Re: [rtcweb] Opening unordered data channel issue

Eric Rescorla <ekr@rtfm.com> Fri, 23 August 2013 19:08 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 23 Aug 2013 12:07:17 -0700
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To: Harald Alvestrand <harald@alvestrand.no>
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Subject: Re: [rtcweb] Opening unordered data channel issue
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+1


On Fri, Aug 23, 2013 at 8:46 AM, Harald Alvestrand <harald@alvestrand.no>wrote;wrote:

> I like this solution (b). Let's Just Do It.
>
>
> On 08/22/2013 05:52 PM, Michael Tuexen wrote:
> > Dear all,
> >
> > at the last IETF in Berlin we discussed how to handle the opening of
> > unordered data channels (no matter wether reliable or not). The problem
> > to be handled is that it is possible that user messages arrive at the
> > receiver before the DATA_CHANNEL_OPEN message is received. The result
> > of the discussion at the meeting was that the best solution is that
> > the sender sends user messages also ordered (on unordered channels)
> > until there is an indication from the peer that the DATA_CHANNEL_OPEN
> > has been processed. This makes sure that the DATA_CHANNEL_OPEN message
> > is not received before user messages and therefore the above problem
> > is solved.
> >
> > The open issue is, what the indication from the peer is. There were
> > two options discussed at the meeting and it was decided that Randall
> > Stewart and myself bring this to the list with the pros and cons
> > of the alternatives. So here are the two options:
> >
> > (a) Use any user message sent from the peer as an indication.
> > (b) Use a new ACK message.
> >
> > Arguments:
> > * Using (b) introduces a 2-way handshake for unordered data channels.
> >   However, it also works for data channels being used unidirectional.
> > * Using (a) stays with the 1-way handshake, but in case of
> >   data channels being used unidirectional you will not see the benefits
> >   of unordered delivery.
> >
> > We had some discussions offline and think that using (b) is the
> > cleaner solution. Please note that this 2-way handshake is not
> > similar to the one we had some time ago. The ACK does not contain
> > any additional information and it does not introduce any delay.
> > You can send user data right after opening the data channel.
> >
> > For consistency we would even propose to use this 2 way handshake
> > for ordered channels. It doesn't have any drawback and would mean
> > that we use the same handshake for all data channels.
> >
> > So the proposed procedure for opening an arbitrary data channel is:
> > 1) The opener sends a DATA_CHANNEL_OPEN message ordered and reliable.
> > 2) The opener can start sending user data immediately.
> >    It will always be sent ordered, no matter whether the data channel
> >    is ordered or not.
> > 3) The peer will send a DATA_CHANNEL_ACK message ordered and reliable
> >    in response to the DATA_CHANNEL_OPEN message.
> > 4) After reception of the DATA_CHANNEL_ACK message,
> >    the opener will sent user messages unordered,
> >    if the data channel is unordered and ordered, if the
> >    data channel is ordered.
> >
> > Any opinions?
> >
> > Best regards
> > Michael
> >
> > _______________________________________________
> > rtcweb mailing list
> > rtcweb@ietf.org
> > https://www.ietf.org/mailman/listinfo/rtcweb
>
>
> --
> Surveillance is pervasive. Go Dark.
>
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