Re: [rtcweb] New Version Notification for draft-jesup-rtcweb-data-01.txt

Eric Rescorla <ekr@rtfm.com> Fri, 11 November 2011 17:34 UTC

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References: <20111031211134.8188.49554.idtracker@ietfa.amsl.com> <4EAF64FF.8020101@jesup.org> <02485FF93524F8408ECA9608E47D9F2007CACFFAC2@nambx05.corp.adobe.com> <474200CA-F509-438B-A9CD-71742F4AF6B7@lurchi.franken.de> <CABcZeBOEUseuR-dHkxxnan1Gy0aKG+07DSTJAGzOt7ii_2aw3A@mail.gmail.com> <20483DC8-9370-47C1-9C99-03624EB9C281@lurchi.franken.de> <CABcZeBOJdFzmVqd02_a=-psKvqDAujAkoWRsFYFK=fNWj+QDqA@mail.gmail.com> <360EF6F3-E5E6-4690-BAA2-211F3CAFDF1F@lurchi.franken.de>
From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 11 Nov 2011 09:33:53 -0800
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Subject: Re: [rtcweb] New Version Notification for draft-jesup-rtcweb-data-01.txt
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On Fri, Nov 11, 2011 at 9:31 AM, Michael Tüxen
<Michael.Tuexen@lurchi.franken.de>; wrote:
> On Nov 11, 2011, at 6:14 PM, Eric Rescorla wrote:
>
>> On Fri, Nov 11, 2011 at 9:01 AM, Michael Tüxen
>> <Michael.Tuexen@lurchi.franken.de>; wrote:
>>> On Nov 11, 2011, at 3:51 PM, Eric Rescorla wrote:
>>>
>>>> On Fri, Nov 11, 2011 at 5:15 AM, Michael Tuexen
>>>> <Michael.Tuexen@lurchi.franken.de>; wrote:
>>>>> Hi Michael,
>>>>>>  o DTLS and SCTP handshakes must be performed serially (no matter which order they happen in), which increases the number of round-trips necessary to establish communication.
>>>>> That is correct. SCTP adds one RTT to whatever DTLS is requiring.
>>>>> So when using SCTP/DTLS/UDP, DTLS needs 3 RTTs (including the initial
>>>>> RTT required for the Cookie exchange).
>>>>> When using DTLS/SCTP/UDP DTLS needs 2 RTTs (since there is no need for
>>>>> the DTLS Cookie).
>>>>
>>>> There's no need for the DTLS cookie in either case, actually, since ICE provides
>>>> the appropriate proof of return routability.
>>> I don't know much about ICE....
>>> So assume that the endpoint willing to accept DTLS connections.
>>> Can't I just send an ClientHello via plain UDP to the endpoint (assuming that I can reach it)?
>>
>> When ICE is involved, there's no real concept of "an endpoint willing to
>> accept DTLS connections". At a high level, the way that ICE works is
>> that the communicating parties establish a session out of band and
>> then use the ICE handshake to bind one or valid 5-tuple flows to the
>> the session. Packets that arrive at one endpoint that aren't part of one
>> of these flows can more or less be discarded. (At least at this stage).
> OK, you you only pass those packets to DTLS, which belong to the 5 tuple
> which you have already communicated with, and discard the others, it is OK.
> So SCTP needs one RTT, DTLS two.

Possibly < two for DTLS, because of resumption and False Start. So, somewhere
between 1 and 2.

Best,
-Ekr