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

[Christer Holmberg <[e-mail]>]

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

Regards,

Christer