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New Member

No sound or Ringback for outbound calls to the pstn E1



I need help with a failure when making calls to the PSTN. First of all, my customer has IP telephony since 2007 and has never done any configuration change to the solution.


Last week the customer started experiencing the following problem. When trying to make outbound calls to the PSTN there was no ringback to the IP phones and once the call established there was no sound in any direction. (The connection to the PSTN is through an E1). I am attaching the configuration for the voice gateway

When the customer was trying to troubleshoot the problem, he issue a "no shut" to a dspfarm profile for transcoding that has been shutdown since the solution was first deployed.

dspfarm profile 200 transcode
 description INE_XCODE_01
 codec g711ulaw
 codec g729br8
 codec g729ar8
 codec g729abr8
 codec g729r8
 maximum sessions 6
 associate application SCCP


After the "no shut", the calls to the pstn started working again but now the customer is not able to use the 15 channels available for calls to the PSTN. Only few calls can be established during the day.


The question is: Why transcoding to the PSTN after the failure when that was not necessary in the past? I should not be needed for calls to the PSTN.


Thanks a lot in advance for the help

Christian Prados

Everyone's tags (1)
Cisco Employee

Hi Christian,You can run

Hi Christian,

You can run 'show sccp connections' during active calls on the gateway to check if all calls are using transcoding resource. A 'debug voice ccapi inout' will also provide codec related details. There is a possibility of some codec or region setting that might have been changed on the gateway or cucm. Because transcoding sessions need dsp resources so they might have used the channels allocated to e1 pri and thereby reducing its capacity to fewer calls. You can try decreasing the number of codecs and maximum sessions in the dspfarm for transcoder to free up some dsps and have the e1 handle more calls.




New Member

Hi Manish, Sorry for not

Hi Manish,


Sorry for not answering before.

I run the "show sccp connections" and the calls are using transcoding. I checked the configuration on the callmanager and confirmed that the gateway and the Ip phones are in the same region which is the default (G.711). I am attaching the "show sccp connections" and the "debug voice ccapi inout".

The customer has 30 lines to the PSTN. I increased the maximum sessions as a workaround so the customer is able to at least make 12 calls to the PSTN using transcoding.


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