Evolving the LTE packet core

Eventually the two voice networks will be bridged via IP multimedia subsystem (IMS), which will link to two technologies across a common service plane. Verizon is taking this approach sooner rather than later, naming Nokia Siemens Networks and Alcatel-Lucent as suppliers of an IMS architecture that will extend common services not only to the two wireless networks, but Verizon Communications and Verizon Business’s wireline networks. Most operators may not have that luxury, though. If they want to offer voice over LTE they’ll either have to launch a separate voice service or find some way of offloading VoIP traffic onto their legacy voice cores.

“Operators are trying to move to an all-IP core to compliment their LTE networks, but the networks won’t show up all-IP from day one,” said Sanjay Bhatia, director of product line management at security and media gateway vendor Genband. For most operators, the focus will be on data because of the sheer growth in that sector, but voice is another story, Bhatia said. They’ve already made sizable investments in their legacy voice networks, while voice minutes and revenues are not growing so rapidly. While those will want to take advantage of the VoIP capabilities of the LTE networks, they don’t want to build a parallel next-generation voice network to support it.

Genband is positioning its media gateway as crossover technology, which will offload VoIP traffic from the LTE access network onto the circuit-switched 2G and 3G network. Genband isn’t the only one. Alcatel-Lucent, Ericsson, Huawei, Kineto, LG, Motorola, Nortel, Samsung, Starent and ZTE have formed a consortium called the Voice-over-LTE via Generic Access  (VoLGA) Forum, with the aim of creating a standard interface between the packet and voice cores. By mid-2009, the Forum plans to publish a set of open specifications, which vendors and operators can use to deploy voice and SMS services interoperable on both networks. Much of the Forum’s work is focused on defining a VoLGA access network controller (VANC), a modified version of the 3GPP’s generic access controller that supports both circuit-switched and IP calls.