be removed as
there is another section (Section 6.2.1) which is dedicated to SCTP
stream id usage.]
Independently from the requested type of negotiation, the application
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
one identifier from the ones unused.
To avoid glare situations, each endpoint can moreover own an
exclusive set of stream identifiers, in which case an endpoint can
only create a data channel with a stream identifier it owns.
Which set of stream identifiers is owned by which endpoint is
determined by convention or other means.
For data channels negotiated with the DCEP, one endpoint owns by
convention the even stream identifiers, whereas the other owns the
odd stream identifiers, as defined in
[I-D.ietf-rtcweb-data-protocol].
For data channels negotiated via some non-DCEP protocol, no
convention is defined by default.
5.2. Generic Non-DCEP Negotiation
[Editor's note: As this document now focuses on SDP offer/answer
negotiation only, should this entire Section 5.2 (and all its sub-
sections) be removed? Parts of the information provided in these
sub-sections might be moved to Section 6, Section 6.2.1 and
Section 6.2.3 as indicated below in further editor notes. Another
option might be to move this section and its sub-section to an
informative appendix.]
5.2.1. Overview
DCEP negotiation only provides for negotiation of data channel
transport parameters and does not provide for negotiation of sub-
protocol specific parameters. Non-DCEP negotiation can be defined to
allow negotiation of parameters beyond those handled by DCEP
negotiation, e.g., parameters specific to the sub-protocol
instantiated on a particular data channel. See Section 6.1.2 for an
example of such a parameter.
[Editor's note: The information in the preceding paragraph might be
moved to Section 6.]
The following procedures are common to all methods of non-DCEP
negotiation, whether in-band (communicated using proprietary means on
an already established data channel) or out-of-band (using SDP offer/
answer or some other protocol associated with the signaling channel).
[Editor's note: The preceding paragraph could be deleted.]
5.2.2. Opening a Data Channel
In the case of non-DCEP negotiation, the endpoint application has the
option to fully control the stream identifier assignments. However
these assignments have to coexist with the assignments controlled by
the data channel stack for the DCEP negotiated data channels (if
any). It is the responsibility of the application to ensure
consistent assignment of stream identifiers.
[Editor's note: The information in the preceding paragraph could be
moved to Section 6.2.1.]
When the application requests the creation of a new data channel to
be set up via non-DCEP negotiation, the data channel stack creates
the data channel locally without sending any DATA_CHANNEL_OPEN
message in-band [Editor's note: The information in this first part of
the sentence could be moved to section 6.2.3], and sets the data
channel state to Connecting if the SCTP association is not yet
established, or sets the data channel state to Open if the SCTP
association is already established. The side which starts non-DCEP
negotiation creates a data channel using underlying data channel
stack API and the data channel is put into open state immediately
(assuming ICE, SCTP procedures were already done). [Editor's note:
The API related information could be deleted.] However, the
application can't send data on this data channel until non-DCEP
negotiation is complete with the peer. This is because the peer
needs to be aware and accept the data channel via non-DCEP
negotiation. The peer after accepting the data channel offer can
start sending data immediately. This implies that the offerer may
get data channel sub-protocol messages before non-DCEP negotiation is
complete and the application should be ready to handle it. [Editor's
note: The information in these last four sentences could be moved to
Section 6.2.3.]
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
the stack. The offerer on the other hand needs to close the data
channel that was opened by invoking relevant data channel stack API
procedures.
[Editor's note: The information in the preceding paragraph could be
moved to Section 6.2.3 (to a new bullet point there).]
It is also worth noting that a data channel stack implementation may
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
non-DCEP means or by even having some local configuration/assumptions
on both the peers.
[Editor's note: The preceding paragraph could be deleted.]
The application then negotiates the data channel properties and sub-
protocol properties with the peer's application using a mechanism
different from DCEP.
[Editor's note: The preceding paragraph could be deleted.]
[ASSUMPTION] The peer MUST then symmetrically create a data channel
with these negotiated data channel properties. This is the only way
for the peer's data channel stack to know which properties to apply
when transmitting data on this channel. [Editor's note: The previous
sentence could be deleted.] The data channel stack MUST allow data
channel creation with any non-conflicting stream identifier so that
both peers can create the data channel with the same stream
identifier. [Editor's note: The information in this sentence could
be moved to Section 6.2.3.]
In case the non-DCEP negotiation is correlated with an SDP offer/
answer exchange that establishes the SCTP association, the SCTP
initialization completion triggers a callback from 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
specific to the data channel user application. Browser based
applications (could include hybrid apps) will use [WebRtcAPI], while
native applications use a compatible API, which is yet to be
specified. See Section 6.2.3 for details on when the data channel
stack can assume the data channel is open, and on when the
application can assume the data channel is open.
[Editor's note: The preceding paragraph could be deleted.]
5.2.3. Closing a Data Channel
When the application requests the closing of a non-DCEP negotiated
data channel, the data channel stack always performs an SCTP SSN
reset for this channel.
[Editor's note: The preceding paragraph could be deleted.]
Depending upon the method used for non-DCEP negotiation and the sub-
protocol associated with the data channel, the closing might in
addition be signaled to the peer via non-DCEP negotiation.
[Editor's note: The preceding paragraph could be deleted.]
6. SDP Offer/Answer Negotiation This section defines an SDP extension by which two clients can
negotiate data channel-specific and sub-protocol-specific parameters
without using DCEP [I-D.ietf-rtcweb-data-protocol]. This SDP
extension only defines usage in the context of SDP offer/answer.
This section defines a method of non-DCEP negotiation by which two Appendix A provides information how data channels work in general and
clients can negotiate data channel-specific and sub-protocol-specific especially summarizes some key aspects, which should be considered
parameters, using the out-of-band SDP offer/answer exchange. This for the negotiation of data channels if DCEP is not used.
SDP extension can only be used with the SDP offer/answer model.
6.1. SDP Syntax 5.1. SDP Syntax
Two new SDP attributes are defined to support SDP offer/answer Two new SDP attributes are defined to support SDP offer/answer
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 negotiation of channel-specific parameters. The second attribute
provides for negotiation of sub-protocol-specific parameters. provides for negotiation of sub-protocol-specific parameters.
6.1.1. 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 one "a=dcmap:" attribute that defines the data channel includes one "a=dcmap:" attribute that defines the data channel
parameters for each data channel to be negotiated. Each such parameters for each data channel to be negotiated. Each such
attribute line specifies the following parameters for a data channel: attribute line specifies the following parameters for a data channel:
SCTP stream identifier, sub-protocol, label, reliability, order of SCTP stream identifier, sub-protocol, label, reliability, order of
delivery, and priority. delivery, and priority.
The intention of exchanging these attributes is to create data The intention in exchanging these attributes is to create, on two
channels on both the peers with the same set of attributes without peers, without use of DCEP [I-D.ietf-rtcweb-data-protocol], matched
actually using the DCEP [I-D.ietf-rtcweb-data-protocol]. It is pairs of oppositely directed data channels having the same set of
assumed that the data channel properties (reliable/partially attributes. It is assumed that the data channel properties
reliable, ordered/unordered) are suitable per the sub-protocol (reliable/partially reliable, ordered/unordered) are suitable per the
transport requirements. sub-protocol transport requirements.
6.1.1.1. dcmap Attribute 5.1.1.1. dcmap Attribute
"a=dcmap:" is a media level attribute having following ABNF syntax. "a=dcmap:" is a media level attribute having following ABNF syntax.
Formal Syntax: Formal Syntax:
Name: dcmap Name: dcmap
Value: dcmap-value Value: dcmap-value
Usage Level: media Usage Level: media
skipping to change at page 11, line 12 skipping to change at page 7, line 12
a=dcmap:3 label="Label 1";ordered=false;max-retr=5 a=dcmap:3 label="Label 1";ordered=false;max-retr=5
a=dcmap:4 label="foo%09bar";ordered=true;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 Note: The last example (a=dcmap:4) shows a 'label' parameter value
which contains one non-printable 'escaped-char' character (the which contains one non-printable 'escaped-char' character (the
tabulator character). tabulator character).
Within an 'a=dcmap' attribute line's 'dcmap-opt' value either only Within an 'a=dcmap' attribute line's 'dcmap-opt' value either only
one 'maxretr-opt' parameter or one 'maxtime-opt' parameter MAY be one 'maxretr-opt' parameter or one 'maxtime-opt' parameter MAY be
present. Both MUST NOT be present. present. Both MUST NOT be present.
6.1.1.2. dcmap-stream-id Parameter 5.1.1.2. 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.
6.1.1.3. label Parameter 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 [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 [I-D.ietf-rtcweb-data-protocol]. The 'label' parameter is
optional. If it is not present, then its value defaults to the empty optional. If it is not present, then its value defaults to the empty
string. 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.
6.1.1.4. 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.
6.1.1.5. 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 maximal number a user message The 'max-retr' parameter indicates the maximal number of times a user
will be retransmitted. The max-retr parameter is optional. If the message will be retransmitted. The max-retr parameter is optional.
max-retr parameter is not present, then the maximal number of If the max-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].
6.1.1.6. 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 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 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].
6.1.1.7. ordered Parameter 5.1.1.7. ordered Parameter
The 'ordered' parameter with value "true" indicates that the receiver The 'ordered' parameter with value "true" indicates that the receiver
MUST dispatch DATA chunks in the data channel to the upper layer MUST 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 and "false" for unordered
delivery with "true" as the default value. Any other value is delivery with "true" as the default value. Any other value is
ignored and default "ordered=true" is assumed. In the absence of ignored and default "ordered=true" is assumed. In the absence of
this parameter "ordered=true" is assumed. This parameter maps to the this parameter "ordered=true" is assumed. This parameter maps to the
ordered or unordered data channel types as defined in ordered or unordered data channel types as defined in
[I-D.ietf-rtcweb-data-protocol]. [I-D.ietf-rtcweb-data-protocol].
6.1.2. 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.
skipping to change at page 14, line 5 skipping to change at page 10, line 5
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.
6.2. Procedures 5.2. Procedures
6.2.1. Managing Stream Identifiers 5.2.1. Managing Stream Identifiers
If an SDP offer/answer exchange (could be the initial or a subsequent 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 one) results in a UDP/DTLS/SCTP or TCP/DTLS/SCTP based media
description being accepted, and if this SDP offer/answer exchange description being accepted, and if this SDP offer/answer exchange
results in the establishment of a new SCTP association, then the SDP results in the establishment of a new SCTP association, then the SDP
offerer owns the even SCTP stream ids of this new SCTP association offerer owns the even SCTP stream ids of this new SCTP association
and the answerer owns the odd SCTP stream identifiers. If this "m" and the answerer owns the odd SCTP stream identifiers. If this "m"
line is removed from the signaling session (its port number set to 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/ 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 based "m" line is renegotiated later on, then the even and odd
SCTP stream identifier ownership is redetermined as well as described SCTP stream identifier ownership is redetermined as well as described
above. above.
This specification allows simultaneous use of SDP offer/answer and This specification allows simultaneous use of SDP offer/answer and
DCEP negotiation. However, an SDP offer/answer exchange MUST NOT be DCEP negotiation. However, an SCTP stream MUST NOT be referenced in
initiated if the associated SCTP stream is already negotiated via a dcmap or dcsa attribute of an SDP offer/answer exchange if the
DCEP. Stream ids that are not currently used in SDP can be used for associated SCTP stream has already been negotiated via DCEP. Stream
DCEP negotiation. Stream id allocation per SDP offer/answer ids that are not currently used in SDP can be used for DCEP
negotiation may not align with DTLS role based allocation. This negotiation. Stream id allocation per SDP offer/answer negotiation
could cause glare conditions when one side trying to do SDP offer/ may not align with DTLS role based allocation. This could cause
answer negotiation on a stream id while the other end trying to open glare conditions when one side trying to do SDP offer/answer
a data channel on the same stream id using DCEP negotiation. To negotiation on a stream id while the other end trying to open a data
avoid these glare conditions this specification recommends that the channel on the same stream id using DCEP negotiation. To avoid these
data channel stack user always selects stream ids per above described glare conditions this specification recommends that the data channel
SDP offer/answer rule even when DCEP negotiation is used. To avoid stack user always selects stream ids per above described SDP offer/
glare conditions, it is possible to come up with a different stream answer rule even when DCEP negotiation is used. To avoid glare
id allocation scheme, but such schemes are outside the scope of this conditions, it is possible to come up with a different stream id
allocation scheme, but such schemes are outside the scope of this
specification. specification.
6.2.2. Negotiating Data Channel Parameters 5.2.2. Negotiating Data Channel Parameters
Conveying a reliable data channel is achieved by including neither Conveying a reliable data channel is achieved by including neither
'max-retr' nor 'max-time' in corresponding SDP offer's or answer's 'max-retr' nor 'max-time' in corresponding SDP offer's or answer's
a=dcmap attribute line. Conveying a partially reliable data channel "a=dcmap" attribute line. Conveying a partially reliable data
is achieved by including only one of 'max-retr' or 'max-time'. By channel is achieved by including only one of 'max-retr' or 'max-
definition max-retr and max-time are mutually exclusive, so at most time'. By definition max-retr and max-time are mutually exclusive,
one of them MAY be present in a=dcmap. If an SDP offer contains both so at most one of them MAY be present in the "a=dcmap" attribute
of these parameters then the receiver of such an SDP offer MUST line. If an SDP offer contains both of these parameters then the
reject the SDP offer. If an SDP answer contains both of these receiver of such an SDP offer MUST reject the SDP offer. If an SDP
parameters then the offerer MAY treat it as an error and MAY assume answer contains both of these parameters then the offerer MAY treat
the associated SDP offer/answer failed and MAY take appropriate it as an error and MAY assume the associated SDP offer/answer failed
recovery actions. These recovery options are outside the scope of and MAY take appropriate recovery actions. These recovery options
this specification. are outside the scope of this specification.
The SDP answer SHALL echo the same subprotocol, max-retr, max-time, The SDP answer SHALL echo the same subprotocol, max-retr, max-time,
ordered parameters, if those were present in the offer, and MAY ordered parameters, if those were present in the offer, and MAY
include a label parameter. They MAY appear in any order, which could include a label parameter. They MAY appear in any order, which could
be different from the SDP offer, in the SDP answer. be different from the SDP offer, in the SDP answer.
When sending a subsequent offer or an answer, and for as long as the 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 data channel is still open, the sender MUST replicate the same
information. information.
skipping to change at page 15, line 36 skipping to change at page 11, line 36
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>
6.2.3. Opening a Data Channel 5.2.3. Opening a Data Channel
The procedure for opening a data channel using SDP offer/answer The procedure for opening a data channel using SDP offer/answer
negotiation starts with the agent preparing to send an SDP offer. If negotiation starts with the agent preparing to send an SDP offer. If
a peer receives an SDP offer before starting to send a new SDP offer a peer receives an SDP offer before starting to send a new SDP offer
with data channels that are to be SDP offer/answer negotiated, or with data channels that are to be SDP offer/answer negotiated, or
loses an SDP offer glare resolution procedure in this case, it MUST loses an SDP offer glare resolution procedure in this case, it MUST
wait until the ongoing SDP offer/answer completes before resuming the wait until the ongoing SDP offer/answer completes before resuming the
SDP offer/answer negotiation procedure. SDP offer/answer 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
through SDP offer/answer negotiation performs the following: through SDP offer/answer negotiation performs the following:
o Creates data channels using stream identifiers from the owned set o Creates data channels using stream identifiers from the owned set
(see Section 6.2.1). (see Section 5.2.1).
o Generates a new SDP offer. o Generates a new SDP offer.
o Determines the list of stream identifiers assigned to data o Determines the list of stream identifiers assigned to data
channels opened through SDP offer/answer negotiation. channels opened through SDP offer/answer 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 SDP offer/answer negotiated data channel, as if any, for each SDP offer/answer negotiated data channel, as
described in Section 6.1 and in Section 6.2.2. described 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 Parses and applies the SDP offer. Note that the typical parser o Parses and applies the SDP offer. Note that the typical parser
normally ignores unknown SDP attributes, which includes data normally ignores unknown SDP attributes, which includes data
channel related attributes. channel related attributes.
o Analyzes the channel parameters and sub-protocol attributes to o Analyzes the channel parameters and sub-protocol attributes to
skipping to change at page 16, line 33 skipping to change at page 12, line 33
o For accepted data channels, it creates peer instances for the data o For accepted data channels, it creates peer instances for the data
channels with the agent using the channel parameters described in channels with the agent using the channel parameters described in
the SDP offer. Note that the agent is asked to create data the SDP offer. Note that the agent is asked to create data
channels with SCTP stream identifiers contained in the SDP offer channels with SCTP stream identifiers contained in the SDP offer
if the SDP offer is accepted. if the SDP offer is accepted.
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 SDP offer/answer negotiated data attributes needed for each SDP offer/answer negotiated data
channel, as described in Section 6.1 and in Section 6.2.2. channel, as 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 for which the expected dcmap and o Closes any created data channels for which the expected dcmap and
dcsa attributes are not present in the SDP answer. dcsa attributes are not present in the SDP answer.
o Applies the SDP answer. o Applies the SDP answer.
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established SCTP association, as soon as it creates an SDP offer/ established SCTP association, as soon as it creates an SDP offer/
answer negotiated data channel based on information signaled in answer negotiated data channel based on information signaled in
the SDP offer. the SDP offer.
o At the agent sending an SDP offer to create a new SDP offer/answer o At the agent sending an SDP offer to create a new SDP offer/answer
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.
6.2.4. Closing a Data Channel Note: DCEP is not used, that is neither the SDP offerer nor the SDP
answerer send an in-band DCEP DATA_CHANNEL_OPEN message.
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
negotiated via SDP offer/answer, the data channel stack always negotiated via SDP offer/answer, the data channel stack always
performs an SCTP SSN reset for this channel. performs an SCTP 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.
The intention to close a data channel can be signaled by sending a 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 new SDP offer which excludes the "a=dcmap:" and "a=dcsa:" attribute
skipping to change at page 18, line 21 skipping to change at page 14, line 24
A closed data channel using local close (SCTP SSN reset), without an A closed data channel using local close (SCTP SSN 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 SSN reset of both incoming and outgoing streams is completed). SCTP SSN reset of both incoming and outgoing streams is completed).
This restriction is to avoid the race conditions between arrival of This restriction is to avoid the race conditions between arrival of
"SDP offer which reuses stream" with "SCTP SSN reset which closes "SDP offer which reuses stream" with "SCTP SSN reset which closes
outgoing stream" at the peer. outgoing stream" at the peer.
6.2.5. 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 is negotiated yet. The DTLS * Initial SDP offer: No data channel is negotiated yet. The DTLS
connection and SCTP association is negotiated and, if agreed, connection and SCTP association is negotiated and, if agreed,
established as per [I-D.ietf-mmusic-sctp-sdp]. established as per [I-D.ietf-mmusic-sctp-sdp].
* Subsequent SDP offer: All the SDP offer/answer negotiated data * Subsequent SDP offer: All the SDP offer/answer negotiated data
channels are expected be closed now. The DTLS/SCTP association channels are expected be closed now. The DTLS/SCTP association
remains open for SDP offer/answer or DCEP negotiation of data remains open for SDP offer/answer or DCEP negotiation of data
channels. channels.
SDP answer has no a=dcmap attributes SDP answer has no "a=dcmap" attributes
* Initial SDP answer: Either the peer does not support dcmap * Initial SDP answer: Either the peer does not support dcmap
attributes or it rejected all the data channels. In either attributes or it rejected all the data channels. In either
case the offerer closes all the SDP offer/answer negotiated case the offerer closes all the SDP offer/answer negotiated
data channels that were open at the time of initial offer. The data channels that were open at the time of initial offer. The
DTLS connection and SCTP association will still be setup. DTLS connection and SCTP association will still be setup.
* Subsequent SDP answer: All the SDP offer/answer negotiated data * Subsequent SDP answer: All the SDP offer/answer negotiated data
channels are expected be closed now. The DTLS/SCTP association channels are expected be closed now. The DTLS/SCTP association
remains open for future SDP offer/answer or DCEP negotiation of remains open for future SDP offer/answer or DCEP negotiation of
data channels. data channels.
SDP offer has no a=dcsa attributes for a data channel. SDP offer has no "a=dcsa" attributes for a data channel.
* This is allowed and indicates there are no sub-protocol * This is allowed and indicates there are no sub-protocol
parameters to convey. parameters to convey.
SDP answer has no a=dcsa attributes for a data channel. SDP answer has no "a=dcsa" attributes for a data channel.
* This is allowed and indicates there are no sub-protocol * This is allowed and indicates there are no sub-protocol
parameters to convey in the SDP answer. The number of dcsa parameters to convey in the SDP answer. The number of dcsa
attributes in the SDP answer does not have to match the number attributes in the SDP answer does not have to match the number
of dcsa attributes in the SDP offer. of dcsa attributes in the SDP offer.
7. Examples 6. Examples
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 \
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=dcmap:0 subprotocol="BFCP";label="BFCP" a=dcmap:0 subprotocol="BFCP";label="BFCP"
SDP answer: SDP answer:
m=application 10002 UDP/DTLS/SCTP webrtc-datachannel m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 10.10.10.2 c=IN IP4 10.10.10.2
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=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
the data channel created with the SDP offer/answer negotiation close the data channel created with the SDP offer/answer negotiation
option. The SCTP association will still be setup over DTLS. At this option. The SCTP association will still be setup over DTLS. At this
point the offerer or the answerer may use DCEP negotiation to open point the offerer or the answerer may use DCEP negotiation to open
data channels. data 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 \
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=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 text/ a=dcsa:2 accept-types:message/cpim text/plain text/
a=dcsa:2 path:msrp://alice.example.com:10001/2s93i93idj;dc a=dcsa:2 path:msrp://alice.example.com:10001/2s93i93idj;dc
SDP answer: SDP answer:
m=application 10002 UDP/DTLS/SCTP webrtc-datachannel m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 10.10.10.2 c=IN IP4 10.10.10.2
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=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
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
skipping to change at page 21, line 9 skipping to change at page 17, line 9
(after SCTP/DTLS association is setup). The data channel with stream (after SCTP/DTLS association is setup). The data channel with stream
id 0 is free and can be used for future DCEP or SDP offer/answer id 0 is free and can be used for future DCEP or SDP offer/answer
negotiation. negotiation.
Continuing on the earlier example in Figure 1. Continuing on the earlier example in Figure 1.
Subsequent SDP offer: Subsequent 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:existing a=connection:existing
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=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: Subsequent SDP answer:
m=application 10002 UDP/DTLS/SCTP webrtc-datachannel m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 10.10.10.2 c=IN IP4 10.10.10.2
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=connection:existing a=connection:existing
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=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 above example is a continuation of the example in Figure 1. The The above example is a continuation of the example in Figure 1. The
SDP offer now removes the MSRP data channel with stream id 2, but SDP offer now removes the MSRP data channel with stream id 2, but
opens a new MSRP data channel with stream id 4. The answerer accepts opens a new MSRP data channel with stream id 4. The answerer accepts
the entire offer. As a result the offerer closes the earlier the entire offer. As a result the offerer closes the earlier
negotiated MSRP related data channel and both offerer and answerer negotiated MSRP related data channel and both offerer and answerer
may start using new the MSRP related data channel. may start using new the MSRP related data channel.
8. Security Considerations 7. Security Considerations
No security considerations are envisaged beyond those already No security considerations are envisaged beyond those already
documented in [RFC4566]. documented in [RFC4566].
9. IANA Considerations 8. IANA Considerations
9.1. Subprotocol Identifiers 8.1. Subprotocol Identifiers
Registration of new subprotocol identifiers is performed using the Registration of new subprotocol identifiers is performed using the
existing IANA table "WebSocket Subprotocol Name Registry". existing IANA table "WebSocket Subprotocol Name Registry".
The following text should be added following the title of the table. The following text should be added following 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 The following reference should be added to under the heading
reference: "RFC XXXX". reference: "RFC XXXX".
This document assigns no new values to this table. This document assigns no new values to this table.
NOTE to RFC Editor: Please replace "XXXX" with the number of this NOTE to RFC Editor: Please replace "XXXX" with the number of this
RFC. RFC.
9.2. New SDP Attributes 8.2. New SDP Attributes
9.2.1. dcmap 8.2.1. dcmap
[Editor's note: This section still needs to be completed.] [Editor's note: This section still needs to be completed.]
9.2.2. dcsa 8.2.2. dcsa
[Editor's note: This section still needs to be completed.] [Editor's note: This section still needs to be completed.]
10. 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 Roni Even, Christian Groves, and Gavin Llewellyn, and to thank Roni Even, Christian Groves,
Christer Holmberg, Paul Kyzivat, Jonathan Lennox, and Uwe Christer Holmberg, Paul Kyzivat, Jonathan Lennox, and Uwe
Rauschenbach for their invaluable comments. Rauschenbach for their invaluable comments.
11. CHANGE LOG 10. CHANGE LOG
11.1. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-02' 10.1. 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 sub-protocol-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 sub-
protocol-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 5.1.1 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 5.1.1.5 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 5.2.1 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 6 addition of the previously missing
colons to the "a=sctp-port" attribute lines.
10.2. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-02'
o Move of reference [I-D.ietf-rtcweb-jsep] from the list of o Move of reference [I-D.ietf-rtcweb-jsep] from the list of
normative references to the list of informative references. normative references to the list of informative references.
o Addition of [IANA-SDP-Parameters] to the list of informative o Addition of [IANA-SDP-Parameters] to the list of informative
references and addition of following two sentences to the first references and addition of following two sentences to the first
paragraph after the ABNF definition: "Note however that not all paragraph after the ABNF definition: "Note however that not all
SDP attributes are suitable as "a=dcsa:" parameter. SDP attributes are suitable as "a=dcsa:" parameter.
[IANA-SDP-Parameters] contains the lists of IANA registered [IANA-SDP-Parameters] contains the lists of IANA registered
session and media level or media level only SDP attributes." session and media level or media level only SDP attributes."
skipping to change at page 23, line 18 skipping to change at page 20, line 27
"SDP offer/answer negotiation" and removal of term "external "SDP offer/answer negotiation" and removal of term "external
negotiation" from the terminology list in Section 3. negotiation" from the terminology list in Section 3.
o Throughout the document replacement of "internal negotiation" with o Throughout the document replacement of "internal negotiation" with
"DCEP" and removal of terms "internal negotiation" and "in-band "DCEP" and removal of terms "internal negotiation" and "in-band
negotiation" from the terminology list in Section 3. negotiation" from the terminology list in Section 3.
o Addition of "SCTP Stream Sequence Number (SSN)" to the list of o Addition of "SCTP Stream Sequence Number (SSN)" to the list of
terms. terms.
o In Section 6.2.1 replacement of sentence "However, a single stream o In Section 5.2.1 replacement of sentence "However, a single stream
is managed using one method at a time." with "However, an SDP is managed using one method at a time." with "However, an SDP
offer/answer exchange MUST NOT be initiated if the associated SCTP offer/answer exchange MUST NOT be initiated if the associated SCTP
stream is already negotiated via DCEP". stream is already negotiated via DCEP".
o In Section 6.2.2 replacement of sentence "By definition max-retr o In Section 5.2.2 replacement of sentence "By definition max-retr
and max-time are mutually exclusive, so only one of them can be 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 present in a=dcmap" with "By definition max-retr and max-time are
mutually exclusive, so at most one of them MAY be present in mutually exclusive, so at most one of them MAY be present in
a=dcmap". a=dcmap".
o Move of reference [WebRtcAPI] from list of normative references to o Move of reference [WebRtcAPI] from list of normative references to
list of informative references. list of informative references.
o Removal of almost all text parts, which discussed JavaScript or o Removal of almost all text parts, which discussed JavaScript or
other API specific aspects. Such API specific aspects were mainly other API specific aspects. Such API specific aspects were mainly
discussed in sub-sections of Section 5 and Section 6. discussed in sub-sections of Section 5 and Section 5 of draft-
ietf-mmusic-data-channel-sdpneg-02.
11.2. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-01' 10.3. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-01'
o New Section 4 regarding applicability to SDP offer/answer only. o New Section 4 regarding applicability to SDP offer/answer only.
o Addition of new Section 9.1 "Subprotocol identifiers" as o Addition of new Section 8.1 "Subprotocol identifiers" as
subsection of the "IANA Considerations" related Section 9. Also subsection of the "IANA Considerations" related Section 8. Also
removal of the temporary note "To be completed. As [I-D.ietf- removal of the temporary note "To be completed. As [I-D.ietf-
rtcweb-data-protocol] this document should refer to IANA's rtcweb-data-protocol] this document should refer to IANA's
WebSocket Subprotocol Name Registry defined in [RFC6455]." WebSocket Subprotocol Name Registry defined in [RFC6455]."
o In Section 6.2.2: o In Section 5.2.2:
* In the first paragraph replacement of the sentence "If an SDP * In the first paragraph replacement of the sentence "If an SDP
offer contains both of these parameters then such an SDP offer offer contains both of these parameters then such an SDP offer
will be rejected." with "If an SDP offer contains both of these will be rejected." with "If an SDP offer contains both of these
parameters then the receiver of such an SDP offer MUST reject parameters then the receiver of such an SDP offer MUST reject
the SDP offer." the SDP offer."
* In the second paragraph capitalization of "shall" and "may" * In the second paragraph capitalization of "shall" and "may"
such that both sentences now read: "The SDP answer SHALL echo such that both sentences now read: "The SDP answer SHALL echo
the same subprotocol, max-retr, max-time, ordered parameters, the same subprotocol, max-retr, max-time, ordered parameters,
skipping to change at page 24, line 22 skipping to change at page 21, line 31
different from the SDP offer, in the SDP answer." different from the SDP offer, in the SDP answer."
* In the third paragraph replacement of the sentence "The same * In the third paragraph replacement of the sentence "The same
information MUST be replicated without changes in any information MUST be replicated without changes in any
subsequent offer or answer, as long as the data channel is subsequent offer or answer, as long as the data channel is
still opened at the time of offer or answer generation." with still opened at the time of offer or answer generation." with
"When sending a subsequent offer or an answer, and for as long "When sending a subsequent offer or an answer, and for as long
as the data channel is still open, the sender MUST replicate as the data channel is still open, the sender MUST replicate
the same information.". the same information.".
o In Section 6.2.2 the mapping of data channel types defined in o In Section 5.2.2 the mapping of data channel types defined in
[I-D.ietf-rtcweb-data-protocol] to the SDP "a=dcmap" attribute [I-D.ietf-rtcweb-data-protocol] to the SDP "a=dcmap" attribute
parameters were illustrated using example "a=dcmap" attribute parameters were illustrated using example "a=dcmap" attribute
lines. Replacement of these example "a=dcmap" attribute lines lines. Replacement of these example "a=dcmap" attribute lines
with just the "a=dcmap" attribute parameters being relevant for with just the "a=dcmap" attribute parameters being relevant for
the channel type. the channel type.
o In Section 6.2.5 the description of bullet point "SDP offer has no o In Section 5.2.5 the description of bullet point "SDP offer has no
a=dcmap attributes - Initial SDP offer:" was "Initial SDP offer: a=dcmap attributes - Initial SDP offer:" was "Initial SDP offer:
No data channel negotiated yet." Replacement of this description No data channel negotiated yet." Replacement of this description
with "Initial SDP offer: No data channel is negotiated yet. The with "Initial SDP offer: No data channel is negotiated yet. The
DTLS connection and SCTP association is negotiated and, if agreed, DTLS connection and SCTP association is negotiated and, if agreed,
established as per [I-D.ietf-mmusic-sctp-sdp]." established as per [I-D.ietf-mmusic-sctp-sdp]."
o In Section 6.2.5 in both bullet points related to "Subsequent SDP o In Section 5.2.5 in both bullet points related to "Subsequent SDP
offer" and "Subsequent SDP answer" replacement of "All the offer" and "Subsequent SDP answer" replacement of "All the
externally negotiated data channels must be closed now." with "All externally negotiated data channels must be closed now." with "All
the externally negotiated data channels are expected be closed the externally negotiated data channels are expected be closed
now.". now.".
o In Section 5.2.2's sixth paragraph beginning with "[ASSUMPTION]" o In Appendix A.2.2's sixth paragraph beginning with "[ASSUMPTION]"
replacement of the two occurrences of "must" with "MUST". replacement of the two occurrences of "must" with "MUST".
o In Section 6.1.1.1 in the definition of the ABNF rule "dcmap-opt" o In Section 5.1.1.1 in the definition of the ABNF rule "dcmap-opt"
there was a comment saying that "Either only maxretr-opt or there was a comment saying that "Either only maxretr-opt or
maxtime-opt is present. Both MUST not be present." Removal of maxtime-opt is present. Both MUST not be present." Removal of
the second normative sentence and instead addition of following the second normative sentence and instead addition of following
new paragraph to the end of this section: "Within an 'a=dcmap' new paragraph to the end of this section: "Within an 'a=dcmap'
attribute line's 'dcmap-opt' value either only one 'maxretr-opt' attribute line's 'dcmap-opt' value either only one 'maxretr-opt'
parameter or one 'maxtime-opt' parameter is present. Both MUST parameter or one 'maxtime-opt' parameter is present. Both MUST
NOT be present." NOT be present."
o In Section 6.1.1.7 replacement of the first sentence "The o In Section 5.1.1.7 replacement of the first sentence "The
'ordered' parameter with value "true" indicates that DATA chunks 'ordered' parameter with value "true" indicates that DATA chunks
in the channel MUST be dispatched to the upper layer by the in the channel MUST be dispatched to the upper layer by the
receiver while preserving the order." with "The 'ordered' receiver while preserving the order." with "The 'ordered'
parameter with value "true" indicates that the receiver MUST parameter with value "true" indicates that the receiver MUST
dispatch DATA chunks in the data channel to the upper layer while dispatch DATA chunks in the data channel to the upper layer while
preserving the order.". preserving the order.".
o In Section 6.2.3's first paragraph replacement of the one o In Section 5.2.3's first paragraph replacement of the one
occurrence of "must" with "..., it MUST wait until ...". occurrence of "must" with "..., it MUST wait until ...".
o In Section 6.2.4: o In Section 5.2.4:
* In the second paragraph replacement of "must" with "... whether * In the second paragraph replacement of "must" with "... whether
this closing MUST in addition ..." this closing MUST in addition ..."
* In the third paragraph replacement of the sentence "The port * In the third paragraph replacement of the sentence "The port
value for the "m" line SHOULD not be changed (e.g., to zero) value for the "m" line SHOULD not be changed (e.g., to zero)
when closing a data channel ..." with "The offerer SHOULD NOT when closing a data channel ..." with "The offerer SHOULD NOT
change the port value for the "m" line (e.g., to zero) when change the port value for the "m" line (e.g., to zero) when
closing a data channel ...". closing a data channel ...".
* In the last but two paragraph replacement of the sentence "... * In the last but two paragraph replacement of the sentence "...
then an SDP offer which excludes this closed data channel then an SDP offer which excludes this closed data channel
SHOULD be generated." with "... then the client SHOULD generate SHOULD be generated." with "... then the client SHOULD generate
an SDP offer which excludes this closed data channel.". an SDP offer which excludes this closed data channel.".
* In the last but one paragraph replacement of "must" with "The * In the last but one paragraph replacement of "must" with "The
application MUST also close...". application MUST also close...".
o In Section 6.1.2 addition of following note after the formal o In Section 5.1.2 addition of following note after the formal
definition of the 'a=dcsa' attribute: "Note that the above definition of the 'a=dcsa' attribute: "Note that the above
reference to RFC 4566 defines were the attribute definition can be reference to RFC 4566 defines were the attribute definition can be
found; it does not provide any limitation on support of attributes found; it does not provide any limitation on support of attributes
defined in other documents in accordance with this attribute defined in other documents in accordance with this attribute
definition." definition."
11.3. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-00' 10.4. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-00'
o In Section 3 "WebRTC data channel" was defined as "A bidirectional o In Section 3 "WebRTC data channel" was defined as "A bidirectional
channel consisting of paired SCTP outbound and inbound streams." channel consisting of paired SCTP outbound and inbound streams."
Replacement of this definition with "Data channel: A WebRTC data Replacement of this definition with "Data channel: A WebRTC data
channel as specified in [I-D.ietf-rtcweb-data-channel]", and channel as specified in [I-D.ietf-rtcweb-data-channel]", and
consistent usage of "data channel" in the remainder of the consistent usage of "data channel" in the remainder of the
document including the document's headline." document including the document's headline."
o In Section 5 removal of following note: 'OPEN ISSUE: The syntax in 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. [I-D.ietf-mmusic-sctp-sdp] may change as that document progresses.
In particular we expect "webrtc-datachannel" to become a more In particular we expect "webrtc-datachannel" to become a more
general term.' general term.'
o Consistent usage of '"m" line' in whole document as per [RFC4566]. o Consistent usage of '"m" line' in whole document as per [RFC4566].
o In Section 6.1.1 removal of the example dcmap attribute line o In Section 5.1.1 removal of the example dcmap attribute line
'a=dcmap:2 subprotocol="BFCP";label="channel 2' as there are 'a=dcmap:2 subprotocol="BFCP";label="channel 2' as there are
already four examples right after the ABNF rules in already four examples right after the ABNF rules in
Section 6.1.1.1. Corresponding removal of following related note: Section 5.1.1.1. Corresponding removal of following related note:
"Note: This document does not provide a complete specification of "Note: This document does not provide a complete specification of
how to negotiate the use of a WebRTC data channel to transport how to negotiate the use of a WebRTC data channel to transport
BFCP. Procedures specific to each sub-protocol such as BFCP will BFCP. Procedures specific to each sub-protocol such as BFCP will
be documented elsewhere. The use of BFCP is only an example of be documented elsewhere. The use of BFCP is only an example of
how the generic procedures described herein might apply to a how the generic procedures described herein might apply to a
specific sub-protocol." specific sub-protocol."
o In Section 6.1.1 removal of following note: "Note: This attribute o In Section 5.1.1 removal of following note: "Note: This attribute
is derived from attribute "webrtc-DataChannel", which was defined is derived from attribute "webrtc-DataChannel", which was defined
in old version 03 of the following draft, but which was removed in old version 03 of the following draft, but which was removed
along with any support for SDP external negotiation in subsequent along with any support for SDP external negotiation in subsequent
versions: [I-D.ietf-mmusic-sctp-sdp]." versions: [I-D.ietf-mmusic-sctp-sdp]."
o Insertion of following new sentence to the beginning of o Insertion of following new sentence to the beginning of
Section 6.1.1.1: "dcmap is a media level attribute having Section 5.1.1.1: "dcmap is a media level attribute having
following ABNF syntax:" following ABNF syntax:"
o Insertion of new Section 6.1.1.2 containing the dcmap-stream-id o Insertion of new Section 5.1.1.2 containing the dcmap-stream-id
specifying sentence, which previously was placed right before the specifying sentence, which previously was placed right before the
formal ABNF rules. Removal of the sentence 'Stream is a mandatory formal ABNF rules. Removal of the sentence 'Stream is a mandatory
parameter and is noted directly after the "a=dcmap:" attribute's parameter and is noted directly after the "a=dcmap:" attribute's
colon' as this information is part of the ABNF specification. colon' as this information is part of the ABNF specification.
o In Section 6.1.1.1 modification of the 'ordering-value' values o In Section 5.1.1.1 modification of the 'ordering-value' values
from "0" or "1" to "true" or "false". Corresponding text from "0" or "1" to "true" or "false". Corresponding text
modifications in Section 6.1.1.7. modifications in Section 5.1.1.7.
o In Section 6.1.1.1 the ABNF definition of "quoted-string" referred 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 to rule name "escaped-char", which was not defined. Instead a
rule with name "escaped" was defined. Renamed that rule's name to rule with name "escaped" was defined. Renamed that rule's name to
"escaped-char". "escaped-char".
o Insertion of a dedicated note right after the "a=dcmap:4" o Insertion of a dedicated note right after the "a=dcmap:4"
attribute example in Section 6.1.1.1 regarding the non-printable attribute example in Section 5.1.1.1 regarding the non-printable
"escaped-char" character within the "label" value. "escaped-char" character within the "label" value.
o In Section 6.1.2's second paragraph replacement of "sctp stream o In Section 5.1.2's second paragraph replacement of "sctp stream
identifier" with "SCTP stream identifier". identifier" with "SCTP stream identifier".
o In first paragraph of Section 6.2.1 replacement of first two o In first paragraph of Section 5.2.1 replacement of first two
sentences 'For the SDP-based external negotiation described in sentences 'For the SDP-based external negotiation described in
this document, the initial offerer based "SCTP over DTLS" owns by this document, the initial offerer based "SCTP over DTLS" owns by
convention the even stream identifiers whereas the initial convention the even stream identifiers whereas the initial
answerer owns the odd stream identifiers. This ownership is answerer owns the odd stream identifiers. This ownership is
invariant for the whole lifetime of the signaling session, e.g. it 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 does not change if the initial answerer sends a new offer to the
initial offerer.' with 'If an SDP offer/answer exchange (could be initial offerer.' with 'If an SDP offer/answer exchange (could be
the initial or a subsequent one) results in a UDP/DTLS/SCTP or the initial or a subsequent one) results in a UDP/DTLS/SCTP or
TCP/DTLS/SCTP based media description being accepted, and if this TCP/DTLS/SCTP based media description being accepted, and if this
SDP offer/answer exchange results in the establishment of a new SDP offer/answer exchange results in the establishment of a new
SCTP association, then the SDP offerer owns the even SCTP stream SCTP association, then the SDP offerer owns the even SCTP stream
ids of this new SCTP association and the answerer owns the odd ids of this new SCTP association and the answerer owns the odd
SCTP stream identifiers. If this "m" line is removed from the SCTP stream identifiers. If this "m" line is removed from the
signaling session (its port number set to zero), and if usage of 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 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 renegotiated later on, then the even and odd SCTP stream
identifier ownership is redetermined as well as described above.' identifier ownership is redetermined as well as described above.'
o In Section 6.2.3 the first action of an SDP answerer, when 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. receiving an SDP offer, was described as "Applies the SDP offer.
Note that the browser ignores data channel specific attributes in Note that the browser ignores data channel specific attributes in
the SDP." Replacement of these two sentences with "Parses and the SDP." Replacement of these two sentences with "Parses and
applies the SDP offer. Note that the typical parser normally applies the SDP offer. Note that the typical parser normally
ignores unknown SDP attributes, which includes data channel ignores unknown SDP attributes, which includes data channel
related attributes." related attributes."
o In Section 6.2.3 the second sentence of the third SDP answerer 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 action was "Note that the browser is asked to create data channels
with stream identifiers not "owned" by the agent.". Replacement with stream identifiers not "owned" by the agent.". Replacement
of this sentence with "Note that the agent is asked to create data of this sentence with "Note that the agent is asked to create data
channels with SCTP stream identifiers contained in the SDP offer channels with SCTP stream identifiers contained in the SDP offer
if the SDP offer is accepted." if the SDP offer is accepted."
o In Section 6.2.4 the third paragraph began with "A data channel 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 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 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 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 data channel (unless all data channels are being closed and the
SCTP association is no longer needed), since this would close the SCTP association is no longer needed), since this would close the
SCTP association and impact all of the data channels. If the SCTP association and impact all of the data channels. If the
answerer accepts the SDP offer then it MUST also exclude the answerer accepts the SDP offer then it MUST also exclude the
corresponding attribute lines in the answer. ..." Replacement of corresponding attribute lines in the answer. ..." Replacement of
this part with "The intention to close a data channel can be this part with "The intention to close a data channel can be
signaled by sending a new SDP offer which excludes the "a=dcmap:" signaled by sending a new SDP offer which excludes the "a=dcmap:"
skipping to change at page 28, line 15 skipping to change at page 25, line 24
value for the "m" line SHOULD not be changed (e.g., to zero) when 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 closing a data channel (unless all data channels are being closed
and the SCTP association is no longer needed), since this would and the SCTP association is no longer needed), since this would
close the SCTP association and impact all of the data channels. close the SCTP association and impact all of the data channels.
If the answerer accepts the SDP offer then it MUST close those If the answerer accepts the SDP offer then it MUST close those
data channels whose "a=dcmap:" and "a=dcsa:" attribute lines were data channels whose "a=dcmap:" and "a=dcsa:" attribute lines were
excluded from the received SDP offer, unless those data channels excluded from the received SDP offer, unless those data channels
were already closed, and it MUST also exclude the corresponding were already closed, and it MUST also exclude the corresponding
attribute lines in the answer." attribute lines in the answer."
o In Section 6.2.4 the hanging text after the third paragraph was 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 "This delayed close is to handle cases where a successful SDP
answer is not received, in which case the state of session should answer is not received, in which case the state of session should
be kept per the last successful SDP offer/answer." Replacement of be kept per the last successful SDP offer/answer." Replacement of
this sentence with "This delayed closure is RECOMMENDED in order this sentence with "This delayed closure is RECOMMENDED in order
to handle cases where a successful SDP answer is not received, in 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 which case the state of the session SHOULD be kept per the last
successful SDP offer/answer." successful SDP offer/answer."
o Although dedicated to "a=dcmap" and "a=dcsa" SDP syntax aspects o Although dedicated to "a=dcmap" and "a=dcsa" SDP syntax aspects
Section 6.1.1 contained already procedural descriptions related to Section 5.1.1 contained already procedural descriptions related to
data channel reliability negotiation. Creation of new data channel reliability negotiation. Creation of new
Section 6.2.2 and moval of reliability negotiation related text to Section 5.2.2 and moval of reliability negotiation related text to
this new section. this new section.
11.4. Changes against 'draft-ejzak-mmusic-data-channel-sdpneg-02' 10.5. 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 29, line 32 skipping to change at page 26, line 41
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.
11.5. Changes against '-01' 10.6. 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 WebRTC data channel close procedures. o Clarifications on WebRTC data channel close procedures.
11.6. Changes against '-00' 10.7. 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 WebRTC 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.
12. References 11. References
12.1. Normative References 11.1. Normative References
[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,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566, Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <http://www.rfc-editor.org/info/rfc4566>. July 2006, <http://www.rfc-editor.org/info/rfc4566>.
skipping to change at page 31, line 5 skipping to change at page 28, line 11
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-14 (work in progress), March 2015. mmusic-sctp-sdp-14 (work in progress), March 2015.
12.2. Informative References 11.2. Informative References
[I-D.ietf-rtcweb-data-protocol] [I-D.ietf-rtcweb-data-protocol]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel
Establishment Protocol", draft-ietf-rtcweb-data- Establishment Protocol", draft-ietf-rtcweb-data-
protocol-09 (work in progress), January 2015. protocol-09 (work in progress), January 2015.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007, RFC 4960, DOI 10.17487/RFC4960, September 2007,
<http://www.rfc-editor.org/info/rfc4960>. <http://www.rfc-editor.org/info/rfc4960>.
skipping to change at page 32, line 19 skipping to change at page 29, line 24
<http://www.iana.org/assignments/sdp-parameters/ <http://www.iana.org/assignments/sdp-parameters/
sdp-parameters.xhtml>. sdp-parameters.xhtml>.
[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-20150210, Browsers", World Wide Web Consortium WD-webrtc-20150210,
February 2015, February 2015,
<http://www.w3.org/TR/2015/WD-webrtc-20150210/>. <http://www.w3.org/TR/2015/WD-webrtc-20150210/>.
Appendix A. Generic Data Channel Negotiation Aspects When Not Using
DCEP
This appendix summarizes how data channels work in general and
discusses some key aspects, which should be considered for the out-
of-band negotiation of data channels if DCEP is not used.
A WebRTC application creates a data channel by providing a number of
setup parameters (sub-protocol, label, reliability, order of
delivery, priority). The application also specifies if it wants to
make use of the negotiation using the DCEP
[I-D.ietf-rtcweb-data-protocol], or if the application intends to
negotiate data channels using the SDP offer/answer protocol.
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
the SCTP association on top of which data channels will run:
m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 79.97.215.79
a=max-message-size:100000
a=sctp-port:5000
a=setup:actpass
a=connection:new
a=fingerprint:SHA-1 \
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-
datachannel", and will not use other formats in the "m" line for
other protocols such as t38. [I-D.ietf-mmusic-sctp-sdp] supports
only one SCTP association to be established on top of a DTLS
association.
Note: Above SDP media description does not contain any channel-
specific information.
A.1. Stream Identifier Numbering
Independently from the requested type of negotiation, the application
creating a data channel can either pass to the data channel stack the
stream identifier to assign to the data channel or else let the data
channel stack pick one identifier from the ones unused.
To avoid glare situations, each endpoint can moreover own an
exclusive set of stream identifiers, in which case an endpoint can
only create a data channel with a stream identifier it owns.
Which set of stream identifiers is owned by which endpoint is
determined by convention or other means.
For data channels negotiated with the DCEP, one endpoint owns by
convention the even stream identifiers, whereas the other owns the
odd stream identifiers, as defined in
[I-D.ietf-rtcweb-data-protocol].
For data channels negotiated via some protocol different from
DCEP, no convention is defined by default.
A.2. Generic Data Channel Negotiation Not Using DCEP
A.2.1. Overview
DCEP negotiation only provides for negotiation of data channel
transport parameters and does not provide for negotiation of sub-
protocol specific parameters. DCEP-less data channel negotiation can
be defined to allow negotiation of parameters beyond those handled by
DCEP, e.g., parameters specific to the sub-protocol instantiated on a
particular data channel.
The following procedures are common to all methods of data channel
negotiation not using DCEP, whether in-band (communicated using
proprietary means on an already established data channel) or out-of-
band (using SDP offer/answer or some other protocol associated with
the signaling channel).
A.2.2. Opening a Data Channel
In the case of DCEP-less negotiation, the endpoint application has
the option to fully control the stream identifier assignments.
However these assignments have to coexist with the assignments
controlled by the data channel stack for the DCEP negotiated data
channels (if any). It is the responsibility of the application to
ensure consistent assignment of stream identifiers.
When the application requests the creation of a new data channel to
be set up via DCEP-less negotiation, the data channel stack creates
the data channel locally without sending any DATA_CHANNEL_OPEN
message in-band. However, even if the ICE, DTLS and SCTP procedures
were already successfully completed, the application can't send data
on this data channel until the negotiation is complete with the peer.
This is because the peer 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 immediately. This implies that the offerer
may receive data channel sub-protocol messages before the negotiation
is complete and the application should be ready to handle 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
the stack. The offerer on the other hand needs to close the data
channel that was opened by invoking relevant data channel stack API
procedures.
It is also worth noting that a data channel stack implementation may
not provide any API to create and close data channels; instead the
data channels may be used on the fly as needed just by communicating
via non-DCEP means or by even having some local configuration/
assumptions on both the peers.
The application then negotiates the data channel properties and sub-
protocol properties with the peer's application using a mechanism
different from DCEP.
The peer then symmetrically creates a data channel with these
negotiated data channel properties. This is the only way for the
peer's data channel stack to know which properties to apply when
transmitting data on this channel. The data channel stack must allow
data channel creation with any non-conflicting stream identifier so
that both peers can create the data channel with the same stream
identifier.
A.2.3. Closing a Data Channel
When the application requests the closing of a data channel
negotiated without DCEP, the data channel stack always performs an
SCTP SSN reset for this channel.
Depending upon the method used for DCEP-less negotiation and the sub-
protocol associated with the data channel, the closing might in
addition be signaled to the peer via SDP offer/answer negotiation.
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
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