Why not support VoLTE?What is the countermeasure?LINE Mobile's DOCOMO Line Old Plan Change specifications -ITMEDIA MOBILE

　LINE Mobile announced on March 8 that the voice call SIM that uses the NTT DOCOMO line will not be able to make voice calls with "VoLTE" onwards on those that have contracted for the old plan.。When I reported this on ITMEDIA Mobile, there was a great response on SNS.

　In the first place, what is "VOLTE" and why it doesn't support VoLTE?

　VoLTE is a mechanism for providing voice calling services in the mobile communication standard called "LTE (Long Term Evolution)".

　In the original LTE, you can only communicate with data (packet) (the background is omitted).Therefore, in the early LTE (4G) smartphone, communication was switched to 3G / 2g when making voice calls (only 3G in Japan).However, if you switch to 3G / 2G and make a voice call, the switching standard will cause problems such as "data communication is instantaneous or slow" or "you cannot do any data communication".

　Therefore, based on the technology called "VOICE OVER IP), which realizes voice calls on the Internet line, a mechanism that allows LTE to use voice calls has been developed.That is VOLTE.In Japan, each carrier supports VoLTE voice calls during 2014.

　VOLTE also supports "HD calls", which is higher sound quality than 3G / 2G voice calls, and "HD+call", which is even higher sound quality.It is attractive to be able to talk with a very clear voice if you call with the corresponding terminals.

　Let's go back to the main topic because the story was so on the side.Why is the "only" voice call SIM using LINE Mobile's docomo line, "only" that contracts for the old plan not compatible with VoLTE?I asked LINE Mobile's spokeswoman (questions and answers are in place).

　I couldn't tell you about why VoLTE would not be compatible.However, it can be said that this "system renovation" has a major change to the network side.

　There are two ways to use voice calls on LINE Mobile using a voice call SIM of the old plan of docomo line, even after April 6 (planned).

　One is to turn off the Volte function of the terminal.With Android smartphones and iPhones that support VoLTE, VoLTE can be disabled by setting as follows.

　Settings → Network and Internet → Mobile network → "Call with 4G line" is turned off

( *) The name and position of the item may differ depending on the manufacturer and terminal.

　Select LINE Mobile phone number (SIM card) with mobile communication → Mobile communication plan → Voice call and data → turn off "VOLTE"

　When VoLTE is disabled, voice calls are performed on a 3G (FOMA) network.However, the following restrictions occur.

　If the price plan is changed to the current "Basic Plan" (voice call SIM is 1210 yen per month including tax), VOLTE can be used after the system renovation.The plan change will be applied from the first day of the month after the procedure.

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