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Cellphones produce radio frequency waves. They use Ni or Li batteries to power this. One cell in an analog system uses one-seventh of the available duplex voice channels. A cellphone carrier typically gets 832 radio frequencies to use in a city. Each cellphone uses 2 frequencies which are incoming or ongoing. There are around 395 voice channels per carrier. The other 42 frequencies are used for control channels. Which means, each cell has around 56 voice channels available. When the user wants to make a call, the cell phone sends a message to the tower, asking to be connected to a given telephone number. If the tower has sufficient resources to grant the request, a device called a switch patches the cell phones signal throughout to a channel on the public switched telephone network or otherwise known as the PSTN. This call now takes up a wireless channel as well as a PSTN channel that will be held open until the call is completed. This is how a cell phone works.
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