LectureWeek 2

Networks , The Internet and the World Wide Web

OVERVIEW AND HISTORY

TELECOMMUNICATIONS MORSE CODE TELETYPE MACHINES

MORSE CODE

Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment

Wikipedia

Morse Code

Morse Code Device

History (Contd)

Telephone

Now Sending Pictures, Voice and Data is possible

TV Fax Machine, Mobile Phones

OVERVIEW AND HISTORY (2)

Computer Communications Started after Telecommunications In 50's, 60's Computer used for Data Processing

Only

History (2) Contd

Advanced Network Systems developed by Military and NASA

NETWORKS

Telephone is oldest Network system. Can be connected using Handset and wires. Still exist and very popular.

Connection

For n people total connection needs n(n-1)/2 wires or lines.

Therefore for 100 people need 100(100-1)/2 lines

This is not feasible for economic and technical reasons when n is a large number.

So switching centers were developed.

Switching Centers

Switching Centers

Originally an operator would connect people. the operator’s role is carried out by computer

programs and is referred to as switching. Hence it is now called the P.S.T.N, the Public

Switched Telephone Network.

Computer Networks

The simplest Computer Network is two Personal computers (PC’s) connected

This would require them to be in the same room.

Question ???

How can two PC’s be connected together that are not in the same building, town or even country. Is there an existing network that can be used?

Under-sea Cables, Satellite ..

PSTN

The problem is that the P.S.T.N. was designed to carry voice signals, that is analogue or continuously variable signals.

Computers work with digital signals. How do we get around this?

PSTN (Contd)

PSTN (Contd)

Modem

The above diagram shows from left to right a computer sending digital signals to a modem.

The modem modulates the digital signal to an analogue signal then sends the signal down a phone line.

At the other end of the phone line another modem demodulates the incoming signal from an analogue signal to a digital one.

Modem stands for Modulate Demodulate

Why Network Computers?

Shared Resources (1) Hardware Printers Plotters Scanners Modems

Shared Resources (2) Software

Software stored centrally on a computer with a large amount of memory and hard disk storage capacity.

Software can be downloaded to the networked computers.

This centralized computer is called a server (File/Domain/Web etc )

Communication Security

Contd.

Communications Electronic Mail systems (Email) File Transfer Protocol (FTP) Internet and Intranet Access World Wide Web Access

Contd.

Security Control of Passwords Control Loading of Software Virus Prevention and Detection

NETWORK TYPES OR CATEGORIZATION Networks can be described by either their SIZE or

by their TOPOLOGY Topology means the logical organization of the

Network

SIZE

Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN) Campus Area Network (CAN)

TOPOLOGY

Star Network Bus Network Ring Network Mesh Network

Star Topology

Bus Topology

Ring Topology

Mesh Network

THE INTERNET

Network of Networks Communicating together using common

protocols TCP/IP is widely used protocol.

It includes commercial (.com.np or .com), educational (.edu.np ), other research networks (.org.np, .net ), Government (.gov.np) and military networks (.mil.np)

WORLD WIDE WEB (WWW) One of the services available using the Internet

to provide a distributed information retrieval system.

It was invented and developed at the Cern High – Energy Physics laboratory in Geneva and introduced to the public in 1991.

The Web is a collection of documents containing text and graphics that are linked together using Hypertext links

WWW (Contd)

These links allow you to jump to another page instead of reading in a linear manner.

The Web uses the Hypertext Transfer Protocol, (HTTP), for the exchange of Hypertext Markup Language, (HTML), documents. Hypertext links, embedded inside documents, refer to other documents by their Uniform Resource Locators (URL).

Intranet

Any network which provides similar services within an organization.

The commonest example is the use by a company of one or more World-Wide Web servers on an internal TCP/IP network for distribution of information within the company.

Extranet

The extension of a company's intranet out onto the Internet, e.g. to allow selected customers, suppliers and mobile workers to access the company's private data and applications via the World-Wide Web.

This is in contrast to, and usually in addition to, the company's public web site which is accessible to everyone.

Information !!!

http://learning.londonmet.ac.uk/computing/IC_Link/

Extended Programme Username: ic_ed Password ic_ed_oct11

Thank You