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Unable to configure the available DSP to be used for hardware conferencing in Cisco CallManager on an IOS voice gateway with DSP resources already allocated

Core Issue

This is Working As Designed (WAD).


Conferencing needs a dedicated Digital Signal Processor (DSP) resource. If a DSP is assigned for a conferencing session, then it cannot be used for transcoding or voice call initiations, or terminations. However, transcoding and voice calls can share the resource of a single DSP.

Note: Conferencing needs a dedicated DSP, but not a dedicated packet-voice DSP module (PVDM)2. For example, PVDM2-64 contains four DSPs. If one DSP is used for conferencing, the other three DSPs can still be used for other purposes.

Once the DSPs are assigned to the PRI, they cannot be used for other purposes. However, you can use the remaining DSPs.

Refer to these documents for more information:

Version history
Revision #:
1 of 1
Last update:
‎06-22-2009 03:32 PM
Updated by: