Sunday, January 18, 2009

The Internet, Intranets, and Extranets

The Internet, Intranets, and Extranets
Internet : a collection of interconnected networks all freely exchanging information.

The ancestor of the internet was ARPANET, a project started by the U.S. Department of Defense (DOD) in 1969 as both an experiment in reliable networking and a means to link DOD and military research contractors, including a large number of universities doing military-funded research.
Internet Protocol (IP) :
Conventions that enable traffic to be routed one network to another as need.

How the Internet Works
The various networks that are linked to form the Internet work pretty much the same way, they pass data around in chunks called packets, each of which carries the address of its sender and its receiver. The set of conventions uses to pass packets from one host to another is known as the Internet Protocol (IP) , which operates at the network layer of the seven layer OSI model. Many protocols are connection with IP. The best known is the Transport Control Protocol (TCP), which operates at the transport layer and is used in combination with IP by most internet applications.
Backbone is one of the Internet’s high-speed , long distance communications links
Each computer on the Internet has an assigned address called its Uniform Resource Locator, or URL , to identify it from other hosts.
ตัวอย่างของ URL ก็เช่น
เรามาพิจารณาส่วนของ URL กันทีละส่วน
The “http” specifies the access method and tells your software to access this particular file using HyperText Transport Protocol.
The “www” part of address signifies that the address is associated with the World Wide Web.
The “” part of the address is the domain name that identifies the Internet host site and must adhere to strict rules. It always has at least two part separated by dots. For all countries except the USA , the rightmost part of the domain name is the country code (th for Thailand, au for Australia, etc.)

Accessing the Internet
There are three ways to connect to the Internet. ได้แก่
Connect via LAN server : This approach requires the user to install on his or her PC a network adapter card and Open Datalink Interface (ODI) or Network Driver Interface Specification (NDIS) packet drivers. These drivers allow multiple transport protocols to run on network card simultaneously. LAN servers are typically connected to the Internet at 56 Kbps or faster.
Connect via SLIP/PPP : This approach requires a modem an d the TCP/IP protocol software plus Serial Line Internet Protocol (SLIP) or Point to Point Protocol (PPP) software. SLIP and PPP are two communications protocols that transmit packets over telephone lines,allowing dial-up access to the Internet. The speed of this Internet connection is limited to the slower of your computer’s modem and the speed of your modem of the SLIP/PPP server to which you connect .
Connect via an on-line service : This approach requires nothing more than what is required to connect to any of the on-line information services- a modem, standard communications software, and on-line information service account.

Internet Service Providers
Internet Service Provider (ISP) is any company that provides individuals or organizations with access to the Internet.

E-Mail : E-Mail or Electronic mail enables you to send text, binary files, sound, and images to others.
Telnet : a terminal emulation protocol that enables users to log on to other computers on the Internet to gain access to public files.
File Transfer Protocol (FTP) : a protocol that describes a file transfer process between a host and a remote computer. FTP allows users to copy a file from one computer to another.
Usenet : a system closely allied with the Internet that use e-mail to provide a centralized news service. It is actually a protocol that describes how groups of messages can be stored on and sent between computers.
Newsgroups : an on-line discussion groups that focus on specific topic.
Chat room : a facility that enables two or more people to engage in interactive “conversations” over the Internet.
Voice-Over-IP (VOIP) : technology that enables network managers to route phone calls and fax transmissions over the same network they use for data.
Content Streaming : a method for transferring multimedia files over the Internet so that the data stream of voice and pictures plays continuously, without a break, or very few of them. It also enables users to browse large files in real time.

World Wide Web : a collection of tens of thousands of on dependently-owned computers that work together as one in an Internet service. These computers, called Web servers.
The Web is a menu-based system that uses the client/server model. It organizes Internet resources throughout the world into a series of menu pages, or screens, that appear on your computer.
The Web site is like a magazine, with a cover page called a homepage that has graphics, titles, and black and blue text.
Hypermedia : tools that connect the data on Web pages, allowing users to access topics in whatever order they wish.
Hypertext Markup Language (HTML) : is a standard page description language for Web pages.
HTML tags : codes that let the Web browser know how to format text: as a heading, as a list , or as body text and whether images, sound, and other elements should be inserted.
Web Browsers : software that creates a unique , hypermedia-based menu on your computer screen and provides a graphical interface to the Web.
Applet : a small program embedded in Web pages.
Search engine : a Web search tool.
Java : an object-oriented programming language from Sun Microsystems based on C++ that allows small programs –applet- to be embedded with in an HTML document.
Push technology : technology that enables users to automatically receive information over the Internet rather than searching for it using a browser.

Intranet : an internal corporate network built using Internet and World Wide Web standards and products that allows employees of an organization to gain access to corporate information.
Firewall : a device that sits between your internet network and the outside Internet and limits access into and out of your network based on your organization’s access policy.
Extranet : a network based on Web technologies that links selected resources of the intranet of a company with its customers, suppliers, or other business partners.

Summary of Internet, Intranet, and Extranet

Users Importance of reliability and performance Is there a need for user Authentication?
Internet Anyone Low No
Intranet Employees Low Yes
Extranet Selected business partners High Yes

Secured intranet and extranet access applications usually require the use of a virtual private network (VPN) . A virtual private network is a secure connection between two points across the Internet.
Tunneling : the process by which VPNs transfer information by encapsulating traffic in IP packets and sending the packets over the Internet.
Privacy and Security
Cryptography is the process of converting a message into a secret code and changing the encoded message back to regular text. The original conversion is called encryption. The unencoded message is called plaintext. The encoded message is call ciphertext.
Digital signature : an encryption technique used to meet the critical need for processing on-line financial transactions.

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