Message Routing
The Oracle Communications Core Session Manager provides two major types of routing that use the routing precedence parameter in the sip registrar. Routing precedence can be set to either registrar (HSS) or local policy. Routing precedence is set to registrar by default. There are additional controls that the user may configure to refine message routing.
Registrar routing uses the configured subscriber database and registration cache to route the call. Local policy routing lets you configure routing decisions within the Oracle Communications Core Session Manager’s local policy routing functionality.
Within the context of local policy routing, the Oracle Communications Core Session Manager chooses the next hop through the network for each SIP session based on information received from routing policies and constraints. Routing policies can be as simple as routing all traffic to a proxy or routing all traffic from one network to another. Routing policies can also be more detailed, using constraints to manage the volume and rate of traffic that can be routed to a specific network. For example, you can manage volume and rate of traffic to enable theOracle Communications Core Session Manager to load balance and route around softswitch failures.
When a message arrives at the Oracle Communications Core Session Manager, it determines whether it is coming from a session agent. If so, the Oracle Communications Core Session Manager checks whether that session agent is authorized to make the call. Local policy is then checked to determine where to send the message.
Depending on whether the Oracle Communications Core Session Manager is performing originating or terminating services for the call, described in the chapter on operations within the IMS core, it performs those services prior to routing to the endpoint.
If the Oracle Communications Core Session Manager is unable to proceed with routing a request, it replies to the UA that sent the request with a 4xx response.
This chapter provides an overview of registrar routing for perspective, but focuses on local policy routing. Local policy routing is configuration intensive, allowing precise route specification. As a result, configuring local policy routing is a complex process requiring that the user understand the purpose and interaction of multiple configuration elements. This chapter also provides descriptions and configuration instruction on additional routing controls, such as the use of multistage and UA capability routing.