Based on history, telegraph signal transmission via cable is first modern technology telecommunication system that to develop. Telegraph introduced on 1837 in England and 1845 in France. On March 1876, Alexander Graham Bell demonstrating telephone equipment and possibility for development telephone system, example telephone system with distant voice transmission. This important invention of Alexander Graham Bell is very seldom and basic of telephone system development right now.
Graham Bell is demonstrating point-to-point telephone connection. On that network, costumer who wants to call can choose available link for build one connection with called costumer. So that before information trading started a costumer who called understands will be called then on every link need a signaling. If costumer who called is in busy state (talk), one indication to explain that state also must be given to costumer who calling with using signaling method.
Generally can explained that for n terminal, need n(n-1)/2 link. Let’s see n terminal on several condition/destination. For connecting first terminal to all terminals, we need (n-1) link. On that condition, second terminal already connected with first terminal, so that for connecting to other terminal need (n-2) link. For third terminal, need (n-3) link, and so forth. So that total link, that is:
L = (n-1) + (n-2) + ….. + 1 + 0 = n(n-1)/2
Network with point-to-point link between all terminals known as fully connected networks. The total link needed on one fully connected network will be very big with moderate change from n value. Example, we need 1225 link for build full connection between 50 costumers. The consequence is, used practical of Bell discover on one big scale network will to appear with request not only in telephone equipment and two wire cable but also to appear with need of switching system or central.
With deploying switching system, costumers not connected directly to the other costumers, but connecting to switching system, so that if one costumer want to communicating with other costumers, then on that switching system will build a connection between them. On that configuration, all costumers only need one link to connected to switching system, so that total link equivalent with total costumer who connected to system
On utilization switching system, signaling need to build or release one connection. Signaling must acquire enabling switching system for detection is that a costumer who called on busy state? If yes, indicating to costumer who calling. Formed function by a switching system to build and release a connection known as control functions.
