[SIPForum-discussion] Regarding Early Media and Preconditions.

[Stephen James]

The scenario is an MGCF (SIP - ISUP interworking IMS - PSTN). SIP preconditions 
are in use. 


We receive an INVITE with SDP as follows (modified for security)

v=0
o=- 3553598070 3553598070 IN IP4 10.0.0.10
s=-
c=IN IP4 10.0.0.10
t=0 0
m=audio 59068 RTP/AVP 0
a=sendrecv
a=curr:qos local none
a=curr:qos remote none
a=des:qos mandatory local sendrecv
a=des:qos mandatory remote sendrecv

Now, according to 3264, once this offer is sent, the UAC should be ready to 
receive media; however
the preconditions seem to contradict this. And in actuality the bearer is not 
set up and the UAC cannot
receive the early media.

In the MGCF we need to play an announcement due to network conditions. Since the 
SDP is indicating
sendrecv, that should be possible. The UAC does not receive our packets. 

- Should we complete the preconditions sequence prior to playing early media?
  - This is 183, PRACK, 200 OK (Prack), UPDATE, 200 OK (UPDATE)
- Should the UAC not put a=sendrecv in the SDP when in fact it cannot receive 
early media?
  - This would be more explicit in the need to complete the preconditions.


 
Stephen James 
sjames_1958 at yahoo.com
 
We are not princes of the earth, we are the descendants of worms, and any 
nobility must be earned.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sipforum.org/pipermail/discussion/attachments/20120813/3f011e99/attachment-0002.html>