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UCCX - RTP is lost when UCCX call over WAN is routed to an agent

Sujin Jebakar

Dear All,

We have the following Telephony set up.

Call Manager(4.1) --> Voice Gateway (site A - UK)   <------->   Voice Gateway (Site B - India) --> Call Manager (7.1) --> UCCX (7.1)

Site A, is our client telephony set up in the UK where as Site B is our offshore telephony set up in India. In India, we have offshore team located at various locations however they are all registered with a Call Manager in Site B. Local users are registered with the call manager through a LAN where as remote users are registered through WAN.

We developed a skill based call routing IVR script in the UCCX system. To execute the script, a telephony trigger has been crated in the UCCX system. Calls originated from any Cisco IP Phones registered with Call Manager in Site B, triggers the UCCX IVR application and selects an available agent from the skill set. Customer and agent would be able to hear each other when the UCCX has been routed to an agent.

The same script when triggered by a call from Site A, caller is able to hear IVR prompts and able to select menu options. It also routes the caller to an available agent. This call goes blank as soon as it has been answered by an agent (neither caller nor agent could hear each other). Also this call remain active for 15 sends before being dropped. However direct calls to any IP extensions in India from UK are working perfectly fine. Only the calls routed through UCCX system has this issue.

UCCX uses system default codec G711, where as calls received over WAN are G729. Codec G729 is getting translated to G711 by using a Transcoder in the voice gateway before being sent to the call manager.

We tried software MTP resource to work with the TRanscoder but normal calls are failing when a MTP resource is enabled.

Could you please help me if anyone came across similar problem in the past? Please share your opionions/solutions.

Note: I heard that Inter Cluster Trunk (ICT) set up would have worked fine for this requirement. But client is not ready to directly integrate their call manager with our call manager in India. They raised security oncerns to implement ICT. This is the reason why we are using gateway <-to-> gateway set up.




Gaurav Purohit

i think the phone is trying to negotiate codec different to G711 (check the enterprise parameter to supress G722, or at least on the phone).


Hi Sujin,

Please check the below discussion,

Hope it helps.


Please rate helpful posts..


Hello Sujin,

2 days ago, I faced same problem like you excatly .... I found the reason, as you said you are working with IVR (UCCX) system and ACD is involved to pickup any agent, during hold the caller will hear a music and after that the call is sent to the agnet in silent mode.....did you know that MOH server of CUCM is involved during queuing and it is streaming the music to the caller ?

If you just reset MOH server for pub and sub CUCMs or permit the GW to access MOH server through MRGL, your problem will be solved !!!!



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