Hybrid network architectures employ gateways to bridge SS7 and IP networks. This hybrid bridging serves two ends. First, it gives the provider access to an existing community of SS7-compliant mobile and fixed devices, which enables it to grab market share in the short term. Second, it gives the provider time to plan an orderly transition to IMS that avoids the point solution trap.

The hybrid transition

A successful hybrid network strategy starts with a good understanding of IMS. Anointed as the grail of the fixed-mobile convergence transition, IMS is nevertheless still a developing concept. It is not a discrete technology, but rather a set of standards with many variations. Providers who want to build IMS infrastructures have few clear guideposts to follow. Even analysts have a hard time counting IMS deployments; many of what purport to be IMS implementations turn out to be point solutions upon closer examination.

Given its fuzzy parameters, the best way for a provider to think of IMS is as a blueprint for a long-term home renovation. The blueprint has a floor plan of all the rooms, but since the renovation starts with the kitchen, that’s the only room with all the details filled in. When the homeowner decides to do the bathroom or master bedroom, they can fill in the details when they’re ready.

IMS implementations fit into the same general mold as the home blueprint. It doesn’t matter so much what gets done first, as long as it all fits together at the end. In the house example, that means that all the rooms share wiring, plumbing, heating and cooling systems. In IMS that means that services should share a common support structure. Starting to build that support structure is where the hard choices start. In the long term, providers can’t afford to have a separate support structure for every service. In the short term, however, it would be prohibitively expensive to build a support structure complying with IMS standards, many of which are not finalized.

The practical route is to implement modules of an IMS-compliant support structure in areas where the standards have solidified and are economically justified then use gateways to integrate the new service with the hybrid infrastructure. For example,  a provider that wants to implement a new prepaid service needs access, provisioning, and the prepaid service itself.