S3 Computer Literacy

Internet Technology

Connecting to the Internet – Hardware Requirement

MODEM 56K or Broadband MOdulation and DEModulation Telephone Line

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 th

e 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

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.

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 conne

ct 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.

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.

Broadband Access - ADSL

ADSL a technology for transmitting digital informa

tion at a high bandwidth on existing phone lines to homes and businesses.

ISP adopting this technology in HK: Netvigator ( 網上行 )

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 ).

Broadband Access - ADSL

ADSL (Asymmetric Digital Subscriber Line) Asymmetric ( 不對稱 ) between download s

peed is faster. Download Speed – 1.5Mbps to 8Mbps Upload Speed – 16Kbps to 640Kbps Components – Network card, ADSL MODEM,

Telephone Line

Broadband Access –Cable TV Network

Cable TV Network A Cable MODEM is used to enables user to c

onnect 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 )

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

Broadband vs Dial-up Access Faster connection speed – up to 1.5Mbps

to 10Mbps. No dialing required. Simultaneous use of data and voice con

nections ie: unlike dial-up access, user can talk on the

phone while surfing the Internet.

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.

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

TCP and IP

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

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

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.

IP Address – Format

The IP address system currently using is called the IPv4 addressing system.

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?

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.

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.

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.

Domain Name System (DNS) At the command window, type in the command “p

ing www.google.com.hk”, what did you find? Why? To connect to a specific computer, we need to kno

w its IP address. Connect to the Yahoo! webpage, we need to know i

ts address, ie: type http://68.142.226.41 in the Internet browser.

It is inconvenient to remember the meaningless IP address.

DNS Server

DNS Server responsible for translating the address into the corresponding IP address.

Try to get to the nba.com

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)

Web Browser A software application used to display W

eb pages. Two most popular browsers are Netscap

e 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.

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?