How Phone Land Lines Work
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Modern Phone Network
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The modern land line network, also called the Public Switched Telephone Network (PSTN), consists of copper wiring, optic fibers, digital switches, and digital concentrators. When connecting international calls or cell phones, satellite systems or microwave towers may also be needed.
The phone in a home or office is connected to the phone company's external bridge by dedicated copper wires. The external bridge is the beige box outside the home or office and is connected to each telephone jack by at least one pair of copper wires. One copper wire serves as the data connection while the other wire supplies the phone with power.
The external bridge is then connected to the phone company's local exchange by fiber optic cables. The local exchange is a building full of telephone equipment, such as digital switches and concentrators, that routes calls. When routing long distance and international calls, microwave towers and space satellites may be used, which send and receive calls as pulses of electromagnetic radiation.
Voice Digitization
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Converting telephone conversations to digital signals begins with picking up the phone handset, which signals for the digital switch to play a dial tone. When a number is dialed, the network routes the call to the destination phone and signals for the phone to ring. When the destination phone is answered, voice digitization begins with the speaker's voice.
Each phone has a diaphragm in the mouthpiece, which vibrates when a speaker talks. The vibrations are converted into electricity, which flows throughout the land line network until it reaches the destination phone.
The destination phone converts the electrical signals back into audible output that the listener hears through the phone's speaker. Because the phone network has cabling running in both directions, both parties can speak and listen at the same time.
Advantages & Disadvantages
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The primary disadvantage of a land line network is that it relies on many intersections, physical wiring and types of hardware to work. Duplication and alternate routing help alleviate the risk of network failure if just one piece of hardware fails.
Security is one of the advantages of land line phones as is the clarity of calls made on land line networks when compared with cellular phone networks. The reliability of 911 calls is fully supported on land line phones, while cell phone networks do not fully support emergency calls.
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