IMS Integration: Routed Calls as Originating or Terminating

In IP Multimedia Subsystem (IMS) deployments, SIP Server can route calls parked on a Media Server using a call-originating leg or terminating leg. Call-originating legs, compared to call-terminating legs, contain the orig parameter in the Route header of an INVITE request that SIP Server sends to the IMS.

Originating legs are subject to HSS interactions and might pass through a chain of application servers serving originating calls. Note that this processing consumes network and CPU resources.

For more information about termination and initiation INVITEs in the IMS, see the 3GPP TS 24.229 V9.0.0 (2009-06)—Technical Specification 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP).

Feature Configuration

The Application-level ims-use-term-legs-for-routing configuration option enables this feature.

ims-use-term-legs-for-routing

Default Value: false
Valid Values: true, false
Changes Take Effect: Immediately

For use in IMS environments only. When set to true, SIP Server uses a call-terminating leg to route calls on behalf of the Routing Point after a treatment is applied. When set to false, SIP Server uses a call-originating leg to route calls after a treatment is applied.