Making the world smaller

  Telecommunication is moving 

at a dizzy pace

The word communication is sometimes synonymous with prosperity and civilization. As a matter of fact, the index of prosperity of a nation is perhaps greatly dependent on the communication facilities it offers -- roadways, railways, telecommunication and so on. Civilized people have always communicated. The evolution of the modes of meaningful and long-distance communication started from the prehistoric age when geographically scattered people, communicated through Smoke signals. The different patterns of smoke indicated the message conveyed. Then came Drum beating. Drummers sitting at hilltops relayed intelligence to distant places. The pattern of notes helped discriminate the messages relayed. These went on for centuries until people mastered the art of writing and exchanging information took place by Pigeon post and later through the Postal service.

The dawn of the 19th century suddenly sparkled with the invention of the Telegraph, the first milestone of modern communication, by Samuel Morse. Morse code, a combination of short and long duration electrical signals sent over wire, conveyed meaningful information. This was the starting point of long-distance communication. The human voice, a form of sound energy, was converted into it's electrical counterpart and sent over wires. Over many years, voice communication passed into Telegraph. Other applications followed rapidly; Telex for transport of typed characters, Fax or Facsimile for still images and hand-written texts, Radio broadcasting for speech and music  and Television for moving images and associated sound. Modern communication, the main focus of this article, has taken a dramatic upswing in the late Sixties following significant development of the Digital Computer.

Basically there are two ways in which information or a message of any type, Voice,Texts or Images can be transported between a sender and a receiver through the Telecommunication Network,  using appropriate media : Analog or Digital. Analog means that a continuous range of frequencies is transmitted. The sound one hears and the image one sees consist of such a continuous range. Digital transmission means that a stream of on/off pulses known as bits, short form of binary digits are sent the way, the data travel in computer circuits.

The source (voice microphone or TV camera output) and the destination (hand set, or Radio/TV set at home) of information are predominantly analog by nature and will always have the highest degree of penetration in the human society, that is telephone, Radio and Television users are many times more than the Telex and computer users. At the same time, transportation of information over long distances using digital communication technique is inherently more reliable and superior quality. So, considerable effort went to digital transportation of information to replace analog communication, taking it for granted that techniques existed to code analog information into digital form at source and decode in a reverse at the destination to suit the characteristics of terminal equipments. The technique of coding is broadly known as pulse code modulation.

How does the computer comes so heavily into telecommunication? Let us illustrate by an example: You must have noticed that just a pair of lines goes out of your home telephone set. Yet you can talk to anybody, anywhere you like. This means the Telephone Exchange, the multiway switch, does the switching function depending on the number dialled. Most of the telephone exchanges in our country are still Strowger or Cross-bar exchanges. Whereas the Digital switches of today are highly specialised computer, programmed, specifically for processing of streams of bits. For the most part such switches are neutral to what the streams represent - voice, texts or Images. 

In this case the computer does the switching function,  perhaps most efficiently. This is the real time application of the computer, meaning that the end-to-end connectivity is matured before the telephone conversation begins. The property of programmability, storage and the speed of computer is exploited in non-real time applications.

In electronic mailing, texts in the form of letters or reports are entered into the source computer with the mailing code of the destination. The computer finally takes care of transporting the mail to it's destination. For example,  a message from Calcutta to New York is to be posted. The communication Network is spread between these points with intermediate stations, say, at Bombay, Rome, Amsterdam and London. It is quite likely that the entire link, i.e. Calcutta, Bombay, Rome, Amsterdam, London and New York may not remain free at that instant. The computer keeps hunting the availability of free link and keeps on sending the message in parts for storage at an intermediate node with all the book-keeping of part of the message sent till the entire message finds its intended destination with multiple hops. In computer terminology this is termed as packet switching of message.

The circumstances favouring digital transmission stem mainly from two factors. First, the reliability of high speed digital transmission at reduced cost, second, an unified approach in squeezing voice data and image in digital format will help getting rid of multiple standards of telecommunication. The approach is known as Integrated Services Digital Network (ISDN), a bold and feasible step towards modern communication. It is, of course, recognised that there has already been large investments in existing telecommunication switches and other facilities in many parts of the world, and economic factors would make it impossible to change immediately to ISDN in many areas, particularly in developing countries. But ISDN is definitely going to be the vehicle of communication of the 21st century.