There is no actual standard for what the bars showing the connection actually mean. It is up to each phone manufacturer to select the conditions required for each bar. It could for example be that they are showing how good the strength of the signal from the cell tower is. If you are close to a cell tower you would expect a strong signal and therefore many bars. However this does not say anything about how much resources the cell towers have to spare your phone. It could be that there are hundreds of phones connected to the same cell tower, all with good connection to the tower, but they still need to share the same frequency space and the same outgoing connections.
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