1. Essentials Guide
  2. Oracle USM Supporting the IMS Core
  3. S-CSCF Selection Based on Capabilities
  4. Selection Process with an SLRM

Selection Process with an SLRM

The capabilities-oriented S-CSCF selection algorithm on the Oracle SLRM uses standard Oracle CSM selection criteria in addition to capabilities criteria. This criteria includes cluster configuration, S-CSCF resource utilization and SLRM synchronization.

The general approach to selection within this scenario include the following principles:

  • Only Oracle CSMs with all mandatory capabilities can be selected.
  • The process gives priority to the Oracle CSMs in the cluster with the most optional capabilities, and is best able to take on new users.

The capabilities-oriented S-CSCF selection algorithm uses the following high-level steps, including the SLRM's selection steps, within the I-CSCF function to arrive at a selection:

  1. Determine that the capabilities algorithm is required:
    1. No server-name in the LIA or UAA.
    2. Capability list exists.
    3. Assigned S-CSCF flag is not set.
    4. Mandatory/Optional Capabilities received in UAA/LIA.
  2. Execute capabilities selection:
    1. Ensure the S-CSCF capabilities database is configured.
    2. Build capable S-CSCF list. This list contains all S-CSCFs from the S-CSCF capability database that support the Mandatory capabilities.
    3. Ensure that the capable S-CSCF list is not empty. If the capable S-CSCF list is empty, return an error to the UE.

  3. Execute SLRM's selection procedure, cycle through all Oracle CSMs in the cluster:

    1. Identify applicable cluster. Begin to cycle through cluster.
    2. Determine whether Oracle CSM is in capable list.
    3. Determine whether Oracle CSM is at 100% utilization.
    4. Determine whether the next Oracle CSM support more optional capabilities.
    5. Determine whether the selected Oracle CSM is synchronized.
    6. Determine whether the next Oracle CSM using fewer resources.
  4. Complete capabilities selection process using optional capabilities as criteria:
    1. An S-CSCF has the most optional capabilities.

      (If so, forward message.)

    2. The local S-CSCF can take on more users and has all mandatory capabilities and most optional capabilities.

      (If so, forward message locally.)

    3. Use round robin to select the S-CSCF that has most optional capabilities.

      (If so, forward message.)

  5. Forward message:
    1. Forward to selected S-CSCF.
    2. Remove selected S-CSCF from capabilities list.
    3. If there is an error, for example, the SIP response requires a re-assignment, check the assigned flag.
    4. If the assigned flag is set, return to the top.

      If the assigned is not set, return to the step that checks whether the capable S-CSCF list is empty.

    5. If the capable S-CSCF list is empty, return an error to the UE.

      If the capable S-CSCF list is not empty yet, perform SLRM's selection procedure again.