The following are the basic requirements for working of a communication system.
1. The sender (source) who creates the message to be transmitted
2. A medium that carries the message
3. The receiver (sink) who receives the message
In data communication four basic terms are frequently used.
Data : A collection of facts in raw forms that become information after processing.
Signals : Electric or electromagnetic encoding of data.
Signaling : Propagation of signals across a communication medium.
Transmission : Communication of data achieved by the processing of signals.