Are SIP-based femto cells the way forward‾

So far femto cells have been more about hype than deployment, yet ABI Research has predicted that Europe will have the largest femto cell market, with 16.6 million units shipped annually by 2012. The total global market will 36 million units by then, worth €2.67 billion. Which technology will dominate in the air remains to be seen.


The unlicensed mobile access (UMA) protocol - originally designed for dual-mode Wi-Fi handsets such as BT's Fusion, and Orange's Unik - has found a new role as a femto protocol. Vendors endorsing this approach include NEC and Kineto.


While the Femto Forum remains technology agnostic, Comverse has just added its weight to the SIP-based lobby, with VP Erik Larsson of Comverse France describing UMA as "transitional only, used because it is available" and, he argued, because the approach of running traffic across macro cells over the RAN [radio access network] is too expensive - as shown by the low take-up of T-Mobile's ZuHause in Germany.


He pointed out even when the home zone is in effect a simple extension of the fixed network (using WiFi, GSM or 3G), the UMA approach still demands a dual-mode phone that gobbles up the battery.


On the other hand, Larsson insisted, "SIP-based femto cells can work with any 3G phone and exploit backhaul via the broadband link to get all the price benefits. They work by encapsulating SMS and voice, and sending them through a packet data gateway to the IMS core."


The trouble is, despite all the airtime IMS was given in 2005, there are few deployments. Opponents also say the SIP-based approach to femto technology is too complicated.


Larsson is nothing daunted: "No, there haven't been big IMS implementations, rather it's incremental. As operators need to upgrade TDM elements, they are moving to next generation network switches, so it is a gradual process, but it is happening. All our platforms are IMS-ready and we're demonstrating voice calls and incoming and outgoing SMS with Ubiquisys and Tatara Systems."


He concluded, "This approach is about reducing capex and opex for operators, and making services cheaper for consumers. We're talking to fixed and mobile operators in Western Europe, particularly the smaller mobile ones which are looking to grow this way, without investing in separate overlaid core networks."