SDP-based Data Channel Negotiation
draft-ietf-mmusic-data-channel-sdpneg-02
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8864.
|
|
|---|---|---|---|
| Authors | Keith Drage , Raju Makaraju , Juergen Stoetzer-Bradler , Richard Ejzak , Jerome Marcon | ||
| Last updated | 2015-04-10 | ||
| Replaces | draft-ejzak-mmusic-data-channel-sdpneg | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
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| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Ari Keränen | ||
| IESG | IESG state | Became RFC 8864 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
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| Send notices to | "Ari Keranen" <ari.keranen@ericsson.com> |
draft-ietf-mmusic-data-channel-sdpneg-02
MMUSIC K. Drage, Ed.
Internet-Draft M. Makaraju
Intended status: Standards Track J. Stoetzer-Bradler
Expires: October 12, 2015 Alcatel-Lucent
R. Ejzak
J. Marcon
Unaffiliated
April 10, 2015
SDP-based Data Channel Negotiation
draft-ietf-mmusic-data-channel-sdpneg-02
Abstract
The Real-Time Communication in WEB-browsers (RTCWeb) working group is
charged to provide protocols to support direct interactive rich
communications using audio, video, and data between two peers' web-
browsers. For the support of data communication, the RTCWeb working
group has in particular defined the concept of bi-directional data
channels over SCTP, where each data channel might be used to
transport other protocols, called sub-protocols. Data channel setup
can be done using either the internal in-band band (also referred to
as 'internal' for the rest of the document) Data Channel
Establishment Protocol or some external out-of-band simply referred
to as 'external negotiation' in the rest of the document . This
document specifies how the SDP offer/answer exchange can be used to
achieve such an external negotiation. Even though data channels are
designed for RTCWeb use initially they may be used by other protocols
like, but not limited to, the CLUE protocol. This document is
intended to be used wherever data channels are used.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 12, 2015.
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Applicability Statement . . . . . . . . . . . . . . . . . . . 4
5. Data Channels . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Stream Identifier Numbering . . . . . . . . . . . . . . . 5
5.2. Generic External Negotiation . . . . . . . . . . . . . . 6
5.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 6
5.2.2. Opening a Data Channel . . . . . . . . . . . . . . . 6
5.2.3. Closing a Data Channel . . . . . . . . . . . . . . . 7
6. SDP-based External Negotiation . . . . . . . . . . . . . . . 8
6.1. SDP Syntax . . . . . . . . . . . . . . . . . . . . . . . 8
6.1.1. SDP Attribute for Data Channel Parameter Negotiation 8
6.1.1.1. dcmap Attribute . . . . . . . . . . . . . . . . . 8
6.1.1.2. dcmap-stream-id Parameter . . . . . . . . . . . . 10
6.1.1.3. label Parameter . . . . . . . . . . . . . . . . . 10
6.1.1.4. subprotocol Parameter . . . . . . . . . . . . . . 10
6.1.1.5. max-retr Parameter . . . . . . . . . . . . . . . 10
6.1.1.6. max-time Parameter . . . . . . . . . . . . . . . 11
6.1.1.7. ordered Parameter . . . . . . . . . . . . . . . . 11
6.1.2. Sub-Protocol Specific Attributes . . . . . . . . . . 11
6.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . 12
6.2.1. Managing Stream Identifiers . . . . . . . . . . . . . 13
6.2.2. Negotiating Data Channel Parameters . . . . . . . . . 13
6.2.3. Opening a Data Channel . . . . . . . . . . . . . . . 14
6.2.4. Closing a Data Channel . . . . . . . . . . . . . . . 16
6.2.5. Various SDP Offer/Answer Scenarios and Considerations 17
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
9.1. Subprotocol identifiers . . . . . . . . . . . . . . . . . 20
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10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
11. CHANGE LOG . . . . . . . . . . . . . . . . . . . . . . . . . 21
11.1. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-01' . . . . . . . . . . . . . . . . . . . . . . . 21
11.2. Changes against 'draft-ietf-mmusic-data-channel-
sdpneg-00' . . . . . . . . . . . . . . . . . . . . . . . 23
11.3. Changes against 'draft-ejzak-mmusic-data-channel-
sdpneg-02' . . . . . . . . . . . . . . . . . . . . . . . 26
11.4. Changes against '-01' . . . . . . . . . . . . . . . . . 27
11.5. Changes against '-00' . . . . . . . . . . . . . . . . . 27
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
12.1. Normative References . . . . . . . . . . . . . . . . . . 28
12.2. Informative References . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
The RTCWeb working group has defined the concept of bi-directional
data channels running on top of SCTP/DTLS. RTCWeb leaves it open for
other applications to use data channels and its in-band or out-of-
band protocol for creating them. Each data channel consists of
paired SCTP streams sharing the same SCTP Stream Identifier. Data
channels are created by endpoint applications through the WebRTC API,
or other users of data channel like CLUE, and can be used to
transport proprietary or well-defined protocols, which in the latter
case can be signaled by the data channel "sub-protocol" parameter,
conceptually similar to the WebSocket "sub-protocol". However, apart
from the "sub-protocol" value transmitted to the peer, 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 signaled in-
band or out-of-band (or both). In particular, the SDP offer
generated by the application includes no channel-specific
information.
This document defines SDP-based out-of-band negotiation procedures to
establish data channels for transport of well-defined sub-protocols.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Terminology
This document uses the following terms:
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Data channel: A WebRTC data channel as specified in
[I-D.ietf-rtcweb-data-channel].
Data channel stack: An entity which, upon application request,
runs data channel protocol to keep track of states, sending and
receive data. If the application is browser based JavaScript
application then this stack resides in the browser. If the
application is a native application then this stack resides in
application and accessible to it via some sort of APIs.
Data channel properties: fixed properties assigned to a data
channel at the time of its creation. Some of these properties
determine the way the data channel stack transmits data on this
channel (e.g., stream identifier, reliability, order of
delivery...).
DCEP - Data Channel Establishment Protocol defined in
[I-D.ietf-rtcweb-data-protocol].
External negotiation: Data channel negotiation based on SDP offer/
answer outlined in this specification.
Internal negotiation: Data channel negotiation based on the Data
Channel Establishment Protocol defined in
[I-D.ietf-rtcweb-data-protocol].
In-band: transmission through the peer-to-peer SCTP association.
In-band negotiation: data channel negotiation based on the Data
Channel Establishment Protocol defined in
[I-D.ietf-rtcweb-data-protocol].
Out-of-band: transmission through the application signaling path.
Peer: From the perspective of one of the agents in a session, its
peer is the other agent. Specifically, from the perspective of
the SDP offerer, the peer is the SDP answerer. From the
perspective of the SDP answerer, the peer is the SDP offerer.
Stream identifier: the identifier of the outbound and inbound SCTP
streams composing a data channel.
4. Applicability Statement
The mechanism in this specification only applies to the Session
Description Protocol (SDP) [RFC4566], when used together with the SDP
offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of
scope of this document, and is thus undefined.
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5. Data Channels
This section summarizes how data channels work in general. Note that
the references to 'browser' here is intentional as in this specific
example the data channel user is a Webrtc enabled browser.
A WebRTC application creates a data channel via the data channel API,
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 in-band negotiation using
the DCEP [I-D.ietf-rtcweb-data-protocol], or if the application
intends to perform an "external negotiation" using some other in-band
or out-of-band mechanism.
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, and one
attribute per protocol assigned to the SCTP ports:
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
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.
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Which set of stream identifiers is owned by which endpoint is
determined by convention or other means.
For data channels negotiated in-band, 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 externally negotiated, no convention is defined
by default.
5.2. Generic External Negotiation
5.2.1. Overview
In-band negotiation only provides for negotiation of data channel
transport parameters and does not provide for negotiation of sub-
protocol specific parameters. External negotiation can be defined to
allow negotiation of parameters beyond those handled by in-band
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.
The following procedures are common to all methods of external
negotiation, whether in-band (communicated using proprietary means on
an already established data channel) or out-of-band (using SDP or
some other protocol associated with the signaling channel).
5.2.2. Opening a Data Channel
In the case of external 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 in-band 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 external negotiation, the data channel stack creates
the data channel locally without sending any DATA_CHANNEL_OPEN
message in-band, 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 external negotiation creates 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). However, the application can't send data on this data channel
until external negotiation is complete with the peer. This is
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because peer needs to be aware and accept the data channel via
external negotiation. The peer after accepting the data channel
offer can start sending data immediately. This implies that the
offerer may get data channel message before external 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 are used on the fly as needed just by communicating via
external means or by even having some local configuration/assumptions
on both the peers.
The application then externally negotiates the data channel
properties and sub-protocol properties with the peer's application.
[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. 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.
In case the external 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.
5.2.3. Closing a Data Channel
When the application requests the closing of an externally negotiated
data channel, the data channel stack always performs an in-band SSN
reset for this channel.
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Depending upon the method used for external negotiation and the sub-
protocol associated with the data channel, the closing might in
addition be signaled to the peer via external negotiation.
6. SDP-based External Negotiation
This section defines a method of external 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 SDP offer/answer model.
6.1. SDP Syntax
Two new SDP attributes are defined to support external negotiation of
data channels. The first attribute provides for negotiation of
channel-specific parameters. The second attribute provides for
negotiation of sub-protocol-specific parameters.
6.1.1. SDP Attribute for Data Channel Parameter Negotiation
Associated with the SDP "m" line that defines the SCTP association
for data channels (defined in Section 4), each SDP offer and answer
includes one "a=dcmap:" attribute that defines the data channel
parameters for each data channel to be negotiated. Each such
attribute line specifies the following parameters for a data channel:
SCTP stream identifier, sub-protocol, label, reliability, order of
delivery, and priority.
The intention of exchanging these attributes is to create data
channels on both the peers with the same set of attributes without
actually using [I-D.ietf-rtcweb-data-protocol]. It is assumed that
the data channel properties (reliable/partially reliable, ordered/
unordered) are suitable per the sub-protocol transport requirements.
6.1.1.1. dcmap Attribute
"a=dcmap:" is a media level attribute having following ABNF syntax.
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Formal Syntax:
Name: dcmap
Value: dcmap-value
Usage Level: media
Charset Dependent: no
Syntax:
dcmap-value = dcmap-stream-id
[ SP dcmap-opt *(";" dcmap-opt) ]
dcmap-opt = ordering-opt / subprotocol-opt / label-opt
/ maxretr-opt / maxtime-opt
; Either only maxretr-opt or maxtime-opt
; is present.
dcmap-stream-id = 1*DIGIT
ordering-opt = "ordered=" ordering-value
ordering-value = "true" / "false"
subprotocol-opt = "subprotocol=" quoted-string
label-opt = "label=" quoted-string
maxretr-opt = "max-retr=" maxretr-value
maxretr-value = <from-Reliability-Parameter of
I-D.ietf-rtcweb-data-protocol>
; number of retransmissions
maxtime-opt = "max-time=" maxtime-value
maxtime-value = <from-Reliability-Parameter of
I-D.ietf-rtcweb-data-protocol>
; milliseconds
quoted-string = DQUOTE *(quoted-char / escaped-char) DQUOTE
quoted-char = SP / quoted-visible
quoted-visible = %21 / %23-24 / %26-7E ; VCHAR without " or %
escaped-char = "%" HEXDIG HEXDIG
DQUOTE = <from-RFC5234>
integer = <from-RFC5234>
Examples:
a=dcmap:0
a=dcmap:1 subprotocol="BFCP";max-time=60000
a=dcmap:2 subprotocol="MSRP";ordered=true;label="MSRP"
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
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Note: The last example (a=dcmap:4) shows a 'label' parameter value
which contains one non-printable 'escaped-char' character (the
tabulator character).
Within an 'a=dcmap' attribute line's 'dcmap-opt' value either only
one 'maxretr-opt' parameter or one 'maxtime-opt' parameter is
present. Both MUST NOT be present.
6.1.1.2. dcmap-stream-id Parameter
The 'dcmap-stream-id' parameter indicates the SCTP stream identifier
within the SCTP association used to form the data channel.
6.1.1.3. label Parameter
The 'label' parameter indicates the name of the channel. It
represents a label that can be used to distinguish, in the context of
the WebRTC API, an RTCDataChannel object from other RTCDataChannel
objects. This parameter maps to the 'Label' parameter 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 string.
Note: The empty string may also be explicitly used as 'label' value,
such that 'label=""' is equivalent to the 'label' parameter not being
present at all. [I-D.ietf-rtcweb-data-protocol] allows the
DATA_CHANNEL_OPEN message's 'Label' value to be an empty string.
6.1.1.4. subprotocol Parameter
The 'subprotocol' parameter indicates which protocol the client
expects to exchange via the channel. 'Subprotocol' is an optional
parameter. If the 'subprotocol' parameter is not present, then its
value defaults to the empty string.
6.1.1.5. max-retr Parameter
This parameter indicates that the data channel is partially reliable.
The 'max-retr' parameter indicates the max times a user message will
be retransmitted. The max-retr parameter is optional. If the max-
retr parameter is not present, then the maximal number of
retransmissions is determined as per the generic SCTP retransmission
rules as specified in [RFC4960]. This parameter maps to the 'Number
of RTX' parameter defined in [I-D.ietf-rtcweb-data-protocol].
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6.1.1.6. max-time Parameter
This parameter indicates that the data channel is partially reliable.
A user message will no longer be transmitted or retransmitted after a
specified life-time given in milliseconds in the 'max-time'
parameter. The max-time parameter is optional. If the max-time
parameter is not present, then the generic SCTP retransmission timing
rules apply as specified in [RFC4960]. This parameter maps to the
'Lifetime in ms' parameter defined in
[I-D.ietf-rtcweb-data-protocol].
6.1.1.7. ordered Parameter
The 'ordered' parameter with value "true" indicates that the receiver
MUST dispatch DATA chunks in the data channel to the upper layer
while preserving the order. The ordered parameter is optional and
takes two values: "true" for ordered and "false" for unordered
delivery with "true" as the default value. Any other value is
ignored and default "ordered=true" is assumed. In the absence of
this parameter "ordered=true" is assumed. This parameter maps to the
ordered or unordered data channel types as defined in
[I-D.ietf-rtcweb-data-protocol].
6.1.2. Sub-Protocol Specific Attributes
In the SDP, each data channel declaration MAY also be followed by
other SDP attributes specific to the sub-protocol in use. Each of
these attributes is represented by one new attribute line, and it
includes the contents of a media-level SDP attribute already defined
for use with this (sub)protocol in another IETF specification. Sub-
protocol-specific attributes might also be defined for exclusive use
with data channel transport, but should use the same syntax described
here for other sub-protocol-specific attributes.
Each sub-protocol specific SDP attribute that would normally be used
to negotiate the subprotocol using SDP is replaced with an attribute
of the form "a=dcsa:stream-id original-attribute", where dcsa stands
for "data channel sub-protocol attribute", stream-id is the SCTP
stream identifier assigned to this sub-protocol instance, and
original-attribute represents the contents of the sub-protocol
related attribute to be included.
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Formal Syntax:
Name: dcsa
Value: dcsa-value
Usage Level: media
Charset Dependent: no
Syntax:
dcsa-value = stream-id SP attribute
attribute = <from-RFC4566>
Example:
a=dcsa:2 accept-types:text/plain
Note that the above reference to RFC 4566 defines were the attribute
definition can be found; it does not provide any limitation on
support of attributes defined in other documents in accordance with
this attribute definition.
Thus in the example above, the original attribute line "a=accept-
types:text/plain" is represented by the attribute line "a=dcsa:2
accept-types:text/plain", which specifies that this instance of MSRP
being transported on the sctp association using the data channel with
stream id 2 accepts plain text files.
As opposed to the data channel "a=dcmap:" attribute parameters, these
parameters are subject to offer/answer negotiation following the
procedures defined in the sub-protocol specific documents.
The same syntax applies to any other SDP attribute required for
negotiation of this instance of the sub-protocol.
Note: This document does not provide a complete specification of how
to negotiate the use of a data channel to transport MSRP. Procedures
specific to each sub-protocol such as MSRP will be documented
elsewhere. The use of MSRP is only an example of how the generic
procedures described herein might apply to a specific sub-protocol.
6.2. Procedures
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6.2.1. Managing Stream Identifiers
If an SDP offer / answer exchange (could be the initial or a
subsequent one) results in a UDP/DTLS/SCTP or TCP/DTLS/SCTP based
media description being accepted, and if this SDP offer / answer
exchange results in the establishment of a new SCTP association, then
the SDP offerer owns the even SCTP stream ids of this new SCTP
association and the answerer owns the odd SCTP stream identifiers.
If this "m" line is removed from the signaling session (its port
number set to zero), and if usage of this or of a new UDP/DTLS/SCTP
or TCP/DTLS/SCTP based "m" line is renegotiated later on, then the
even and odd SCTP stream identifier ownership is redetermined as well
as described above.
This specification allows simultaneous use of external and internal
negotiation. However, a single stream is managed using one method at
a time. Stream ids that are not currently used in SDP can be used
for internal negotiation. Stream id allocation per SDP based
external negotiation may not align with DTLS role based allocation.
This could cause glare conditions when one side trying to do external
negotiation on a stream id while the other end trying to open a data
channel on the same stream id using internal negotiation. To avoid
these glare conditions this specification recommends that the data
channel stack user always selects stream ids per above described SDP
offer / answer rule even when internal negotiation is used. To avoid
glare conditions, it is possible to come up with a different stream
id allocation scheme, but such schemes are outside the scope of this
specification.
6.2.2. Negotiating Data Channel Parameters
Conveying a reliable data channel is achieved by including neither
'max-retr' nor 'max-time' in corresponding SDP offer's or answer's
a=dcmap attribute line. Conveying a partially reliable data channel
is achieved by including only one of 'max-retr' or 'max-time'. By
definition max-retr and max-time are mutually exclusive, so only one
of them can be present in a=dcmap. If an SDP offer contains both of
these parameters then the receiver of such an SDP offer MUST reject
the SDP offer. If an SDP answer contains both of these parameters
then the offerer MAY treat it as an error and MAY assume the
associated SDP offer/answer failed and MAY take appropriate recovery
actions. These recovery options are outside the scope of this
specification.
The SDP answer SHALL echo the same subprotocol, max-retr, max-time,
ordered parameters, if those were present in the offer, and MAY
include a label parameter. They MAY appear in any order, which could
be different from the SDP offer, in the SDP answer.
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When sending a subsequent offer or an answer, and for as long as the
data channel is still open, the sender MUST replicate the same
information.
Data channel types defined in [I-D.ietf-rtcweb-data-protocol] are
mapped to SDP in the following manner, where "ordered=true" is the
default and may be omitted:
DATA_CHANNEL_RELIABLE
ordered=true
DATA_CHANNEL_RELIABLE_UNORDERED
ordered=false
DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT
ordered=true;max-retr=<number of retransmissions>
DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED
ordered=false;max-retr=<number of retransmissions>
DATA_CHANNEL_PARTIAL_RELIABLE_TIMED
ordered=true;max-time=<lifetime in milliseconds>
DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED
ordered=false;max-time=<lifetime in milliseconds>
6.2.3. Opening a Data Channel
The procedure for opening a data channel using external negotiation
starts with the agent preparing to send an SDP offer. If a peer
receives an SDP offer before getting to send a new SDP offer with
data channels that are to be externally negotiated, or loses an SDP
offer glare resolution procedure in this case, it MUST wait until the
ongoing SDP offer/answer completes before resuming the external
negotiation procedure.
The agent that intends to send an SDP offer to create data channels
through SDP-based external negotiation performs the following:
o Creates data channels using stream identifiers from the owned set
(see Section 6.2.1).
o As described in Section 5.2.2, if the SCTP association is not yet
established, then the newly created data channels are in the
Connecting state, else if the SCTP association is already
established, then the newly created data channels are in the Open
state.
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o Generates a new SDP offer. In the case of browser based
applications the browser generates the offer via the createOffer()
API call [I-D.ietf-rtcweb-jsep].
o Determines the list of stream identifiers assigned to data
channels opened through external negotiation.
o Completes the SDP offer with the dcmap and dcsa attributes needed,
if any, for each externally-negotiated data channel, as described
in Section 6.1 and in Section 6.2.2.
o Sends the SDP offer.
The peer receiving such an SDP offer performs the following:
o Parses and applies the SDP offer. Note that the typical parser
normally ignores unknown SDP attributes, which includes data
channel related attributes.
o Analyzes the channel parameters and sub-protocol attributes to
determine whether to accept each offered data channel.
o For accepted data channels, it creates peer instances for the data
channels with the agent using the channel parameters described in
the SDP offer. Note that the agent is asked to create data
channels with SCTP stream identifiers contained in the SDP offer
if the SDP offer is accepted.
o As described in Section 5.2.2, if the SCTP association is not yet
established, then the newly created data channels are in the
Connecting state, else if the SCTP association is already
established, then the newly created data channels are in the Open
state.
o Generates an SDP answer.
o Completes the SDP answer with the dcmap and optional dcsa
attributes needed for each externally-negotiated data channel, as
described in Section 6.1 and in Section 6.2.2.
o Sends the SDP answer.
The agent receiving such an SDP answer performs the following:
o Closes any created data channels (whether in Connecting or Open
state) for which the expected dcmap and dcsa attributes are not
present in the SDP answer.
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o Applies the SDP answer.
Any data channels in Connecting state are transitioned to the Open
state when the SCTP association is established.
Each agent application MUST wait to send data until it has
confirmation that the data channel at the peer is in the Open state.
For WebRTC, this is when both data channel stacks have channel
parameters instantiated. This occurs:
o At both peers when a data channel is created without an
established SCTP association, as soon as the data channel stacks
report that the data channel transitions to the Open state from
the Connecting state.
o At the agent receiving an SDP offer for which there is an
established SCTP association, as soon as it creates an externally
negotiated data channel in the Open state based on information
signaled in the SDP offer.
o At the agent sending an SDP offer to create a new externally
negotiated data channel for which there is an established SCTP
association, when it receives the SDP answer confirming acceptance
of the data channel or when it begins to receive data on the data
channel from the peer, whichever occurs first.
6.2.4. Closing a Data Channel
When the application requests the closing of a data channel that was
externally negotiated, the data channel stack always performs an in-
band SSN reset for this channel.
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.
The intention to close a data channel can be signaled by sending a
new SDP offer which excludes the "a=dcmap:" and "a=dcsa:" attribute
lines for the data channel. The offerer SHOULD NOT change the port
value for the "m" line (e.g. to zero) when closing a data channel
(unless all data channels are being closed and the SCTP association
is no longer needed), since this would close the SCTP association and
impact all of the data channels. If the answerer accepts the SDP
offer then the answerer MUST close those data channels whose
"a=dcmap:" and "a=dcsa:" attribute lines were excluded from the
received SDP offer, unless those data channels were already closed,
and the answerer MUST also exclude the corresponding attribute lines
in the answer. In addition to that, the SDP answerer MAY exclude
other data channels which were closed but not yet communicated to the
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peer. So, the offerer MUST inspect the answer to see if it has to
close other data channels which are now not included in the answer.
If a new SDP offer/answer is used to close data channels then the
data channel(s) SHOULD only be closed by the answerer/offerer after a
successful SDP answer is sent/received.
This delayed closure is RECOMMENDED in order to handle cases where
a successful SDP answer is not received, in which case the state
of the session SHOULD be kept per the last successful SDP offer/
answer.
If a client receives a data channel close indication (due to inband
SSN reset or some other reason) without associated SDP offer then the
client SHOULD generate an SDP offer which excludes this closed data
channel.
The application MUST also close any data channel that was externally
negotiated, for which the stream identifiers are not listed in an
incoming SDP offer.
A closed data channel using local close (SCTP reset), without an
additional SDP offer/answer to close it, may be reused for a new data
channel. This can only be done via new SDP offer/answer, describing
the new sub-protocol and its attributes, only after the corresponding
data channel close acknowledgement is received from the peer (i.e.
SCTP reset of both incoming and outgoing streams is completed). This
restriction is to avoid the race conditions between arrival of "SDP
offer which reuses stream" with "SCTP reset which closes outgoing
stream" at the peer
6.2.5. Various SDP Offer/Answer Scenarios and Considerations
SDP offer has no a=dcmap attributes
* Initial SDP offer: No data channel is negotiated yet. The DTLS
connection and SCTP association is negotiated and, if agreed,
established as per [I-D.ietf-mmusic-sctp-sdp].
* Subsequent SDP offer: All the externally negotiated data
channels are expected be closed now. The DTLS/SCTP association
remains open for external or internal negotiation of data
channels.
SDP answer has no a=dcmap attributes
* Initial SDP answer: Either the peer does not support dcmap
attributes or it rejected all the data channels. In either
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case offerer closes all the externally negotiated data channels
that were open at the time of initial offer. The DTLS/SCTP
association will still be setup.
* Subsequent SDP answer: All the externally negotiated data
channels are expected be closed now. The DTLS/SCTP association
remains open for future external or internal negotiation of
data channels.
SDP offer has no a=dcsa attributes for a data channel.
* This is allowed and indicates there are no sub-protocol
parameters to convey.
SDP answer has no a=dcsa attributes for a data channel.
* This is allowed and indicates there are no sub-protocol
parameters to convey in the SDP answer. The number of dcsa
attributes in the SDP answer does not have to match the number
of dcsa attributes in the SDP offer.
7. Examples
SDP offer:
m=application 10001 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 10.10.10.1
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
a=dcmap:0 subprotocol="BFCP";label="BFCP"
SDP answer:
m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 10.10.10.2
a=max-message-size:100000
a=sctp-port 5002
a=setup:passive
a=connection:new
a=fingerprint:SHA-1 \
5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA
Figure 1: Example 1
In the above example the SDP answerer rejected the data channel with
stream id 0 either for explicit reasons or because it does not
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understand the a=dcmap attribute. As a result the offerer will close
the data channel created with the external negotiation option. The
SCTP association will still be setup over DTLS. At this point the
offerer or the answerer may use internal negotiation to open data
channels.
SDP offer:
m=application 10001 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 10.10.10.1
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
a=dcmap:0 subprotocol="BFCP";label="BFCP"
a=dcmap:2 subprotocol="MSRP";label="MSRP"
a=dcsa:2 accept-types:message/cpim text/plain text/
a=dcsa:2 path:msrp://alice.example.com:10001/2s93i93idj;dc
SDP answer:
m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 10.10.10.2
a=max-message-size:100000
a=sctp-port 5002
a=setup:passive
a=connection:new
a=fingerprint:SHA-1 \
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=dcsa:2 accept-types:message/cpim text/plain
a=dcsa:2 path:msrp://bob.example.com:10002/si438dsaodes;dc
Figure 2: Example 2
In the above example SDP offer contains data channels for BFCP and
MSRP sub-protocols. SDP answer rejected BFCP and accepted MSRP. So,
the offerer should close the data channel for BFCP and both offerer
and answerer may start using MSRP data channel (after SCTP/DTLS
association is setup). The data channel with stream id 0 is free and
can be used for future internal or external negotiation.
Continuing on the earlier example in Figure 1.
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Subsequent SDP offer:
m=application 10001 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 10.10.10.1
a=max-message-size:100000
a=sctp-port 5000
a=setup:actpass
a=connection:existing
a=fingerprint:SHA-1 \
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=dcsa:4 accept-types:message/cpim text/plain
a=dcsa:4 path:msrp://alice.example.com:10001/2s93i93idj;dc
Subsequent SDP answer:
m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 10.10.10.2
a=max-message-size:100000
a=sctp-port 5002
a=setup:passive
a=connection:existing
a=fingerprint:SHA-1 \
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=dcsa:4 accept-types:message/cpim text/plain
a=dcsa:4 path:msrp://bob.example.com:10002/si438dsaodes;dc
Figure 3: Example 3
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
opens a new MSRP data channel with stream id 4. The answerer
accepted the entire offer. As a result the offerer closes the
earlier negotiated MSRP related data channel and both offerer and
answerer may start using new the MSRP related data channel.
8. Security Considerations
No security considerations are envisaged beyond those already
documented in [RFC4566]
9. IANA Considerations
9.1. Subprotocol identifiers
Registration of new subprotocol identifiers is performed using the
existing IANA table "WebSocket Subprotocol Name Registry".
The following text should be added following the title of the table.
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"This table also includes subprotocol identifiers specified for usage
within a WebRTC data channel."
The following reference should be added to under the heading
reference: "RFC XXXX".
This document assigns no new values to this table.
NOTE to RFC Editor: Please replace "XXXX" with the number of this
RFC.
10. Acknowledgments
The authors wish to acknowledge the borrowing of ideas from other
internet drafts by Salvatore Loreto, Gonzalo Camarillo, Peter Dunkley
and Gavin Llewellyn, and to thank Christian Groves, Christer
Holmberg, Paul Kyzivat, Jonathan Lennox, and Uwe Rauschenbach for
their invaluable comments.
11. CHANGE LOG
11.1. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-01'
o New Section 4 regarding applicability to SDP offer/answer only.
o Addition of new Section 9.1 "Subprotocol identifiers" as
subsection of the "IANA Considerations" related Section 9. Also
removal of the temporary note "To be completed. As [I-D.ietf-
rtcweb-data-protocol] this document should refer to IANA's
WebSocket Subprotocol Name Registry defined in [RFC6455]."
o In Section 6.2.2:
* In the first paragraph replacement of the sentence "If an SDP
offer contains both of these parameters then such an SDP offer
will be rejected." with "If an SDP offer contains both of these
parameters then the receiver of such an SDP offer MUST reject
the SDP offer."
* In the second paragraph capitalization of "shall" and "may"
such that both sentences now read: "The SDP answer SHALL echo
the same subprotocol, max-retr, max-time, ordered parameters,
if those were present in the offer, and MAY include a label
parameter. They MAY appear in any order, which could be
different from the SDP offer, in the SDP answer."
* In the third paragraph replacement of the sentence "The same
information MUST be replicated without changes in any
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subsequent offer or answer, as long as the data channel is
still opened at the time of offer or answer generation." with
"When sending a subsequent offer or an answer, and for as long
as the data channel is still open, the sender MUST replicate
the same information.".
o In Section 6.2.2 the mapping of data channel types defined in
[I-D.ietf-rtcweb-data-protocol] to the SDP "a=dcmap" attribute
parameters were illustrated using example "a=dcmap" attribute
lines. Replacement of these example "a=dcmap" attribute lines
with just the "a=dcmap" attribute parameters being relevant for
the channel type.
o In Section 6.2.5 the description of bullet point "SDP offer has no
a=dcmap attributes - Initial SDP offer:" was "Initial SDP offer:
No data channel negotiated yet." Replacement of this description
with "Initial SDP offer: No data channel is negotiated yet. The
DTLS connection and SCTP association is negotiated and, if agreed,
established as per [I-D.ietf-mmusic-sctp-sdp]."
o In Section 6.2.5 in both bullet points related to "Subsequent SDP
offer" and "Subsequent SDP answer" replacement of "All the
externally negotiated data channels must be closed now." with "All
the externally negotiated data channels are expected be closed
now.".
o In Section 5.2.2's sixth paragraph beginning with "[ASSUMPTION]"
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"
there was a comment saying that "Either only maxretr-opt or
maxtime-opt is present. Both MUST not be present." Removal of
the second normative sentence and instead addition of following
new paragraph to the end of this section: "Within an 'a=dcmap'
attribute line's 'dcmap-opt' value either only one 'maxretr-opt'
parameter or one 'maxtime-opt' parameter is present. Both MUST
NOT be present."
o In Section 6.1.1.7 replacement of the first sentence "The
'ordered' parameter with value "true" indicates that DATA chunks
in the channel MUST be dispatched to the upper layer by the
receiver while preserving the order." with "The 'ordered'
parameter with value "true" indicates that the receiver MUST
dispatch DATA chunks in the data channel to the upper layer while
preserving the order.".
o In Section 6.2.3's first paragraph replacement of the one
occurrence of "must" with "..., it MUST wait until ...".
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o In Section 6.2.4:
* In the second paragraph replacement of "must" with "... whether
this closing MUST in addition ..."
* In the third paragraph replacement of the sentence "The port
value for the "m" line SHOULD not be changed (e.g., to zero)
when closing a data channel ..." with "The offerer SHOULD NOT
change the port value for the "m" line (e.g., to zero) when
closing a data channel ...".
* In the last but two paragraph replacement of the sentence "...
then an SDP offer which excludes this closed data channel
SHOULD be generated." with "... then the client SHOULD generate
an SDP offer which excludes this closed data channel.".
* In the last but one paragraph replacement of "must" with "The
application MUST also close...".
o In Section 6.1.2 addition of following note after the formal
definition of the 'a=dcsa' attribute: "Note that the above
reference to RFC 4566 defines were the attribute definition can be
found; it does not provide any limitation on support of attributes
defined in other documents in accordance with this attribute
definition."
11.2. Changes against 'draft-ietf-mmusic-data-channel-sdpneg-00'
o In Section 3 "WebRTC data channel" was defined as "A bidirectional
channel consisting of paired SCTP outbound and inbound streams."
Replacement of this definition with "Data channel: A WebRTC data
channel as specified in [I-D.ietf-rtcweb-data-channel]", and
consistent usage of "data channel" in the remainder of the
document including the document's headline."
o In Section 5 removal of following note: 'OPEN ISSUE: The syntax in
[I-D.ietf-mmusic-sctp-sdp] may change as that document progresses.
In particular we expect "webrtc-datachannel" to become a more
general term.'
o Consistent usage of '"m" line' in whole document as per [RFC4566].
o In Section 6.1.1 removal of the example dcmap attribute line
'a=dcmap:2 subprotocol="BFCP";label="channel 2' as there are
already four examples right after the ABNF rules in
Section 6.1.1.1. Corresponding removal of following related note:
"Note: This document does not provide a complete specification of
how to negotiate the use of a WebRTC data channel to transport
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BFCP. Procedures specific to each sub-protocol such as BFCP will
be documented elsewhere. The use of BFCP is only an example of
how the generic procedures described herein might apply to a
specific sub-protocol."
o In Section 6.1.1 removal of following note: "Note: This attribute
is derived from attribute "webrtc-DataChannel", which was defined
in old version 03 of the following draft, but which was removed
along with any support for SDP external negotiation in subsequent
versions: [I-D.ietf-mmusic-sctp-sdp]."
o Insertion of following new sentence to the beginning of
Section 6.1.1.1: "dcmap is a media level attribute having
following ABNF syntax:"
o Insertion of new Section 6.1.1.2 containing the dcmap-stream-id
specifying sentence, which previously was placed right before the
formal ABNF rules. Removal of the sentence 'Stream is a mandatory
parameter and is noted directly after the "a=dcmap:" attribute's
colon' as this information is part of the ABNF specification.
o In Section 6.1.1.1 modification of the 'ordering-value' values
from "0" or "1" to "true" or "false". Corresponding text
modifications in Section 6.1.1.7.
o In Section 6.1.1.1 the ABNF definition of "quoted-string" referred
to rule name "escaped-char", which was not defined. Instead a
rule with name "escaped" was defined. Renamed that rule's name to
"escaped-char".
o Insertion of a dedicated note right after the "a=dcmap:4"
attribute example in Section 6.1.1.1 regarding the non-printable
"escaped-char" character within the "label" value.
o In Section 6.1.2's second paragraph replacement of "sctp stream
identifier" with "SCTP stream identifier".
o In first paragraph of Section 6.2.1 replacement of first two
sentences 'For the SDP-based external negotiation described in
this document, the initial offerer based "SCTP over DTLS" owns by
convention the even stream identifiers whereas the initial
answerer owns the odd stream identifiers. This ownership is
invariant for the whole lifetime of the signaling session, e.g. it
does not change if the initial answerer sends a new offer to the
initial offerer.' with 'If an SDP offer / answer exchange (could
be the initial or a subsequent one) results in a UDP/DTLS/SCTP or
TCP/DTLS/SCTP based media description being accepted, and if this
SDP offer / answer exchange results in the establishment of a new
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SCTP association, then the SDP offerer owns the even SCTP stream
ids of this new SCTP association and the answerer owns the odd
SCTP stream identifiers. If this "m" line is removed from the
signaling session (its port number set to zero), and if usage of
this or of a new UDP/DTLS/SCTP or TCP/DTLS/SCTP based "m" line is
renegotiated later on, then the even and odd SCTP stream
identifier ownership is redetermined as well as described above.'
o In Section 6.2.3 the first action of an SDP answerer, when
receiving an SDP offer, was described as "Applies the SDP offer.
Note that the browser ignores data channel specific attributes in
the SDP." Replacement of these two sentences with "Parses and
applies the SDP offer. Note that the typical parser normally
ignores unknown SDP attributes, which includes data channel
related attributes."
o In Section 6.2.3 the second sentence of the third SDP answerer
action was "Note that the browser is asked to create data channels
with stream identifiers not "owned" by the agent.". Replacement
of this sentence with "Note that the agent is asked to create data
channels with SCTP stream identifiers contained in the SDP offer
if the SDP offer is accepted."
o In Section 6.2.4 the third paragraph began with "A data channel
can be closed by sending a new SDP offer which excludes the dcmap
and dcsa attribute lines for the data channel. The port value for
the m line should not be changed (e.g., to zero) when closing a
data channel (unless all data channels are being closed and the
SCTP association is no longer needed), since this would close the
SCTP association and impact all of the data channels. If the
answerer accepts the SDP offer then it MUST also exclude the
corresponding attribute lines in the answer. ..." Replacement of
this part with "The intention to close a data channel can be
signaled by sending a new SDP offer which excludes the "a=dcmap:"
and "a=dcsa:" attribute lines for the data channel. The port
value for the "m" line SHOULD not be changed (e.g., to zero) when
closing a data channel (unless all data channels are being closed
and the SCTP association is no longer needed), since this would
close the SCTP association and impact all of the data channels.
If the answerer accepts the SDP offer then it MUST close those
data channels whose "a=dcmap:" and "a=dcsa:" attribute lines were
excluded from the received SDP offer, unless those data channels
were already closed, and it MUST also exclude the corresponding
attribute lines in the answer."
o In Section 6.2.4 the hanging text after the third paragraph was
"This delayed close is to handle cases where a successful SDP
answer is not received, in which case the state of session should
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be kept per the last successful SDP offer/answer." Replacement of
this sentence with "This delayed closure is RECOMMENDED in order
to handle cases where a successful SDP answer is not received, in
which case the state of the session SHOULD be kept per the last
successful SDP offer/answer."
o Although dedicated to "a=dcmap" and "a=dcsa" SDP syntax aspects
Section 6.1.1 contained already procedural descriptions related to
data channel reliability negotiation. Creation of new
Section 6.2.2 and moval of reliability negotiation related text to
this new section.
11.3. Changes against 'draft-ejzak-mmusic-data-channel-sdpneg-02'
o Removal of note "[ACTION ITEM]" from section "subprotocol
parameter". As [I-D.ietf-rtcweb-data-protocol] this document
should refer to IANA's WebSocket Subprotocol Name Registry defined
in [RFC6455].
o In whole document, replacement of "unreliable" with "partially
reliable", which is used in [I-D.ietf-rtcweb-data-channel] and in
[I-D.ietf-rtcweb-data-protocol] in most places.
o Clarification of the semantic if the "max-retr" parameter is not
present in an a=dcmap attribute line. In section "max-retr
parameter" the sentence "The max-retr parameter is optional with
default value unbounded" was replaced with "The max-retr parameter
is optional. If the max-retr parameter is not present, then the
maximal number of retransmissions is determined as per the generic
SCTP retransmission rules as specified in [RFC4960]".
o Clarification of the semantic if the "max-time" parameter is not
present in an a=dcmap attribute line. In section "max-time
parameter" the sentence "The max-time parameter is optional with
default value unbounded" was replaced with "The max-time parameter
is optional. If the max-time parameter is not present, then the
generic SCTP retransmission timing rules apply as specified in
[RFC4960]".
o In section "label parameter" the sentence "Label is a mandatory
parameter." was removed and following new sentences (including the
note) were added: "The 'label' parameter is optional. If it is
not present, then its value defaults to the empty string. Note:
The empty string may also be explicitly used as 'label' value,
such that 'label=""' is equivalent to the 'label' parameter not
being present at all. [I-D.ietf-rtcweb-data-protocol] allows the
DATA_CHANNEL_OPEN message's 'Label' value to be an empty string."
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o In section "subprotocol parameter" the sentence "Subprotocol is a
mandatory parameter." was replaced with "'Subprotocol' is an
optional parameter. If the 'subprotocol' parameter is not
present, then its value defaults to the empty string."
o In the "Examples" section, in the first two SDP offer examples in
the a=dcmap attribute lines 'label="BGCP"' was replaced with
'label="BFCP"'.
o In all examples, the "m" line proto value "DTLS/SCTP" was replaced
with "UDP/DTLS/SCTP" and the "a=fmtp" attribute lines were
replaced with "a=max-message-size" attribute lines, as per draft-
ietf-mmusic-sctp-sdp-12.
11.4. Changes against '-01'
o Formal syntax for dcmap and dcsa attribute lines.
o Making subprotocol as an optional parameter in dcmap.
o Specifying disallowed parameter combinations for max-time and max-
retr.
o Clarifications on WebRTC data channel close procedures.
11.5. Changes against '-00'
o Revisions to identify difference between internal and external
negotiation and their usage.
o Introduction of more generic terminology, e.g. "application"
instead of "browser".
o Clarification of how "max-retr and max-time affect the usage of
unreliable and reliable WebRTC data channels.
o Updates of examples to take into account the SDP syntax changes
introduced with draft-ietf-mmusic-sctp-sdp-07.
o Removal of the SCTP port number from the a=dcmap and a=dcsa
attributes as this is now contained in the a=sctp-port attribute,
and as draft-ietf-mmusic-sctp-sdp-07 supports only one SCTP
association on top of the DTLS connection.
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12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, June
2002.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[I-D.ietf-rtcweb-jsep]
Uberti, J., Jennings, C., and E. Rescorla, "Javascript
Session Establishment Protocol", draft-ietf-rtcweb-jsep-09
(work in progress), March 2015.
[I-D.ietf-rtcweb-data-channel]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data
Channels", draft-ietf-rtcweb-data-channel-13 (work in
progress), January 2015.
[I-D.ietf-mmusic-sctp-sdp]
Holmberg, C., Loreto, S., and G. Camarillo, "Stream
Control Transmission Protocol (SCTP)-Based Media Transport
in the Session Description Protocol (SDP)", draft-ietf-
mmusic-sctp-sdp-14 (work in progress), March 2015.
[WebRtcAPI]
Bergkvist, A., Burnett, D., Jennings, C., and A.
Narayanan, "WebRTC 1.0: Real-time Communication Between
Browsers", World Wide Web Consortium WD-webrtc-20130910,
September 2013,
<http://www.w3.org/TR/2013/WD-webrtc-20130910/>.
12.2. Informative References
[I-D.ietf-rtcweb-data-protocol]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel
Establishment Protocol", draft-ietf-rtcweb-data-
protocol-09 (work in progress), January 2015.
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[RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC
4960, September 2007.
[RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message
Session Relay Protocol (MSRP)", RFC 4975, September 2007.
[RFC4976] Jennings, C., Mahy, R., and A. Roach, "Relay Extensions
for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
September 2007.
[RFC5547] Garcia-Martin, M., Isomaki, M., Camarillo, G., Loreto, S.,
and P. Kyzivat, "A Session Description Protocol (SDP)
Offer/Answer Mechanism to Enable File Transfer", RFC 5547,
May 2009.
[RFC6135] Holmberg, C. and S. Blau, "An Alternative Connection Model
for the Message Session Relay Protocol (MSRP)", RFC 6135,
February 2011.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC
6455, December 2011.
[RFC6714] Holmberg, C., Blau, S., and E. Burger, "Connection
Establishment for Media Anchoring (CEMA) for the Message
Session Relay Protocol (MSRP)", RFC 6714, August 2012.
Authors' Addresses
Keith Drage (editor)
Alcatel-Lucent
Quadrant, Stonehill Green, Westlea
Swindon
UK
Email: keith.drage@alcatel-lucent.com
Maridi R. Makaraju (Raju)
Alcatel-Lucent
2000 Lucent Lane
Naperville, Illinois
US
Email: Raju.Makaraju@alcatel-lucent.com
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Juergen Stoetzer-Bradler
Alcatel-Lucent
Lorenzstrasse 10
D-70435 Stuttgart
Germany
Email: Juergen.Stoetzer-Bradler@alcatel-lucent.com
Richard Ejzak
Unaffiliated
Email: richard.ejzak@gmail.com
Jerome Marcon
Unaffiliated
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