Trunk Call: Explained !
What is trunk call?
A long distance call made within country used to call a trunk call.
HOW DID IT WORKED?
A Line Diagram to understand the system
Before STD (Subscriber Trunk dialing) has even started, there were time when there was a middle ground for Phone calls. which connects two person's call, named telephone exchange.
Telephone Exchange station
Closer look at of telephone exchange circuit board
ones you subscribe to the service, the one end of the telephone line connects to your telephone and another end of the line connects to the telephone exchange.
In the early days of telephones, you couldn’t dial a number yourself. You had to call an operator at the telephone exchange of your phone company to connect you for any phone call. Later on, you could make local calls yourself, but had to call the operator to connect you to someone whose phone was connected to a different telephone exchange in the same city or elsewhere. The two telephone exchanges were connected by a trunk line. the trunk line is the bundle of small wires brought together to make a thick single wire. trunk as a word means the main, core, or central part, before subsidiary parts diverge. A tree trunk, not the branches. the line was pretty thick almost like the tree trunk. this was the reason it called trunk line, and call made through trunk line called trunk call.
Telephone Trunk line
Individual circuits in that trunk are not dedicated to a particular subscriber but can be used by any subscriber as and when needed. The number of circuits in such a trunk is less than the number of subscribers connected to the exchange, because not all subscribers are supposed to need a trunk circuit at the same time. If more subscribers would need to use a trunk circuit at the same time than there are circuits in that particular trunk, some of them would get a ‘busy’ signal because all trunk circuits would be in use. This is just the rough information of how it works. The actual system is much more complicated!
Bonus
Know more:
S.T.D : Subscriber Trunk Dialing
I.S.D : International Subscriber Dialing
P.C.O : Public Call Office