Subject Name: Basics of Information Technology

UNIT: 6 (Basics of Networking)

Computer Network

A computer network may be defined as an “interconnected collection of autonomous computers”. Two computers are said to be interconnected if they are able to exchange information. The connection need not be via a copper wire; fiber optics, microwaves, and communication

satellites can also be used. The term “autonomous computers” means, the computer system that can be controlled by itself by

having own memory unit, control unit, and processor.

Network Benefits

Provide Convenience : Computers on network can backup their files over the network.

Allow Sharing : Networked computers can share resources, such as disks & printers.

Facilitate Communications : Sending and receiving email, transferring files, and videoconferencing.

Generate Savings : Networked computers can provide more computing power for less money. Several small computers connected on a network can provide as mush as or more computing power than a single, large computer and will cost much less. Also, since resources can be shared, not everyone needs their own peripherals, which can result in a substantial cost savings.

Provide Reliability : If one part of a network is down, useful work may still be possible using a different network path.

Simplify Scalability : It is relatively easy to add more computers to an existing network.

Types of Computer Networks:

Local Area Network (LAN)

Privately-owned networks within a single building or campus of upto a few kilometers in size.

LANs often use a transmission technology consisting of a single cable to which all the machines the machines are attached.

Traditional LANs run at speeds of 10 to 100 Mbps, have low delay (tens of microseconds) and make very few errors.

Newer LANs may operate at higher speeds, upto hundreds of megabits/seconds.

LANs might be related to the telephone lines.

Metropolitan Area Network (MAN)

A bigger version of a LAN.

It cover a group of nearby corporate offices or a city and might be either private or public.

Might be related to the local cable television network.

Wide Area Network (WAN)

Spans a large geographical area, often a country or continent.

It contains a collection of machines intended for running user (i.e., application) programs. These machines are called as hosts.

Internetworks

Internetwork is a collection of interconnected networks is called an Internetwork or Internet

Introduction to Internet

It is a “network of networks” that consists of millions of smaller domestic, academic, business, and government networks, which together carry various information and services, such as electronic mail, online chat, file transfer, and the interlinked web pages and other resources of the World Wide Web.

Internet is a collection of interconnected computer networks, linked by copper wires, fiber-optic cables, wireless connections, etc.

The Internet sometimes called the “Information Superhighway”, is a worldwide publicly accessible series of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP).

Protocols

Set of rules.

The procedures by which computers communicate with each other are called protocols.

What makes the interconnection possible is the use of a set of communication standards, procedures and formats in common among the networks and the various devices and computational facilities connected to them.

Interconnected Networks & Communication

The Internet is essentially a “network of networks”, the communication among which depends on a common set of protocols.

The protocol that determines how the computers connect, send, and receive information on the Internet is Transmission Control Protocol/Internet Protocol (TCP/IP).The TCP permits communication between the various computers on the Internet, and IP specifies how data is routed from computer to computer.

The TCP/IP provides “Simple Mail Transfer Protocol (SMTP)” for sending an email message, and “Hypertext Transfer Protocol (HTTP)” for a Web Page request.

TCP/IP divides the information to be sent into smaller pieces called packets and then transmit them over Internet.

Network Connections

Connecting to the Internet from homes generally requires the use of a modem and a regular telephone line (copper wire) to connect to an Internet Service Provider (ISP).

A second modem at the ISP’s end completes the connection and slower the two modem speeds determines the maximum connection speed, usually 56 kbps.

Modem (Modulator – Demodulator), is a device needed to convert data from digital to analog and analog to digital.

Business, organization, network typically uses Network Interface Cards (NIC) instead of modems. These systems have a higher speed connection, usually 56 kbps or better, to their ISPs. Such connections are usually leased from the telephone company.

Another option is an Integrated Services Digital Network (ISDN) which is slightly more expensive but uses regular telephone lines and replaces modems with special adaptors upto five times faster than traditional modems.

Sender’s ComputerNetwork

Via phone line

Local Area NetworkNetwork

Destination Computer

Physical Components

In addition to various software protocols, Internet includes a host of physical components as well:

Servers

Routers

Communication Media

Server: Servers are the computers that answers the requests for services, such as list servers, mail servers, & news servers.

Router: Routers are the special-purpose computers that directs data packets along the network. Routers can detect whether the part of the network is down or congested and can then reroute traffic just like a traffic cop.

Communication Media: Communication media provides means to transport packets of information like:

Copper Wires – transmit messages as electrical impulses. Fiber Optic Cables – uses light waves to transmit messages. Radio waves, Microwaves, Infrared Light & Visible Light – all carry messages through air.

Message

Modem

ISP

ModemNSP

Router

Router

Message

Domain Name

The term domain name has multiple related meanings:

A name that identifies a computer or computers on the internet. These names appear as a component of a Web site's URL, e.g. wikipedia.org. This type of domain name is also called a hostname.

The following example illustrates the difference between a URL (Uniform Resource Locator) and a domain name:

URL: http://www.example.net/index.htmlDomain name: www.example.net