There is more to WiMAX networks than base stations and subscriber devices. The core network plays a crucial role in delivering the performance operators need.

WiMAX operators are busy these days. The first networks using Mobile WiMAX (802.16e) have launched commercially over the past few months, and operators expect WiMAX Forum-certified equipment will be available by early summer. Many other operators are trialing equipment, preparing RFPs, and choosing vendors.

Operators have also started developing—or thinking about—the services they need to roll out to attract new subscribers and differentiate their offering from that of their wireline and wireless competitors. Reliability and robust performance are imperatives, but operators are also thinking about how to manage traffic effectively over their networks to ensure the high level of subscriber experience they have promised.

In the early stages of deploying new the WiMAX technology, operators focus most attention on the wireless interface between base stations and subscriber devices. Many operators are so busy deploying base stations and testing devices that they have neglected the part of the network that ensures everything runs smoothly and securely: the WiMAX core network. The WiMAX core enables operators to manage traffic more efficiently, squeezing out more Mbps from the same access infrastructure and spectrum assets by optimizing traffic across base stations according to account subscriber location, base station, and backhaul capacity.

Providing compelling services over WiMAX is another challenge for operators. A brute-force approach focused on simply offering more bandwidth is likely to backfire. Wireline and Wi-Fi operators can frequently provide higher bandwidth, and mobile subscribers with small devices often do not need a fat pipe anyway.

Fortunately, WiMAX operators have more powerful ways to develop competitive services that are currently not available to wireless or wireline subscribers. QoS and prioritized access allow operators to give priority to specific data types (e.g., give voice priority over data), applications (e.g., video streaming over Internet browsing), or subscribers (e.g., high-paying enterprise users over prepaid consumer users). The ability to control specific traffic flows, for instance, allows operators to slow down peer-to-peer traffic when the network is running at capacity or to charge additional fees for specific services or content.

Advanced billing capabilities give operators increased flexibility in accommodating pre- and post-paid subscribers, roaming visitors and occasional users and in meeting demand from different market segments. Operators are increasingly worried about high traffic levels generated by their subscribers, and advanced billing features offer indirectly a way to manage traffic by creating different classes of services to segment the market.

The WiMAX core network supports all these functions through the Access Service Network (ASN) gateway and the Connectivity Service Network (CSN). The ASN gateway manages traffic and works in concert with the CSN elements to provide QoS, security, authentication, billing, mobility management, hot-lining, and lawful intercept. The CSN includes the authentication, authorization, and accounting (AAA), dynamic host configuration protocol (DHCP), billing, and policy function servers, plus a Home Agent if support for roaming and mobility is needed.

Multiple core network elements with different feature sets are available to meet the requirements of different type of operators. In line with the open-standards approach followed for base station and subscriber device interoperability, the WiMAX Forum has developed specifications for the interfaces among all the core network elements, base stations, and subscriber devices. As a result, operators can select among network elements from multiple vendors and expect them to interoperate, as long as their interfaces comply to with the specifications.

Interoperability in the core network is a powerful tool for WiMAX operators, as it allows them to pick and choose the solution that is most cost effective and best suited to their needs. However, formalizing core network and service requirements, and assessing different core network solutions, requires additional effort from operators. While leaving the planning for the core network to a later stage may seem tempting, it pays to think from the beginning not only about how to build the network but also about how to manage it and maximize its revenue opportunity.

Monica Paolini is the founder and president of Senza Fili Consulting and can be contacted at monica.paolini@senzafiliconsulting.com. Senza Fili Consulting provides expert advisory services on wireless data technologies and services.