Sunday, December 22, 2013

Voice over LTE - VoLTE

What is VoLTE? 
 Operation of Voice over LTE(VoLTE) system for providing a unified format of voice traffic on LTE, and other systems including CSFB (Circuit Switched Fall Back), and SV-LTE(Simultaneous Voice & LTE).
This approach is based on the IP Multimedia Subsystem (IMS) network, with specific profiles for control and media planes of voice service on LTE defined by GSMA in PRD IR.92. This approach results in the voice service (control and media planes) being delivered as data flows within the LTE data bearer. This means that there is no dependency on (or ultimately, requirement for) the legacy Circuit Switch voice network to be maintained.

  • Circuit-switched fallback (CSFB)|
    In this approach, LTE just provides data services, and when a voice call is to be initiated or received, it will fall back to the circuit switched domain. When using this solution, operators just need to upgrade the MSC instead of deploying the IMS, and therefore, can provide services quickly. However, the disadvantage is longer call setup delay.
  • Simultaneous voice and LTE (SVLTE)
    In this approach, the handset works simultaneously in the LTE and circuit switched modes, with the LTE mode providing data services and the circuit switched mode providing the voice service. This is a solution solely based on the handset, which does not have special requirements on the network and does not require the deployment of IMS either. The disadvantage of this solution is that the phone can become expensive with high power consumption.
Issues for Voice services over LTE
 Unlike previous cellular telecommunications standards including GSM, LTE does not have dedicated channels for circuit switched telephony. Instead LTE is an all-IP system providing an end-to-end IP connection from the mobile equipment to the core network and out again.
 In order to provide some form of voice connection over a standard LTE bearer, some form of Voice over IP, VoIP must be used.
 The aim for any voice service is to utilise the low latency and QoS features available within LTE to ensure that any voice service offers an improvement over the standards available on the 2G and 3G networks.
 However to achieve a full VoIP offering on LTE poses some significant problems which will take time to resolve. With the first deployments having taken place in 2010, it is necessary that a solution for voice is available within a short timescale.

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