Service delivery platforms, or SDPs, and their relationship with IP multimedia subsystem concepts is a confusing topic.

SDPs provide service providers with a common platform for service creation and delivery, together with interfaces to back-office systems, third-party providers and network elements.

But first, let's consider where IMS services stand in general:

• A number of service providers have signaled a commitment to purchase and deploy IMS infrastructure equipment. This has accelerated with consolidation.

• Competition across cable TV providers and traditional telcos continues to build, especially in wireless and video services.

• No killer services are in sight. Early services appear to focus on unified messaging, dual-mode voice services and some peer-to-peer consumer video services. However, operators want to enable the next generation of services without knowing exactly what they might be. (In fact, this is one of the primary objectives of an SDP.)

• Operators generally agree that third-party providers and independent applications developers are key to a successful ecosystem. After all, that was one of the primary motivators behind the adoption of session initiation protocol/HTTP concepts within IMS.

Against this backdrop, SDPs can be a core component of operator strategy for new IMS service launches while transitioning legacy services as well. For providers like Sprint, which may need to support a cable partner's converged services, an SDP strategy could be even more crucial. One critical aspect is the co-location of a set of common functions across various services, thus enabling a general subscriber management capability while reducing duplication. However, there is no overarching standard that defines SDPs. As a result, multiple vendor interpretations of SDPs exist, and they are not necessarily consistent.

Several service providers are making a serious effort to develop a services-based architecture that supports both legacy services and new IMS services. This architecture fundamentally alters the old silo approach to service delivery. However, vendors use inconsistent definitions of SDPs and have tended to apply IMS and SDP labels somewhat loosely. This variation can be particularly challenging because it exacerbates integration expenses for operators that have gone through a similar exercise with IMS in multi-vendor settings.

Two distinct approaches have emerged: a legacy SDP approach with roots in IT segments, primarily offered by systems integrators, and a more IMS-based SDP approach that reuses existing IMS interfaces and capabilities. IMS networking and software vendors typically take this direction.

For service providers that already have invested in IMS core network infrastructure, it could be important to deploy SDPs that leverage the IMS embedded base as much as possible. For example, network functions, such as network quality of service and policy management, could be leveraged from IMS rather than replicating these functions within an SDP platform. On the other hand, co-locating common functions across services within an SDP provides efficiency and reuse.

Some of the specific architectural issues involve questions such as what is the initial set of services planned for deployment in the next 12 to 24 months; where is the optimal boundary and interface point between IMS and SDP; and which functions are located in the IMS core and which are within the SDP cloud?

In the final analysis, several ambitious SDP programs have delivered relatively little value to operators because the complexity and management demands of the SDP overwhelmed the relatively short, focused list of new services. This has been especially true of mobile operator SDPs. Operators should begin with a thoughtful strategy based on a 12- to 24-month service road map and design an SDP that accommodates uncertain future needs. This approach will enable operators to develop SDP architecture that supports their goals of service innovation and lower expense.

PK Prasanna is IMS/convergence lead for inCode, a global wireless business and technology consulting firm. You can reach him at pprasanna@incodewireless.com.