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Like the evolution of voice services, broadband data services are rapidly migrating from a single provider, fixed connection environment to a multiple provider, wireless offering. The promise of wireless broadband is that, regardless of where a subscriber is located or the current capabilities of the incumbent wireline service provider, broadband data services are readily available over the air. One wireless delivery technology that makes this both possible and practical is WiMAX.
Whether due to its sheer bandwidth capabilities or emerging extensions that will add mobility, WiMAX�s ability to enable premium mobile broadband services is unparalleled. Its underlying media access control (MAC) protocol, borrowed substantively from the cable industry�s DOCSIS standard, offers wireless Internet service providers (WISP) the ability to precisely manage the quality of service (QoS) to the individual subscriber and application in real time.
What this means for the subscriber is nearly flawless delivery of IP data. For the WISP, it means the ability to offer high quality, revenue generating applications, such as voice over IP, streaming video, gaming, and commercial services. The manner in which QoS can be dynamically allocated in WiMAX networks, thereby providing a template for reference applications that can be deployed by WISPs, is discussed below.
Technology
WiMAX�s MAC layer includes a traffic scheduler that is primarily responsible for queuing both upstream and downstream data flows by shaping the IP flows at the MAC layer with firmware located in the base station. Previous broadband wireless technologies offered only coarse prioritization capabilities. WiMAX, however, based on the core IEEE 802.16 standard, offers a menu of QoS management techniques that are available for applications to request parameterized QoS, defined by precise allocation of bandwidth, latency, and jitter to each specific service flow. Within this framework, external network elements, acting on behalf of applications and service provider policies, can direct the traffic scheduler in the base station regarding how to shape the traffic.
For VoIP, this means that the CODEC-specific bandwidth can be scheduled with a latency that minimizes dropped packets. For real-time, high resolution streaming video, the bandwidth can be temporarily and dynamically increased � beyond the WISP�s statically provisioned values.
While WiMAX service providers can statically provision their access networks and provide best-effort treatment to most IP data, QoS policy management technology offers them the unique ability to intelligently manage their network and become a �Smart RAN.�
By managing the data flow specific to each application and/or content, WISPs can differentiate their own walled garden services from those of third-party content providers, such as Vonage (News - Alert) or Google (News - Alert). Leveraging this capability, a WISP not only gains the ability to further monetize the value of its underlying capital investment, but it also becomes a mission-critical partner, particularly to its business customers. Quality of service policy management is an essential ingredient in order for WISPs to offer service level agreements to its most demanding, and often highest margin,
customers.
Architecture
The IEEE has specified how QoS is scheduled at the MAC layer and is currently being expanded by the WiMAX Forum to specify the architecture for delivering new services. Included in the emerging WiMAX standards is the ability to dynamically request premium delivery from the base station on behalf of applications and subscribers authorized by the WISP. While the standards are not yet complete, the WiMAX Forum already has incorporated many of the concepts associated with the IP Multimedia Subsystem (News - Alert) (IMS), a service delivery framework standardized by 3GPP. This framework specifies a common functional platform for next-generation converged multimedia services.
The policy decision function (PDF) is responsible for dynamically allocating network resources on behalf of premium delivery walled garden services, whether voice, video, or gaming. The PDF, combined with the intelligent edge SIP proxy, otherwise called the P-CSCF (call session control function), reserves and commits resources when a call is initiated (or received) by the WISP subscriber.
When the call goes off-hook, the SIP message is processed by the P-CSCF, which authorizes the call by verifying the subscriber in the subscriber database (known as the HSS). It then requests the network resources required for the specific CODEC from the PDF. The PDF can admit or deny a request for quality of service depending on whether the network resources are available over the subscriber-specific RAN, and on the WISP usage policies. If the VoIP service is charged incrementally, as opposed to a flat fee, the PDF generates a RADIUS event message to a billing system. It further maps the IMS core to a multitude of base stations, thereby allowing the service provider to centrally locate its policy management and, in particular, coordinate its network policies with other network elements and even access network types.
In addition to SIP-based communications, this architecture can support premium delivery legacy desktop applications, such as peer-to-peer PC gaming, file transfers, and VoIP. While centrally hosted application servers can dynamically request bandwidth for the duration of an authorized user�s session, peer-to-peer or third-party applications can use a Client Smart Agent, similar to an IMS SIP Client, to monitor application network usage and signal for quality of service on behalf of authorized applications. The Agent is authenticated and authorized by either the P-CSCF or a discreet application function, which performs similar functionality in concert with a specific application�s resource requirements.
By adopting a best-of-breed IMS architecture for WiMAX, service providers can confidently start deploying new, premium delivery services today with an eye on the future. For example, toll quality SIP-based VoIP can be deployed with a PDF, SIP proxy, and/or session border controller (SBC), feature server, and media gateway, in addition to a WiMAX compatible base station. Once the service provider has comfortably deployed its voice service, additional services can be supported, such as video, PC games, and commercial services. This requires gracefully adding additional application and feature services to the aforementioned core network elements.
Because the PDF plays the crucial role of applying service provider policies to the performance of applications over the RAN, it must incorporate a rich rule set that accounts for application types, base station capability, and business logic. In addition, it should be capable of maintaining ongoing sessions (called statefulness) in case of system failures and emergency preemption.
Conclusion
While many competing access network technologies claim quality of service capability, none are nearly as robust as the 802.16-2000 specification in combination with the WiMAX architecture. By intelligently managing the RAN, WISPs can not only maximize the value of their capital investments, but reduce their operational expenses with carefully coordinated network management policies.
True WiMAX service providers are uniquely positioned to not only maximize subscriber satisfaction in the face of enormous competition, but also to gain incremental revenues associated with differentiated services. To do this, they must implement a centralized approach to policy management that coordinates the performance and functionality of applications that include VoIP, video, and whatever the future may bring. IT
Jay Malin, PhD., is VP of Business Development for CableMatrix, a leading provider of Quality of Service (QoS) policy management solutions for the broadband industry. For more information, please visit the company online at www.cablematrix.com.
If you are interested in purchasing reprints of this article (in either print or PDF format), please visit Reprint Management Services online at www.reprintbuyer.com or contact a representative via e-mail at [email protected] or by phone at 800-290-5460.
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