There are five primary components in any computer network; and these are also known as DATA COMMUNICATIONS SYSTEM COMPONENTS:
To transfer information among various users, spread geographically, we require following basic components in computer network for data communication.
Computers (Senders and Receivers):
§ These are devices used for sending and receiving the data and information, normally these devices are computers.
§ These are the devices which help in communication of data.
§ Communication devices are mainly used for connecting sender and receiver with communication channels for data communication.
§ Followings are some popular communication devices.
§ MODEM stands for Modulator Demodulator.
§ MODEM is coding and decoding device that when data is transmitted from one computer to another computer over a distance through a telephone line or other communication channel then MODEM converts the computer digital signals into signals which can be transmitted on telephone line and vice a versa.
§ MODEM is mainly used for connecting computers, geographically, distributed over a large distance for data communication.
§ Most important use of MODEM is connecting home computer to internet servers.
§ MODEM is also used for connecting an employee of a company with the computer network from a remote location.
§ MODEM is categorised according to its speed and some other features likeanalog or digital MODEM, internal or external MODEM.
§ Analog MODEMs are known as dial-up MODEM and these are used for connecting home computers with Internet.
§ Speed of a MODEM normally ranges from a few kbps to mbps.
§ Digital MODEMs are known as ISDN MODEMs.
§ These are high speed MODEMs and normally used at places where more large of users are connected through same communication channel.
§ Speed of digital MODEMs is measured in mbps.
§ Multiplexer is a device that enables several devices to share common communication channel.
§ A multiplexer scans multiple devices to collect and transmit data on a single communication line to the appropriate destination.
§ The multiple devices are polled together and periodically asked whether there is any data to transmit.
§ This function may be very complex and in some systems there is a separate computer processor devoted to this activity and that is called a front-end processor.
Front End Communication Processor:
§ These are the programmable devices, which control the function of a large computer system in a network.
§ This device supports the operation of a mainframe computer by performing functions which otherwise would required to be performed by performed by mainframe itself.
§ These function include authentication of user by checking his user id and password, coding and decoding of data and control of transmission lines.
§ Due to use of front-end processor, the mainframe computer dedicates its entire time to its key function that data processing.
§ Finally, front-end processor performs allied functions like user authentication, data encryption, etc in a communication network of large computer based system.
§ Front end processor is like an assistant to main frame computer.
§ A hardware device that changes the protocol of one system to the protocol of another.
§ For Example: If you want to connect an IBM data communication network to AT and T data communication network then the protocol convertor converts the message formats one network system to another so that these are compatible for communication with each other.
§ It is similar to a person who translates for two persons who do not speak each other language.
§ A device that connects two networks with each other that are using the same protocol.
§ A device that connects two or more networks with each other having same network protocol.
§ A device also helps to select the best route for data communication when there are multiple paths between them.
§ A device that connects two or more dissimilar networks that the networks having different protocols.
§ This device allows networks of different vendors to communicate each other by translating one vendor’s protocol into another; gateway is a combination of router and protocol converter.
§ Repeater is a device, which simply repeats the incoming signal for outgoing communication on channel but with increased strength.
§ Repeater is also known as amplifier, it amplify the incoming signal for long distance communication.
Remote Access Device:
§ This device contains a bank of modem that a collection of modems to serve as central point for access of data from various distant or remote locations.