Introduction to the Internet and Web

Introduction

By the turn of the century, information, including access to the Internet, will be the basis for personal, economic, and political advancement. The popular name for the Internet is the information superhighway.

Whether you want to find the latest financial news, browse through library catalogs, exchange information with colleagues, or join in a lively political debate, the Internet is the tool that will take you beyond telephones, faxes, and isolated computers to a networked information frontier.

The Internet supplements the traditional tools you use to gather information, Data Graphics, News and correspond with other people.

What is I N T E R N E T ?

• The largest network of networks in the world.

What is I N T E R N E T ?

Continue…… • A network of networks, joining many government, computers university together and infrastructure for the use of E-mail, bulletin boards, file archives, hypertext documents, databases resources.

and other and private providing an computational

What is I N T E R N E T ?

Continue…… • The vast collection of computer networks which form and act as a single huge network for transport of data and messages across distances which can be anywhere from the same office to anywhere in the world.

Brief History of Internet

• ARPA – Advanced Research Project Agency. • 1969 January 2 – started an experimental Computer Network.

• Concept – No Server, but equal importance/participation to every computer in the Network.

• Even if, one or two node destroyed that will not affect the Network.

Paul Baran

• Paul Baran developed the field of

packet switching

networks while conducting research at the historic RAND organization.

Vinton Cerf

• Father of Internet • Co-designer of the

TCP/IP

networking protocol.

Brief History of Internet

Continue…… • First named as ARPANET • This is renamed as INTERNET – TCP/IP (Transmission Control Protocol/Internet Protocol)

Internet Growth Trends

• 1977: 111 hosts on Internet • 1981: 213 hosts • 1983: 562 hosts • 1984: 1,000 hosts • 1986: 5,000 hosts • 1987: 10,000 hosts • 1989: 100,000 hosts • 1992: 1,000,000 hosts • 2001: 150 – 175 million hosts • 2002: over 200 million hosts • By 2010, about 80% of the planet will be on the Internet

Internet Services

• Electronic Mail (e-mail) • World Wide Web • Telnet • File Transfer Protocol (FTP) • Internet Telephone • Web TV/Radio • Internet Relay Chat • News Groups

How to Connect to Internet

Basic Communication

• Computer Networks interconnects computers to exchange data and resource sharing.

• Internet uses some kind of media to connect computers/networks together.

– Eg:- Telephone line

Basic Communication

• Communication is done by passing electrical signals across wires.

• Telephone wires are using Analog Signals for communication.

• Computers are using Digital Signals for processing.

MODEM Modulator - Demodulator

• A modem is a device needed for communication across a dial-up telephone connection or for long distance communication across a wire.

• A modem supports two-way communication because it contains a modulator for the signal being sent and a demodulator for the signal being received.

MODEM Modulator - Demodulator

• When a computer interacts with a modem, it sends and receives digital data; the modem encodes the data for transmission.

modem - 1 transmission line modem - 2

Computer A Computer B

Introduction to Computer Networks

Computer Networks

Computer network connects two or more autonomous computers.

The computers can be geographically located anywhere.

Introduction to Computer Networks

Uses of Computer Networks

Resource Sharing

Hardware (computing resources, disks, printers) Software (application software)

Information Sharing

Easy accessibility from anywhere (files, databases) Search Capability (WWW)

Communication

Email Message broadcast

Remote computing Distributed processing (GRID Computing)

Introduction to Computer Networks

L A N

Network in small geographical Area (Room, Building or a Campus) is called LAN • LAN- Local Area Network – used by schools and businesses – used to connect around 10-500 computers in a building – only accessible from within the building

Local Area Network

• A computer communication technology is classified as a Local Area Network (LAN) if it provides a way to interconnect multiple computers across short distances. LANs are inexpensive, highly reliable, and convenient to install and manage.

Local Area Network

continue… • A computer needs additional hardware to connect it to a local area network. The hardware consists of a circuit board that plugs into the computer and a cable that attaches the circuit board to the LAN. Once connected, a computer uses the network interface to send and receive data.

Local Area Network

continue… • Because each computer attached to a LAN contains interface hardware that isolates the computer from the LAN, the speed of the LAN does not depend on the speed of the computers that attach to it. As a result, heterogeneous computers can communicate across a LAN.

Network Interface Card

• The primary function of a network interface card (NIC) is to provide a physical link to a computer network. This connection allows computers to communicate with servers, as well as other computers on the network.

Network Interface Card

continue… • Each NIC has a unique serial number, which is called a MAC address. Every computer connected to the network is required to have a unique MAC address that is stored on the network interface card. If you are building a home network or utilizing broadband Web access, your NIC connects you to the outside world.

Network Interface Card

continue… • Network interface cards are either wired (LAN) or wireless. Both NICs are generally compatible with Windows and other popular operating systems. Most NICs use network drivers, which are computer programs that allow software applications to communicate with network hardware.

Network Interface Card

continue… • The necessary drivers are usually integrated into the computer system. The drivers usually installs automatically when the hardware is turned on.

V P N

• Virtual Private Networks (VPNs) are essentially software applications that use a public network, such as the Internet, to link computers together.

M A N & W A N

Network in a City is called MAN (Metropolitan Area Network) Network spread geographically (Country or across Globe) is called WAN (Wide Area Network)

Introduction to Computer Networks

Network Concepts

• Network Hardware – Servers- powerful computers dedicated to controlling all of the systems on the network. All networked computers are connected to the server in some way – Printers- One of the reasons networks were developed was to make a single printer accessible by many different computers – Computers- individual machines that are connected to the server – Network Interface Card (NIC)- a device that is installed into a computer to give it a terminal that can run a cable to access the network

Introduction to Computer Networks

Network Software

• Network Operating System – the system software run on the server – An operating system (OS) is software that computers use to run the environment that allows you to access applications and create files. Without an OS, a computer is useless.

• Networked Applications – computer programs located on the network that are accessed by individual computers – This makes loading software on individual computers unnecessary.

OS Logos

Computer Networks

Data Transmission Media

Data Transmission Media

Data Transmission Media

Data Transmission Media

Data Transmission Media

Data Transmission

Packet Switching

• This is the basic communication technology that Internet uses.

• In Networks multiple devices shares hardware facilities.

• Arranging for multiple devices to share a single transmission path lowers cost because it uses fewer wires and fewer switching machines.

Packet Switching

continue… • Granting one party exclusive access of a shared transport path can be impractical because it can delay all other parties.

• To avoid long delays, network technologies limit the amount of data that a computer can transfer on each turn – Packet Switching (1960) • The unit of data that can be transferred at one time is called a packet.

SIMPLE SWITCHED NETWORK

1 4 2 3 7 5 3 6

Packet Switching

• Messages are broken up into small packets • Each packet is transmitted individually .

• Packets may even follow different routes to the destination. • At each node the entire packet is received, stored, and then forwarded (

store-and-forward networks

) • At the destination the packets are reassembled into the original message. • Used in the Internet

Packet

• • packets are split into three parts:

header

- The header contains instructions about the data carried by the packet. – Length of packet – Packet number – Protocol ( what type of packet is being transmitted: e-mail, Web page, streaming video) – Destination address – Originating address

payload

- actual data of the packet

Packet

•

trailer

/footer- It contains a couple of bits that tell the receiving device that it has reached the end of the packet. It may also have some type of error checking. The most common error checking used in packets is

Cyclic Redundancy Check (CRC)

.

Packet

• Each computer attached to a network is assigned a unique number called its address.

• A packet contains the address of the computer that sent it and the address of the computer to which it is sent.

• Although packet switching technologies limit the amount of data in a packet, they allow the sender to transmit any size packet up to the maximum.

header payload trailer

A



T

 1

P

time T A P • header + trailer carry control information for switching (the source and the final destination addresses, etc.)

Inside the packet switching router

Packet Switching

continue… • Packet Switching avoids delays.

• To avoid long delays, network technologies limit the amount of data that a computer can transfer on each turn – Packet Switching (1960) • The unit of data that can be transferred at one time is called a packet.

Packet Switching

continue… • A packet switching system permits multiple pairs of computers to communicate across a shared network with minimal delay because it divides each conversation into small packets and arranges for the computers that share a network to take turns sending packets.

Packet Switching

continue… • Because packet switching systems adapt instantly as computers become ready to send data or others finish sending data, each computer receives a fair share of network resources at any given time.

Packet Switching

continue… • Like most computer network, the Internet is a packet switching system. Internet hardware includes physical wires shared among multiple users.

• Packet switching allows many communications to proceed simultaneously, without requiring an application to wait for all other communication to complete.

Packet Switching

continue… • As a consequence, whenever a user transfers data across the Internet, network software on the sending machine divides the data into packets, and network software on the receiving machine must reassemble the packets to produce the data.

• All data is transferred across the Internet in packets. Packets from many machines traverse the Internet at the same time.

• •

http://www.pbs.org/opb/nerds2.0.1/geek_glossary/packet_switching_flash.html

http://www.webopedia.com/TERM/P/packet_switching.html

B A

Example

C out of order D in order E

Delays in datagram networks

Delays in datagram networks

node 1 host 1 node 2

transmission time Waiting Time Waiting Time

time host 2

Total Delay

Advantages

• Line efficiency – Single node to node link can be shared by many packets over time • Packets are accepted even when network is busy – Delivery may slow down • Priorities can be used

Disadvantages

– Excessive congestion: packet delay and high loss – Packet header overhead – Provides no transparency to a user

ISPs and Network Connections

• Internet Service Providers(ISPs) and Fees.

– A company that provides Internet Access and Services is known as an ISP.

• ISP charges for its services.

– A charge for using the Internet.

– A charge for a physical connection to the Internet • Types of Billing.

– Flat rate per month – independent of the number of minutes a customer uses the service, but charges more for transfers large volume of data.

– Charges for the connection, for dedicated connection. – More for connections capable of transferring larger volume of data.

Addresses on the Web:IP Addressing

• Each computer on the internet does have a unique identification number, called an IP (Internet Protocol) address.

• The IP addressing system currently in use on the Internet uses a four-part number.

• Each part of the address is a number ranging from 0 to 255, and each part is separated from the previous part by period, • For example, 106.29.242.17

IP Addressing

• The combination of the four IP address parts provides 4.2 billion possible addresses (256 x 256 x 256 x 256).

• Members of various Internet task forces are working to develop an alternate addressing system that will accommodate the projected growth.

• However, all of their working solutions require extensive hardware and software changes throughout the Internet.

Domain Name Addressing

• Most web browsers do not use the IP address to locate Web sites and individual pages.

• They use domain name addressing.

• A

domain name

is a unique name associated with a specific IP address by a program that runs on an Internet host computer.

• The program, which coordinates the IP addresses and domain names for all computers attached to it, is called

DNS (Domain Name System ) software

.

• The host computer that runs this software is called a

domain name server.

Domain Name Addressing

• Domain names can include any number of parts separated by periods, however most domain names currently in use have only three or four parts.

• Domain names follow hierarchical model that you can follow from top to bottom if you read the name from the right to the left.

• For example, the domain name gsb.uchicago.edu is the computer connected to the Internet at the Graduate School of Business (gsb), which is an academic unit of the University of Chicago (uchicago), which is an educational institution (edu).

• No other computer on the Internet has the same domain name.

Uniform Resource Locators

• The IP address and the domain name each identify a particular computer on the Internet.

• However, they do not indicate where a Web page’s HTML document resides on that computer.

• To identify a Web pages exact location, Web browsers rely on Uniform Resource Locator (URL).

• URL is a four-part addressing scheme that tells the Web browser:  What transfer protocol to use for transporting the file   The domain name of the computer on which the file resides The pathname of the folder or directory on the computer on which the file resides  The name of the file

Structure of a Uniform Resource Locators

protocol pathname http://www.chicagosymphony.org/civicconcerts/index.htm

Domain name filename http => Hypertext Transfer Protocol

HTTP

• The transfer protocol is the set of rules that the computers use to move files from one computer to another on the Internet.

• The most common transfer protocol used on the Internet is the Hypertext Transfer Protocol (HTTP).

• Two other protocols that you can use on the Internet are the File Transfer Protocol (FTP) and the Telnet Protocol

How to find information on the Web?

• A number of search tools have been developed and available to you on certain Web sites that provide search services to help you find information.

• Examples:  Yahoo  www.yahoo.com

 Excite  Lycos  www.excite.com

 www.lycos.com

 AltaVista  www.alta-vista.com

 MSN WebSearch  www.search.msn.com

How to find information on the Web?

• You can find information by two basic means.

•

Search by Topic

and

Search by keywords

.

• Some search services offer both methods, others only one.

• Yahoo offers both.

 Search by Topic You can navigate through topic lists  Search by keywords You can navigate by entering a keyword or phase into a search text box.