In today’s fast world, telephone is a necessity. Telephony is not limited to earth. We can also converse from earth to any other planet e.g. moon, mars etc. It depends upon the condition whether to use wireless connection or wired connection for communication. Links can be made using optical fibers, ground waves, sky waves etc. The diagram below shows direct linkage between the two telephones. This type of linkage is known as point to point linkage.
Also a detailed block diagram is also shown below:
The above link is established between two stations one is x and other is y. At station z microwave source is placed. The signal flow in the circuit is shown with the help of arrows. In the above circuit we have used splitter, amplifiers, modulators, demodulators, splitters etc. Parabolic antenna reflectors are used in these systems. The main work of filter is to purify the coming signals. It discards the unwanted signal and passes the filtered signal to the system.
The links established using the micro waves are usually affected by the noise. On the other hand the co-axial cable links are not affected by noise. If we talk about the optical fibers the energy loss in optical fibers is almost zero.
Three generations of telephone exchanges are established.
1. Step by step or Strowger type
2. Cross bar exchange
3. Processor controlled.
All the call setup and other interconnections are done by the exchanges.