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

Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com> Tue, 25 November 2014 07:08 UTC

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From: =?iso-8859-1?Q?Stefan_H=E5kansson_LK?= <stefan.lk.hakansson@ericsson.com>
To: Justin Uberti <juberti@google.com>
Thread-Topic: [rtcweb] JSEP: Why always offer actpass?
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Date: Tue, 25 Nov 2014 07:08:30 +0000
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Subject: Re: [rtcweb] JSEP: Why always offer actpass?
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On 25/11/14 02:11, Justin Uberti wrote:
> Quoth RFC5763, Section 5:
>
>     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.)

>
>
> However I concur that the existing roles should be maintained, e.g. the
> answerer must choose active or passive appropriately.

Agreed.

> Chrome will fail
> upon an attempted role change.
>
> On Mon, Nov 24, 2014 at 7:36 AM, Stefan Håkansson LK
> <stefan.lk.hakansson@ericsson.com
> <mailto:stefan.lk.hakansson@ericsson.com>> wrote:
>
>     Hi,
>
>     I'm looking into the JSEP draft. One thing that seems strange is that in
>     every offer the role offered is "actpass", also for existing
>     connections. As I read section 7.3 of
>     https://www.rfc-editor.org/rfc/rfc4145.txt the established roles should
>     be maintained in such situations.
>
>     What is the reason for the always offering "actpass" also for
>     established roles/connections?
>
>     Stefan
>
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