The word ‘’Telephone’’ is derived from Greek meaning distance voice and could be defined as a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be heard directly.
In 1876, Alexander Graham Bell was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice.
A traditional landline telephone system, also known as plain old telephone service (POTS), commonly carries both control and audio signals on the same twisted pair of insulated wires. The control and signaling equipment consists of three components, the ringer, the hookswitch, and a dial. The ringer, or beeper, light or other device alerts the user to incoming calls. The hookswitch signals to the central office that the user has picked up the handset to either answer a call or initiate a call. A dial, if present, is used by the subscriber to transmit a telephone number to the central office when initiating a call. The dual-tone multi-frequency signaling (DTMF) with pushbutton telephones has replaced rotary technology type of dialing since the 1960s.
A major expense of wire-line telephone service is the outside wire plant. Telephones transmit both the incoming and outgoing speech signals on a single pair of wires. A twisted pair line rejects electromagnetic interference (EMI) and crosstalk better than a single wire or an untwisted pair. The strong outgoing speech signal from the microphone (transmitter) does not overpower the weaker incoming speaker (receiver) signal with sidetone because a hybrid coil and other components compensate the imbalance. The junction box arrests lightening and adjusts the line's resistance to maximize the signal power for the line length.