Apple Terminal Case—iOS16.4 Icon Display Inconsistency During Calls

For Apple iOS 16.4 mobile users who [enable 5G] and make calls without turning on the [Independent 5G Voice] switch, how is the icon next to the signal box displayed?

After multiple tests, there are three forms of expression:

1. The dial icon will show 4G.

2. About ten seconds after the call was connected, the icon changed from 5G to 4G.

3. Keep the 5G icon on during the call.

So the question is, why does the same phone behave differently when making calls?

For Apple users with iOS 16.4 mobile device [5G enabled], when the [Independent 5G Voice] switch is not turned on, the user does not support VoNR, that is, when making a call, the EPS Fallback process falls back to 4G for the call.

So why is the icon not 4G, and why are there multiple representations? We captured the logs and conducted a detailed comparative analysis, and the results are as follows:

According to the analysis, the judgment process of the icon display of iOS16.4 on Apple terminals is as follows:

iOS 16.4 according to operator requirements:

• The anchor cell keeps the 5G icon for 30 seconds after the terminal detects the NR cell signal at the bottom layer. After 30 seconds, it is determined whether the 5G icon is displayed based on whether SCG is added. If SCG is not added, it is determined whether the 5G icon is displayed based on whether upperLayerIndication is configured in SIB2.
• The non-anchor cell determines whether to display the 5G icon based on whether sib2 is configured with upperLayerIndication.

Note : iPhone iOS 16.4 determines that a 4G cell is an anchor cell only when two conditions are met at the same time: the base station sends B1 measurement + the terminal bottom layer measures the NR cell.