Chapter 7: The Internet, Intranets, and Extranets
Agenda • What is the Internet • IP Addresses • How the Internet Works • The Domain Name System (DNS) • How E-mail Finds its Way • Internet Communication Protocols • How to Connect to the Internet • Internet Services • Basic Internet Software • Telnet Software • FTP Software • The World Wide Web • Intranets and Extranets • Virtual Private Networks • Privacy and Security
What is the Internet • The Internet is a collection of interconnected networks, all freely exchanging information. • The Internet is actually a network of networks: tens of thousands of computers connected in a web, talking to one another through a common communications protocol.
IP Addresses • Every node on the Internet has a unique Internet number called an IP address. IP addresses are 32 bits long and consist of four parts (called dotted-quads) that are separated by the period. For example: 188.8.131.52 • The octets are numbers in each quad and are used to identify a particular network and a host node on that network. In general, the leading portion of each IP address identifies the network number and the last number identifies the specific computer.
How the Internet Works • On this "highway" of network connections, routers provide Internet traffic control. The primary purpose of routers is to find the best path among available alternatives by which to send data. • The Internet transmits a message from one computer to another either directly (in the same network) or through a router till the message reaches its destination. • Messages are passed around in chunks, called packets, each of which carries the address of the sender and the receiver. • The set of conventions used to pass packets from one computer to another is the combination of the Transport Control Protocol (TCP) and the Internet Protocol (IP).
The Domain Name System (DNS) • Because the IP addresses are hard to remember, the Internet supports the use of a text name that can be substituted for the IP address. The text version of the IP address is called a domain name. Each domain name is mapped to a particular numeric address. • To translate and track domain names, we use the Domain Name System (DNS), which is a set of distributed databases containing IP addresses and their corresponding domain names. DNS servers perform the translation back and forth between names and numbers (i.e., saclink.CSUS.edu). • The top-level domain indicates the class of institution to which the server belongs to the Internet (i.e., edu). • The second-level domain is registered by an organization (i.e., CSUS). • The first item is the name of the host computer, or the hostname (i.e., saclink).
How E-mail Finds its Way The e-mail address consists of several segments that combine geographical and conceptual information. For example: Sytsai@saclink.csus.edu • The sytsai element identifies the user or organization (who) • The @ symbol connects the (who) with (where) • The saclink.CSUS is the sub-domain and the domain (where) • The edu identifies the type of the organization (what)
Internet Communication Protocols • TCP/IP is the Internet’s suite of network protocols that allow different computers to communicate. • The Transmission Control Protocol (TCP) is responsible of end-to-end message delivery in terms of priority, error free, in sequence, no loss or duplication. • The Internet Protocol (IP) operates at the network layer, breaks the message into packets called datagrams, and provides addresses for each datagram. • Underneath TCP/IP sit various media protocols that help move the data over various networks on the Internet. • HTTP (Hypertext Transport Protocol) is used by WWW applications • NNTP (Network News Transport Protocol) is used by Usenet news applications • SMTP (Simple Mail Transport Protocol) is used by E-mail applications
How to Connect to the Internet • On-Line service connection requires using a communications software and modem to connect to an on-line information service company that provides internet services. An example would be connecting to the Internet through America On-Line. • SLIP/PPP connection requires using a modem and several types of software like TCP/IP, Serial Line Internet Protocol (SLIP) or Point to Point Protocol (PPP) to connect to an Internet host. An example would be connecting to the CSUS server from home. • Network connection is the highest and most expensive level of connectivity. This approach requires using a network adapter card and a communications stack directly connected to an Internet server. An example would be connecting to the Internet when you use a PC in the computer labs at CSUS.
Internet Services - I • E-mail: sends text, sound, and images to others. • Telnet: logs on to another computer and access its public files. • FTP: copies a file between two computers. • Usenet and newsgroup: an on-line discussion group of a specific topic. • Chat rooms: enables tow or more person to carry on on-line text conversation in real time. • Internet phone: enables voice communication between two person with proper hardware and software. • Internet video conferencing: supports simultaneous voice and visual communications.
Internet Services - II • Content streaming: continuously transfers and plays multimedia files over the Internet between two locations. • Instant messaging: allows two or more person to communicates instantly on the Internet, • Shopping on the Web: allows people to purchase products and services over the Internet. • Web auctions: lets people bid on products and services. • Music, radio, and video on the Internet: lets user play or download music, radio, and video. • Office on the Web: allows people to access files and information through a Web site. • Internet sites in 3-D: views products and images at a different angles.
Internet Services - III • Free software and services: allows people to obtain free software, advice, and information on the Internet.
Basic Internet Software Servers over the Internet that offer different services like e-mail and web services. Several types of software are needed to access those services. The most significant types of software that you need are: • Web Browsing Software • Telnet Software • FTP Software
Telnet Software • Telnet is a user command used to access a remote computer. Telnet software enables the user to log on to another computer and access any applications and data to which the user has been granted access.
FTP Software • A file transfer protocol (FTP) program is used to download a file from the host computer to the PC or vice versa. FTP clients with graphical interfaces allow you to drag and drop files from an FTP site to a local computer.
The World Wide Web • The World Wide Web, uses the client/server model, to organize Internet resources into a series of menu pages (screens) that appear on your computer. • Data can exist on the Web in any computer file like word processing files, graphic images, video and audio files. • Hypertext Markup Language (HTML) is the standard page description language for Web pages. HTML documents contain Uniform Resource Locators (URLs) which is a standard way of coding the hypertext links to other documents on the Web. • Web browsers, like Netscape Communicator and Internet Explorer, are software applications that request a page from the Web server and display it on the user’s local computer. They receive HTML documents by using a Uniform Resource Locator (URL), which is the address of the file accessible on the WWW. • Browsers must be able to understand and interpret hypertext markup language (HTML) codes in the HTML documents.
Intranets and Extranets • An Intranet is an internal corporate network built using the Internet and W3 standards and products. One of the intranet’s most obvious virtues is its ability to slash the need of paper. Any employee can view the same electronic information. • An Extranet is a network based on Web technologies that links selected resources of the intranet of a company with its customers, suppliers, or other business partners
Privacy and Security • Cookie and fraud • Cryptography is the process of converting a message into a secret code and changing the encoded message back to regular text. • Encryption is the original conversion of a message into a secret code. Decryption is the encrypted message conversion back to regular text. • Digital Signature is an encryption technique used to meet the critical need for processing on-line financial transactions. • Firewalls are devices that sit between the internal network and the outside Internet and limit access into and out of the internal network.
Virtual Private Network (VPN)A secure connection between two computers across the Internet
Points to Remember • What is the Internet • IP Addresses • How the Internet Works • The Domain Name System (DNS) • How E-mail Finds its Way • Internet Communication Protocols • How to Connect to the Internet • Internet Services • Basic Internet Software • Telnet Software • FTP Software • The World Wide Web • Intranets and Extranets • Virtual Private Networks • Privacy and Security