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

[Christian Groves <[e-mail]>]

Hello Christer,

I think that for the signaling we must specify a way of negotiating at 
the SDP level whether CLUE is supported. I agree there's lots of ways it 
could be done but we need to indicate which one/s CLUE should use.

So for the SDP O/A procedures and example I think you have to assume the 
use of draft-ejzak-mmusic-data-channel-sdpneg otherwise you can't say 
its a CLUE data channel according to the SDP given. You're just opening 
a generic channel, which may or may not be clue. Particularly in the 
Answerer's case, it doesn't know that the Offer is going to use the 
channel for CLUE.

However:
m=application 54111 SCTP/DTLS 54111
a=sctpmap:54111 webrtc-datachannel max-message-size=100000 streams=1
a=dcmap:54111 stream=2;label="CLUE 1"; subprotocol="CLUE"; max_retr=3

would unambiguously define it as a CLUE data channel.

Regards, Christian

On 17/02/2014 11:16 AM, Christer Holmberg wrote:
> Hi Christian,
>
> If you want to negotiate usage of CLUE (or, any other specific usage of a webrtc-datachannel) in SDP, one option is to use Richard's draft. The usage of that draft is listed as an open issue in the CLUE data channel draft.
>
> SIP also provides other mechanisms, e.g. media feature tags, for indicating support of features.
>
> Regards,
>
> Christer
>
> Sent from my Sony Ericsson Xperia arc S
>
> Christian Groves <[e-mail]> wrote:
>
>
> 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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