1. Essentials Guide
  2. Oracle CSM Supporting the IMS Core
  3. Oracle Communications Core Session Manager as Registrar
  4. Registration Handling for Online and Offline Operation Modes

Registration Handling for Online and Offline Operation Modes

The Oracle Communications Core Session Manager provides a means of running in offline mode. Offline mode provides the Oracle Communications Core Session Manager with a graceful means of taking itself out of service without impacting active sessions. This mode can operate in conjunction with other Oracle infrastructure elements, including the SLRM or network management systems. Users or management software put the Oracle Communications Core Session Manager into offline mode because the resource may not be currently required or for system maintenance.

The Oracle Communications Core Session Manager normally operates in online mode, fielding SIP messaging and providing location services. When set to offline mode, it begins releasing UE registrations, allowing the IMS infrastructure to move its UEs to other S-CSCFs. In addition, it stops handling calls for unregistered users. The combination of these two actions effectively takes the Oracle Communications Core Session Manager completely out of service after it has released registrations for all its UEs.

The user can explicitly set their Oracle Communications Core Session Manager online or offline using the command set-system-state. The user can confirm this operational mode using the show system-state command.

Note:

The SCZ7.2.5 release enhanced the set-system-state control to add registration management to the legacy system state mechanism.

Releasing Registrations

When set to offline mode, the Oracle Communications Core Session Manager begins taking itself out of service as an S-CSCF. This process may last a long time because the Oracle Communications Core Session Manager continues to service:
  • UEs with active sessions; and
  • UEs that are not yet marked for release.
Offline mode does not use timers to control its operation. Instead, the Oracle Communications Core Session Manager simply waits for UEs to become eligible, marks them for release, and then begins to release them. The process does not need to be completed either. The user or management applications can set it back to online mode at any time.

When the Oracle Communications Core Session Manager goes back into online mode, it begins to accept calls and registrations for all UEs that are not still marked for release. Instead, the system completes the release process doe those UEs, which must then re-register. The system replies to any registration or originating service requests from UEs marked for release with a 504 message. The system continues to provide terminating services for these UEs.

Offline Registration Release Procedure

When set to offline, the Oracle Communications Core Session Manager first identifies UEs in the registration cache that have registration event subscriptions and marks them for deletion (dirty). Recall that the Oracle Communications Core Session Manager does not release any UE currently engaged in a session. For UEs in the cache without registration event subscriptions, the Oracle Communications Core Session Manager waits for registration refreshes. When they refresh, the Oracle Communications Core Session Manager marks them for release and begins to release them.

The release procedure consists of the Oracle Communications Core Session Manager performing following steps:

  1. Mark UEs in the registration cache as candidates for de-registration.
  2. Send an SAR to the HSS with ADMINISTRATIVE_DEREGISTRATION action for each marked UE. The Oracle Communications Core Session Manager does this to remove itself as the assigned S-CSCF. This allows other Oracle Communications Core Session Managers become the S-CSCF for this UE.
  3. Send deregister requests to application servers to which the Oracle Communications Core Session Manager performed third party registration for the UE.
  4. Remove the UE from the registration cache.
  5. Send reg-event NOTIFYs to application servers that have reg-event subscriptions for the UE.
  6. Send reg-event NOTIFYs to all the UEs contacts.
  7. Send reg-event NOTIFYs to the P-CSCFs that have reg-event subscriptions for the UE.

Interaction with SLRM

If there is ome or more SLRMs within your deployment, the Oracle Communications Core Session Manager notifies them when it goes offline. This notification mechanism is the same as that used by the Oracle Communications Core Session Manager to indicate that it is low on resources. The Oracle Communications Core Session Manager advertises to the SLRM that it has no resources to handle registrations. When going back online, the Oracle Communications Core Session Manager simply re-advertises its resources, resuming normal operation with the SLRM.

Interaction with UEs

Actions the Oracle Communications Core Session Manager may take while receiving REGISTER, De-register and REGISTER REFRESH requests in off-line mode depend on the state of the affected UEs. These actions, and the conditions that invoke them include:

  • Send a 504 to the originating UE - See list of 504 cases below.
  • Send a 200OK to the originating UE:
    • De-registers for users not marked for deletion, allowing normal de-registration.
  • Send a 200OK, and lower the registration expiration timer to 3 minutes:
    • REGISTER refresh request for an existing contact with active sessions.
    • REGISTER refresh request for a new contact for an existing user not marked for deletion.

Actions the Oracle Communications Core Session Manager may take while receiving INVITE requests in off-line mode, depending on the state of the affected UEs, include:

  • Send a 504 to the originating UE - See list of 504 cases below.
  • Perform originating services:
    • The originating user is a registered UE in the cache.
    • The originating user is an unregistered UE in the cache.
  • Perform terminating services - forward to contacts:
    • The terminating user is a registered UE in the cache.
    • Originating Services performed, terminating UE is not in the cache.
  • Perform unregistered services - Send 480, temporarily unavailable:
    • The Oracle Communications Core Session Manager has completed originating services for an unregistered UE that is in the cache.

While in offline mode, the Oracle Communications Core Session Manager returns a 504 error message to the originating UE under the following REGISTER, De-register and REGISTER REFRESH request conditions:

  • Initial register for an inactive user not in cache.
  • Initial register for an inactive user marked as dirty in cache.
  • Refresh register for an inactive user in registered state in the cache.
  • Refresh register for an inactive user marked as dirty in cache.
  • Deregister for an inactive user in registered state in the cache.
  • Deregister request for an inactive user marked as dirty in cache.

The Oracle Communications Core Session Manager returns a 504 error message to the originating UE under the following INVITE request conditions:

  • Call from a UE that is not in the cache.
  • Call from a UE calling that is marked as dirty in cache.
  • OOB call requesting orig service for a user not in the cache.
  • OOB call requesting orig service for a user marked as dirty.
  • OOB call requesting term service for a user is not in cache.
  • OOB call requesting term service for a user marked as dirty.

The 504 Local Response Codes

The Oracle Communications Core Session Manager uses the following two local response codes to override the 504 response for REGISTER methods and indicate why it cannot serve the UE.

  • csm-releasing-users-register
  • csm-releasing-users-invite