Cellphones
Bell Labs, in the U.S, discovered cell phone Technology. Over the years, as technology improved, cell phones have become more sophisticated and less expensive. It has been in the last 10 years that cell phones have been approachable financially to the average world citizen. And in the last five years, technology has improved to the point where they are as common, and as in the case of the nation of Finland, even more common, than landlines. Usage has changed from being primarily business and emergencies only to entertainment, and family lifestyle related. The purposes for the new and ever-changing cell phone technology differ depending on where you reside in the world. Bell Labs originally discovered cell phone technology in the 1940's. Twenty years later the United States finally connected the cellular system with the Public Switched Telephone Network (PSTN), which is your regular phone service. An analog and a digital cellular system connect mobile customers to the PSTN in the United States. The cellular phone system works in many different layers. The basics for setting up a cellular phone for mobile use, and the details about how the phone message is passed through channels on radio frequencies. When you buy a cell phone, the phone is equipped with a lightweight low powered battery. The battery allows for signals from the phone to be picked up by towers within the area where you are placing a telephone call. The tower then connects you to the wire line side of the phone system, and your phone call is completed. For this to occur, the tower must identify the cell phone to know your current location and your 'home' system. All cell phones have codes used to identify the phone, the owner, and the service provider, such as Cellular One or Sprint. The Electronic Serial Number (ESN) is used to identify the phone. It is a 32-bit number stored in your phone when it is manufactured. The number used to identify the owner is your ten-digit phone number assigned to you when you buy the phone. In cellular system terms, this is the Mobile Identification Number (MIN). Finally, the number used to identify your service provider is the System Identification Code (SID), which is a 5 digit number assigned by the FCC to each cell phone carrier. All of these codes are used in making your cell phone function properly. The process is similar for receiving calls. When you turn on your phone, a SID is transmitted on a frequency and is compared with the SID programmed into your phone. If the SID's match, it means you have service from your home service provider, and you are able to make and receive calls. The MTSO keeps track of your cell phones location, so when the MTSO gets a call from the PSTN or another cellular service, it will check its database and see which cell you are located in. The MTSO picks a frequency pair for your phone to answer the call on, and once it tells your phone which frequencies to use, the call connects and you receive the call. The original cellular phone system in the United States was analog. It is referred to as Advanced Mobile Phone Service (AMPS).