Re: [clue] CLUE Data Channel: SDP Offer/Answer Proceudres

[Christian Groves <[e-mail]>]

Hello Christer,

With the use of webrtc-datachannel how do I negotiate via SDP whether I 
want to use clue or not?

A SCTP association (and thus webrtc-datachannel) for example could be 
used for BFCP,CLUE and T.38. It seems wasteful to establish the SCTP 
association to figure out that the endpoints support webrtc-datachannel 
put don't support the application that you want.

In the example in section 4.6 there's no way of distinguishing that 
description for CLUE vs BFCP vs anything else. Its not a CLUE data 
channel is a generic data channel.

Regards, Christian

On 16/02/2014 1:03 AM, Christer Holmberg wrote:
> Hi,
>
> The draft submission deadline has passed, but I still wrote some more text, shown below, for the SDP Offer/Answer Procedures section.
>
> Regards,
>
> Christer
>
> PS. Note that I will be on vacation next week, so I will once again do my best trying to stay away from e-mails :)
>
> -----------------------
>
> 4.  SDP Offer/Answer Procedures
>
> 4.1.  General
>
>     This section describes how the SDP media description ("m=") line for
>     a CLUE data channel is created, and how it is used in SDP offers and
>     answers.
>
>     NOTE: The proceudres associated with "m=" lines for other media types
>     (e.g. audio and video) used in a CLUE session are outside the scope
>     of this document.
>
>     OPEN ISSUE #3: It is FFS whether the SDP-based WebRTC Data Channel
>     Negotiation mechanism [I-D.ejzak-dispatch-webrtc-data-channel-sdpneg]
>     will be used with the CLUE data channel.
>
>     NOTE: If [I-D.ejzak-dispatch-webrtc-data-channel-sdpneg] will be used
>     with the CLUE data channel, a new associated 'sub-protocol' value
>     needs to be registered with IANA.
>
> 4.2.  SDP Media Description Fields
>
>     The field values of the "m=" line for the CLUE data channel are set
>     as following:
>
>     +----------------+----------------+------------------------+----------------+
>     |     media      |      port         |      proto               |      fmt         |
>     +----------------+----------------+------------------------+----------------+
>     | "applicationS |   DTLS port   | "UDP/TLS/UDPTL" |   SCTP port   |
>     |                    |     value       |                             |     value       |
>     +----------------+----------------+------------------------+---------------+
>
>                       Table 1: SDP "proto" field values
>
> 4.3.  SDP sctpmap Attribute
>
>     The field values of the SDP sctpmap attribute associated with the
>     CLUE data channel "m=" are set as following:
>
>     +---------------------+---------------------------+-----------------------+---------+
>     | sctpmap-number |         app                  | max-message-size | stream |
>     +---------------------+---------------------------+-----------------------+---------+
>     |  fmt value of       | "webrtc-datachannel" |  Implemenation     |  "1"     |
>     | the "m=" line      |                                |     specific             |           |
>     +---------------------+---------------------------+-----------------------+---------+
>
>                       Table 2: SDP "proto" field values
>
> 4.4.  SDP Offerer Procedures
>
>     The procedures for the offerer follow the normal proceures defined in
>     [ref-to-3264].
>
>     When the offerer creates an offer, which contains an "m=" line for a
>     CLUE data channel, it assigns the field values to the "m=" line
>     according to the procedures in Section 4.2.  In addition, the offerer
>     MUST insert an SDP sctpmap attribute associated with the "m=" line.
>
>     In an offer, the offerer MUST NOT insert more than one "m=" line for
>     a CLUE data channel.
>
>     NOTE: CLUE does not support the usage of multiple CLUE data channels.
>
>     The offerer MUST NOT insert more than one SDP sctpmap attributes in
>     an "m=" line for a CLUE data channel.
>
>     If an offerer, in a subsequent offer, wants to disable the CLUE data
>     channel, it assigns a zero port value to the "m=" line associated
>     with the CLUE data channel.  The answerer MUST NOT insert an SDP
>     sctpmap attribute associated with the "m=" line.
>
> 4.5.  SDP Answerer Procedures
>
>     The procedures for the answerer follow the normal proceures defined
>     in [ref-to-3264].
>
>     If the answerer receives an offer, which contains an "m=" line for a
>     CLUE data channel, and the answerer accepts the "m=" line, it creates
>     and inserts an "m=" line in the associated answer.  The answerer
>     assigns the field values to the "m=" line according to the procedures
>     in Section 4.2.
>
>     If, in the offer, a zero port value has been assigned to the "m="
>     line for the CLUE channel, or it the answerer does not accept the
>     "m=" line, but accepts other "m=" lines in the offer (i.e. the
>     answerer will not reject the whole offer), it still inserts an "m="
>     line for a CLUE data channel in the associated answer.  The answerer
>     then assigns a zero port value to the "m=" line.  The answerer MUST
>     NOT insert an SDP sctpmap attribute associated with the "m=" line.
>
> 4.6.  Example
>
>          m=application 54111 SCTP/DTLS 54111
>          a=sctpmap:54111 webrtc-datachannel max-message-size=100000 streams=1
>
>            Figure 1: SDP Media Description for a CLUE data channel
>
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