What are Transcoders in Cisco IP Telephony? Use of Transcoder?

What is a Transcoder or XCode in Cisco IP Telephony? What are the uses of Transcoder?

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Transcoders are hardware devices which takes the media stream of one codec and converts it from one compression type to another compression type. Cisco Unified Communications Manager (CUCM) invokes a transcoder on behalf of endpoint devices.

Example: Let’s say Phone A using Codec G.711 and Phone B using Codec G.729 Codec. Phone A calls Phone B and Phone B picks the call. If there is no transcoder being used between them, the call will disconnect as Phone A and Phone are using different Codecs. A transcoder can convert a stream from G.711 codec to G.729 codec. It helps to communicate between two different type of codecs. So, if transcoder will be used between them, the call will not disconnect.

Transcoder configuration has to be done at the Gateway and Cisco Unified Communications Manager (CUCM).

  • Determine DSP resource requirements. You can check the requirements using DSP calculator in Cisco Website – https://www.cisco.com/c/en/us/applications/dsp-calc.html
  • Enable SCCP on Interface on Gateway
  • Configure transcoding
  • Enable DSP Farm Services
  • Configure a DSP farm profile
  • Associate a DSP farm profile to CUCM
  • Verify if DSP’s are registered

Sample Transcoder Configuration on the Gateway:

voice-card 0
dspfarm
dsp services dspfarm

sccp local Loopback0
sccp ccm 192.168.0.192 identifier 2 priority 2 version 7.0
sccp ccm 192.168.0.193 identifier 1 priority 1 version 7.0
sccp
!
sccp ccm group 1
bind interface Loopback0
associate ccm 1 priority 1
associate ccm 2 priority 2
associate profile 1 register INXcode
!
dspfarm profile 1 transcode
codec g729r8
maximum sessions 2
associate application SCCP
no shut

Sample Transcoder Configuration on CUCM

You have to also configure transcoder in Cisco Unified Communications Manager under Media Resources > Transcoder

  • Click on Add New
  • Transcoder Type – Select “Cisco IOS Enhanced Media Termination Point”
  • Description – Enter a short description about the Transcoder
  • Device Name – Enter the same transcoding name that you entered in the gateway Command Line Interface
  • Device Pool – Enter an appropriate Device Pool
  • Click on Save

Once done, you can see the Registration status on CUCM. The Transcoder has to be registered with CUCM.

Verfication that can be done on Gateway:

Show sccp connection

show dspfarm session

show dspfarm all

General Transcoder issue

The common causes for Transcoder registration issues:

  • Cisco IP Voice Media Streaming Application (IPVMA) service is not running.
  • Transcoder is in shutdown state or its name does not match.
  • Type of Transcoder configuration does not match either in Gateway or CUCM.
  • Network connectivity / DNS issues.
  • Access list in the path filtering SCCP
Hope this helps!

 

 

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