Today computer is available in many offices and homes and therefore there is a need to share data and programs among various computers with the advancement of data communication facilities. The communication between computers has increased and it thus it has extended the power of computer beyond the computer room. Now a user sitting at one place can communicate computers of any remote sites through communication channel. The aim of this chapter is to introduce you the various aspects of computer network. 4.2 OBJECTIVES
After going through this lesson you will be in a position to: * explain the concept of data communication
* understand the use of computer network
* identify different components of computer network
* identify different types of network
* explain communication protocols
* understand what is internet and email and its uses in modern communication * appreciate the use of satellite communication.
4.3 DATA COMMUNICATION
We all are acquainted with some sorts of communication in our day to day life. For communication of information and messages we use telephone and postal communication systems. Similarly data and information from one computer system can be transmitted to other systems across geographical areas. Thus data transmission is the movement of information using some standard methods. These methods include electrical signals carried along a conductor, optical signals along an optical fibers and electromagnetic areas. Suppose a manager has to write several letters to various clients. First he has to use his PC and Word Processing package to prepare his letter. If the PC is connected to all the client's PCs through networking, he can send the letters to all the clients within minutes. Thus irrespective of geographical areas, if PCs are connected through communication channel, the data and information, computer files and any other program can be transmitted to other computer systems within seconds. The modern form of communication like e-mail and Internet is possible only because of computer networking. Basic Elements of a Communication System
The following are the basic requirements for working of a communication system. 1. A sender (source) which creates the message to be transmitted. 2. A medium that carries the message.
3. A receiver (sink) which receives the message.
In data communication four basic terms are frequently used. They are * 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. 4.3.1 Communication Protocols
You may be wondering how do the computers send and receive data across communication links. The answer is data communication software. It is this software that enables us to communicate with other systems. The data communication software instructs computer systems and devices as to how exactly data is to be transferred from one place to another. The procedure of data transformation in the form of software is commonly called protocol. The data transmission software or protocols perform the following functions for the efficient and error free transmission of data. 1. Data sequencing: A long message to be transmitted is broken into smaller packets of fixed size for error free data transmission. 2. Data Routing: It is the process of finding the most efficient route between source and destination before sending the data. 3. Flow control: All machines are not equally efficient in terms of speed. Hence the flow control regulates the process of sending data between fast sender and slow receiver. 4. Error Control: Error detecting and recovering is the one of the main function of communication software. It ensures that data are...