WHAT IS VOLGA ?
VoLGA is a technology approach for mobile operators to deliver voice and SMS over LTE.Mobile operators evaluating Long Term Evolution (LTE), the next-generation, all-IP mobile access network, realize they must support voice and SMS services from the beginning. So The VoLGA Forum was initiated to specify and promote an approach for extending traditional GSM and UMTS circuit-switched services over LTE access networks.
WHY VOLGA ?
There are few disadvantage with the current working specification of LTE network in the approach to support voice and SMS. The problem with IMS-based VoLTE is that:
(1) The specifications have not been completed. There is no agreed approach.
(2) IMS is an all IP technology, and there is no circuit switched connection. Mobile operators on the other hand have circuit switched networks. So the proposed method is to use CSFB to support SMS and circuit related service.CS Fallback (CSFB) was defined in 3GPP as an interim step to overcoming the voice over LTE problem. Unfortunately, CSFB provides a sub-standard user experience, as well as being costly and non-trivial to implement.The concept of CS Fallback is to force the user/handset to drop an LTE connection and fall back to a 2G or 3G network to place or receive calls. The process of falling back adds substantial delays to call connect times and may incur additional call drops during network handovers.
So With VoLGA, mobile operators will be able to re-use their existing MSCs to do VoLTE. LTE transport network supports 8 different priority queues, so mobile operators have the ability to prioritize voice (or other services) at different rates. VoLGA will be just another packet application running over LTE.
What is the VoLGA Forum?
Voice over LTE via Generic Access (VoLGA) Forum Comprised of leaders in the wireless industry, the VoLGA Forum seeks to enable mobile operators to deliver mobile voice and messaging services over LTE access networks based on the existing 3GPP Generic Access Network (GAN) standard.
Technical Aspects of VOLGA
VoLGA is based on the existing 3GPP Generic Access Network (GAN) standard (The purpose of GAN is to extend mobile services over a generic IP access network).
The concept behind the VOLGA is to connect the already existing Mobile Switching Centers to the LTE network via a gateway.As no fallback to a legacy network is required, call setup times are not increased and the user's quality of experience is consistent with that of the 2G or 3G voice environment.
On the network side, VoLGA only requires software enhancements to the circuit to packet gateways which already exist for GAN. No modifications are required on the Mobile
Switching Centers or the LTE core and access network nodes.Thus enabling the rapid deployment of VOLGA in existing network.
On the mobile device side, the protocol stack initially developed for GAN can also be re-used in large parts. The two main software additions required are to include the LTE access
technology as a radio bearer together with a modified handover procedure.
The only new network element introduced is the VoLGA Access Network Controller (VANC). All other network elements and the interfaces between them already exist and are reused without any modifications.
On the LTE side, the VANC connects to the Packet Data Network Gateway (P-GW) via the standard SGi interface. From an LTE core network point of view the VANC looks like any other IP based external node and IP packets exchanged between a wireless device and the VANC are transparently forwarded through the Evolved Packet Core (EPC) network.
Other interface like Sv interface used by VoLGA for circuit switched handovers
Read the below white papaer for a Deatiled call flow and techinical Architecture of VOLGA