Computer Network / Data Comnunication

Computer Network -

              What do you understand by Data Communication 

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 similary restricted geographical area, and is considered remote if the devices are farther apart.

           For data communication to occur, the communicating 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. 

Delivery -  

          The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user. 

Accuracy -

          The system must deliver data accurately. data that have been altered in transmission and left uncorrected are unusable.

Timeliness -

           The system must deliver data in a timely manner. Data delivered late are useless. in the case of video, audio, and voice data, timely delivered means delivering data as they are produced, in the same order that they are produced, and without significant delay, this kind of delivery is called real-time transmission.

         Components of Data Communication 

A data communication system is made up of five components.

Message -

The message is the information (Data) to be communicated. It can consist of text, numbers, pictures, sound, or video or may combination of these.

Sender -

       The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on.

Receiver -

         The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.

Medium -

         The transmission medium is the physical path by which a message travels from sender to receiver. It can consist of twisted pair wire, coaxial cable, fiber-optic cable, laser, or radio waves (terrestrial or satelite microwave).

Protocol -

           A protocol is a set of rules that govern data communication. It represents an agreements between the communicating 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.

                   Distributed Processing 

Network use distributed processing, in which a task is divided among multiple computers. Instead of a single large machine being responsible for all aspects of a process, each separate computer (usually a personal computer or workstation) handles a subset.

       Advantages of distributed processing include the following:

1. Security/encapsulation -

A system designer can limit the kinds of interactions that a given user can have with the entire system. For example, a bank can allow users access to their own accounts through an automated teller machine (ATM) without allowing them access to the bank's entire database.