РефератыИностранный языкTeTelecommunication Essay Research Paper Telecommunication1 IntroductionComputer and

Telecommunication Essay Research Paper Telecommunication1 IntroductionComputer and

Telecommunication Essay, Research Paper


Telecommunication


1. Introduction


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.


2. The Beginnings


2.1. Dot Dot Dot Dash Dash Dash Dot Dot Dot


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.


2.2. Mr. Watson, Come Here!


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


patent 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


two 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


sound 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


resistance 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.


2.3. Please Wait, I’ll Connect You.


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


switchboard 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.


2.4. The Free Press Reported That President Carter…….


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.


3. From The Carterfone to the 14,400


3.1. I’ll Patch Her Up On The Carterfone, Captain.


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.


3.2. So Gentelmen A’ Will Be 65


With more and more electronic communication and the invention of VDTs


the shortcomings of the Baudot code were realized. So in 1966, several


telecommunications companies devised a replacement for the Baudot code. The


result was the American Standard Code for Information Interchange, or ASCII.


ASCII uses 7 bits of code, allowing it to represent 128 characters without a


shift code. The code defined 96 printable characters (A through Z in upper- and


lowercase, numbers from 0 to 9, and various punctuation marks) and several


control characters such as carriage return, line feed, backspace etc. ASCII


also included an error checking mechanism. An extra bit, called the parity bit,


is added to each character. When in even parity mode, the bit would have a


value of one if there was an even number of ones and zero if there was an odd


number of ones. IBM invented it’s own code which used 8 bits of code giving 256


character possibilities. The code was called EBCDIC, for Extended Binary Coded


Decimal Interchange Code and was not sequential. The Extended ASCII was


designed so that PCs could again attain compatibility with the IBM machines.


The other upper 128 characters of the EASCII code include pictures such as lines,


hearts and scientific notation. In 1969 guidelines were set for the


construction of serial ports. The RS-232C standard was established to define a


way to move data over a communications link. The RS-232C is commonly used to


transmit ASCII code but can also transmit Baudot and EBCDIC data. The connector


normally uses a 25 pin D shell connector with a male plug on the DTE (Data


Terminal Equipment) and a female plug on the DCE (Data Communications Equipment).


3.3. Hello Joshua, Would You Like To Play A Game…


In the 1950s a need arose to connect computer terminals across ordinary


telephone lines. This need was fulfilled by AT&T’s Bell 103 modem. A modem


(modulator/demodulator) is used to convert the on-off digital pulses of computer


data into on-off analog tones that can be transmitted over a normal telephone


circuit. The Bell 103 operated at a speed of 300 bits per second, which at that


time was more than ample for the slow printing terminals of the day. The Bell


103 used two pairs of tones to represent the on-off states of the RS-232C data


line. One pair for the modem that is calling and the other pair for the modem


answering the call. The calling modem sends data by switching between 1070 and


1270 hertz, and the answering modem by switching between 2025 and 2225 hertz.


The principle on which the Bell 103 operated is still in use today. During the


sixties and seve

nties the concept of mainframe networks arose. A mainframe


consisted of a very powerful computer to which thousands of terminals were


connected. The mainframe worked on a timesharing process. Timesharing was when


many users on terminals could use limited amounts of the host computer’s


resources, thus letting many parties access the host at the same time. This


type of network, however, was very expensive, and since on time sharing you


could only use small amounts of the host’s total computing power (CPU), the use


of the terminal was slow and sluggish. In the late seventies the personal


computer was introduced to the public. A personal computer consisted of a


monitor, a keyboard, a CPU (Central Processing Unit), and various other


connectors and memory chips. The good things about PCs were that they did not


have to share their CPU and that the operating costs of these systems were much


less that that of their predecessors. The computers could, with a software


package, emulate terminals, and be connected to the mainframe network. Bell


laboratories came up with the 212a unit which operated at the speed of 1200 bits


per second. This unit, however, was very susceptible to noise interference.


3.4. Hey Bell! I Can Hang Myself Up!


After the breakup of the AT&T empire that controlled the modem industry,


many other companies started to create new designs of modems. Hayes


Microcomputer Products, took the lead in the PC modem business. Hayes pioneered


the use of microprocessor chips inside the modem itself. The Hayes Smartmodem,


introduced in 1981, used a Zilog Z-8 CPU chip to control the modem circuitry and


to provide automatic dialing and answering. The Hayes unit could take the phone


off the hook, wait for the dialtone, and dial a telephone number all by itself.


The Hayes Smartmodems sometimes had more powerful CPUs than the computers that


they were connected to. The next advancement was the invention of the 2400 bits


per second modem. The specifications came from the CCITT, an industry standard


setting organization composed of hundreds of companies world wide. The new


standard was designated as V.22bis and is still in use today. Other CCITT


standards that followed were the V.32 (9600 bps), the V.32bis (14400 bps), the


V42 (error control), and the V42bis (data compression). Virtually all modems


today conform to these standards. The next big computer invention was the fax


modem. It uses the on-off data transmission just as a modem but for the purpose


of creating a black and white image. Each on-off signal represents a black or


white area on the image. The image is sent as a set of zeros and ones and is


then reconstructed on the receiving end.


4. LANs


4.1. I Donnwanna File-Share!


Network Operating Systems (OS) are actually a group of programs that


give computers and peripherals the ability to accept requests for service across


a network and give other computers the ability to correctly use those services.


Servers share their hard disks, attached peripherals such as printers and


optical drives, and communication devices. They inspect requests for proper


authorization, check for conflicts and errors and then perform the requested


service. There is a multitude of different types of servers. File servers are


equipped with large hard drives that are used to share files and information, as


well as whole applications. The file-server software allows shared access to


specific segments of the data files under controlled conditions. Print servers


accept print jobs sent by anyone on the network. These servers are equipped


with spooling software (saving data to disk until the printer is ready to accept


it) that is vital in the situations where many requests can pour in at the same


time. Network Operating Systems package requests from the keyboard and from


applications in a succession of data envelopes for transmission across the


network. For example, Novell’s NetWare will package a directory request in an


IPX (Internetwork Packet Exchange) packet, and the LAN adapter will then package


the IPX request into an Ethernet frame. In each step information about data and


error control data is added to the packet.


4.2. Eight Go In One Comes Out


The Network Interface Card or LAN adapter, is an interface between the


computer and the network cabling. Within the computer it is responsible for the


movement of data between the RAM (Random Access Memory) and the card itself.


Externally it is responsible for the control of the flow of data in and out of


the network cabling system. Since typically computers are faster than the


network, the LAN adapter must also function as a buffer between the two. It is


also responsible for the change of the form of data from a wide parallel stream


coming in eight bits at a time to a narrow stream moving one bit at a time in


and out of the network port. To handle these tasks the LAN adapters are


equipped with a microprocessor and 8-64K of RAM. Some of the cards include


sockets for ROM chips called Boot ROM. These chips allow computers without hard


drives to boot operating systems from the file server.


4.3. Take Your Turn!


Ethernet and Token Ring network adapters use similar systems of


electrical signaling over the network cable. These signals are very similar to


the Baudot and Morse codes. A technique called Manchester encoding uses voltage


pulses ranging from -15v to +15v in order to transmit the zeros and ones. The


network cable has only one drawback, it can only carry signals from one network


card at a time. So each LAN architecture needs a media-access control (MAC)


scheme in order to make the network cards take turns transmitting into the cable.


Ethernet cards listen to the traffic on the cable and transmit only if there is


a break in the traffic when the channel is quiet. This technique is called


Carrier-Sense Multiple Access With Collision detection (CSMA/CD). With


collision detection, if two cards start transmitting at the same time, they see


the collision, stop, and resume some time later. Token Ring networks use a much


more complex process called token passing. Token Ring cards wait for permission


in order to transmit into the cable that forms an electrical loop. The cards


use their serial numbers in order to find the master interface card. This card


starts a message called a token. When a card with information to send receives


the token, it sends the data across the network. After the addressed interface


card receives the information and returns it to the originating card, the token


is given back to the master to be passed onto the next card. The ARCnet network


uses a very similar system to that of the Token Ring. Instead of using a token,


the master card keeps a table of all active cards and polls each one in turn,


giving permission to transmit.


4.4. Tied In A Knot


Various types of cabling are used to connect the LAN adapters to the


servers. Unshielded twisted pair wires offer rather slow speed, are very


inexpensive, are small, and can only span very short distances. These cables


use the RJ-45 connector. Coaxial cable offers fast speed, is rather expensive,


has a medium sized diameter, and can span medium distances. Coaxial cable uses


BNC connectors. The shielded twisted pair cable offers fast speed, is more


expensive than the coaxial cable, has a large diameter, and can only span short


distances. These cables use the IBM data connector. The fiber optic cable is


the fastest possible type of data transfer, costs astronomical amounts of money,


has a tiny diameter, and can span very long distances. This cable uses the ST


fiber optic connector. Wiring hubs are used as central points for the cables


from the network interface cards.


5.5. Loves Me, Loves Me Not, Server Based, Peer To Peer…


There are two general types of LANs. The Server-based networks rely on


one major server to store data, offer access to perhiperals, handle the printing


and accomplish all the work associated with network management. The Server-


based networks have a high start up cost, but offer high security as well as


ease of operation. These networks become more economical as more computers are


added to the network. In Peer to peer networks the network responsibilities are


divided among many computers. Some act as file servers, others as print servers,


some as CD-ROM servers, tape drive servers, etc. The Startup cost of these


networks is much cheaper, but when more computers are added to the network, some


of the servers may not be able to handle the extra activity.


5. Links Between LANs


5.1. She Just Won’t Send Sysop!


Most networks have very short information transfer ranges. But, in an


ever shrinking world the need for links between LANs has never been higher.


This section will explain the components and information needed to link LANs.


When an electric current travels over a long length, it’s charge decreases, and


it is susceptible to electromagnetic interference. To combat the length problem


a component has been devised. A repeater is a little box that is inserted


between a cable. It’s primary function is to amplify the weakening pulse and


send it on it’s way. Bridges are used to analyze the station address of each


Ethernet packet and determine the destination of the message. The Routers strip


the outer Ethernet packets of a data packet in order to get the data. This data


is sent to other routers in other places of the world and then repackaged by


those routers. The removal of the excess data packets by the routers decreases


the time required to transfer that data. If networks use the same addressing


protocol, bridges can be used to link them, however, if they use different


addressing protocols, only routers may be used. During these times MANs


(Metropolitan Area Networks) are in use and development today. These use


routers that are connected preferably via a fiber optic cable, to create one


large network.


5.2. Pluto Calling Earth!


Any networks larger than 1000m typically rely on telephone digital lines


for data transfer. These networks are called Circuit Switched Digital Networks .


Circuit Switched Digital Networks utilize a switching matrix at the central


office of a telephone company that connects local calls to long distance


services. The Telephone companies now offer dial up circuits with signaling


rates of 56, 64, and 384 kilobits per second as well as 1.544 megabits per


second. Another type of LAN to LAN connections are packet switching networks.


These are services that a network router calls up on a digital line. They


consist of a group of packet switches that are connected via intraswitch trunks


(usually fiber optic) that relay addressed packets of information between them.


Once the packet reaches the destination packet switch, it sends it via another


digital connection to the receiving router.

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