Question

A newly deployed Cisco 8865 phone running SIP firmware boots, obtains an IP address via DHCP, and successfully downloads its configuration file from the CUCM TFTP server. However, the phone displays 'Registration Rejected' and never registers to CUCM. Packet captures show the phone sends a SIP REGISTER, but the CUCM node it targets is a subscriber that is NOT running the Cisco CallManager service. The phone was manually configured with a single CUCM group containing only that subscriber. What is the most likely cause of the registration failure?

Accepted Answer

The subscriber node in the assigned CUCM group does not have the Cisco CallManager (CCM) service activated, so it cannot accept SIP registrations.

Answer

The phone's device security profile requires TLS, but the phone is attempting registration over UDP.

Answer

The DHCP scope is missing option 150, preventing the phone from resolving the correct registrar.

Answer

The phone firmware version does not match the CUCM device pack, causing a codec negotiation failure.