CME Media Resources - Transcoding

CME support transcoding between G711 and G729 for the following features:

  1. 3-way Ad-Hoc software conferencing
  2. Call-Forward or Call-Transfer (one leg of a hairpin call is using G711 while the other is using G729).
  3. MoH (G711 MoH stream is transcoded to G729 phone)
  4. CUE (G729 calls forwarded to CUE which is using G711 only should be transcoded)

  • Meet-me conferencing not supported
  • Multiple-party ad-hoc conferencing not supported

By default codec configuration on SCCP phones will be used for internal calls within CME. Also, it will always be used in best effort mode trying to achieve minimum bandwidth and DSPs utilization. For external calls crossing trunks, codec configuration won't be used at all. External codec will be used by SCCP phones. This has been changed by introducing dspfarm-assistkeyword which will force codec configuration to be used in internal and external negotiations.

If the codec g729r8 dspfarm-assist command is configured for a SCCP phone and a DSP resource is not available when needed for transcoding, a phone registered to the local Cisco Unified CME router will use G.711 instead of G.729r8. This is not true for nonSCCP call legs; if DSP resources are not available for the transcoding required for a conference, for example, the conference is not created.

Configuration Steps

1) Configure DSP resources

For C5510 DSP Resources

voice-card slot
 dsp services dspfarm
sccp local interface-type interface-number
sccp ccm ip-address identifier identifier-number
sccp ip precedence value
sccp ccm group group-number
 bind interface interface-type interface-number
 associate ccm identifier-number priority priority-number
 associate profile profile-identifier register device-name
 keepalive retries number
 switchover method {graceful | immediate}
 switchback method {graceful | guard timeout-guard-value | immediate | uptime uptime-timeout-value}
 switchback interval seconds
dspfarm profile profile-identifier transcode
 codec codec-type
 maximum sessions number
 associate application sccp
 dspfarm connection interval seconds >>> Time to monitor media inactivity before deleting RTP stream
 dspfarm rtp timeout seconds >>> Time to wait before termination RTP session due to errors such as port unreachable

For C549 DSP Resources

voice-card slot
 dsp services dspfarm
sccp local interface-type interface-number
sccp ccm ip-address priority priority-number
dspfarm transcoder maximum sessions number

2) Register DSP resources with CME to act as DSP host

 ip source-address ip-address [port port] [any-match | strict-match]
 sdspfarm units number
 sdspfarm transcode sessions number
 sdspfarm tag number device-number

Note: You can unregister all active calls’ transcoding streams with the sdspfarm unregister forcecommand


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