[EMAIL PROTECTED] wrote:
> From: Anders Kristensen <[EMAIL PROTECTED]>
>
> There are legitimate usecases for SDP with no m= lines, see RFC 3725.
>
> Interesting!
>
> Though I see that RFC 3725 section 9.2 runs into a similar question to
> the one that started this thread:
>
> Therefore, it sends an INVITE (1) with SDP that contains no media
> lines. User A is interested in supporting preconditions, and does
> not want to ring its phone until resources are reserved. Since
> there are no media streams in the INVITE, it can't reserve
> resources for media streams, and therefore it can't ring the phone
> until they are conveyed in a subsequent offer and then reserved.
> Therefore, it generates a 183 with the answer, and doesn't alert
> the user (2).
>
> To get the desired behavior, the condition for ringing can't be
> "resources are reserved for all media streams" (since there are no
> media streams in the offer, resources are already reserved for all of
> them), the condition needs to be "resources are reserved for all
> accepted media streams and there must be at least one accepted media
> stream". (We also have to allow for two offered media streams, one of
> which the UA can't process -- we don't want to wait for resources to
> be reserved for that stream!)
Maybe. But this is a little bit different.
It may be that in the case of a medialess call the UA can auto-answer
without alerting. The user of the device is likely not so interested if
there is no media, so potentially the device could just answer and
postpone alerting until media are added to the session.
But this depends strongly on the details of the UI of the device. In
general a device probably doesn't want to accept a medialess call unless
it has some way to know that it will eventually turn into something useful.
Paul
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