1 Lecture 9 The Internet Introduction to Information Technology With thanks to Dr. Haipeng Guo Dr. Ken Tsang 曾镜涛 Room E408 R9

2 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 FTP Search Engines

3 What is a Network? Collection of computers and devices connected to share information and resources

4 What is a LAN? Local Area Network Network in limited geographical area such as home or office building

5 What is a WAN? Wide Area Network Network that covers large geographic area using many types of media

6 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

7 History of the Internet the USSR launched Sputnik, the first artificial earth satellite 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

8 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

9 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

10 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

11 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

12 Connecting to the Internet  At home Through Phone modem Through DSL / ADSL Through Cable modem  At office Through LAN  Wireless connection Through hotspots

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

14 ChinaNet: the largest Internet backbone in China Owned by China Telecom 336 Mbps connection to the Global Internet

15 Chinese Education and Research network 8 Mbps connection to the Global Internet ChinaNet: the largest Internet backbone in China

16 Internet Service Provider (ISP) User PC Network Access Point

17 Connecting via Phone Modem A computer A phone modem card Connecting to a phone jack Username and password and a number to dial up to the ISP’s computer Usually 64 kbps (bits per second) at most

18 Connecting via DSL/ADSL  DSL: Digital Subscriber Line  ADSL: Asymmetric DSL Downloading faster than uploading

19 Cable Modem DSL and Cable Modem connections are both broadband connections Faster than 128 kbps

20 Connecting via LAN A computer Hub or switch or router network card

21 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

22 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

23 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 Internet

24 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

25 Try it – ipconfig & ping

26 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

27 Domain Name System  The very last section of the domain is called its top-level domain (TLD) name

28 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

29 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

30 nslookup

31 Client/Server Model All of the machines on the Internet are either servers or clients. Web server, server, DNS server, ftp server, game server……

32 How data travels the Internet  Messages are divided into fixed-sized, numbered packets  Network devices called routers are used to direct packets between networks

33 Routers Routers determine the path between you and an Internet server

34 Try it – Tracert (trace route)

35 Network Protocols  Network protocols are layered such that each one relies on the protocols that underlie it  Sometimes referred to as a protocol stack

36 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

37 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)

38 Internet Applications: WWW  World Wide Web  Worldwide collection of electronic documents web browser web server

39 Internet Applications:  address:  client  server SMTP server POP3 server Sending SMTP (Simple Mail Transfer Protocol) Server handles outgoing mail

40 Internet Applications:  Receiving the POP3 (Post Office Protocol) server handles incoming mails When you check your , your client program connects to the POP3 server

41 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

42 FTP Commands

43 Example of using FTP

44 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

45 Web Crawling

46 Indexing

47 Searching

48 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, , FTP, Search Engine

49  PDF, notes and glossary on the web: /CS/it1010/lectures/10.The.Internet.pdf /CS/it1010/lectures/2x2_10.The.Internet.p df /CS/it1010/lectures/10.Glossary.pdf /CS/it1010/lectures/10.The.Internet.notes. html /CS/it1010/lectures/10.The.Internet.pdf /CS/it1010/lectures/2x2_10.The.Internet.p df /CS/it1010/lectures/10.Glossary.pdf /CS/it1010/lectures/10.The.Internet.notes. html