Re: [rtcweb] JSEP: Why always offer actpass?

Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com> Tue, 25 November 2014 17:38 UTC

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From: =?iso-8859-1?Q?Stefan_H=E5kansson_LK?= <stefan.lk.hakansson@ericsson.com>
To: "Makaraju, Maridi Raju (Raju)" <Raju.Makaraju@alcatel-lucent.com>, "Justin Uberti" <juberti@google.com>
Thread-Topic: [rtcweb] JSEP: Why always offer actpass?
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Date: Tue, 25 Nov 2014 17:38:32 +0000
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Subject: Re: [rtcweb] JSEP: Why always offer actpass?
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On 25/11/14 17:28, Makaraju, Maridi Raju (Raju) wrote:
>>> o  The endpoint MUST use the setup attribute defined in [RFC4145
>> <https://tools.ietf.org/html/rfc4145>].
>>> The endpoint that is the offerer MUST use the setup attribute
>>> value of setup:actpass and be prepared to receive a client_hello
>>> before it receives the answer.  The answerer MUST use either a
>>> setup attribute value of setup:active or setup:passive.  Note
>>> that if the answerer uses setup:passive, then the DTLS handshake
>>> will not begin until the answerer is received, which adds
>>> additional latency. setup:active allows the answer and the DTLS
>>> handshake to occur in parallel.  Thus, setup:active is
>>> RECOMMENDED.  Whichever party is active MUST initiate a DTLS
>>> handshake by sending a
>>>
>>> ClientHello over each flow (host/port quartet).
>>
>> The section quoted seem to refer to the initial offer/answer, later
>> in that document (section 6.6, with heading "Session Modification")
>> there is wording that (to me at least) hints at keeping the
>> established roles in subsequent offers.
>>
>> A different question is the value of initially offering actpass
>> when ICE is mandatory to use. ICE connectivity checks will happen
>> before the DTLS handshake, so perhaps initially offering passive
>> would make sense. (actpass is a MUST according to 5763, OTOH 5763
>> is only an informal ref to JSEP.)
>
> <Raju> Limiting it to "passive" would force the peer and/or
> intermediaries to support DTLS client functionality as well. IMHO,
> this may limit the success rate. If a peer or middlebox does not
> support DTLS client functionality then it can always return
> "passive", which may involve bit more delay in DTLS setup. But it is
> not that bad as the SDP offerer must wait for SDP answer
> (a=fingerprint is needed) before the DTLS can be setup successfully
> anyway. </Raju>

Thanks Raju, seems this was a bad proposal - forget you heard it!

Do you have an opinion on my main "topic": that subsequent offers should 
offer the already negotiated role, rather than always "actpass"?

Br,
Stefan

>
> BR Raju
>