Many operators realize IMS is a longer term evolution and there is an immediate need to bring voice and SMS services to LTE.  VoLGA, or Voice over LTE via the existing 3GPP UMA/GAN standard, brings voice and SMS services as packet applications to LTE.  The VoLGA Forum was formed to harness the growing industry momentum for the VoLGA specification. 

The alternative to VoLGA is to deliver all voice sessions over the existing 2G/3G network.  Known as CS Fallback (CSFB), this approach switches the handset over to 2G or 3G network to make  and receive calls.  As a consequence, any ongoing data sessions in the handset are also forced to switch over to 2G or 3G for the duration of the call.  SMS can also be delivered through the CSFB mechanism as well.  It is delivered as special control messages added to the LTE network to support CSFB.   

CSFB is positioned as an interim solution, but further understanding of the implementation details show it’s a costly, misguided step with no obvious connection to a future IMS telephony service core.

• Voice over LTE  Operators are investing in LTE because it is the lowest-cost, highest-performance RAN technology available.  Yet, CSFB forces operators and users back to the existing 2G/3G access network.  VoLGA delivers today’s voice and SMS services natively over LTE as a packet application.
• Same user experience  CSFB requires the handset to ‘fall back’ to the 2G/3G network, so users will experience an extended delay in placing or receiving calls.  The handset must suspend any LTE data sessions, find and re-attach to the 2G/3G network, and then begin the process of connecting the user.  With VoLGA, users get the performance they expect from mobile voice services.
• Support for IMS + voice over LTE  Many operators are beginning to invest in IMS for non-telephony applications, such as those defined in the rich communication suite (RCS).  Yet CSFB forces any combinational IMS services back to the 3G network (they aren’t supported on 2G).  VoLGA supports combinational voice and IMS RCS applications over LTE today. 
• Support for LTE femtocells  With VoLGA, voice and SMS services are supported through LTE femtocells today.  CSFB, on the other hand, forces a handset off an LTE femtocell and back to the 2G/3G network for all voice services.  This means either LTE femtocells have to incur the cost of an extra 3G radio or LTE femtocells only support data services.
• Support for voice on all LTE devices  It is likely that LTE will be deployed in laptop datacards, MIDs, netbooks and even home routers before it arrives in traditional handsets.  VoLGA can be embedded into all these devices to bring voice and SMS services. CSFB is handset-centric.
• No MSC upgrades  VoLGA is implemented with a VoLGA Access Network Controller (VANC) which is external to the existing MSC service core.  CSFB requires a costly new upgrade and new interfaces to an operator’s MSC network, at a time when many operators are looking to reduce investment in MSC infrastructure.
• Low operational disruption  The VoLGA controller is external to the existing MSCs, and therefore can be deployed and integrated to the network without changing the software in the MSCs in the network.  MSC network upgrades are complex procedures operators do not want to do very often.  MSCs are connected to so many systems that operators run multi-month IOTs in their labs to make sure nothing goes wrong with each new MSC software load before authorizing the software to be loaded into their production network.  The cutover from old to new software must be glitch free.  This means extensive manpower goes into planning every detail, testing every possible thing that could go wrong, and making the cutover in the production network only when the operator is satisfied that nothing could go wrong 
• Infrastructure support  Operators must check with their MSC suppliers for timing and cost of a release which supports CSFB.  VoLGA products will be available from Kineto (and other vendors) in early 2010. 
• Devices/client support  All major handset vendors (Nokia, Samsung, LG, Sony Ericsson, RIM, HTC, etc.) already support the 3GPP GAN standard, and should be able to support VoLGA relatively quickly.  In addition, VoLGA can be supported in non-handset devices by mid-2010.