You are asking two different questions. More inline.
Subbu Rajendran wrote:
> Hi,
> SIP RFC 2543 uses c=0.0.0.0 method to put a call on hold. RFC 3264 has
> introduced a=sendonly/recvonly/inactive/sendrecv attributes that can be used
> put media to one way, hold and 2-way. However what should be the precedence
> to be followed? Consider the case below
The current recommendation for putting a call on hold is to use sendonly
or inactive, rather than c=0. But that isn't normative behavior. We
haven't standardized "putting on hold".
However reinviting with c=0 and/or a=sendonly is all legal. There are
reasons to do so that have nothing to do with hold.
> A Re-INVITE with SDP
> v=0
> o=user1 53655765 2353687637 IN IP4 192.168.1.100
> s=-
> c=IN IP4 0.0.0.0
> t=0 0
> m=audio 6001 RTP/AVP 0
> a=rtpmap:0 PCMU/8000
> a=recvonly
>
> How should the SIP endpoint receiving this Re-INVITE interpret the SDP,
> w.r.t the flow of media. Which method should be given preference.
> Any help in this context is very much appreciated.
When on the receiving side, you need to respond appropriately to what
has been offered, taking it at face value. You cannot draw any reliable
conclusion about the feature that led to this signaling. It *might* mean
you have been put on hold. Or it might simply mean that the offerer
can't handle the media right now for some other reason.
In this case, since the IP address of the media is 0, which is unusuable
for sending media, you definitely won't be able to send media, or even
RTCP. Because of the a=sendonly, you still have the opportunity to
respond with either a=recvonly or a=inactive depending on whether you
want to receive media in this case.
Thanks,
Paul
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