A data communication system is made up of five components.They are:-
1.Message
2.Sender
3.Receiver
4.Medium
5.protocol

A typical data communication system components is shown in the figure below:

1.Message:The message is the information(data)to be communicated.It can consist of text,numbers,pictures,sound or video- or any combination o these.

2.Sender:The senderis the device that sends the data message.It can be a computer,workstation,telephone handset,video camera and so on.

3.Receiver:The receiveris the device that receives the message.It can be a computer,workstation,telephone handset,television and so on.

4.Medium:The transmission mediumis the physical path by which a message travels from sender to receiver.It can sonsist of twisted pair wire,coaxial cable,fiber-optic cable,laser or radio waves(terrestrial or satellite microwave).

5.Protocol:A protocolis a set of rules that govern data communication.It represents an agreement between the communication devices.Without a protocol,two devices may be connected but not communicating,just as a person speaking French cannot be understood by a person who speaks only Japanese.

Data communication is the exchange of data(in the form of 0s and 1s) between two devices via some form of transmission medium(such as a wire cable).Data communication is considered local if the communicating devices are in the same building or a similarly restricted geographical area and is considered remote if the devices are father apart.
For data communication to occur,the communication devices must be part of a communication system made up of a combination of hardware and software.The effectiveness of a data communication system depends on three fundamental characteristics:-

1. Delivery:The system must deliver data to the correct destination.Data must be received by the intended device .2.Accuracy:The system must deliver data accurately.Data that have been altered in transmission and left uncorrected are unusable.
3.Timeliness:The system must deliver data in timely manner.Data delivered late are useless.In case if video,audio and voice data,timely delivery means delivering data as they are produced in the same order that they are produced and without significant delay.This type of delivery is called real-time transmission.