Download ISP

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 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
Is ISP running the Internet?
 No single organization runs the
Internet.
 It is a large network of networks.
 These networks are linked by highspeed 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
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.
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
information 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 speed 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 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)
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
connections
 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 resent 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
“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.
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 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.
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?