Chapter 7 The Internet and Intranets

The Internet The world’s largest computer network Consists of thousands of interconnected networks ARPANET: Ancestor of the Internet Started by the Department of Defense to link DOD & military research contractors Split into two networks MILNET: all military sites Reduced ARPANET: non-military sites

The Internet [Figure 7.1]

How the Internet Works The Internet transmits data from one computer (host) to another. [Figure 7.2] continued...

How the Internet Works Messages are routed through the multiple networks that make up the Internet by using special protocols. Internet Protocol (IP) The set of conventions used to pass packets from one host to another Transport Control Protocol (TCP) Used in connection with IP Operates at the transport layer

How the Internet Works Each computer on the Internet has an assigned address to identify it from other hosts (e.g., ). Most also have names, which are much easier to remember than the numbers (e.g, flash.acme.com).

Internet Zones com: commercial sites edu: educational sites mil: military sites gov: government sites net: networking organizations org: organizations firm: businesses/firms store: businesses offering goods for purchase info: information service providers web: entities related to World Wide Web activities arts: cultural and entertainment activities rec: recreational activities nom: individuals

Three Ways to Access the Internet Connect via LAN server Connect via SLIP/PPP Connect via an on-line service

Three Ways to Access the Internet [Figure 7.3]

Requirements for Connecting via LAN Server Network adapter card Open Datalink Interface (ODI) or Network Driver Interface Specification (NDIS) Communications stack Software that provides a set of communications protocols that perform the complete functions of the seven layers of the OSI communications model

A Communications Stack for Accessing the Internet [Figure 7.4]

Requirements for Connecting via SLIP/PPP Modem and the TCP/IP protocols Serial Line Internet Protocol (SLIP) or Point to Point Protocol (PPP) software (communications protocols that transmit packets over telephone lines, allowing dial-up access to the Internet)

Requirements for Connecting via an On-Line Service Modem Standard communications software On-line information service account

Internet Services [Table 7.2]

Electronic Mail ( ) A way of sending an electronic message between individuals or computers Often called a store and forward system Allows to be stored until it can be forwarded to the next computer

Electronic Mail ( ) Typical message includes: “From” line “To” line “Subject” line “Message”

Usenet and Newsgroups Usenet A system closely allied with the Internet that uses to provide a centralized news service Newsgroup An on-line discussion group that focuses on a particular topic

Sample Newsgroup: Sewing Newsgroup [Sewing Newsgroup]

Finding Information and Downloading Files Telnet A terminal emulation protocol that lets a user log on to another computer on the Internet to gain access to publicly available files File Transfer Protocol (FTP) Describes the file transfer process between a host and a remote computer

Internet Phone and Videoconferencing Services Internet phone service Enables users to communicate with other Internet users around the world who have compatible equipment and software Internet videoconferencing Supports both voice and visual communications An emerging service

World Wide Web Involves over 30,000 independently owned computers that work together as one in an Internet Service Also known as the Web, WWW, or W3 A menu-based system that uses the client/server model continued...

World Wide Web Data exists on the Web as: ASCII characters Word processing files Audio files Graphic images Any other sort of data that is stored in a computer file continued...

World Wide Web A web site is like a magazine, with a cover page (home page) that has graphics, titles, and black and blue text. Hypertext: Blue, underlined type which links the on- screen page to other documents or Web sites Hypermedia Connects data on pages, allowing users to access topics in any order continued...

World Wide Web Uniform Resource Locators (URLs) A standard way of coding the location of the Hypertext Markup Language (HTML) documents Hypertext Transfer Protocol (HTTP) A set of rules that allows the Web user to retrieves a document

World Wide Web Hypertext Markup Language (HTML) Standard page description language for Web pages HTML tags Codes that let the browser know how to format the text [Figure 7.5]

Business Uses of the Web In 1991, the Commercial Internet Exchange (CIX) Association was established to allow businesses to fully connect to the Internet. Now businesses use the Internet for many applications: , customer information web sites, advertising direct sales web sites, on-line shopping.

Web Browsers A Web tool that creates a unique, hypermedia- based menu as a graphical interface to the Web Applets Small programs embedded in Web pages

Search Engines Web search tools that help users find the information they seek Two types of Web search tools Directories: List of Web sites classified by topic Indexes: Allow users to find specific documents through keyword searches

Developing Web Content Web authors work with several standards to create their pages. Two main problems limit creativity. Confusing HTML standards Slow communications speeds Virtual Reality Modeling Language (VRML) A language for creating 3-D scenes on the Internet

Java Object-oriented program language from Sun Microsystems based on C++ Allows small programs (applets) to be embedded within an HTML document

Downloading an Applet from a Web Server [Figure 7.6]

Intranets Internal corporate networks built using Internet and World Wide Web standards and products Most companies have the foundation for an intranet: a network that uses the Internet’s TCP/IP. Next stage of intranet usage: Interactive transaction-based applications

Common Intranet Uses [Table 7.7]

Managing the Internet and Intranets Although the Internet is a huge, global network, it is managed at the local level; no centralized governing body controls the Internet. The Internet Society and the Internet Activities Board (IAB) are the closest things to centralized governing bodies.

Service Bottlenecks Primary cause: phenomenal growth in traffic Other causes More than half of Web users have slow modems (14.4 Kbps or less) Inefficient software and software glitches

Cryptography The process of converting a message into a secret code and changing the encoded message back into regular text Digital Signature A technique used to meet security needs for the processing of on-line financial transactions

Cryptography [Figure 7.8]

Firewalls A device that sits between the internal network and the outside Internet Purpose: To limit access into and out of a network based on an organization’s access policy Can be set up to allow access from specific hosts and networks or to prevent access from specific hosts