Symptom

Incoming/outgoing calls on PRI on an MGCP gateway fail with MGCP message "400 Voice call setup failed-Incoming-Outgoing call collision"

Conditions

An incoming call should fail on a channel due to insufficient DSP resources. All subsequent calls on the same channel will fail, even when DSP resources become available. When running with debug mgcp packet enabled, the call is released with a "400 Voice call setup failed-Incoming-Outgoing call collision" even when there are no other active calls on the PRI trunk that could lead to a call collision. Please use caution and take necessary steps (like ensuring that console logging is disabled) prior to running any debugs on an IOS gateway to prevent system degradation. If logging is enabled, look for the system message "%FLEXDSPRM-5-OUT_OF_RESOURCES: No dsps found either locally or globally". This would indicate that a call failed at some point due to lack of dsp resources which is the trigger for this problem.

Workaround

Once in this state, reload the gateway to recover the timeslots. To prevent this problem, ensure that DSP resources are not over-subscribed. This is especially true when using DSP resources for transcoding and conferencing on the gateway. The use of the DSP calculator ('search for 'DSP calculator' at www.cisco.com) available on www.cisco.com can help estimate the needed dsps for your configuration.

Further Problem Description