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The Cellular Network
A cellular network is the system for how a cell phone connects to the Public Switched Telephone Network (PSTN). The PSTN is the main connection between you and whomever you're trying to reach. Unfortunately, it's not as easy as simple as going through the PSTN and getting to whomever you want. First, your call goes to the base station nearest to you. If you've ever seen a cell phone tower, that's a base station. Base Stations are placed so that they can, theoretically, cover any cell phone, anywhere. The pattern, called a cluster, is shown here:
Clusters can include 4, 7, 12, or 21 base stations. However, the coverage a base station has differences in the way they're shown for display purposes (fictitious), what they should be theoretically (ideal), and what the signal coverage actually is (real). Geographical and other radio waves cause the abnormal signal coverage. This is why a cell phone may have good coverage some places, but poor coverage in other places.
Each base station cluster then connects to a Mobile Switching Center (MSC) through land lines. The MSC stores information about the subscribers located within the cluster and is responsible for directing calls to them. Each MSC connects with the other MSCs and the PSTN. The overall Cellular Network is shown here:
890-915 MHz channels are used for base transmissions, while 935-960 MHz is used for mobile transmission. The number of subscribers in a cluster depends on where the cluster is located. Rural areas wont have as much subscribers as urban areas.