By

Rachit Mehta 9TH D

•In September 1940, George Stibitz used a Teletype machine to send instructions

for a problem set from his Model at Dartmouth College to his Complex Numbers

Calculator in New York and received results back by the same means. Linking output

systems like teletypewriters to computers was an interest at the Advanced Research

Projects Agency (ARPA) when, in 1962, J.C.R. Licklider was hired and developed a

working group he called the "Intergalactic Network", a precursor to the ARPANET

•Early networks of communicating computers included the military radar system

Semi-Automatic Ground Environment(SAGE), started in the late 1950s

•The commercial airline reservation system semi-automatic business research

environment(SABRE) which went online with two connected mainframes in 1960.

•In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing System

for distributed users of large computer systems. The same year, at Massachusetts

Institute of Technology, a research group supported by General Electric and Bell Labs

used a computer to route and manage telephone connections.

•Throughout the 1960s Leonard Kleinrock, Paul Baran and Donald Davies independently

conceptualized and developed network systems which used packets that could be used

in a network between computer systems.

•1965 Thomas Merrill and Lawrence G. Roberts created the first wide area network .

•The first widely used telephone switch that used true computer control was introduced

by Western Electric in 1965.

•In 1969 the University of California at Los Angeles, the Stanford Research Institute,

University of California at Santa Barbara, and the University of Utah were connected as

the beginning of the ARPANET network using 50 Kbit/s circuits.

•Commercial services using X.25 were deployed in 1972, and later used as an underlying

infrastructure for expanding TCP/IP networks.

Computer networkconnects two or moreautonomous computers.

The computers can begeographically locatedanywhere.

Computer Networks

Resource SharingHardware (computing resources, disks, printers)Software (application software)

Information SharingEasy accessibility from anywhere (files, databases)Search Capability (WWW)

CommunicationEmailMessage broadcast

Remote computing

Distributed processing (GRID Computing)

Computer Networks

CATEGORIES

OF

NETWORKS

Categories of networks

The network topologydefines the way inwhich computers,printers, and otherdevices are connected.A network topologydescribes the layout ofthe wire and devices aswell as the paths usedby data transmissions.

The way computers are connected

Please note= This topic is not in course but is necessary to know…

Network in small geographical Area (Room, Buildingor a Campus) is called LAN (Local Area Network)

Network in a City is call MAN (Metropolitan AreaNetwork)

Network spread geographically (Country or acrossGlobe) is called WAN (Wide Area Network)

Computer Networks

Allow resource sharing between computers.

Computers

Peripheral devices

Transmission medium (e.g. cable)

3 types of topology

Bus topology

Star topology

Ring topology

Figure 6-4LANs

Hub – a device that facilitates connection

LAN acts logically like a bus.

Star –

the dominant topology today.

MAN

Uses services provided by a network service

provider. (Tel. Company)

Individual users’ computers

Organizations’ LANs

Many Tel. Company provide a popular MAN service

called SMDS (Switched Multimegabit Data Services)

Prior to SMDS's arrival in 1995,

the only way to connect LANs was through

a dedicated private line.

WAN

The connection of individual computers or

LANs over a large area (country, world).

User using a telephone line to connect to

an ISP (Internet Service Provider) is using

a WAN.

Negotiates fee

ISP

Tel. company

Connecting devices

WiFI: Short for ‘wireless fidelity’. A term for certain types of wireless

local area networks (WLAN) that use specifications conforming to IEEE

802.11b. WiFi has gained acceptance in many environments as an

alternative to a wired LAN. Many airports, hotels, and other services offer

public access to WiFi networks so people can log onto the Internet and

receive emails on the move. These locations are known as hotspots.

LAN: A computer network that spans a relatively small area. Most LANs are

confined to a single building or group of buildings. However, one LAN can

be connected to other LANs over any distance via telephone lines and

radio waves.

There IS a difference between these two items. WiFi is a Wireless Network

like a wireless home network or a hotspot at a local coffee shop or the

airport or a WiFi cafe. A Wireless Card is an Adapter placed inside the

computer or the Laptop which is needed to access the WiFi Network you

wish to connect to.

•Communications satellites – The satellites use microwave radio as their

telecommunications medium which are not deflected by the Earth's

atmosphere. The satellites are stationed in space, typically 35,400 km

(22,000 mi) (for geosynchronous satellites) above the equator. These

Earth-orbiting systems are capable of receiving and relaying voice, data,

and TV signals.

• A global area network (GAN) is a network used for supporting mobile

across an arbitrary number of wireless LANs, satellite coverage areas,

etc. The key challenge in mobile communications is handing off the user

communications from one local coverage area to the next. In IEEE Project

802, this involves a succession of terrestrial wireless LANs.

• Terrestrial microwave – Terrestrial microwaves use Earth-based transmitter

and receiver. The equipment looks similar to satellite dishes. Terrestrial

microwaves use low-gigahertz range, which limits all communications to

line-of-sight. Path between relay stations spaced approx, 48 km (30 mi)

apart.