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Subscriber-Centric Policy Management:
Laying The Groundwork For IMS

To Converge IP Access, Providers Must Converge Rules
to Manage Subscribers, Applications and Network Resources

By Russ Freen, Bridgewater Systems


Service providers worldwide are preparing to implement fixed/wireless convergence architectures based on the IP Multimedia subsystem (IMS) standard originally developed by the 3GPP standard group. IMS aims to create an IP services layer that operates independently of underlying networks, thus yielding seamless subscriber access to IP multimedia applications from any device over any network.

In the IMS vision, easier usage begets more usage. The broadband subscriber on the road will be able to open their cell phone or laptop PC browser and immediately link to IP services via a 3G network, hotel WiFi network or corporate or home wireless LAN. Afforded this maximum flexibility and mobility, the subscriber will call on IP services for information, entertainment, and productivity more often.

The service provider implementing IMS will be transforming its infrastructure to an all-IP network. This convergence of networks will produce substantial savings over the costs of operating multiple different networks for different services. Additionally, the shift to all-IP services positions the service provider to tailor application experiences on a subscriber by subscriber or subscriber-centric basis. For example, a bandwidth-intensive video-telephony data session allocated more resources should yield commensurately more revenue than a standard VoIP call.

This subscriber-centric vision can be accomplished only through implementation of subscriber-centric policy management that empowers service providers to tune the allocation of network resources to the subscribers willingness to pay. Put another way, per-subscriber, multi-network access requires a mechanism to right-size both resource allocation and pricing of each service based on the resources each subscriber consumes.

Only through correlating each subscriber to the services they use can service providers monetize the true value of their networks. In the bargain, subscriber-centric policy management will prove crucial to creating innovative business models that make tiers and bundles of basic and premium IP services irresistible to subscribers, as well as easily managed for service providers.

Laying The Groundwork
From the subscribers point of view, IMS and fixed/mobile convergence will provide a single point of entry to IP services, regardless of the device or the fixed or mobile access network used.

Subscriber-centric policy management paves the way for this network independence by providing a repository of subscriber profiles, application requirements and rules for bringing subscribers and applications together. The service provider controls the definition of these rules, or policies, and the policy management system enforces those rules on a per-subscriber basis.

The IMS architecture directly addresses policy through what it describes as the Policy Decision Function (PDF) and Home Subscriber Server (HSS). These components of the architecture include centralized subscriber and application profiles and policies. The HSS leverages the profiles to enforce policy in the network through a logical chain of processes. As the subscriber registers with the network, the HSS consults the policy database to learn the roaming permissions, account status time-of-day permissions and based on these provides the subscriber with the ability to access the IMS framework. The subscriber then accesses an application, which is authorized by the HSS at the point of request. During the authorization process the HSS consults the policy database once again to learn the application-specific permissions and other policies to be applied to this subscriber. The HSS then authorizes access, directing the call processing elements to allow a session to commence.

The DSL, cable or 3G service provider can implement subscriber-centric policy management for a single network today. Doing so will yield immediate benefits, including the powers to correlate subscribers with usage, to enforce fair usage of bandwidth and to leverage granular usage intelligence to develop new services and service bundles.

Implementing subscriber-centric policy in the near term also positions the provider to extend these benefits of subscriber control across both fixed and wireless networks, laying the groundwork for offering device- and network-independent access to applications in the future. The same subscriber profile, application profile and policies applied to a cable network today, for example, could be applied to WiFi, WiMAX or mobile access in the future.

The IMS vision contemplates a radical departure from the relatively static operations and business processes of historical communications networks. IMS requires subscriber-centric policy management because making IP applications available over any network requires a focus on the subscriber, rather than on any given network.

Traditional telephone networks have been engineered for largely predictable peak calling periods. Such engineering practices cannot help but produce under-utilized networks, because much of the peak capacity will remain unused throughout the rest of the year. Additionally, capacity allocation in traditional phone and data access networks has been largely a fixed and network-centric affair: a DSL subscriber signs on and gets a fixed amount of bandwidth for the duration of his online activity. In effect, resource allocation policies are impersonal and network-centric: they are determined by network capacity for predictable events and effectively engineered into the network as a one-time-only task.

By contrast, traffic patterns and capacity demand in the IP multimedia realm cannot reliably be known in advance, either in aggregate or per subscriber. Nor can the provider rely on provisioning the exact same bandwidth to each subscriber or application every time, since the subscriber may enjoy various QoS permissions. For example a subscriber may be using a 300-Kb/s mobile data connection one moment, and the next moment use a 3-Mb/s cable modem connection. Resource sharing among thousands of unpredictable subscribers must be managed not just once, but dynamically and continually.

Hence, service providers must respond to a primary challenge presented by dynamically changing subscriber and application requirements. Automating resource allocation on a per-subscriber basis through policy definition addresses this challenge. Only then can the provider ensure service availability and QoS both in the aggregate and for each subscriber.

The multi-network nature of IMS presents another key challenge: scalability of operations. Implementing subscriber-centric policy management in a multi-network environment will involve managing millions of subscriber profiles, possibly hundreds of service and application profiles and supporting tens of thousands of simultaneous user authentication, service access and mediation transactions.

The Benefits
Subscriber-centric policy management can provide a powerful edge to providers engaged in IMS competition. As triple play services proliferate, and as boundaries between fixed and mobile networks blur, the battle increasingly will put ownership of the subscriber relationship at stake. This trend already is well underway as wireless, cable and telephone companies all face the dual challenges of wooing each others subscribers while defending against attrition among their own.

Most service providers now believe that enabling subscribers to tailor applications to their personal needs and desires will prove crucial to generating more loyalty and greater willingness to pay for value. This provides the surest path to retaining customers, growing market share and increasing average revenue per user (ARPU).

Subscriber-centric policy management benefits service providers in this quest by supplying them with a unified view of the subscriber and by supplying one set of converged service credentials and single sign-on. The converged authentication process also ensures service continuity across network-to-network handoffs via centralized subscriber tracking.

The subscriber-centric model further aids the provider by simplifying correlation of services to users. These correlations, in turn, enable dynamic, real-time control of personalized service access.

On the front end of this system, providers can leverage this correlation to simplify service definition and provisioning and to accelerate creation of complex services and service bundles. Providers can define service tiers based on anything that is easily measured and simply controlled, such as monthly consumption, bandwidth and QoS. In sophisticated systems, application-specific tiers are possible, such as tiers with and without VoIP features.

At the same time, per-subscriber policy enforcement can be applied to fair use of bandwidth. Subscribers who threaten the quality experience of other subscribers, and threaten the providers revenue model, with peer-to-peer or other bandwidth hungry applications can be identified and redirected to a portal where they can be offered fair connection characteristics.

Some control also can be shared with the subscriber via a self-management Web portal. Providers can enable each subscriber to choose a unique lineup of applications, which also will reduce the providers operational costs by effectively recruiting the customer to provision services.

These benefits all owe their genesis to the power to set policies and enforce them dynamically.

A fundamental shift is afoot in communications. In the any-network future, IP applications are becoming less tied to infrastructure and more closely tied to the subscriber. Subscriber-centric policy management is essential to every service provider determined to thrive through that shift. IT

Russ Freen is the co-founder and chief technology officer for Bridgewater Systems, a developer of subscriber-centric policy management software for IP-based services. For more information, please visit

If you are interested in purchasing reprints of this article (in either print or PDF format), please visit Reprint Management Services online at or contact a representative via e-mail at [email protected] or by phone at 800-290-5460.


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