A telephone network is a telecommunication network used for telephone calls between two or more people (www.wikipedia.com ). In the olden days telephones were connected directly to each other, they had to have a direct link to a particular person they would like to keep in touch with. For example, say they are four people, namely A, B, C and D, and this people are friends who would like to keep in touch with each other, so what would happen is, A would have a direct link to B, C and D and in order for B to keep in touch with C he would also need a direct link to C, which means a special telephone for each person, in that case A would have 3 different phones linking to each friend.
All this changed ever since the invention of telephone exchange happened. A telephone exchange network is a telecommunication system used in the public switched telephone network. There are two main types of telephone exchange namely, manual service exchange and automatic exchange. With manual service, the customer calls the operator to connect the call to the third party, and this is only possible if the number is in the same central office and on the operators switchboard, if it is not, the operator plugs it into the trunk for the destination switchboard and asks the operator that answers to connect the call, but if the number is in the same central office the operator plugs the ringing cord into the jack of the switchboard. With the automatic exchange service, the caller dials a destination telephone number to the automatic switching system. As soon as the caller removes the handset from its switch hook, the exchange automatically senses the off hook which than the exchange gives the caller a tone indicating that it is ready to receive dialed digits. The Dual Tone - Multi Frequency (DTMF) tones generated by the telephone are than processed and establish a connection to the destination.