Clients

Clients act on behalf of the user equipment (UEs) to request policy/charging authorization and enforce policy/charging rules received from the PCRFs/OCSs. The clients send requests to the PCA, which ensures the requests are sent to the PCRF/OCS in charge of policy/charging for the subscriber associated with the UE.

PCA supports four different types of Policy Clients, referred to by 3GPP as AF, PCEF, BBERF, and CTF:

• The AF uses the Rx Diameter interface.
• The PCEF uses the Gx Diameter interface.
• The BBERF uses the Gxx Diameter interface.
• The CTF uses the Gy/Ro Diameter interface

How many connections a Clientmight initiate towards the PCA and how those connections are used are in customer control. The capabilities of the client, however, affect the functionality of the solution as shown in Table 3-4.

Table 3-4 Client Connection Capability

Number of Connections Supported by Policy and Charging Client (per Diameter host)	Effect on Solution Capability
1	Site Redundancy cannot be supported. Diameter signaling throughput is limited to the capacity of the connection. Extra latency to reconnect in the event of a connection drop.
2	Site Redundancy supported if secondary connection is configured to connect to PCA mate site. If both connections go to a single site and the policy and charging client has the capability to use both connections simultaneously, Diameter signaling throughput may be doubled vs. only one connection. This configuration requires multiple Diameter connections to a single Diameter host - something that is not supported by RFC 6733, but which many vendors support to allow capacity beyond what a single connection can support. Extra latency is avoided in the event of a single connection drop because the other connection can be used without waiting for reconnect and Capabilities Exchange. PCA Mated Triplet is not supported, since the client would become isolated if the two DSRs with which it has connections fail.
3	PCA Mated Triplet is supported if the client has one connection to each DSR in the triplet. PCA Mated Pair is supported if and only if the client has at least one connection to each DSR in the pair. The extra connection to one of the two DSRs provides the opportunity for higher availability and throughput.
>3	There are many scenarios possible, depending on the capabilities of the policy and charging client. For example, there might be two connections to the primary PCA (for capacity) and two to each mate PCA.

Any Diameter Request can be sent to either PCA in the mated pair, but to avoid possible race conditions between signaling and replication, messages in a Diameter session should be sent to the same PCA Site when possible.