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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. -1- 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 -2- 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 -3- 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 1 http 2 www.info.gov.hk 2 3 4 http: The beginning of the URL contains the protocol. This is usually "http" (Hypertext Transfer Protocol) or "ftp" (File 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 URL, http://webcast.info.gov.hk/, the “webcast” is the name of 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. -4- TLD com edu gov mil net org 3 Affiliation Commercial Education government military Network resources nonprofit organizations Directory. It shows what follows the domain name is a directory containing the resources for a particular topic. info/hkin/ 4 air_services.html Filename. The specific filename of the file that is retrieved from the server and sent to user’s PC over the Internet. In this case, 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 -5- 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 -6-