iphone 4G phone Call why would break the network 4G phone network problem

Source: Internet
Author: User
Compared with the 2g/3g, 4G the biggest feature is to provide more than 100Mbps peak rate, since the speed can be seconds off 20M of optical fiber fixed network, it is used for voice calls is a piece of cake? It is a pity that the problem arises here.

Since the current LTE network (4G) does not support voice services, so whether it is Td-lte (mobile 4G) or Fdd-lte (possibly Unicom/telecom 4G), the system will automatically disconnect the 4G signal when a call comes in, automatically fall back to the 2g/3g signal to complete voice calls, Wait until you finish the call and then turn back to the 4G network. In other words, the current 4G data service (4G Internet access) cannot be performed simultaneously with voice calls.

Thus, for example: When you are using the 4G network to watch the news, suddenly want to call a friend (or a friend to call you), the phone needs to first switch 4G network to 2G/3G mode, and this switch time in 2 seconds ~15 seconds (specific time depending on the phone end and operator side of the optimization). In other words, in the period of signal switching, your phone is not dialed out, and the other side is not a hit.

Therefore, some users use the 4G mobile phone when dialing a call off line; When someone calls you, it always prompts "Sorry, the subscriber you dialed is temporarily unreachable". Fortunately, these problems only happen occasionally, and not all 4G handsets will appear.
Why not all 4G mobile phones will have this problem, 4G online can also be the first time to connect the phone, and even do not affect the network connection when the call? To answer this question, we need to understand three voice call solutions in the 4G era.

Three voice schemes in the 4G era

After entering the 4G era, three solutions were derived from the field of voice communication, namely "CSFB" (Circuit switched fallback), "Sglte" (simultaneousgsm and LTE), and "VoLTE" (Voice Over LTE).

CSFB: Call Networking any one

All 4G Internet access encountered a phone call problem, the basic can be determined to choose the CSFB scheme, on behalf of mobile phones have oppo Find7 and Apple iphone 5S and so on. The CSFB program's mobile phone only has a set of RF chips, either for networking or for phone calls. The biggest drawback of the scheme is that 4G can not switch to the 2G/3G network in time, resulting in a short period of time to dial out, not to come in; the phone also needs to wait a period of time to switch to 4G network to continue the Internet. Want to reduce the impact to the minimum, can only look forward to mobile phone manufacturer system update and operator network optimization upgrade. If you are worried about missing an important phone call, you can notify the business by calling SMS to prevent leakage of telephone calls.

Small Tips

are CSFB solutions, but there are still some differences between the products of different carriers. For the iphone 5S, for example, mobile 4G will automatically switch to 2G when the phone calls (when the phone is not on the Internet), telecom 4G version of the call will switch to the CDMA1X network (when the call is not available), but the Unicom version of the call when the opportunity to switch to the 42MB/S 3G network, Voice calls can also use a high-speed hspa+ network. Another example, Huawei P7 Mobile version adopted the Sglte scheme, but the Unicom version is CSFB.

Different versions of the same model of mobile phones, RF-related chips may differ. For example, this picture is the iphone 5S two version of the RF chip area contrast map

Sglte: Call networking two not delay

Sglte (also known as "dual standby") scheme the biggest feature of the mobile phone is the built-in support of both LTE and GSM RF chips, can be achieved at the same time 2G calls and 4G networking. This type of mobile phone representative has Samsung Galaxy Note 3 n9008v and Lenovo Vibe Z2 Pro (K920), and so on, its appearance is the signal bar of a single card phone will also appear 4g/3g and 2G two line signal icon. Although the Sglte can simultaneously realize the Internet and call characteristics, but the two sets of RF transmitter system will also bring relatively higher power consumption, is also a fish and bear bear can not have the sequelae of it.

VoLTE: Just think about it.

VoLTE should be the most 4G perfect, it is built on the 4G network based on the End-to-end voice scheme, can bring lower access latency (dial-up wait time), and the probability of falling off the line is close to zero. Unfortunately, before the full popularization of 4G network, VoLTE is only the ideal "utopia".


In a word, the contradiction between 4G and voice calls exists, but it can be avoided. Just, different brands in the design of 4G mobile phones will be favored CSFB or Sglte, the final option is not in the hands of consumers. Therefore, whether your 4G mobile phone in the internet can be a smooth access to the phone, or whether the phone can be normal network, these are based on the premise of the mobile phone hardware. If you do not have the operator's restrictions, the individual is recommended to choose a network of two not delay Sglte scheme, the additional power consumption can be solved by mobile, but missed the important phone is difficult to make up.

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