Choice of Medium:

All the transmission channels discussed in the foregoing paragraphs can be used as point to point connections or as broadcast systems. Transmitting information electronically or photonically is considered in two aspects - telecommunications and broadcasting. The former is a direct interchange of information within limited groups of talkers and listeners (which may be terminals of computers as well as people). Thus, there is a certain amount of interaction. Broadcasting is the mass distribution of information to large markets with one 'speaker' and many "listeners' and no real interaction. 

Because of the increasing linking up of the two forms with computers, the traditional distinction is being blurred and now you get systems like electronic mail, which can either he broadcast of telecommunication and cable TV broadcasting systems which carry telecommunications. And any given transmission circuit could be made up of a mixture of terrestial microwaves, cable and satellite links. Thus, a given service could be transmitted over more than one of channel. For example, a television program can be broadcast let us say normally - as you get it at home via satellite or via broadband coaxial cable using radio frequency. 

The decision on which medium to use is determined by factors such as the distance involved, the area to be covered and the type of information to be sent. For example, terrestial microwave radio transmission requires line-of-sight communication and for long distances repeaters must be added. If the medium has to accommodate video or high speed data then a broad bandwidth such as is provided by satellite and coaxial, fibre optical cables will be required.