1. Policy and Charging Application User Guide
  2. Configuration
  3. PCA Configuration
  4. PCA Routing of Diameter Messages

5.4.3 PCA Routing of Diameter Messages

PCA routes Diameter messages depending on certain criteria:
  • Answer message or Request message
  • New session Request or in-session Request
  • New binding or existing binding new session Request

Peer Routing

PCA always attempts to route using Peer Route Tables. The Diameter Routing Function attempts to use Peer Route Tables in a predefined precedence:
  1. Peer Route Table configured for the originating Peer Node (Diameter, and then Configuration, and then Peer Nodes)

    If a match is found, the specified Peer Route Table is used.

  2. Peer Route Table configured for the Diameter Application-ID of the policy session initiation request being routed (Diameter, and then Configuration, and then Application Ids)

    If the ingress Peer Node is configured as Not Selected, that entry is skipped and the Application Ids configuration is checked.

  3. Default Peer Route Table

    If no match is found in the Application-Ids configuration, the Default Peer Route Table is used.

  4. Destination-Host Routing

    If no Peer Routing Rule matches in the Default Peer Route Table, PCA will attempt to route the Request using Destination-Host routing (for example, to a connection or Alternate Implicit Route List associated with the destination Peer Node).

Routing of Session Initiation Requests for New Bindings

PCA allows a Peer Route Table to be configured for use when a new binding is created. This Peer Route Table can specify Peer Routing Rules to:
  • Allow new bindings to be routed, for example, based on the Origin-Host or Origin-Realm of the PCEF
  • Cause new bindings to be load-shared across all local PCRFs.

The Peer Route Table to use for new bindings is specified in the Policy and Charging, and then Configuration, and then Policy DRA, and then Site Options screen on the SOAM at each site.

If the Peer Route Table for new bindings is set to Not Selected, the Diameter Routing Function uses the precedence described in Peer Routing.

Routing of Session Initiation Requests for Existing Bindings

Sessions for subscribers that are already bound to a PCRF must be routed to the bound PCRF, or to a PCRF that shares state with the bound PCRF if the PCRF supports sharing of policy state. For existing bindings, no Peer Route Table is configured in the PCA application Site Options. Instead, the Diameter Routing Function uses the precedence described in Peer Routing.

Routing of Requests from PCRF to a Policy Client

In order to route Requests initiated by the PCRF, routing must be configured such that Requests from any PCRF can be routed to any Policy Client in the network. This type of routing is used to route RAR and ASR requests. For Requests from PCRFs to Policy Clients, no Peer Route Table is configured in the PCA application Site Options. Instead, the Diameter Routing Function uses the precedence described in Peer Routing.

Routing of In-Session Requests

In-session Requests are Requests within a Diameter session other than the Request that established the Diameter session. CCR-U, CCR-T, and STR are all examples of in-session Requests. In-session Requests are routed using the predefined precedence of Peer Route Tables described in Peer Routing.

Routing of Answer Messages

All Diameter Answer messages are routed over the same path on which the Request was routed, using hop-by-hop routing. No routing configuration is necessary to route Answer messages.