Computer Networks Basics
Computer Networks are everywhere. You find them in small and large organizations, schools and government offices. All of us directly or indirectly are users of computer networks. Therefore it is important to know what networks are and how they help us.
Computer networks enhance the computer's ability to exchange, share, preserve and protect information. When a computer is not connected to a network, it is called a standalone environment. Sharing of information is not possible. But computers connected over a network can make information exchange easier and faster. People can concentrate on getting their work done rather than on moving information around.
Networks range from small, privately owned Local Area Networks (LANs) to very large Wide Area Networks (WANs) that are country wide. People use computer networks for sending e-mails, home shopping, video conferencing, chatting and web browsing. Computer networks are largely used for by banks and financial companies for transactions. For students and researchers, computer network is a means of access to huge volume of information available from remote databases. In the following sections we will explore various aspects of networking.
Need for Networks
Today most organizations have established computer networks. The primary goals of networking are:-
• Communication
• Reliability
• Resource Sharing
There is an increasing demand for communicating data between various locations.
Most applications today need online access to information stored in computers at a different location. There is also a need to share costly resources both software and hardware, among many users in an organization. Networks can increases the reliability of computing system. This is achieved by providing redundant data storage and communication paths. People need to share files and programs easily. Thus computer networks are very essential in most applications
Definition
A Computer Network is a group of computers connected by cable or other media so that they can exchange information. One of the most significant trends in modern computing is the growth of the use of networked computers. The old concept of a central computer serving all the processing needs has been replaced by the networking concept in which separate and interconnected computers do the job. Computer Networks emerged from the merging of computers and communications.
Advantages of Networks
The goals of computer networks are hardware sharing, software and information sharing and communication. When a hardware device is attached to a computer network, all the computers that are part of the network can access that hardware part, if sufficient permission is given. Similarly, there is no need to store all the software in every computer. The software that is a stored in the hard disk of a computer can be shared by other computers. In the Internet, websites are having lot of information in the form of text, audio and video. By accessing the website we can share all those information. Communication is the process of passing information from one computer to other computer.
1. Resource sharing : A computer network, facilitates sharing of resources. Users on a network can share information, expensive hardware and software. Centrally snored information (Databases) can be accessed by everyone. Any user connected to the network can use a hardware resource such as a printer or CD-ROM drive or a modem connected to any other computer.
2. Reliability : Networking gives the ability to continue operating in spite of hardware problems by having alternate sources of data files and CPU's.
3. Economy : Small computers have a higher price/performance ratio as com-pared to large computers (mainframes).
4. Protecting Information : A network provides a more secure environment for a company's important information. Networks provide several layers of security by way of user authentication and file and directory permissions.
5. Scalability : The ability to increase computing capacity by adding more computers with increase in load.
6. Communication : A network can serve as a powerful communication medium among widely separated people.
Terminologies Used
A computer network consists of several components that are interconnected. They are computer systems(servers or clients), shared peripherals and many connecting devices and network interface unit. Let us explore some of the commonly used terms related to networking.
Nodes
An individual computer connected to a network is called a workstation or node. The nodes may be running their own operating system. These machines can have local storage, memory and processor. Some type of LANs also use dumb nodes. A dumb node does not have any local operating system. It only serves the purpose of input or output. It is also called a terminal. Dumb nodes are not suitable for applications that have a graphical user interface. A user has to first log in to the network's primary server through the node. Only if a user performs a login, he/she will get access to network resources. Nodes are connected to the network using a network adapter also called Network Interface Unit (NIU).
Servers
A server is a computer that gives some kind of service to other computer in the network. Client -server computing applications have two ends - back end, that runs on the server and front end that runs on the nodes. The front end part of the applications is usually called the client.
Servers may be dedicated or non-dedicated. A dedicated server is exclusively used for a specific task. It cannot be used as a workstation. On the other hand, non-dedicated servers can also be used as workstations (nodes). Some dedicated servers do not allow users to logon locally. Usually primary network servers are dedicated.
Servers have many purposes. They share their resources like storage space or peripherals. Servers also authenticate users in the network. They allow users to share applications. Different types of servers are: 1. Primary Server 2. File Server -3. Application- Server 4. Print Server, and many- more.
1. Primary Server
This is usually the main server in a LAN. It runs a network operating system. Users have to first log on to the primary server.
2. File Server
As the name implies, a file server serves files for users in the network. It keeps users' files and programs in its disk storage in separate folders. When clients request files, the server locates the files and sends them to the client. A file server also implements access protection for files, such as who can read/write or execute a file.
3. Application Server
An application server provides specific services at the application level. For example, a database server maintains a database and gives others access to the information. Similarly a gateway server enables traffic between two networks. An email server stores and forwards email messages. A web server hosts a web site. Any computer with sufficient hardware capabilities (configuration) can be used as an application server. Appropriate server programs must be installed and running in the computer.
4. Print Server
A print server is used to provide printing service (network printing) for all users in a Local Area Network. A print server can be a dedicated server that runs a print server program. The print server receives and schedules print jobs from other users. One or two printers connected to the server can thus be shared by all users.
Protocols
In addition to network hardware such as cables and interfacing units, networks also require some rules and conventions for computers to communicate with each other. The rules and conventions used for communication is called protocol. A Protocol is an agreement between communicating devices on how communication must proceed. For two devices to communicate, they must use the same protocol. Protocols are implemented in hardware level and software level. Generally a network architecture specifies several layers of protocols. Each layer will perform specific tasks in network communication. Sonic protocols are general and others are application specific.
Network Interface Unit (NIU)
A NIU is used to connect a computer or other device to a network. Every computer in a network must have a network interface unit (also called network adapter) to connect it to the network. It is this unit that handless transmission of data in and out of the device or computer. The NIU consists of electronic circuits that handle transmission of data, error detection at low level, framing of series of bits for transmission etc. It may also contain some firmware (program in Read Only Memory) that helps to boot up and initialize the networking environment. NIU's are usually fixed in the computer's expansion slots.