1. Essentials Guide
  2. Oracle USM Supporting the IMS Core
  3. Oracle Communications Unified Session Manager as Registrar
  4. Releasing Unregistered Users

Releasing Unregistered Users

When a call arrives at an Oracle Communications Unified Session Manager either to or from a user that is not registered at that Oracle Communications Unified Session Manager, it performs a location query with the HSS to determine if the unknown UE is registered at another S-CSCF. If there is no registration, the Oracle Communications Unified Session Manager takes ownership of the UE. The system stores information about these UEs in its registration cache, labelled "NEVER REGISTERED". Barring any further, related action within the infrastructure, the UE would remain homed to the Oracle Communications Unified Session Manager. Upon expiry of this feature's timer, the Oracle Communications Unified Session Manager sends an SAR to the HSS, providing an assignment type of ADMINISTRATIVE_DEREGISTRATION for the UE. This allows the UE to be a user at a different S-CSCF the next time it is a call sender or receiver. A common use case for this scenario is a roaming UE.

When the Oracle Communications Unified Session Manager issues the SAR, it also marks the UE as 'dirty' (in the process of being de-assigned) to accommodate the following operational scenarios:

  • The UE attempts to register—The Oracle Communications Unified Session Manager rejects the register, replying with a 504 error message.
  • The UE has existing calls—The Oracle Communications Unified Session Manager continues to support the call, based on a stored copy of the service profile.
  • A new call arrives—The Oracle Communications Unified Session Manager rejects the call. The Oracle Communications Unified Session Manager replies with a '480, Temporarily Unavailable' error message if the UE is the callee; the Oracle Communications Unified Session Manager responds with a 504 if the UE is the caller.

The user can configure the unreg-cache-expiry parameter in seconds on a per-registrar basis. This syntax is shown below. 

ORACLE(sip-registrar)# unreg-cache-expiry 120

The parameter accepts values in the range of 0 to 604800, with 0 specifying that the Oracle Communications Unified Session Manager does not cache unregistered users. A setting of 0 means the Oracle Communications Unified Session Manager takes ownership, downloads service profiles, and then releases the user after the call without caching.

Handling Public Service Identities (PSIs)

Public Service Identities (PSI) appear as unregistered users in the Oracle Communications Unified Session Manager. PSIs appear as either Distinct PSIs or Wildcarded PSIs. Similar to unregistered users, the Oracle Communications Unified Session Manager takes ownership of the PSI if it is unassigned and a call is made to or from it. By default, PSIs are not released. However, the user can configure the psi-cache-expiry option in seconds on a per-registrar basis to cause the Oracle Communications Unified Session Manager to release PSIs. This syntax is shown below. 

ORACLE(sip-registrar)# options psi-cache-expiry=120