The policy server, also known as the policy and charging rules function (PCRF), is essential for service providers to adopt a broader set of strategic policy use cases. These new use cases focus on personalization and adding value to cloud, over-the-top, and machine-to-machine (M2M) services, as well as a more sophisticated approach to managing network resources.
The significance of the policy server will continue to grow as service providers migrate to LTE and offer voice and video over LTE. These services will increase Diameter signalling traffic and require application prioritization to ensure quality of service (QoS). The proliferation of M2M devices and applications and new cloud services will further elevate policy’s role as operators prioritize services to meet service level agreements and QoS requirements.
The capabilities and flexibility of any policy server depend on the number of distinct triggers, conditions and actions that it can process. These, in turn, rely on the number of devices with which it can interoperate. The policy server’s capabilities, therefore, grow exponentially by increasing the number of devices it supports and by expanding the scope of functionality on the interfaces between it and other enforcement points. Its role is to create and apply policy rules based on a variety of parameters – subscriber profiles, application usage, device type, and network conditions – that are distributed to policy endpoints on the network, which control the flow of traffic.
Policy integration with complex charging and billing systems is a particular pain point for operators. Heavy Reading notes that the single-biggest barrier that operators face in deploying a policy architecture is the difficulty in integrating policy and charging. The analyst firm also found that operators have run into major challenges implementing online charging systems due to the complexity and high costs associated with customization, professional services, and integration with gateways and policy servers. Less than a tenth of the operators intend to deploy pre-integrated policy and charging solutions in the medium term to solve integration issues.
The 3GPP architecture specifies several interfaces – Gx, Gy or Gz – to online and offline charging systems (OCS/OFCS) through the policy and charging enforcement function (PCEF). However, the 3GPP doesn’t define how this integration is implemented in practice.
In Release 11, the organization defines a new interface, called the Sy interface, to create a direct link between the PCRF and charging systems. The Sy interface eliminates the need to do usage tracking over both the Gx and Gy interfaces simultaneously, improving messaging efficiency and eliminating the possibility of accounting synchronization problems between the PCRF and OCS. Most importantly, it eliminates the need for complex and costly pre-integration between the policy server and OCS. Because of the critical importance of this link, support for the Sy interface is a key criterion for service providers selecting a policy server.