Over the last few weeks I have been testing OCS R2 mediation server in the lab and I came across a curious problem. Inbound calls from our Cisco environment failed to generate ringback. We are currently deploying using the Cisco ISR setup as an IP-IP GW but this also affected direct SIP when inbound calls passed through the Cisco environment from the PSTN. Cisco have a bug identified (CSCsw34198) and hopefully this will be fixed soon.
The cause of the issue. Early media sort of. Or should I say the flow of messages that allow early media. Below is an excerpt from the bug.
Symptom:Once early media is cut-through in SIP-TDM Gateway using 183/Progress message and later followed by ALERT/180, then the VTSP SPI will suppress the packet as Gateway needs the play local ringback. And later again 183/Progress is received on the Gateway the media is not flowing through as the packets are suppressed in this state and the packets will be unsuppressed only when 200OK/Connect is received.
When first early media is cut-through and later followed by ALERT/180, which suppress the packet as to feed local ringback will reopen for packet only in 200OK/Connect. So any 183/Progress message again used to re-establish the early media between ALERT/180 and Connect/200OK fails.
This problem does not seem to be just limited to OCS R2 integration though, which means it may speed up the resolution.