Types of Computer Networks:
Based on their size, computer networks are classified into :-
1. Local Area Networks (LANs)
2. Metropolitan Area Networks (MANs)
3. Wide Area Networks (WANs)
LANs
LANs are privately owned networks with a geographical coverage of less than a kilometre. They are usually setup within buildings or a campus. Usually a single cable structure is used. LANs operate at data transfer rates of 10 to 100 mega bits per second (Mbps). Different topologies can be used for implementing LANs. Channel allocation is an important design issue for LAN protocol. Error rate is comparatively low.
MANs
MANs can interconnect offices across a big city. They are a bigger version of LANs. Usually there are no switching elements. MAN's carry data and voice sometimes. A popular structure of MAN is the DQDB (Distributed Queue Dual Bus)
WANs
It spans across large geographical area such as countries and continents. A WAN consists of hosts and subnets (Communication subnet). Subnets may use long distance optical fibre cables or satellites for communication. Subnets also have routers that perform routing of packets. LANs may be connected to WANs. WANs use one of packet switching, message switching or circuit switching for data communication.
Internetwork
The term Internetwork' means interconnected networks. There are different networks in the world each of which is a WAN. When several such WANs are interconnected, it forms a 'internetwork'. When these are interconnected, a lot of issues are to be considered because, the different WANs are not similar. They may have different protocols, packetsize etc. Therefore some 'gateways' are required to interconnect them. A gateway of a computer or group of computers that connect to this similar networks.
Intranets
A Intranet is a privately owned 'Enterprise - wide' network. Distant offices of bigger organization can establish communication through a Intranet. Each office typically has a LAN and router that forwards packets. A dedicated or leased communication infrastructure is required for a Intranet. Intranets serve many purposes such as running an enterprise - wide information system, on-line access of data bases, file transfers between offices etc.
Internet and Intranet
Internet is a very large network of computers that interconnect many different networks in different parts of the world. There are millions of computers connected to the Internet. It is a global network. The computers in the Internet are of different types. But they can all communicate with each other, because all computers follow the same protocol. The off cal protocol used on the Internet is TCP / IP-Transmission Control Protocol/ Internet Protocol.
The Internet offers a variety of services and tools such as, e-mail, FTP (File Transfer Protocol), WWW (World Wide Web), Telnet etc. The Internet is a public network. It is accessible by anyone. On the other hand, Intranet is a private network owned by an organization. It is an enterprise-wide network built using Internet technology that runs various applications for the organization. It would interconnect various offices of the organization. Various uses of intranets are, file transfer, access to central databases. etc.
Hardware and Software Requirements for Internet Connection
The hardware and software requirements for making a connection to the Internet are as follows:
1. A personal computer with the facility to connect a modern.
2. A modem for connecting the computer to the communication network such as telephone line or cable connection. Modem can be internal or external. The speed of modern shall be as high as posssible.
3. For a dial-up connection, the user must have a telephone connections.
4. The user must have a account registered with a ISP (Internet service provider) such as BSNL, VSNL, Asianet etc. A TCP/IP account is preferable over a shell account. This provides access to all Internet services.
5. The computer must have an operating system such as Windows or Linux and also a web browser software like Internet Explorer, Google Chrome, Firefox etc. Some Internet related software are available to configure e-mail facility in the computer, Example are Microsoft Outlook, Eudora, Pine etc.