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Voice Over LTE Generic Access (VoLGA) full explained

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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

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.

posted May 15, 2014 by Rahul Chandel

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