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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
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