A Cisco Unified Communications Manager (CUCM) cluster is configured with a SIP trunk to a Cisco Unified Border Element (CUBE) for PSTN connectivity. Users report that outbound calls to a specific area code fail, but all other calls succeed. The CUCM route pattern for that area code is configured with a route list that includes the SIP trunk. The CUBE shows that it receives the INVITE but rejects it with a 488 Not Acceptable Here. Which CUCM configuration should be checked first to resolve this issue?
A 488 Not Acceptable Here often results from a codec mismatch between CUCM and CUBE. The region assigned to the SIP trunk determines which codec is offered. If the region is set to a codec that CUBE does not support or that is not allowed on the dial peer, CUBE rejects the call with 488. Checking the region and associated codec is the first step.
Why this answer
A 488 Not Acceptable Here response from CUBE indicates that the media description (SDP) in the INVITE is not acceptable. The region assigned to the SIP trunk in CUCM defines the codec that will be offered for calls traversing that trunk. If the region forces a codec that CUBE cannot support or that is not configured on the dial peer, CUBE rejects the call.
Therefore, the region configuration should be verified first.
Exam trap
The trap here is assuming that a 488 error is always a CUBE dial-peer issue, when it can also originate from a CUCM region codec mismatch that forces an unsupported codec toward CUBE.