Re: [rtcweb] PRANSWER is unusable for serial forking

Iñaki Baz Castillo <> Tue, 09 October 2012 09:25 UTC

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From: =?UTF-8?Q?I=C3=B1aki_Baz_Castillo?= <>
Date: Tue, 9 Oct 2012 11:24:38 +0200
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To: Roman Shpount <>
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Subject: Re: [rtcweb] PRANSWER is unusable for serial forking
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2012/10/9 Roman Shpount <>om>:
> SIP does not have serial forking.

SIp has serial forking but just at signaling level, not at media level :)

> Offer/Answer does not describe something
> like this.


> We either need to define it and make it something that describes
> some set of existing scenarios or add support for something that is defined.

IMHO the solution is described in other mail thread (maybe in rtcweb
WG): implement cloning. Example:

- My JS SIP app sends an INVITE with SDP and receives a 183 response
with To-tag "AAAA" and SDP A, so I already have a media stream.

- Later the voicemail system answers the call so replies a 200 with
To-tag "BBBB" and SDP B. Since To-tag is different I do know (as per
RFC 3261/3264) that I should create another media "session" sharing my
local SDP (but cloning it). And I also want to close the previous one.

Of course, for this we need some API method like
"cloneLocalDescription(new_remote_sdp_object)" or whatever.

AFAIR this has been recently discussed in rtcweb WG.

Iñaki Baz Castillo