PCRFs are responsible for authorizing and making policy decisions based on knowledge of subscriber resource usage and the capabilities allowed by the subscriber's account. In order to perform this function, all policy requests for a given subscriber must be routed to the same PCRF.
Rather than provisioning a fixed relationship between a subscriber and a PCRF, the P-DRA function of PCA dynamically assigns subscribers to PCRFs using a load distribution algorithm and maintains state about which subscribers are assigned to which PCRF. The relationship between a subscriber and a PCRF can change any time the subscriber transitions from having no Diameter policy sessions to having one or more Diameter policy sessions. Once a policy session exists, however, all policy sessions for that subscriber are routed to the assigned PCRF.
PCA can interact with any 3GPP Release 9 compliant PCRF. Because these PCRFs come from different vendors, there are differences in how they are deployed in the network and how they “look” to the P-DRA function. The following PCRF configurations differ mainly in addressing and sharing of state across Diameter connections:
- A PCRF that shares state across different Diameter hostnames.
- Each Diameter hostname can all support Gx, Gxx, S9, Gx-Prime and Rx Diameter interfaces. This type of PCRF is supported by PCA.
- Each hostname has a different connection for each different interface type. This type of PCRF is supported by PCA.
- There is a different Diameter hostname for each connection for a specific Diameter interface. All of the Diameter hostnames share state. This type of PCRF is supported by PCA.
- There are different Diameter hostnames for different policy client vendors. Policy state is shared across the Diameter hostnames, but origin based routing is required to select a set of PCRFs for distribution of the initial binding depending on the policy client type. This type of PCRF is supported by PCA, but requires use of Diameter Routing Function PCRF selection as described in PCRF Selection for New Bindings.
- There is a different Diameter hostname for each connection. This type of PCRF is supported by PCA, but requires use of Diameter Routing Function PCRF selection based on the vendor type of the policy client as described in PCRF Selection for New Bindings.
- A PCRF that has one Diameter hostname, but supports a number of connections to that hostname using different IP addresses.
Each connection can support Gx, Gxx, S9, Gx-Prime and Rx Diameter interfaces. This type of PCRF is supported by PCA.