Switching of Mobile Networks

Hello All,

I would like to know how the mobile knows which frequency(2G/3G/4G) it is using while communicating?
for e.g. when i am moving, sometimes mobile shows it is in 3G network and sometimes in 4G Network. so i want to know when mobile network switch from 3G to 4G or vice versa, what really happens inside the mobile (hardware level)?

Thank you in advance.

The name of this phenomenon is: intra-mode handover (and some time, vertical handover or intra-RAT handover):

https://en.wikipedia.org/wiki/Handover
https://its-wiki.no/images/9/9a/Basics_Handover.pdf

Thank you for replying. But what i am actually looking for is what happens when mobile receives the signal or before transmitting the signal.

for e.g. : I am texting somebody. first the signal will go through triplexer then modulation of the signal. after that filtering of signal will take place. then it will go through power amplifier and in the last, mobile antenna will transmit the signal. In this whole process how my mobile knows which frequency or band or 2G/3G/4G network it is using for transmitting signal?