I noticed on a SIP trace that when Jabber is taking a call off hold that it sends 2 SIP re-INVITE's -- one with SDP and the second with no SDP. Can someone explain why this is so ? What is the purpose of the 2nd re-INVITE ?
Putting a call on hold a re-INVITE is sent with the following in the SDP, most lines omitted
c=IN IP4 0.0.0.0 ** this is indicating call is put on hold
m=audio 20346 RTP/AVP 0 8 18 111 101
a=inactive *** this also indicates call on hold
But when taking the call off hold there are 2 re-INVITE's sent, first re-INVITE has this SDP, most omitted
c=IN IP4 0.0.0.0
m=audio 28386 RTP/AVP 0 101 ** I notice the port # has changed here
a=inactive
And the 2nd re-INVITE has no SDP ?? I notice it is sent after the ACK from our SBC is sent for the first re-INVITE.
