Synchronization

Synchronization refers to authentication procedures when the (REFRESH TIMING) is found to be stale. This is not an authentication failure.

The UA may send an AUTS in response to the challenge, indicating that the authentication vector sequence is "out-of-range". Upon receipt of the AUTS, the S-CSCF sends a new authorization vector request to the HSS. The HSS checks the AUTS and, if appropriate sends a new set of authentication vectors back the the S-CSCF. Next the S-CSCF sends 401 Unauthorized back to the UA. Assuming the UA still wants to register, this would trigger a new registration procedure.