#evaloution

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- ---------

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 – -----------

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