Re: [rtcweb] Data Channel Protocol: Prevent DATA_CHANNEL_OPEN glare

[Christer Holmberg <[e-mail]>]

Hi,

>>>> As is defined in the data channel protocol, an entity can send data once DATA_CHANNEL_OPEN has been sent, before the associated DATA_CHANNEL_ACK is received.
>>>> 
>>>> The draft also says that, if both endpoints send DATA_CHANNEL_OPEN at the same time, using different stream id values, the result may be TWO data channels, with data sent on both.
>>>> 
>>>> However, as is also indicated, the draft does not provide a mechanism to prevent/handle such glare situation.
>>>> 
>>>> I personally think there shall be a way to prevent such situation, or otherwise I'm sure we are going to end up with interoperability problems.
>>>> 
>>>> Couldn't we e.g. say that, by default, the DTLS client is responsible for sending the DATA_CHANNEL_OPEN? Then there is no risk for glare, and it could even use both an even or odd stream id value.
>>> Section 4 reads:
>>> 
>>>  To avoid glare in opening Channels, each side MUST use either even 
>>> or  odd Streams when sending a DATA_CHANNEL_OPEN message.  The method  
>>> used to determine which side uses odd or even is based on the  
>>> underlying DTLS connection role when used in WebRTC, with the side  
>>> acting as the DTLS client using even stream identifiers.
>>> 
>>> So there is no problem in setting up data channels.
>>> 
>>> This should not be confused by both sides setting up a data channel with the same Label. This ends up in two data channels with the same label.
>>> You can even create more data channels with the same label.
>> 
>> My point is that I don't want to end up with more than one channel.
> And you won't, see above. 

I am not sure I understand. What text do you refer to?

> However, there is no mechanism to ensure uniqueness for labels. The WebRTC API already allows one side to create n data channels with the same label.

I am not saying it should be forbidden to do so. But, for protocol X, I want to end up with ONE data channel between my peers.

If I end up with two data channels for protocol X, can I send data on whichever I want to? 

Regards,

Christer