No Audio for IP Communicator on SIP trunk

[CaseFile]

I am running CUCM 10.5.2
We set up IP Communicator to come in on our VPN.
When we try to use Communicator, it works fine calling both directions to phones registered on CUCM.
It works calling both directions calling out the PRI connected to CUCM.

But there is no audio if a call is placed or received on the SIP trunk attached to CUCM.
The call will ring in, and it can be answered on Communicator, but there is no audio.
The same occurs on outgoing calls, I can see the call in the router with 'sh active calls'.
But the T<sec> never starts counting, it stays at T0, even after the call is answered with no audio.

So the config is:
Communicator > VPN > CUCM > SIP trunk no audio, but connections are made on in and out calls
Communicator > VPN > CUCM > PRI trunk works fine on in and out calls
Communicator > VPN > CUCM > Phones Registered to CUCM works fine on in and out calls

It used to work okay, and our network guru says he has made no changes (he always says that)
Anybody have any idea where my trouble might be ?

 

[thepfy]

How is the SIP trunk connected to CUCM? via a CUBE or direct?

with SIP the call control messages go to Subscriber but the audio runs direct between the two endpoints.
I would check that the SIP trunk can route to the VPN addresses.
It could be the firewall is blocking the port range used for the RTP stream.

 

[CaseFile]

SIP is connected to a CUBE.
But the fact that audio goes directly between SIP and endpoint gives me a direction to look.
Any other suggestions appreciated

 

[thepfy]

If it goes via a CUBE the audio will go via the CUBE.
It may be worth doing some packet captures on the CUBE.
It could be CODEC related.

 

[gnrslash4life]

I would think RTP is being blocked. Codec issues dont result in no audio. They result in failed calls.

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