What is this reason?
From the 5G NSA network.
Early 5G deployment adopts option 3, which is the NSA we often say (non-stand-alone networking).
The so-called NSA (non-independent network), as the name suggests, is the 5G system (5G base station and 5G core network) is not a separate network, but a 4G LTE dual connection network.
In the option 3 deployment mode, no matter whether the option 3 or options 3A / 3X, only 5G base station is introduced into the existing 4G LTE infrastructure, and the core network still uses 4G core network, and 5G base station is connected to 4G base station and 4G Core Network.
Under such an architecture, the 4G base station master is a primary node. It is the control anchor point of the 5G base station, and the network access, connection establishment, and switching, and other control signaling of the 5G mobile phone are processed by the 4G base station.
Simply put, under the NSA network, the 4G base station is the boss, the 5G base station is the younger brother, all actions have been listened to the old command.
So, the problem is coming.
In 2G, 3G, 4G era, mobile phones only access one type of network. If "G" or "E" is displayed, "G" or "E" is displayed, and "3G" or "H is displayed if the network is resides and connects to the 3G network. "If you reside and connect 4G," 4G "or" 4G + "is displayed, and everyone's things, the division of labor is clear, and the icon shows very simple.
But now enters the 5G era, under the NSA network, 4G base station and 5G base station serve 5G mobile phones, this mess, how to display icons?
In response to this issue, the Standards Organization gives a unified standard.
The first thing to solve is that in the idle state, the mobile phone does not connect the 4G base station and 5G base station, even if there is 5G signal coverage, the mobile phone is only residing in the 4G LTE network. At this time, how to let 5G mobile phone users know its Is there a 5G service available?
To this end, the Standard Organization defines the "UpperlayerIndation" in the LTE broadcast system information (SIB2).
This "upper indicator switch" is equivalent to the "5G status indicator". When set to true (open), you can make the UE display 5G icon, so that the 5G user knows the location of the location in the idle state. 5G service is available.
It is mentioned that even if you use it to support 5G mobile phones, if you don't have a 5G package, you will not display 5G icon.
This is because the mobile phone is not allowed to use the 5G network through the "RestrictDCNR" parameter in the "ATTACH ACCEPT" message when the mobile phone is attached to the 4G core network.
"Upper layer indicator switch" solves the above problems, but then, there is a series of issues "how to specifically display 5G icon" in idle state and connection states.
For example, under the NSA network architecture, 4G base station (cell) and 5G base station (cell) are different due to operating frequency bands, and the coverage of the two is not completely overlapping. When the mobile phone is in different signal coverage, how Show 5G icon?
For different specific circumstances, GSMA also defines the following four options:
It is not difficult to see that CONFIG D is the most radical, under Config D configuration, as long as the phone occupies the 4G LTE cell under the NSA network, even if the 5G NR signal coverage is detected, the 5G icon is displayed. Config D is easy to make the user a "false 5G".
Config C, only 5G icon is displayed only if the mobile phone detects 5G NR signal coverage.
For Config B, in the connection state, if only the LTE is connected, the 5G icon is not displayed even if the 5G NR overlay is detected. This means that when the user uses Volte, no matter whether there is 5G overlay at this time, only the 5G icon is displayed, and only 4G icon is displayed.
Config A is most conservative, only 5G icon is displayed when the mobile phone has been connected to the LTE and NR cells.
Why do you have multiple options?
The reason is that the global operator has not reached a consensus on a single option configuration, so a variety of options are used, which can be flexible to display 5G icons according to their own preferences.
For the above four options, the operator can choose different configuration schemes according to the actual needs. If it is radical, you can choose Config D; if you keep a point, you can choose Config C or B. But for Config a is really too conservative, less use.
In order to avoid the 5G icon to display the chaos, the regulator can specify configuration, or operators can ask mobile phone vendors to specify configuration.
In short, sometimes when you see the mobile phone clearly displayed 5G signal, it is not a "fake" when it is occupied by the 4G community, just because 5G NSA network features.
Editor in charge: Tzh, Read more
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