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Problem in transferring call from agent to pstn phone(Error:Resource unavailable)


this is a Contact centre enterprise setup (CUCM 8.5) where there is CUCM,CVP,Voice Gateway and agent using CAD.

Caller calls the CVP IVR number, call gets routed to the free agent.
Call is taken by the agent. Agent now tries to transfer this call to an external number(say mobile phone) and initiates the call. The external mobile phone rings, the mobile phone recipient takes the call and the agent and mobile phone receipient can talk (the  call centre caller is on hold), but the moment the agent presses the transfer button to complete the transfer, the call drops.
The Call flow is PSTN -> Voice Gateway-> CVP(IVR)->SIP Trunk-> CUCM-> Agent -> transfer to external mobile number  .... issue when transfer is completed.

On the voice gateway while running the ISDN debug, I see the error message:

Cause i = 0x80AF - Resource unavailable, unspecified

which looks to me like a codec mismatch. I have checked the region configuration is o.k. on CUCM.

Question: Does this need transcoding?? I don't think so.

The issue is only when the agent presses the transfer button again to complete the transfer,as then the call drops.

However, for the following scenario, the case where call comes to IP Phone as DID from PSTN, and IP Phone call recepient wants to transfer this call to the recepient there is no issue.The Call flow is PSTN -> Voice Gateway-> CUCM-> IP Phone -> call transfer to ext mobile number... No issue

The issues is noted when UCCE is involved.

Any suggestions what and where is the problem.


  • IP Telephony
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Problem in transferring call from agent to pstn phone(Error:Reso

Your SIP trunk is probably configured with MTP enabled and looks like you are running out of MTPs or your MTPs are in region that require transcoding.