After reading this article you will learn about the role of multiplexing in telephone communication.
Other issues that may be important in telephone communications are related to multiplexing.
Since it costs the same amount to lay cables (whether copper or Fibre Optic) for narrowband transmission as it does for broadband transmission, it is natural that the telephone authorities try to send as much transmission as possible using the same cable. This can be done by multiplexing several voice and/or data channels in the same cable.
Two methods of doing this are usually utilised. These are Time Division Multiplexing and Frequency Division Multiplexing. They each utilizes different methods for combining different data and voice streams for transmitting these in the same cable at the same time.
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A brief mention of each of these should help to clear the procedures involved:
1. Time Division Multiplexing is more popular in digital transmission since it can easily be controlled using computers. In fact, this method of multiplexing can only be done for digital data. This method of multiplexing simply follows the principle of allotting a fixed time slice to each stream or channel of data or voice on a round robin basis.
Considering that the physical time required to perform each operation in the transmission of a data or voice stream is much less than the time required to switch between channels, this method of multiplexing can increase the amount of transmission traffic in a cable quite significantly. It is interesting to note that the time slice seems to have been standardised as 125 µs in the telephone world.
2. Frequency Division Multiplexing is less frequently used in multiplexing, because it has many drawbacks compared to Time Division Multiplexing. It requires a great deal of analogue equipment and the modern tendency is to use digital transmission as far as possible; hence its lack of popularity.
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In this method of multiplexing, a fixed frequency band is allotted to each stream and the frequency of each stream is raised to a different frequency level. Since all the streams occupy different frequencies in the spectrum, they can all be multiplexed into a common stream on one cable.