Re: [rtcweb] RTCWEB data channel protocol: Do both endpoints need to send DATA_CHANNEL_OPEN?

[Salvatore Loreto <[e-mail]>]

On Jan 28, 2014, at 10:37 AM, Christer Holmberg <[e-mail]>
 wrote:

> Hi Sal,
>  
>>> As defined in draft-ietf-rtcweb-data-channel-06, a data channel consists of two unidirectional SCTP streams.
>>> exactly it is a pair of one ingoing and one outgoing stream
>>> 
>>> draft-ietf-rtcweb-data-protocol-01 says that, if one endpoint wants to open a data channel, it sends a 
>>> DATA_CHANNEL_OPEN (using a SCTP stream ID value of its choice). Then, the other endpoints sends 
>>> DATA_CHANNEL_ACK on the same SCTP stream (eventhough it is a unidirectional stream).
>>> 
>> not exactly, it says with the same stream identifier
>> 
>>  If a DATA_CHANNEL_OPEN message is received on an unused stream, the
>>  stream identifier corresponds to the role of the peer and all
>>  parameters in the DATA_CHANNEL_OPEN message are valid, then a
>>  corresponding DATA_CHANNEL_ACK message is sent on the stream with the
>>  same stream identifier as the one the DATA_CHANNEL_OPEN message was
>>  received on.
>> that means that means that the outgoing stream should have the same stream identifier of the ingoing one.
>> I understand is not clear at first read, we will try to clarify better 
> 
> Thanks.
> 
> I also think it would be good to add some call flows to the draft.
> 
>>> Q1: Assuming that both endpoints want to use the data channel, do both endpoints need to send DATA_CHANNEL_OPEN 
>>> (on separate SCTP streams)? Or, can one of the endpoints, if it has received DCO, start using the data channel (using a SCTP stream of its choice)?
>> 
>> sorry I don't understand the question.
>> Are you asking for both endpoints trying to open the same channel and how avoid glare in opening channels
>> or you are looking in the scenario where both endpoints want to open to different channels?
> 
> I am not talking about a glare situation.
> 
> I am talking about where an endpoint has received a DCO, and replied with a DCA. Then, that endpoint also wants to use the data channel.

well a DataChannel is bidirectional then it can be used to send data from both the sides once it is open.


> Does it also have to send a DCO? I assume not, but I think it would be good to make that more clear.

you are right, it has not to do.
OK point taken, we will clarify this point also.

br
Salvatore


> 
> Regards,
> 
> Christer
>