OIA_04_Internet_Basics_e_v1 by liaoxiuli

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									                                                                                V1.0 (22/11/2005)

Office and Internet Applications: Internet Applications (11 hours)


1. What is the Internet?

The Internet is a worldwide collection of interconnected networks. It is actually comprised of
thousands of independent networks at academic institutions, military installations,
government agencies, commercial enterprises, and other organizations.


The Internet has its roots in a networking project started by the Pentagon’s Advanced
Research Projects Agency (ARPA), an agency of the U.S. Department of Defense. ARPA’s
goal was to build a network that allowed scientists at different locations to share information
and work together on military and scientific projects and could function even if part of the
network were disabled or destroyed by a disaster such as a nuclear attack. That network,
called ARPANET, became functional in 1969, linking scientific and academic researchers
across the U.S.



2. Who controls or owns the Internet?

Even as the Internet grows, it remains a public, cooperative, and independent network. Each
organization on the Internet is responsible only for maintaining its own network. No single
person, company, institution, or government agency controls or owns the Internet.



3. Internet Access

Most people get access to Internet through an Internet Service Provider (ISP), which is any
company that provides individuals and organizations with access to the Internet. There are
several feasible ways that are presented you how we get access to the Internet. HutchCITY,
Netvigator and I-Cable are three popular ISPs in Hong Kong.



3.1 Dial-up Access
Some homes and small businesses use dial-up access to connect to the Internet. It takes place
when the modem in your computer uses a standard telephone line to connect to the Internet.

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This type of access is relatively an easy and inexpensive way for users to connect to the
Internet. However, a dial-up connection is slow-speed technology.


3.2 Broadband Access
Nowadays, most homes and small businesses use broadband access for higher-speed
connections. These connections use DSL or cable television Internet services. DSL (Digital
Subscriber Line) is technology which enables high-speed transmission of digital data over
regular copper telephone lines. A DSL modem and a network interface card must be used to
establish Internet connection successfully. A cable modem provides high-speed Internet
connections through the cable television network. Similarly, a network interface card is also
required in this case.




                         DSL modem                           Network Interface Card


Generally, broadband access through DSL and cable television is always on. That is, it is
connected to the Internet the entire time the computer is running. With a dial-up access, by
contrast, you must establish the connection to the Internet.


In computer networks, bandwidth is often used to mean the amount of data that can be
carried from one point to another in a given time period. Bandwidth is usually measured in
bits or bytes per second. A modem that works at 57,600 bps has twice the bandwidth of a
modem that works at 28,800 bps. Therefore, higher-speed broadband Internet connections
have a higher bandwidth than dial-up connections.


Reference web site:
Transmission rates of various communications systems   http://www.linktionary.com/b/bandwidth.html



3.3 TCP/IP and Packets
TCP/IP (Transmission Control Protocol/Internet Protocol) is the communications protocol
that permits data transmission over the Internet. A protocol is a set of rules that controls or
enables the connection, communication, and data transfer between two computers. Any
modern operating system, such as Windows 2000/NT/XP or Mac OS) comes with the
software needed to handle TCP/IP communications. Communications over the Internet are


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built around this two-layer protocol.


TCP sets the rules for the packaging of information into packets. Each message, file and so
on to be sent over the Internet is divided and placed into packets for routing over the Internet.
IP handles the address, such that each packet is routed to its proper destination.


How does it work?
When you request a file from an Internet server computer, the TCP layer divides the file into
one or more packets, associates a number with each packet, and then routes them one-by-one
through the IP layer. Each packet has the same destination IP address, but they may take
different paths through the Internet to their destination. At the destination, the TCP layer
waits until all the packets arrive, reassembles them, and then forwards them to users as a
single file.


Each POP (point-of-presence) on the Internet has a unique address with four numbers
separated by periods (for example, 201.18.104.21). A POP is an access point to the Internet.
An ISP may have many POPs so that subscribers can dial local telephone numbers to gain
access. A POP for an ISP may be a leased router or server owned by a common carrier.


When you dial an ISP’s local POP, your dialup connection generally is made through a PPP
(Point-to-Point Protocol) connection to an Internet host. Once a TCP/IP connection is
established, you are on the Internet.



3.4 Software required for Internet Connection
Once users have established an Internet
connection, it is necessary to use a client
program that will let users retrieve and
view Internet resources. A client
program runs on PC and works in
conjunction with a companion server
program that runs on the Internet host
computer. The client program contacts
the server program, and they work
together to give users access to the
resources on the Internet server. Client
programs are designed to work with one or more specific kinds of server programs For
instance, the Microsoft Internet Explorer client software works with the companion Internet

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Explorer server software. A single server computer might have several different server
programs running on it, enabling it to accommodate a variety of clients.


A web browser is one kind of client. Web browsers are application software that enables users
to display and interact with HTML documents hosted by web servers. Microsoft Internet
Explorer and Netscape Communicator are the two most popular browsers. Users give the
browser an Internet address, called the URL, and it goes out over the internet connection,
finds the server site identified in the URL, then downloads the requested file(s) for viewing
on the browser.



3.5 Uniform Resource Locator
The URL (Uniform Resource Locator) is the unique address for a file that is accessible on the
Internet. The URL consists of several portions.


Consider the following URL:

       http://www.info.gov.hk/info/hkin/air_services.html

        1                   2                       3                        4

                         http: The beginning of the URL contains the protocol. This is
  1                      usually "http" (Hypertext Transfer Protocol) or "ftp" (File
http                     Transfer Protocol). Protocol is a set of rules to exchange signal
                         / information. (e.g. Morse code).

                         www: It is the usual name of host server. Consider another
  2                      URL, http://webcast.info.gov.hk/, the “webcast” is the name of
www.info.gov.hk          this host server.


                         info.gov.hk: It is the domain name which is a unique name
                         that identifies an Internet host site. The domain name can be
                         divided into several parts by dots. Let’s start from the right of the
                         domain name, “hk” indicates the country codes (“cn” for China;
                         “jp” for Japan; “ca” for Canada), “gov” is the Top-Level Domain
                         (TLD) which represents government category in this case.
                         Finally, “info” is the name given by government, of course, it
                         might be the name of a business or college, etc. in other cases.

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                         TLD         Affiliation
                         com         Commercial
                         edu         Education
                         gov         government
                         mil         military
                         net         Network resources
                         org         nonprofit organizations

                         Directory. It shows what follows the domain name is a directory
  3
                         containing the resources for a particular topic.
info/hkin/

                         Filename. The specific filename of the file that is retrieved from
  4                      the server and sent to user’s PC over the Internet. In this case,
air_services.html        the file is a HTML file.




3.6 Domain Name System

3.6.1     IP Address
An IP address is a unique number used to identified computer or device on TCP/IP network,
such as on the Internet. An IP network is somewhat similar to the telephone network in that
users have to have the phone number to reach a destination. The major difference is that IP
addresses are often temporary.

                          IP Address          202.100.127.09


Static and Dynamic IP
Each device in an IP network is either assigned a permanent address, i.e. static IP, by the
network administrator or is assigned a temporary address, i.e. dynamic IP. Routers, firewalls
and proxy servers use static addresses as do most servers and printers that serve multiple
users. Client machines may use static or dynamic IP addresses. For home users, the IP
address assigned by Internet Service Provider is typically dynamic IP.



3.6.2    Domain Name
Domain Name is a unique name for an individual, such as company, association, person,
etc…, on the Internet. For example, rthk.org.hk is the domain name for RTHK. It is estimated

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that there are more than 60 million registered domain names.

                    Domain Name               mycompany.com


3.6.3      Domain Name System (DNS)
The domain name system (DNS) interprets user-entered domain names, such as
www.mycompany.com , into IP associated address, such as 202.100.127.09, so data can be
routed to the correct computer. A domain name can identify to more than one IP addresses. A
DNS server is an Internet server that usually is associated with an Internet access provider.




       www.mycompany.com                                              202.100.127.09




                                            DNS server




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