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How it works: Voice over LTE (VoLTE)

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LG VoLTE Voice over LTE

Credit: LG

As almost everyone at this point knows, Long Term Evolution (LTE) cellular technology is the next generation of mobile networks. There will continue to be iterative advances, like LTE Advanced, but the core LTE technology is the new global standard for the foreseeable future.

LTE provides a wide array of improvements versus previous network standards, but there is still a major obstacle in the path to LTE-only cellular networks. Older cellular standards have always included a dedicated communications channel to carry voice calls and operate under roughly the same principles as an analogue phone switchboard. LTE is an all-IP based network standard, so it it does not natively support the antiquated circuit switched protocol. Network providers must revise their entire approach to voice call networks in order to resolve the incompatibility.

Voice over LTE (VoLTE) aims to provide the ability to handle cellular voice calls over LTE. Most major LTE network providers have announced their intentions to at least begin to deploy VoLTE within the next couple years.   For a number of reasons, enabling voice calling over LTE is not so simple as just using a VOIP connection. Carriers need to be able to pass or hand off voice calls, without interruption, between the LTE networks and the legacy 2G and 3G networks. Carriers also want to protect the revenue they get from voice services; so, it is to their advantage to use a dedicated protocol like VoLTE rather than over-the-top VOIP solution.

VoLTE uses the IP Multimedia Core Network Subsystem (IMS) architectural framework.  IMS allows for ubiquitous multimedia access using a common IP interface. This greatly simplifies network management and provides better developer accessibility. Using this framework, connections over different protocols can be bridged together. With the IMS framework, VoLTE is able to inter-operate with circuit switched voice networks without having any dependency on or requirement for them. Additionally, the common IP interface of IMS will allow VoLTE to inter-operate with other voice networking technologies even after legacy circuit switched networks are finally phased out.

Until LTE network footprints expand to meet or eclipse those of their 2G and 3G predecessors, voice network interoperability is only the first step in enabling VoLTE. While engaged in a voice call, a user might pass outside of an LTE coverage area, so that call needs to be able to fall back onto legacy networks. The VoLTE standard accomplishes this with Single Radio Voice Call Continuity (SR-VCC). With SR-VCC, when an LTE tower determines that a user might leave the coverage area during an active connection, it leverages the IMS framework to initiate a second connection over the legacy standards. Both connections are maintained until the LTE signal is lost, the LTE tower determines the user will not leave the coverage area, or the voice call ends.

SR-VCC requires the network provider to have the IMS framework in place, but it also impacts device design. To support SR-VCC, devices must not …read more

Via: Android Authority