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 -
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. 