Re: [rtcweb] Sending of zero-length messages over data channels

On 23 Jul 2014, at 08:00, Makaraju, Maridi Raju (Raju) <Raju.Makaraju@alcatel-lucent.com> wrote:

>  
> In the existing data channel protocol, it's not possible to send zero-length messages, because SCTP prohibits it.
>  
> While this may seem to be an academic point, it does represent a divergence from WebSockets, and this difference could be meaningful to applications who use empty messages for keepalives. Or maybe the Yo app.
>  
> Since we can't send a zero-length SCTP message, I propose we add a PPID_EMPTY value or something similar to indicate a message with empty content.
> [Raju] There is a genuine need for this and the proposal is good.
> However, I am thinking of an alternate proposal to achieve the same but in a generic way.
> Define a PPID_OOB (out of band) or something similar.
> Apps can use this to send a message of non-zero length. For the “Yo” kind of app or empty stream-level heartbeat purpose, app can send a 1 byte length message, which other end’s app ignores.
What do you want to check with the heartbeat purpose? If you can talk to the peer?
That doesn't need to be done for every data channel, but only once for all of them.
As far as I understand, this is done by ICE...

Best regards
Michael
> This approach involves bit more API work for webrtc to have a variation of send(data, oobFlag) and new data type in onmessage(). IMHO, this approach allows more possibilities in future and also the same approach can be used by other SCTP use cases not involving webrtc.
>  
> BR
> raju
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