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Message: <blockquote data-quote="isitha.lk" data-source="post: 18555376" data-attributes="member: 522262">4G වල මෙහෙම කතන්දරයක් තියෙනවා .Voice calls The LTE standard supports only <a href="https://en.wikipedia.org/wiki/Packet_switching" target="_blank">packet switching</a> with its all-IP network. Voice calls in GSM, UMTS and CDMA2000 are <a href="https://en.wikipedia.org/wiki/Circuit_switching" target="_blank">circuit switched</a>, so with the adoption of LTE, carriers will have to re-engineer their voice call network.<a href="https://en.wikipedia.org/wiki/LTE_%28telecommunication%29#cite_note-26" target="_blank">[26]</a> Three different approaches sprang up: Voice over LTE (VoLTE) Main article: <a href="https://en.wikipedia.org/wiki/VoLTE" target="_blank">VoLTE</a>  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. One additional approach which is not initiated by operators is the usage of <a href="https://en.wikipedia.org/wiki/Over-the-top_content" target="_blank">over-the-top content</a> (OTT) services, using applications like Skype and Google Talk to provide LTE voice service.<a href="https://en.wikipedia.org/wiki/LTE_%28telecommunication%29#cite_note-27" target="_blank">[27]</a> Most major backers of LTE preferred and promoted VoLTE from the  beginning. The lack of software support in initial LTE devices as well  as core network devices however led to a number of carriers promoting <a href="https://en.wikipedia.org/wiki/VoLGA" target="_blank">VoLGA</a> (Voice over LTE Generic Access) as an interim solution.<a href="https://en.wikipedia.org/wiki/LTE_%28telecommunication%29#cite_note-28" target="_blank">[28]</a> The idea was to use the same principles as <a href="https://en.wikipedia.org/wiki/Generic_Access_Network" target="_blank">GAN</a>  (Generic Access Network, also known as UMA or Unlicensed Mobile  Access), which defines the protocols through which a mobile handset can  perform voice calls over a customer's private Internet connection,  usually over wireless LAN. VoLGA however never gained much support,  because VoLTE (IMS) promises much more flexible services, albeit at the  cost of having to upgrade the entire voice call infrastructure. VoLTE  will also require Single Radio Voice Call Continuity (SRVCC) in order to  be able to smoothly perform a handover to a 3G network in case of poor  LTE signal quality.<a href="https://en.wikipedia.org/wiki/LTE_%28telecommunication%29#cite_note-29" target="_blank">[29]</a> While the industry has seemingly standardized on VoLTE for the  future, the demand for voice calls today has led LTE carriers to  introduce CSFB as a stopgap measure. When placing or receiving a voice  call, LTE handsets will fall back to old 2G or 3G networks for the  duration of the call.</blockquote>

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