Question

A new batch of SIP endpoints is deployed to a CUCM cluster. The phones obtain DHCP addresses, download their configuration from TFTP, and NTP is synchronized. However, during registration the phones cycle through 'Registering' and never fully register. A packet capture shows the phone sends a SIP REGISTER, and CUCM replies with a '401 Unauthorized' challenge, but the phone never sends a follow-up REGISTER with credentials. The phone's Digest Credentials field on the End User page is blank, and the phone's SIP Profile has 'Enable Digest Authentication' behavior enforced via the associated SIP Security Profile. What is the most likely cause?

Accepted Answer

The SIP Security Profile has Digest Authentication enabled but no matching digest credentials are configured on the associated end user / device, so the phone cannot answer the 401 challenge

Answer

The phones are attempting to register on TCP port 5060 while CUCM only accepts TLS on port 5061

Answer

The codec configured in the phone's Region does not match the CUCM device pool, causing a 488 during registration

Answer

The phone firmware is older than the CUCM load and must be upgraded before a REGISTER is accepted