Telecommunication – Computer And Telephone Networks

Computer and telephone networks inflict a gigantic impact on today’s society. From letting you call John in Calgary to letting you make a withdraw at your friendly ATM machine they control the flow of information. But today’s complicated and expensive networks did not start out big and complicated but rather as a wire and two terminals back in 1844. From these simple networks to the communication giants of today we will look at the evolution of the network and the basis on which it functions. The network is defined as a system of lines or structures that cross.

In telecommunications this is a connection of peripherals together so that they can exchange information. The first such exchange of information was on May 24, 1844 when Samuel Morse sent the famous message “What hath God wrought” from the US Capitol in Washington D. C. across a 37 mile wire to Baltimore using the telegraph. The telegraph is basically an electromagnet connected to a battery via a switch. When the switch is down the current flows from the battery through the key, down the wire, and into the sounder at the other end of the line. By itself the telegraph could express only two states, on or off.

This limitation was eliminated by the fact that it was the duration of the connection that determined the dot and dash from each other being short and long respectively. From these combinations of dots and dashes the Morse code was formed. The code included all the letters of the English alphabet, all the numbers and several punctuation marks. A variation to the telegraph was a receiving module that Morse had invented. The module consisted of a mechanically operated pencil and a roll of paper. When a message was received the pencil would draw the corresponding dashes and dots on the paper to be deciphered later.

Many inventors including Alexander Bell and Thomas Edison sought to revolutionize the telegraph. Edison devised a deciphering machine. This machine when receiving Morse code would print letters corresponding to the Morse code on a roll of paper hence eliminating the need for decoding the code. The first successful telephone was invented by Alexander Graham Bell. He along with Elisha Gray fought against time to invent and patent the telephone. They both patented their devices on the same day-February 14, 1876- but Bell arrived a few hours ahead of gray thus getting the patent on the telephone.

The atent issued to Bell was number 174,465, and is considered the most valuable patent ever issued. Bell quickly tried to sell his invention to Western Union but they declined and hired Elisha Gray and Thomas Edison to invent a better telephone. A telephone battle began between Western Union and Bell. Soon after Bell filed suit against Western Union and won since he had possessed the basic rights and patents to the telephone. As a settlement Western Union handed over it’s whole telephone network to Bell giving him a monopoly in the telephone market.

During his experiments to create a functional telephone Bell pursued wo separate designs for the telephone transmitter. The first used a membrane attached to a metal rod. The metal rod was submerged in a cup of mild acid. As the user spoke into the transmitter the membrane vibrated which in turn moved the rod up and down in the acid. This motion of the rod in the acid caused variations in the electrical resistance between the rod and the cup of acid. One of the greatest drawbacks to this model was that the cup of acid would have to be constantly refilled. The second of Bell’s prototypes was the induction telephone transmitter.

It used the principle of magnetic induction to change ound into electricity. The membrane was attached to a metal rod which was surrounded by a coil of wire. The movement of the rod in the coil produced a weak electric current. An advantage was that theoretically it could also be used both as a transmitter and a receiver. But since the current produced was so weak, it was unsuccessful as a transmitter. Most modern day telephones still use a variation of Bell’s design. The first practical transmitter was invented by Thomas Edison while he was working for the Western Union.

During his experiments Edison noticed that certain carbon compounds change their electrical esistance when subjected to varying pressure. So he sandwiched a carbon button between a metal membrane and a metal support. The motion of the membrane changed the pressure on the carbon button, varying the flow of electricity through the microphone. When the Bell Vs. Western Union lawsuit was settled the rights to this transmitter were also taken over by Bell. The first network of telephones consisted of switchboards. When a customer wanted to place a call he would turn a crank on his telephone terminal at home.

This would produce a current through the line. A light at the witchboard would light up. The caller would tell the operator where he wanted to call and she would connect him by means of inserting a plug into a jack corresponding to the desired phone. In earlier years he found that he could use the ground as the return part of the circuit, but this left the telephone very susceptible to interference from anything electrical. So in the mid 1880s Bell realized that he would have to change the telephone networks from one wire to two wire. In 1889 Almon Brown Strowger invented the telephone dial which eliminated the use for telephone operators.

French inventor Emile Baudot created the first efficient printing telegraph. The printing telegraph was the first to use a typewriter like keyboard and allowed eight users to use the same line. More importantly, his machines did not use Morse code. Baudot’s five level code sent five pulses for each character transmitted. The machines did the encoding and decoding, eliminating the need for operators. After some improvements by Donald Murray the rights to the machine were sold to Western Union and Western Electric. The machine was named the teletypewriter and was also known by it’s nickname TTY.

A service called telex was offered by Western Union. It allowed subscribers to exchange typed messages with one another. The first practical computers used the means of punched cards as a method of storing data. These punched cards held 80 characters each. They dated back to the mechanical vote-counting machine invented by Hermen Hollerith in 1890. But this type of computer was very hard and expensive to operate. They were very slow in computing speed and the punch cards could be very easily lost or destroyed. One of the first VDTs (Video Display Terminal) was the Lear- Siegler ADM-3A.

It could display 24 lines of 80 characters each (a remarkable feat of technology). One of the regulations that AT&T passed was that no other company’s equipment could be physically connected to any of it’s lines or equipment. This meant that unless AT&T invented a peripheral it would not be legal to connected to the telephone jack. In 1966 a small Texas company called Carterfone invented a simple device that could go around these regulations. The Carterfone allowed for a company’s radio to be connected to the telephone system. The top portion of the Carterfone consisted of molded plastic.

When a radio user needed to use the telephone, the radio operator at the base station placed the receiver in the Carterfone and dialed the number. This allowed the user to call through the radio. AT&T challenged the integrity of the Carterfone on the phone lines and lost the battle in court. In 1975 the FCC passed Part 68 rules. They were specifications that, if met would allow third party companies to sell and hook up their equipment to the telephone network. This turned the telephone industry upside down and challenged AT&T’s monopoly in the telephone business.

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