Evolution of Telecommunication technology

What is telecommunication?

Telecommunication is the area of the communication system that relates to transmit information signals among entities which are geographically far apart. An entity may be a computer, a human being, a facsimile machine, a teleprinter, a data terminal and so on.

Evolution of telecommunication:

The information transfers between two entities whose are known as –

   Source : the entity who initiates the information signals.

   Destination : the entity for whom the information signals are destined

To transmit the information signals, we need to establish a connection among source and destination. In modern days connectivity in telecommunication system is achieved by the use of switching systems. Actually evolution of telecommunication is related to the improvement of this switching system. In March 1876, Alexander Graham Bell was able to long distance voice transmission using his telephone sets. There is another man, who also successfully did this, name Jagodish Chandra Bashu. They demonstrated a point to point (direct) connection which is the foundation of modern telecommunication system. A network using point to point connection is shown in figure -

In such a network, a calling subscriber chooses the appropriate or direct link to establish connection with the called subscriber (In telephone conversation, the source is referred to as the calling subscriber and the destination is referred to as the called subscriber.). In order to draw the attention of the called subscriber, some form of signaling is required with each link. If the called subscriber is ready to engage, a suitable indication should be given to the calling subscriber by means of signaling. Now information exchange can begin.

Networks with point to point links among all the entities are known as fully connected networks. The number of links required in a fully connected network becomes very large even with moderate values of users/entities. A fully connected networks is given below-

fully connected network

Suppose, we have n entities. To connect the first entity to all other entities, we require (n-1) links. Now we require (n-2) links for second entity because it is already  connected with first entity. In such a way , we get the total number of links

                   L = (n-1) + (n-2) + (n-3) + ………………….. +2 + 1 + 0 
    

                      = {n(n-1)}/2

So for the number of entities, n = 50 then we required links,  L = 1225

[ To understand the solution of above equation, think:  n = 10

  So,  L = (10 -1) + (10-2) + (10-3) + (10-4) + (10-5) + (10-6) + (10-7) + (10-8) + (10-9) + (10-10)

            =  (10 -1) + (10-2) + (10-3) + (10-4) + (10-5) + 4 + 3 + 2 + 1 + 0

            = (10 -1) + 0 + (10-2) + 1 + (10-3) + 2 + (10-4) + 3 + (10-5) + 4

            = (10 -1) + (10 -1) + (10 -1) + (10 -1) + (10 -1)

            = 5(10 -1)

            = {10(10-1)} / 2

           = {n(n-1)}/2                               [ as n=10 ]

This is the basic easiest way to solve the above equation. Actually any mathematics problem can be solved in several ways ]

So for practical use of Bell’s or Boshu’s invention demanded an exchange office so that all the subscribers are not connected directly to one another. Instead they are connected to the exchange office is known as switching system. A telecommunication network using switching system is shown below –

switching network

In this configuration, only one link per subscriber is required between the subscriber and the switching system and the total number of such links is equal to the number of subscribers connected to the system. Signaling is now required to draw the attention of the switching system to detect whether a called subscriber establish or release a connection. It should also enable the switching system to detect whether a called subscriber is busy and if so indicate the same to the calling subscriber.

The function performed by a switching system in establishing and releasing connections are known as control functions.

The links that run between the switching systems are called trunks and those that run to the subscriber premises are known as subscriber lines.

Early switching systems were manual and operator oriented. Limitations of operator manned switching systems were quickly recognized and automatic exchanges came into existence. There has an interesting story that I will mention in a post later.