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.