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

[Michael Tüxen <[e-mail]>]

On Nov 11, 2011, at 6:33 PM, Eric Rescorla wrote:

> On Fri, Nov 11, 2011 at 9:31 AM, Michael Tüxen
> <[e-mail]> wrote:
>> On Nov 11, 2011, at 6:14 PM, Eric Rescorla wrote:
>> 
>>> On Fri, Nov 11, 2011 at 9:01 AM, Michael Tüxen
>>> <[e-mail]> wrote:
>>>> On Nov 11, 2011, at 3:51 PM, Eric Rescorla wrote:
>>>> 
>>>>> On Fri, Nov 11, 2011 at 5:15 AM, Michael Tuexen
>>>>> <[e-mail]> 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.
Correct.

Best regards
Michael
> 
> Best,
> -Ekr
>