TRANSMISSION in telecommunication

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For understanding the data communication following terminology is discussed: -
·         Communication lines
The medium that carries the message in a data communication system, example of  A 2W telephone line.
  Communication Channel
A channel is defined as a means of one way transmission.
It can carry information in either direction but in only one direction at a time, e.g. A hose pipe. It can carry water in either direction, but the direction of flow depends on which end of pipe is connected to the water tap.
 Simplex Transmission
1.     Message always flows in one direction only.
2.     An input Terminal can only receive and never transmit.
3.     An O/P Terminal can only transmit and never receive.



Half Duplex Transmission
-         A half duplex channel can transmit and receive but not simultaneously.
-         Transmission flow must halt each time and direction is to be reversed.
-         This halt is called the turn-around time and is typically 8 to 10 ms in the case of leased circuits and 50-500 ms in case of 2W telephone line through Public Switched Telephone Network (PSTN). 

Full-duplex Transmission
It is both way communications. If we set up a communication line with two channels, we have the capability of sending information in both directions at the same time. This is called full duplex transmission system. 



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