Tuesday, June 17, 2008

RAN Gateway wins again

I have spent some time considering the pros and cons of the new 3GPP HNB femtocell architecture. It’s too early to call it a standard, but for now, the basic building blocks are in place for putting the spec together.

One of the fundamental building blocks of the HNB effort is a ‘RAN Gateway’ style architecture. In this case, the RAN gateway network element sits ‘parallel’ to an RNC or BSC, and connects into the mobile core network via existing, well defined circuit interfaces (Iu-CS) and packet interfaces (Iu-PS).

Operators evaluating femtocells and femto architectures immediately grasped the benefits of using a RAN gateway approach:

  • All existing circuit and packet services are supported through the femtocell access network as they are supported through the macro RAN network. This is because the RAN gateway uses the same service interfaces as the RNC.
  • A ‘RAN’ gateway is located in the RAN, with a clear demark point into the mobile core network. For operators, they did not need to change the MSC or the service core in any dramatic fashion.

For all the rhetoric and posturing around the benefits of SIP and IMS, operators quickly understood that the most pragmatic approach for femtocell service delivery was through a RAN gateway architecture. In fact, one of the things that the proposals from Huawei, NSN, Alcatel/Lucent and Kineto/NEC/Motorola (ie UMA/GAN) all had in common was a RAN gateway.

From a UMA perspective, one important outcome of the HNB specification is a validation of the RAN gateway architecture operators and vendors alike.

UMA/GAN is, of course, the original RAN gateway architecture.

I harken back to the early days of dual-mode handsets (DMH). The debate raged: IMS/SIP/VCC vs UMA/GAN. It’s taken 3 years for this to sort itself out in the market. Today, it’s clear that UMA/GAN and the RAN gateway architecture is the (only?) choice.

In the last 12 months, the debate started again, this time for femtocells. But just as quickly, a winner was declared: RAN gateway for HNB (a la GAN).

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