Question

A collaboration engineer configures a SIP trunk from Cisco UCM to a partner PBX for interoffice dialing. Users complain that certain calls to the partner site are rejected with a SIP 483 Too Many Hops response, even though the destination is reachable. The engineer confirms the route pattern and partition are correct, and that the partner PBX forwards some calls back through UCM when its local users are unavailable. Which mechanism is preventing these calls from completing, and what is its purpose?

Accepted Answer

The SIP Max-Forwards / hop count value is being decremented to zero as the call loops between UCM and the PBX, preventing an infinite routing loop

Answer

The Call Loop Prevention service parameter is disabled, so UCM cannot detect the returning call and drops it

Answer

The SIP trunk's Session Refresh Timer expired mid-call, causing UCM to tear down the dialog with a 483 response

Answer

The Max Number of Registered Devices limit on the trunk has been exceeded, blocking additional call attempts