1. Essentials Guide
  2. Oracle USM Supporting the IMS Core
  3. S-CSCF Selection Based on Capabilities

S-CSCF Selection Based on Capabilities

Within IMS environments, the I-CSCF identifies target S-CSCF's in response to SIP traffic for which the assigned S-CSCF is not known. Enhanced selection environments can include the HSS offering mandatory and optional capabilities for a user, and the I-CSCF selecting the best S-CSCF based on capabilities the S-CSCF is best suited to support (in addition to standard criteria). The user can configure the I-CSCF resident within Oracle CSM, Oracle USM and Oracle SLRM to support this capabilities-based S-CSCF selection. Resultant operation is compliant with ETSI TS 129 228 and ETSI TS 129 229.

S-CSCF selection based on capabilities utilizes AVP information exchanged with the HSS to identify required and preferred capabilities on a per-user basis. Capabilities themselves vary widely. Examples include administrator routing preferences for divergent service types. Capabilities are manually defined at the HSS for endpoints or groups of endpoints. The Oracle CSM, Oracle USM and Oracle SLRM user configures tables on the I-CSCF that map the S-CSCF's with the capabilities they support. Further configuration enables the I-CSCF to make the best S-CSCF selection, then forward appropriately.

Diameter messaging that can generate capabilities parsing for S-CSCF selection includes UAR/UAA and LIR/LIA traffic. Inclusion of the capabilities AVPs in the message sequence triggers this enhanced S-CSCF selection by the I-CSCF.

Configuration on the HSS and the I-CSCF must be compatible in deployments that use this feature. Configuration required on the Oracle device performing the I-CSCF function includes:

  • servers-capabilities-list—A sip-registrar parameter that allows you to configure the registrar with a servers-capabilities-table.
  • servers-capabilities-table—A multi-instance element that names the table and includes multiple servers-capability.
    • servers-capability—A multi-instance element within the servers-capabilities-table that includes a capability (capability value associated with users and supported by servers in the list) and a server-name-list that identifies the servers that support this capability.

The OCUSM verifies the servers-capabilities-list attribute with the servers-capabilities-table each time it loads the configuration. If the servers-capabilities-table with the name specified in the servers-capabilities-list does not exist , the system outputs the following message:

ERROR: sip-registrar [<object-name>] has invalid servers-capabilities-list entry [<entry-name>]