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Lecture 9

The Internet

Introduction to Information Technology

With thanks to Dr. Haipeng Guo

Dr. Ken Tsang 曾镜涛Email: kentsang@uic.edu.hkhttp://www.uic.edu.hk/~kentsang/IT/IT3.htmRoom E408 R9

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Outline What is the Internet? History of the Internet How to connect to the Internet How the Internet works Software and services supported

by the Internet WWW Email FTP Search Engines

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What is a Network? Collection of computers and

devices connected to share information and resources

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What is a LAN? Local Area Network Network in limited geographical area

such as home or office building

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What is a WAN? Wide Area Network Network that covers large geographic

area using many types of media

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What is the Internet? A network of computer networks

worldwide The Internet is world’s largest WAN Also called the information highway,

the net, or cyberspace

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History of the Internet

1957 - the USSR launched Sputnik, the first artificial earth satellite

1958 - In response, the US Department of Defense established the Advanced Research Projects Agency (ARPA)

Several years later ARPA began to focus on computer networking and communications technology

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Idea of Package Switching In 1961, Dr. Leonard Kleinrock created

the basic principles of packet switching, the technology underpinning the Internet, while a graduate student at MIT

First node on the Internet

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ARPANET In 1969 ARPANET was constructed It is a network of four computers

UCLA SRI (Stanford) UCSB University of Utah

The first message: lo….gin

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Internet Today The Internet has grown from four host

computer systems to many millions By 1984, ARPANET had more than 1,000

individual computers linked as hosts In 1992, the Web Wide Web protocol was

released ARPANET had more than 1 million computers

linked as hosts Today, more than 150 million hosts

connect to the Internet In 2005, China’s Internet population was

111 million

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Who owns the Internet? Nobody owns the Internet! It doesn't mean it is not monitored and

maintained in different ways The computers and devices connected to the

Internet belong to a person or an organization

The Internet Society, a non-profit group established in 1992, oversees the formation of the policies and protocols that define how we use and interact with the Internet

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Connecting to the Internet At home

Through Phone modem Through DSL / ADSL Through Cable modem

At office Through LAN

Wireless connection Through hotspots

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The Internet Backbone

• Typically fiber optic lines• 5 Mbps to over 600 Mbps • Provided by companies such as AT&T, GTE, and IBM

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ChinaNet: the largest Internet backbone in China

• Owned by China Telecom• 336 Mbps connection to the Global Internet

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• Chinese Education and Research network• 8 Mbps connection to the Global Internet

ChinaNet: the largest Internet backbone in China

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Internet Service Provider (ISP)

User PC

Network Access Point

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Connecting via Phone ModemA computer

A phone modem card

Connecting to a phone jack

Username and passwordand a number to dial up to the ISP’s computer

Usually 64 kbps (bits per second) at most

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Connecting via DSL/ADSL DSL: Digital Subscriber Line

ADSL:Asymmetric DSL

Downloading faster than uploading

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Cable Modem

DSL and Cable Modem connections are both broadband connections

Faster than 128 kbps

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Connecting via LANA computer

Hub or switch or router

network card

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DSL and telephone-related terminologies NAP – Network Access Point POP - Point of Presence POTS - Plain Old Telephone Service ISDN - Integrated Services Digital Network PSTN - Public Switched Telephone Network TELCO - Telephone Company

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Wireless Connection

Wireless adapters can plug into a computer's PC card slot A wireless router send signals to

wireless devices and has a wire to send signals to the Internet

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How the Internet works Every computer connected to the

Internet must have a unique address. This is called the IP address. IP stands for Internet Protocol

5.6.7.81.2.3.4

Internet

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IP Address An IP address can be split into

network address, which specifies a specific network

host number, which specifies a particular machine in that network

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Try it – ipconfig & ping

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Domain Name System (DNS) A hostname consists of the computer

name followed by the domain name uic.edu.hk is the domain name

A domain name is separated into two or more sections that specify the organization, and possibly a subset of an organization, of which the computer is a part

Two organizations can have a computer named the same thing because the domain name makes it clear which one is being referred to

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Domain Name System The very last section of the domain is

called its top-level domain (TLD) name

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Domain Name System Organizations based in countries other than

the United States use a top-level domain that corresponds to their two-letter country codes

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Domain Name System The domain name server is used to

translate hostnames into numeric IP addresses it is an example of a distributed database If that server can resolve the hostname, it

does so If not, that server asks another domain

name server

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nslookup

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Client/Server ModelAll of the machines on the Internet are either servers or clients.

Web server, e-mail server, DNS server, ftp server, game server……

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How data travels the Internet Messages are divided into fixed-sized,

numbered packets Network devices called routers are used

to direct packets between networks

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Routers

Routers determine the path between you and an Internet server

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Try it – Tracert (trace route)

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Network Protocols Network protocols are layered such that

each one relies on the protocols that underlie it

Sometimes referred to as a protocol stack

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TCP/IP TCP stands for Transmission Control

Protocol TCP software breaks messages into

packets, hands them off to the IP software for delivery, and then orders and reassembles the packets at their destination

IP stands for Internet Protocol IP software deals with the routing of

packets through the maze of interconnected networks to their final destination

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High-Level Protocols Other protocols built on the

foundation established by the TCP/IP protocol suite Simple Mail Transfer Protocol (SMTP) File Transfer Protocol (FTP) Telnet Hyper Text Transfer Protocol (http)

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Internet Applications: WWW World Wide Web Worldwide collection of electronic

documents web browser

web server

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Internet Applications: E-mail E-mail address: guesswho@uic.edu.hk e-mail client E-mail server

SMTP server POP3 server

Sending email

SMTP (Simple Mail Transfer Protocol) Server handles outgoing mail

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Internet Applications: E-mail Receiving the email

POP3 (Post Office Protocol) serverhandles incoming mails

When you check your e-mail, your e-mail client program connects to the POP3 server

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Internet Applications: FTP FTP stands for File Transfer Protocol FTP client program FTP server Basic steps

Connect to the FTP server Navigate the file structure to find the file

you want Transfer the file End the file transfer session

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FTP Commands

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Example of using FTP

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Internet Applications: Search Engine

Examples: Google, Baidu Web crawling: Search engines use

software called spiders to build lists of the words found on Web sites

Indexing: Keep an index of the words found, and where they

Searching: User builds a query and submits it to the search engine

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Web Crawling

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Indexing

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Searching

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Summary What is the Internet History of the Internet How to connect to the Internet How the Internet works

Client/Server Model, IP Address, DNS, TCP/IP Applications on the Internet

WWW, Email, FTP, Search Engine

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PDF, notes and glossary on the web: http://www.uic.edu.hk/~davetowey/teaching/CS/it1010/lectures/10.The.Internet.pdf http://www.uic.edu.hk/~davetowey/teaching/CS/it1010/lectures/2x2_10.The.Internet.pdf http://www.uic.edu.hk/~davetowey/teaching/CS/it1010/lectures/10.Glossary.pdf http://www.uic.edu.hk/~davetowey/teaching/CS/it1010/lectures/10.The.Internet.notes.html