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S3 Computer Literacy

S3 Computer Literacy

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S3 Computer Literacy

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  1. S3 Computer Literacy Internet Technology

  2. Connecting to the Internet – Hardware Requirement • MODEM • 56K or Broadband • MOdulation and DEModulation • Telephone Line

  3. Connecting to the Internet - ISP • ISP– Internet Service Provider(互聯網服務供應商) • What has ISP done for you? • It sends and receives data for you. • It provides a connection between you and the other of the Internet. • As shown in the animation below, the data is in fact handled by a number of ISP. Animation for connection to the Internet

  4. Is ISP running the Internet? • No single organization runs the Internet. • It is a large network of networks. • These networks are linked by high-speed communication channels called backbones. • Each Internet computer, called a host, is independent.

  5. Connecting to the Internet –Type of Access • Dial-up Access(撥號上網) • It needs • a telephone line • MODEM • User • dials a telephone number given by the ISP to connect to the server of the ISP. • a user name and password to authenticate the user. • User can access hosts on the Internet • Data transfer rate maximum of 56Kbps.

  6. Connecting to the Internet –Type of Access • Broadband Access • Its speed is measured in Mbps (i.e. Mega bit per second) • Unlike dial-up access, it requires a network card / LAN card but no modem required.

  7. Broadband Access - ADSL • ADSL • a technology for transmitting digital information at a high bandwidth on existing phone lines to homes and businesses. • ISP adopting this technology in HK: • Netvigator (網上行)

  8. Get to the Internet • PPPoE • Some broadband Internet service providers (ISPs) identify your computer on their networks using Point to Point Protocol over Ethernet (PPPoE). If your ISP requires you to supply a name and password to access the Internet, it most likely uses this protocol (議定 ).

  9. Broadband Access - ADSL • ADSL (Asymmetric Digital Subscriber Line) • Asymmetric (不對稱) between download speed is faster. • Download Speed – 1.5Mbps to 8Mbps • Upload Speed – 16Kbps to 640Kbps • Components – Network card, ADSL MODEM, Telephone Line

  10. Broadband Access –Cable TV Network • Cable TV Network • A Cable MODEM is used to enables user to connect the PC to a local cable TV line and receive data at about 10Mbps. • ISP adopting this technology in HK: • iCable (有線寬頻)

  11. Broadband Access –Cable TV Network • Cable TV Network • Download and upload speed are the same, but the bandwidth (10Mbps) is shared among users at the same location(e.g. the same building) • Hardware used – Network Card, Cable MODEM

  12. Broadband vs Dial-up Access • Faster connection speed – up to 1.5Mbps to 10Mbps. • No dialing required. • Simultaneous use of data and voice connections • ie: unlike dial-up access, user can talk on the phone while surfing the Internet.

  13. How can we share Internet access in a LAN to a Broadband? • A router(路由器) is needed to connect a LAN to the Internet. • It will share the broadband access from one Internet account among all users in the LAN.

  14. Communication Protocol – TCP/IP • TCP/IP • communication protocol of the Internet • set of rules used in message transmission on the Internet. • computers need to use the same protocol if they need to communicate

  15. TCP and IP

  16. Advantages of TCP/IP • If we send the whole file without breaking it into packets, • the whole message then has to be re-sent if the full message fails to reach its destination • if it is broken down into packets, then only the packet that fail to be sent are resent. Packet Animation

  17. Advantages of TCP/IP • Transmission of data is not affected by the failure of any path: • there are more than one path. Packets of data can be routed around the problem. • the load of the line is evenly distributed. • As long as the operating system supports TCP/IP, the computers can communicate through LAN and Internet. TCP Animation

  18. IP Address • It identifies every host (computer) in any network. • When a packet is transmitted over the Internet, it must carry the addresses of the sender and receiver computers so that the routers can choose the best path.

  19. IP Address – Format • The IP address system currently using is called the IPv4 addressing system.

  20. Question regarding IP Address • What is the range of the each set of numbers? • As each computer in the Internet has a unique IP address, how many computer can be represented in the Internet? • What can we do if the number of IP addresses is not enough?

  21. Real IP and Virtual IP • Imagine if there are not enough IP addresses in a network, what can we do? • The solution is to use Virtual IP.

  22. How Virtual IP works • Some of the IP addresses are reserved for private network (ie: LAN). E.g. 10.X.X.X or 192.168.X.X • The router will not route these IPs to the Internet, ie: it will route the data sending to these IPs inside the LAN.

  23. Static IP and Dynamic IP • Static IP • IP addresses that are fixed every time when the user connect to the Internet. • Dynamic IP • IP addresses that changes every time the user connect to the Internet.

  24. Domain Name System (DNS) • At the command window, type in the command “ping www.google.com.hk”, what did you find? Why? • To connect to a specific computer, we need to know its IP address. • Connect to the Yahoo! webpage, we need to know its address, ie: type http://68.142.226.41 in the Internet browser. • It is inconvenient to remember the meaningless IP address.

  25. DNS Server • DNS Server responsible for translating the address into the corresponding IP address. • Try to get to the nba.com

  26. Web Server • Web Server is a computer that delivers Web pages. • A computer can become a web server by installing Web Server Program like Apache and IIS (Internet Information Server)

  27. Web Browser • A software application used to display Web pages. • Two most popular browsers are Netscape Navigator and Microsoft Internet Explorer (IE). • Plug-in (外掛程式) • The browser cannot play all format of audio or video files, so a plug-in program is needed to add support to these types of files.

  28. Case studies • If the hosts (PCs) can communicate well in the LAN but they have difficulties to get to the Internet, what would be the problem? • If you are a teacher and you have saved some document in a PC at school. You have checked the IP address of this PC is 10.62.43.55, are you able to get access to this PC at your home, why? • Your PC at home cannot access to the web pages, e.g. www.yahoo.com.hk, however, your ISP tells you that your connection to the Internet works fine, what would be the problem?