Computer Networks

COMPUTER NETWORK

A computer network, or simply a network, is a collection of computers and other hardware components interconnected by communication channels that allow sharing of resources and information.

Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network.

Networks are collections of computers, software, and hardware that are all connected to help their users work together.

A network connects computers by means of cabling systems, specialized software, and devices that manage data traffic.

A network enables users to share files and resources, such as printers, as well as send messages electronically (e-mail) to each other.

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GOALS AND APPLICATIONS OF COMPUTER NETWORKS

•         Services Provided By The Network For Companies

•         Services Provided By The Network For People

•         Network Functions

Services Provided By The Network For Companies:

•         Resource sharing

•         High reliability due to the alternative sources of data

•         Money saving

•         Communication medium

Services Provided By The Network For People:

•         Access to remote information (home-shopping, paying bills, digital library)

•         Person to person communication (e-mail, video conferencing)

•         Interactive entertainment (video-on-demand, participation in live TV programs like quiz, contests, etc.)

Network Functions:

Switching  Routing  Flow Control  Speed  Security

Backup  Failure Monitoring  Traffic Monitoring  Network Management

•         Switching:  Ability of a network to connect different channels attached to each node to each other.

•         Routing: Ability of a network to select a path.

•         Flow Control: Control over the rate of traffic.

NETWORK USERS

•         Business of all kinds

•         Education and arts

•         Govt. entities

•         Religious and social organizations

•         Professional Organizations

•         Individuals

HARDWARE REQUIRED FOR NETWORKING

•         NIC (Network Interface Card)

•         Hub

•         Switch

•         Routers

•         Servers

•         Workstation

NETWORK SOFTWARE

•         Network Operating System (NOS)

OTHER NETWORK TERMS

•         Protocol

•         Bandwidth

Types of Computer Networks

•         Local Area Network (LAN)

•         Metropolitan Area Network (MAN)

•         Wide Area Network (WAN)

Local Area Network (LAN)

•         A LAN connects network devices over a relatively short distance.

•         For example, the network in a single integrated campus or at a company location is classified as a LAN.

•         LAN is a computer network that covers an area in one room, one building, or several adjacent buildings.

•         LAN transmission media generally use a cable (UTP, coaxial cable, or fiber optics).

•         But some are not using a cable and is referred to as Wireless LAN (WLAN).

•         LAN speeds ranging from 10 Mbps to 1 Gbps.

Local Area Network

Features of LAN

•         Typically connects computer in a single building or campus.

•         Developed in 1970s.

•         Medium : optical fibres, coaxial cables, twisted pair, wireless.

•         Low latency (except in high traffic periods).

•         High speed networks (0.2 to 100 Mb/sec).

•         Speeds adequate for most distributed systems

•         Problems : Multimedia based applications

•         Typically buses or rings.

•         Ethernet, Token Ring 

Metropolitan Area Network (MAN)

•         MAN is a network that covers an area of one town or with a range of about 10-45 km.

•         Network connecting several banks located in one city or campus that is spread in several locations classified as a MAN.

•         MANs generally use transmission media by micro waves or radio waves.

•         But there also are using leased lines (leased line).

•         The MAN network usually exist to provide connectivity to local ISPs, cable TV, or large corporations. 

Features of MAN

•         Generally covers towns and cities (50 kms)

•         Developed in 1980s.

•         Medium : optical fibers, cables.

•         Data rates adequate for distributed computing applications.

•         A typical standard is DQDB (Distributed Queue Dual Bus).

•         Typical latencies : < 1 msec.

•         Message routing is fast.

Wide Area Network (WAN)

•         Network which includes inter-city, inter-provincial, inter-state, and even between continents called the WAN.

•         Example of a WAN is a network that connects the ATM (Automatic Teller Machine).

•         Another example is the internet.

Wide Area Network

Features of WAN

•         Developed in 1960s. Generally covers large distances (states, countries, continents).

•         Medium : communication circuits connected by routers.

•         Routers forwards packets from one to another following a route from the sender to the receiver.

•         Store-and-Forward Hosts are typically connected (or close to) the routers.

•         Typical latencies : 100ms - 500ms.

•         Problems with delays if using satellites.

•         Typical speed : 20 - 2000 Kbits/s.

Value Added Network (VAN)

•         A Value-added Network (VAN) is a hosted service offering that acts as an intermediary between business partners sharing standards based or proprietary data via shared Business Processes.

•         The offered service is referred to as "Value-added Network Service".

•         VANs usually service a given industry and provide "Value Added Network Services" ("VAN Services" or VANSs). 

Differences Between LAN, MAN and WAN:

Characteristics	LAN	MAN	WAN
Full form	It stands for local area network.	It stands for metropolitan area network.	It stands for wide area network.
Cost	Less costly	More Costly	Costliest
Speed	Up to 10-100 Mbps	5-10 Mbps	256 Kbps to 2 Mbps
Range	1 km	Up to 50 km	Up to 1000 km
Topology	Bus and ring	Distributed Queue Dual Bus [DQDB]	ATM, Frame Relay, Sonet
Location of computers connected in the system	Computers are located within the same building.	Computers are located in the city and are connected using modems or telephone lines so that they can be easily connected with each other.	Computers are distributed all over the country or the continent. The connection is made via satellite communication link or via internet.
Examples	LAN’s example can be an office whose different departments such as personnel, accounting etc. are located in the same building and connected via bus topology.	Example of MAN is bank whose  different branches in a city like Delhi are connected using public telephone exchange and the system are connected with each other using LAN within each branch and different branches are connected using modem and bridges.	WAN’s example is the connection of various branches of MNC such as Infosys. These branches are linked using microwave satellite communication system or internet connection. Each branch has its own LAN circuit. But the different LAN’s in various branches are communicating with head office using WAN link.