The integration of the policy server (the 3GPP-defined policy and charging rules function, or PCRF) with charging and billing systems is emerging as one of the key considerations in the 3GPP Policy and Charging Control (PCC) architecture. This architecture specifies several interfaces – Gx, Gy or Gz – to online (OCS) and offline charging systems (OFCS) through the policy and charging enforcement function (PCEF). However, the 3GPP doesn’t define how to implement this integration, and vendors and service providers have pursued a variety of approaches.

Recently, the 3GPP introduced a new interface, Sy, 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 policy server and OCS. More importantly, it will eliminate the need for complex and costly pre-integration between the policy server and the OCS.

Integration between policy and charging systems is required to charge for services based on subscriber entitlements. Both multi- and single-vendor implementations can support this integration. However, a single-vendor platform that pre-integrates policy and charging functions can ultimately limit a service provider’s choices, signaling efficiency and time-to-market for new services.

The Service Provider Point of View
Heavy Reading surveyed Tier 1 operators in November, and concluded that:

• Operators have run into major challenges implementing OCSs due to complexity and high costs associated with customization, professional services, and integration with gateways and policy servers (graph below).   

• Almost 70 percent of Tier 1 service providers will use the policy server rather than the charging system to perform some charging and rating functions such as quota management (data allowance), rating, and balance management.

• 3GPP standard interfaces are the most popular option for integration of policy and charging.

• Operators are planning deeper integration of policy with existing online and offline charging systems but they are not sure how to do it.

• Less than 10 percent of operators intend to deploy pre-integrated policy and charging solutions in the medium term to resolve integration issues (graph below).

Limitations of Pre-Integrated Policy and Charging
Traditional charging and billing vendors propose solutions that pre-integrate policy and charging as an approach to monetizing mobile data, which has several drawbacks:

• Costly and complex professional services and systems integration. Integrated policy and charging offerings often require higher professional services and systems integration costs to create policy rules and scale with network growth. However, a network-based approach combined with an intuitive rules engine and carrier-grade software and middleware can provide a lower cost of ownership.

• Proprietary interfaces. Integrated policy and charging systems can require extensive customization and professional services to interoperate with other control plane elements, resulting in a higher cost of ownership and slower time-to-market for new services. 

• Poor scalability and reliability. As the network expands with multiple policy servers and charging systems, they need Diameter routing to direct messages to the appropriate system. A pre-integrated approach based on proprietary interfaces is not standards-compliant, making it difficult to scale. Furthermore, policy servers from charging vendors often lack key carrier-grade functionality required to ensure scalability and reliability when the network is congested.

• Increased complexity and cost. Online charging systems are already taxed by a large number of complex integrations with gateways, servers, and nodes as shown in the figure below.

An Alternate Approach
Dozens of tier one operators have elected to deploy a best-in-class policy server sold independently from charging equipment. The first requirement for this to succeed, of course, is interoperability with multiple vendors’ online, offline and legacy charging systems, in addition to a broad array of policy enforcement points.

High performance and scalability are pre-requisites as well, to handle growing data and signaling traffic. A policy server should have standardized Diameter interfaces and incorporate advanced carrier-grade functionality such as high processing power, capacity, overload controls, monitoring, and protection mechanisms.

An independent policy server also needs advanced quota management capabilities to allow service providers to do advanced usage tracking in the policy server for a wide variety of use cases, such as offloading complex charging systems and fair usage in the policy server without an OCS. A policy server can accomplish this with pre-configured use cases and a user-friendly rules engine that allows policies to be deployed quickly and at a lower cost than through charging system customization. In addition, an independent policy server must offer revenue-generating use cases for mobile data services, including day passes, anniversary bonuses, and bandwidth boosts.

Shared data plans are also becoming an important use case as the number of devices per customer grows. These plans require subscriber and device data management to assign multiple device identities to each customer profile, as well as require policy analytics to track and analyze usage.

Conclusion
Global service providers are adopting an approach that leverages a best-of-breed policy server with integrated subscriber data management and analytics for easy policy rule creation, quota and traffic management, and letting existing charging systems do what they do best – charge for services. They are also looking to the new Sy standard interface between policy and charging systems to ensure broad multi-vendor interoperability, eliminate costly integration and avoid lock-in.  Finally, they are deploying a next-generation Diameter signaling architecture to independently scale policy and charging systems to meet the demands of mobile data growth on their networks.

Doug Suriano is chief technology officer and vice president of Engineering at Tekelec.