Policy DRA in Roaming Scenarios

3GPP has defined two roaming scenarios with respect to Policy Control and Charging functions. The Policy DRA can be deployed for various network scenarios as a Policy routing agent, including the roaming scenarios.

In addition to communicating to the Policy Clients and Policy servers through Gx/Gxx, Gx-Prime, and Rx interfaces in their own networks, the Policy DRAs can communicate to each other across the Visited Access and Home Access (or Home Routed Access) networks through the S9 interface, for session binding purposes.

Figure 2-4 illustrates an example Diameter network where the Policy DRAs are located in Home Access and Visited Access networks.

Figure 2-4 Policy DRA in Roaming Scenarios

The Visited Access (also known as Local Breakout) is one of the scenarios where UEs obtain access to the packet data network from the VPLMN where the PCEF is located.

The Home Routed Access is the roaming scenario in which the UEs obtain access to the Packet Data Network from the HPLMN where the PCEF is located.

The S9 reference point is defined in roaming scenarios between HPLMN and VPLMN over which two Diameter applications, S9 and Rx are used. The purpose of the S9 Diameter application is to install PCC or QoC rules from the HPLMN to the VPLMN and transport the events occurred in the VPLMN to the HPLMN.

The S9 protocol makes use of exactly the same commands and messages as the Gx/Gxx protocols, except that a V-PCRF in VPLMN will provide an emergency treatment for any incoming CC-Request (INITIAL_REQUEST) messages. This implies that the Policy DRA does not check the existence of the Called-Station-ID AVP if the IMSI is missing in a CC-Request (INITIAL_REQUEST) over the S9 interface.