The difference between computer and telephone -In networking perspective
Let us consider the old traditional telephone.All telephones are connected by overhead wires(carried over telephone poles on the road side) to the area telephone exchange. Previously a man used to give connections between two phones by manually linking the sockets of the two phones inside the exchange building with a small wire.”the telephone exchange” is the leader of that group of phones. There must be at least a few hundred thousand such little exchanges covering our entire Earth. All these exchanges are linked by unbreakable connections( by wires/cables/optical cables or wireless).In achieving this connectivity whole groups of exchanges should be connected to a very powerful central exchange serving half a country . All such central exchanges will again be connected to just a few dozen “back bone” exchanges so that every one of the hundreds of millions of phones on earth can be linked to any other phone working in any faraway corner of the earth.
Now a days an unimaginably big mesh of strong and durable thick metal wire “coaxial” cables and far more powerful optical fibre cables covers entire earth. (optical fibres can provide a hundred thousand two way channels through a single optical fibre cable).Some of these metal/optical fibre cables are laid for part of the route for hundreds of kilometres on ocean floors encased in very strong rubber and metal casing to last for at least half a century. But this is only half the story about telephones.
Nowadays two way all weather foolproof radio channels are linked by the fixed “geostationary satellites” circling 20000 miles over the earth which relay the radio signals to any part of earth. These satellites are geostationary i.e the stop over our heads 20000 miles above without moving and work in effect like 20000 mile high towers!these satellites have inside them powerful recieving and tranmitting electronic automatic instrument systems. On the earth in every country very powerful recievers and transmitters are fixed on high “tranmission towers” to recive and relay incoming signals or to transmit outgoing signals recieved from the phones linked to faraway exchanges.In this way every phone can be linked to any other phone on earth in fraction of a seond automatically by “direct dialling” by the users. the cell phone is a small size two way radio phone linked to all places on earth by unbreakable all weather radio link through a most modern technology. The land phones in our houses are linked for just four or five miles by the overhead telephone wire over the telephone poles and after that they too are linked to the international radio/optical fibre/coaxial metal cable link. Though this high technology is used engineers still follow the good old rules of”central tephone exchange”.However now all data i.e.all our conversations are converted into strings of billions of 01010101s.the strings are devided into neatly cut “data packets” each containing about 20000 zeroes and ones eqivalent to about 50 sentences of printed alphabets.In this way telephone technology is working wonders and turned entire earth into a small village. .We can talk to a person in america or afica as if he is sittin next to you in your room.
Now we have come to a stage sufficient to discuss how computers in your office,in your town, in your country are connected to a faaraway computer in another part of the world just like phones. we should note that in new technolgy there is no difference between phone and computer.Both work with billions of 01010101s only .in fact cell phone is also a very powerful computer with a powerful “microprocessor chip” inside it containing software to implement the “tcp/ip technlogy “which is the life breathof modern digital networking technology.
due to such modern technology computers in our houses,offices,business establishments can be interconnected with any other computer both within our town and also with computers in any part of the world just like telephones.If a computer is connected with any other computer (in the proper prescribed way through software commands) whole books,songs,vedeos etc lying in your computer’s memory can be sent to any other computer just in fraction of a second. With the most modern optical fibre technology and “broad band internet” matter inside all the books in a big library (if kept in memory of a computer) can be sent into memory of another far away computer in a second! a connection with a strong fat wire called coaxial cable is enough to do this unbelievable feat.
When we want to know about the technology of connecting computers we shold have clear understanding about technology phone networks.Actually modern computers and phones are closely related in technology of networking.it closely follows the old telephone exchange technology.Modern cell phones are actually powerful computers though small in size with two way radio tranmission facility. Cell phones work only on the digital radio technology where all information is sent/recieved only by wireless(radio) and where all information(i.e human conversation or any other data) is sent in units called data packets. The cell phone towers relay the radio sigals from and to the cell phone.originally every computer worked alone all by itself unconnected to any other computer(“stand alone computer”) to carry out tough mathematical caculations for business houses,government departments and universities.but prices of computers came down drastically due to researches in transistor and silicon chip/ printed circuit technologies. After introdction of automatic self-managing “disc operating system” inside computers small computers became very popular.every industry,college,hospital,business etc started to purchase not one but a dozen computers. All computers inside one campus were interconnected to share the huge data in each of “main memories” or “secondary memories”.the technology of linking computers began.a very advanced technology called lan technology to link computers inside same campus was introduced.All the computers in a campus were linked by a long coaxial cable and had to obey orders from a “leader computer” called “server”. Only the two computers selected by server can communicate and share data and all others had to wait and keep quiet. Computers in a lan are connected to other lans (in a faraway part of city or in another town) through “wan” (wide area network) technology much like trunk telephone exchange technology. inside each lan one computer was selected as”router”i.e. a group leader which granted permission to a lan memmber(computer) to talk with a computer of another lan . The routers of all lans in a area were connected to the head router which controlled the wan. the head routers of several wans were connected to routers of still bigger wans which covered a whole country. It is all just like old telephone exhchange system but with “digital packets” transmitted in the routes.
Finally let us reember the main parts of a modern computer to better understand how it can be linked to other computers. in each computer there is a most important part called “main memory” .The data sent into computer through keyboard/ mouse/cd is sent first to the main memory before being sent to processors inside computer. If an answer data is sent out from computer to monitor screen,printer,sound boxes etc,first it reaches the main emory from the processors inside computer. The memory is like a black board in the class room .However the controlling part of computer is the microprocessor.It gives orders to main memory and smaller processors how to process incoming/outgoing data the microprocessor is like the central brain,the commander-in-chief
We come to the last point.when a computer” x “is connected to computer “y “which is ten miles away in another town and we have to send data(written data,sounds like songs,speech or vedeo i.e moving pictures) from x to y what happens?the written data in the main memory of x can be seen in monitor screen of y. the songs and conversatios recorded in main memory of x can be heard though speakers connected to y. Similarly the vedeo files kept inside main memory of “x” can be seen only through monotor screenof”y”. Thus simply by connecting two computers through a cable all data(written data,audio,vedeo)can flow from one to the other.Nowadays hundreds of computers are connected. for data(writtentext,audio or vedeo) to flow to another designated faraway computer,the rules of lan/wan/internet have to be followed very strictly and prescribed software requests/instructions/commands should go between the routers/requesting computers. For this purpose each computer in a netwok is alloted a permanent identification coded number.It is recorded in all computers and routers and is like a telephone directory inside each computer.