#190 SIP remote hold improvements

[Simon Zwahlen]

We've seen compatibility problems with hold/retrieve when testing against some Siemens devices (which use a M5T [Mediatrix] SIP Stack).

The main problem is that the remote sends a re-invite without SDP to retrieve the call.

Attached is a patch against current HEAD with the following changes:
- accept Re-Invite without SDP (while being held) as retrieve from hold
- don't stop the media if the call is retrieved, as the media streams are un-paused
- don't restart the media on invite ack when the call is held, as the media streams are paused

Btw, also needed for compatibility is patch 1429209, but that's another story :-)

[Simon Zwahlen]

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After a bit more thinking about it, I'd rather remove the some things from this patch. Seems like the re-establishment of media channels is correct (but there's another bug associated with this (affects H.323 too, see mailing list)).

Attaching reworked, more trivial patch.

[Simon Zwahlen]

Patch against current HEAD

[Simon Zwahlen]

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Again renewed patch with the following changes:
- accept Re-Invite without SDP (while being held) as retrieve from hold
- don't restart the media on ACK when the call is held, as the media streams are paused

I think I finally got it right this time :-)

[Craig Southeren]

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Applied