When NY calls CAL, they get a fast busy tone. A network Administrator collects Cisco Call manager traces and sees the displayed SIP messages coming from the remote CUCM (CAL Cluster). What is a likely reason for this?

Refer to the Exhibit. A customer has two CUCM clusters (NY and CAL). The customer recently tried to enable inter cluster communication between these clusters. When NY calls CAL, they get a fast busy tone. A network Administrator collects Cisco Call manager traces and sees the displayed SIP messages coming from the remote CUCM (CAL Cluster). What is a likely reason for this?


A. Cisco CTI Manager service is shut down on the CAL cluster
B. The SIP trunk on the CAL cluster is configured incorrectly
C. Cisco Call Manager service is shut down on the CAL cluster
D. The remote cisco IP phone does not support the SIP protocol
E. The SIP service is shut down on the CAL cluster
F. The remote Cisco IP phone is not registered

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8 thoughts on “When NY calls CAL, they get a fast busy tone. A network Administrator collects Cisco Call manager traces and sees the displayed SIP messages coming from the remote CUCM (CAL Cluster). What is a likely reason for this?

    1. For what it’s worth I agree it is B.

      Definitely not F. The remote phone (NY) wouldn’t be sending any SIP to the NY CUCM and across the trunk to CAL if it wasn’t registered. CAL RTMT wouldn’t even know the call failed.

  1. As 503 is a server error which is based on a failure where the requested service or option is unavailable, I would go for E…

  2. You are right k0K0:

    When a 503 service unavailable message comes back from CUCM, it is usually due to one of the following reasons:

    After the SIP trunk was created on CUCM, it was not reset
    The IP address inside of the SIP trunk in CUCM was not configured properly. The IP address on the SIP trunk in CUCM must match the IP address of the CUCM server on the other side in your case.

  3. I think you would get a 404 “Not found” if the call reached the call processing service and the phone was not registered. I like answer B better because of the “Service Unavailable” message (could be a missing CSS in the SIP trunk) although I’m not 100% on that one

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