History of the Telephone
Although Alexander Graham Bell is recognized as the inventor of the first telephone, others were working contemporaneously to create a technique for transmitting sound between remote locations. Bell and a man named Elisha Gray both filed for patents on their designs on Feb. 14, 1876 with Bell beating Gray by only two hours. Gray had designed a functioning electromagnetic receiver two years earlier but Bell beat him in creating the first working transmitter.
The 2-Wire Telephone
Only two wires, labeled "tip" and "ring," are required per telephone circuit. This nomenclature originated during the days when telephone operators used 1/4-inch phono plugs--similar to those used today for stereo headphones--to connect callers. Tip was the tip of the phono plug and the positive side of the circuit. Ring referred to a conductive metal ring insulated from and located behind the tip of the plug, the negative side of the circuit. The "sleeve" on the plug was for ground.
When 2-Wire is Not Enough
When more than one telephone number is needed, an additional two-wire circuit is required. Having multiple pairs of telephone wires allows for separate telephones to be used by different users simultaneously. Each user can initiate or receive calls independently of the others. Additionally, having a multi-line telephone allows one person to be able to call out or receive calls on all numbers from a single telephone.
From 2-Wire to 8-Wire
As requirements for more telephones in a single location grew, the number of 2-wire telephone pairs increased from 2-wire to 8-wire. Most 8-wire connections are used for LAN (local area network) purposes. The majority of telephone connectors are identified as RJ-XX, where RJ stands for "registered jack" and XX is a numerical suffix indicating the number of lines (distinct telephone numbers).
The 6-wire telephone jack, the RJ-11, is the most commonly used today. It can be configured with six conductors but usually has four. Most land-line telephones employ the RJ-11 modular jack. Computers connecting to a network via dial-up mostly use an RJ-11 jack. The 6-wire telephone cord allows for a location to have up to three separate telephone lines. With a multi-line telephone, a business can have one person handle all three lines.