IN.1 Internet Technology

1. IN.1 Internet Technology Basic facts about Internet Terminology of Internet Servers on the Internet Internet access

2. Basic facts about Internet A. Development of Internet • In 1969, the US Defense Department built a network called the ARPANET • Tied together computers of military and universities 1. Allow geographically separated computers to share data 2. Allow communication via e-mails 3. Designed to withstand damage • Data could bypass the damaged part of the network 4. Allow various types of computers to run on it

3. Basic facts about Internet • Initially, ARPANET consisted of four main computers • In 1986, US NSF connected its network of supercomputers to ARPANET Civilian network • NSF allowed anyone to join the network • ARPANET is renamed as “Internet”

4. Basic facts about Internet B. Development of WWW • The popularity of the Internet is due to the World Wide Web (WWW), or the Web • Internet’s fast growing portion • The Web was invented by Dr. Tim Berners-Lee in 1991 • A researcher in CERN • In 1993, Mosaic was developed • The first widely distributed Web browser by Marc Andreessen • Mosaic is the ancestor of today’s Web browsers • e.g. Netscape, Internet Explorer and FireFox

5. Terminology • WWW • TCP/IP • IP Address / Web site address • Domain Name • ISP • URL • VPN

6. 2. WWW World Wide Web (WWW) • Created in 1989. • The collection of hyperlinked documents accessible on the Internet • With a web browser, a user views webpages that may contain text, images, videos, and other multimedia.

7. 2. TCP/IP (1) Transmission Control Protocol (TCP) and Internet Protocol (IP) • Set of rules used in data transmission on the Internet • Data is broken up into small packetsby the sender • Each packet is directed by a series of routers • So, different packets use different routes • Finally, recombined by the receiver.

8. 2. TCP/IP (2) Advantages of TCP/IP: 1. The load of transmission lines is evenly distributed 2. Unaffected by the failure of any path • More than one path, the packets would be routed round the problem 3. Entire message is guaranteed to be transmitted • If packet is not received properly, request re-transmission 4. Different Computers can communicate • for all OS that support TCP/IP

9. 3. IP Address Web site address • On the Internet, computers have unique IP address • each can be uniquely identified • A series of four numbers separated by a period • Each number between 0 and 255 • e.g. 202.148.153.59 • Combination of IP addresses is • 256 x 256 x 256 x 256. • Large organisations: permanent • Home users: temporary • Each packet carries IP addresses of sender and receiver • Similar to the addresses on an envelope

10. 4. Domain Name (1) • IP address • Used by computers • difficult for people to remember • May change if it is shared • Domain • A group of computers under the same organization • Domain name • Text version of IP address • of a server of the organisation • using words separated by periods, e.g. • “Radian.com.hk” • More meaningful and easy-to-remember

11. 4. Domain Name (2) • Top level domains • can be 1. Generic top level domains • e.g. .com, .org, etc. 2. Country-code top level domains • e.g. .hk, .cn, .au, etc. • Second-level domains • under .hk • .com.hk, .org.hk, .net.hk • .edu.hk, .gov.hk, .idv.hk

12. 5. Internet Service Providers (1) Internet • Global collection of networks • Collaborative: • Each member network provides • servers • communication devices and • connecting lines etc. • Directs traffic • The Internet is not run by a single organisation • Large organisations provide Backbones • e.g. UUNET and NASAR • High-speed channels that link the networks

13. 5. Internet Service Providers (2) Internet service providers (ISP) • Offer Internet access to • individuals, companies and organisations. • Have permanent connection to the Internet backbone • Service may be • charged at an hourly rate • fixed monthly amount for unlimited access • means that there is no limit for duration of connection

14. 6. URL Uniform Resource Locator (URL) • Address of a Web page • e.g. http://www.stmc.edu.hk/main/namelist2001/3b.htm • Defining the route to a file on the Web, including • Protocol prefix e.g. http://, ftp://, news:// • Type of host server e.g. www, mail, ftp • Domain name e.g. stmc.edu.hk, gov.hk • Path name e.g. main, namelist2001 • Filename. For example, e.g. 3b.htm, abc.txt, xyz.doc

15. 7. VPN Definition Virtual Private Network (VPN) 虛擬私人網路 • Communications network tunneled thru’ another network and dedicated for a specific network. • Makes WANs like LANs • Establishes a secure tunnelling channel thru’ public network. • Data will be encrypted 加密before sending out to the tunnel.

16. Domain Name Server (DNS) • DNS • Translate domain name into IP address • Maintain a table with • Domain names of organisations and their corresponding IP addresses • For each domain name, e.g. e-mail address or URL • DNS server translates into IP address • Kept by major ISP • the table is updated regularly

17. Web Server • Web Server • Stores collection of Web pages • Accepts HTTP requests form clients • i.e. web browsers • Serves HTTP responses along with optional data contents

18. Proxy Server • Proxy Server • Sits between a client application, such as a web browser, and a real server • Serve the request without contacting the specified server. • If one or more Internet sites are frequently requested, they will be stored in the proxy’s cache • passes all requests and replies unmodified is usually called a gateway or sometimes tunneling proxy

19. Internet Access Countries by number of internet users

20. Internet Access

21. Internet Access for Home Users • 1. Dial-up Access • Using regular modem and telephone line • Temporary link to the Internet • Modem is connected to the serial port • Network interface card (NIC) is not necessary • Inexpensive but slow • 56 kbps • In Hong Kong, need to pay for PNETS • Public Non-Exclusive Telecommunications Service • charging per minute use telephone line • Connection may not be successful due to busy phone line

22. Internet Access for Home Users • 2. Broadband Access (1) Asymmetric Digital Subscriber Line (ADSL) or (2) Cable TV network. • Hardware needed: • NIC and • Special modem • Applying advanced technology over telephone line • very high transfer rate up to 1.5 M to 10 Mbps • Connection is fast and easy because • dial-up is not necessary • Installed by trained technicians

23. Internet Access by Mobile Users • Wireless Service Provider (WSP) • a type of ISP • that uses radio waves • rather than cable • to provide Internet access to users of wireless devices • e.g. handheld computers and mobile phones

24. Internet Access for Network Users • Hardware • Router • to connect a LAN to the Internet • Wireless access point, wireless NIC • more convenient • Access to ISP via 1. broadband with telephone line/optical fibre 2. ISDN with dedicated phone line 3. T1 with a digital line 4. Wireless technology with radio waves/satellites • Unlimited access • Fixed monthly payment.