Voice Over LTE Generic Access (VoLGA) full explained

Question

VoLTE - VoLGA

• Both CS Fallback (CSFB) and VoLGA rely on the existing circuit voice network, but VoLGA is not approved by 3GPP yet.

Overview:

• VoLGA is architecture independent and uses the UMA/GAN (Unlicensed Mobile Access/ Generic Access Network) protocol.
• This was originally adopted for Wi-Fi/3G fixed-mobile convergence and as such did find its way into the 3GPP.
• VoLGA does not require modifications in the LTE RAN or Core, or the MSC, but uses a separate gateway controller.
• A technological approach for delivering voice and SMS services over LTE access networks
• Leverages a mobile operator’s existing core voice network
• Derived from the existing 3GPP GAN standard
• A technological approach for delivering voice and SMS services over LTE access networks
• Leverages a mobile operator’s existing core voice network
• VoLGA is architecture independent and uses the UMA/GAN (Unlicensed Mobile Access/Generic Access Network) protocol - Derived from the existing 3GPP GAN standard (originally adopted for Wi-Fi/3G fixed-mobile convergence)
• VoLGA re-uses this principle by replacing the Wi-Fi (GAN-based) access with LTE access on an LTE/UE new dual mode mobile device (both GSM/UMTS and LTE).
• VoLGA does not require modifications in the LTE RAN or Core, or the MSC, but uses a new separate gateway controller (VANC).
• The VoLGA Access Network Controller (VANC) , as a GAN gateway between LTE and CS domain, securely connects a subscriber to the infrastructure of a network operator and voice calls and other circuit switched services such as SMS are then securely transported between the mobile device and the Gateway.
• VoLGA is a stronger contender than CSFB. From technical view, VoLGA seems to be a much better starting point. VoLGA would further delay IMS deployment.

VoLGA Pros and Cons:

Pros:

• Voice and Data over LTE
• Call setup times as good as 3G
• Preserves CS core investments
• External controller (VANC) minimizes impact to core network - No MSC upgrades
• Supports simultaneous voice/ data over LTE
• VoLGA will support all existing circuit services as well as IMS RCS - Supports combinational IMS/ RCS + Voice over LTE
• Delivering voice over LTE validates LTE QoS capabilities
• Voice services delivered natively through LTE femtocell
• The VoLGA forum decided to use the SRVCC as the means to handover VoLGA calls from LTE to GSM or UMTS.
• No VoLGA specific features required in the MSC or SGSN for VoLGA is a great plus for deployment in a running network.

Cons:

• Not 3GPP standardized yet - VoLGA is currently not a work item in 3GPP
• Not fully standardized yet as the stage 3 specification has not yet been finalized
• Limited operator support
• GAN-based dual-mode mobile phones is required
• SRVCC-capable mobile is required
• Only T-Mobile strongly enthusiastic right now
• Scaling and Roaming
• Limited LTE Coverage if only hotspots at the initial phase
• It also requires changes to handsets, as well as a mechanism for allowing the network to trigger LTE-to-3G/2G handovers for VoLGA calls, originally defined as part of SR-VCC (single radio voice call continuity).

VoLGA Interface:

• All other network elements and the interfaces between them already exist and are reused without any modifications.

• A-interface is used to connect the VANC to a GSM MSC (Mobile Switching Center).

• The Iu-interface is used to connect the VANC to the UMTS MSC.

• No changes are required on these network nodes to support voice, SMS and other services over the LTE network.

• SGi: SGi is defined in TS 23.401. It is the reference point between the P-GW and the packet data network. The "packet data network" is the CS core network connected by VANC in this specification.

• Sv: Sv is defined in TS 23.216, where it is defined as the reference point between the MME/SGSN and MSC Server. In this specification, Sv applies to two interfaces:

1. between the MME and HOSF, and
2. between the HOSF and MSC Server.
   HOSF = Handover Selection Function

• Z1 (UE – VANC): Z1 is the reference point between the UE and VANC, which is based on the Up interface defined in TS 43.318.

• Z3 (VANC – HOSF): Z3 is the reference point between the VANC and HOSF. It is based on GTPv2-C as specified in TS 29.274. The Z3 reference point is used for the creation and deletion of VANC-UE bindings in the HOSF, and to route the SRVCC PS to CS Handover Request message to the VANC.