CSCI-235 Micro-Computer Applications The Internet

 Communications and Networking LAN (Local Area Network) LAN (Local Area Network) WAN (Wide Area Network) WAN (Wide Area Network) The Internet is a global, interconnected computer network in which every computer connected to it can exchange data with any other connected computer The Internet is a global, interconnected computer network in which every computer connected to it can exchange data with any other connected computer

 History of Internet The ARPANet (precursor to the Internet) became a reality in 1969 The ARPANet (precursor to the Internet) became a reality in 1969 Advanced Research Project Agency (ARPA)Advanced Research Project Agency (ARPA) Intended to connect only military installations and universities participating in government projectsIntended to connect only military installations and universities participating in government projects It employed dedicated cables, buried undergroundIt employed dedicated cables, buried underground The data transfer was 56K bits/sec, roughly the same as dial-up services todayThe data transfer was 56K bits/sec, roughly the same as dial-up services today

By 1980, close to 100 sites were connected to the ARPANet By 1980, close to 100 sites were connected to the ARPANet Satellite connections provided links to select cities outside the continental U.S.Satellite connections provided links to select cities outside the continental U.S.

 Internet Growth

© Prentice-Hall, Inc A Quick Timeline 

© Prentice-Hall, Inc The Future of the Internet  Key changes in the Internet need to take place to handle the growing number of users and the speed of the connections  Future changes include: More bandwidth More bandwidth Internet 2 (I2) is being developed and tested to establish gigabits per second Points of Presence (gigaPOP)Internet 2 (I2) is being developed and tested to establish gigabits per second Points of Presence (gigaPOP)

© Prentice-Hall, Inc The Internet and Web: What’s the Difference?  The Internet is the physical connection of millions of networks  The Web uses the Internet for its existence  The Web consists of hypertext embedded on Web pages that are hosted on Web sites

© Prentice-Hall, Inc Web Site  A Web site is a collection of related Web documents that are made available to the public  The index page, or home page, is the first page of a Web site  Web pages are individual Web documents

© Prentice-Hall, Inc Tim Berners-Lee  Worked at CERN lab in Geneva Thought his work would be easier if he could link to colleagues’ computers Thought his work would be easier if he could link to colleagues’ computers Envisioned a network of computers much like a spider web Envisioned a network of computers much like a spider web Used links to transfer data from one site to another location Used links to transfer data from one site to another locationlinks  CERN site considered the birthplace of the World Wide Web  ners-Lee ners-Lee ners-Lee

© Prentice-Hall, Inc Marc Andreessen  Developed the first graphical browser Called Mosaic Called Mosaic Led to Netscape Navigator Led to Netscape Navigator

© Prentice-Hall, Inc Web Browsers and Servers  Web browsers display a Web document and enable users to link to other Web pages The first browsers were text-only The first browsers were text-only Mosaic was the first graphical browser Mosaic was the first graphical browser  Web servers respond to the requests of browsers. They find and send requested resources back to the browser

Architecture of WWW

Browser

© Prentice-Hall, Inc  Web addresses are an addressing system that identifies where a Web resource is located  The uniform resource locator (URL) is the standard used to identify Web resources  The URL consists of: URL Web Addresses (URLs) Protocol identifies the means of access Server contains the domain name of the Web server help/shop/ Path identifies the location of the document shop-01.html Resource specifies the filename of the resource

© Prentice-Hall, Inc HTML Document Web Page Design  Authors use a markup language called Hypertext Markup Language (HTML) to create Web pages  The markup language consists of codes that identify portions and special effects in the document

© Prentice-Hall, Inc Page Created HTML Document Click to view an HTML document and the page that it creates. Click again

© Prentice-Hall, Inc IP Addresses  IP address – Each computer connected to the Internet is given an address composed of numbers and periods. Example:  Every machine on the Internet has a unique IP address  Windows command WINIPCFG.EXE (IPCONFIG.EXE for Windows 2000/XP) 

19.19 Dotted-decimal notation and binary notation for an IPv4 address

Find the error, if any, in the following IPv4 addresses. Example Solution a. There must be no leading zero (045). b. There can be no more than four numbers. c. Each number needs to be less than or equal to 255. d. A mixture of binary notation and dotted-decimal notation is not allowed.

Finding the classes in binary and dotted-decimal notation

Find the class of each address. a b c d Example Solution a. The first bit is 0. This is a class A address. b. The first 2 bits are 1; the third bit is 0. This is a class C address. c. The first byte is 14; the class is A. d. The first byte is 252; the class is E.

19.23 Default masks for classful addressing

Two levels of hierarchy in an IPv4 address

A frame in a character-oriented protocol

© Prentice-Hall, Inc Domain Name Domain Names  Domain Name System (DNS) – Enables users to type names of Web sites and Web pages as well as IP addresses  UNIX command nslookup 

Port addresses

© Prentice-Hall, Inc Ports  Any server machine makes its services available to the Internet using numbered ports, one for each service that is available on the server  Clients connect to a service at a specific IP address and on a specific port  If a firewall is not protecting the port, you can connect to the port from anywhere on the Internet and use the service

© Prentice-Hall, Inc Ports  If you were to set up your own machine and load Web server software on it, you could put the Web server on port 918, or any other unused port, if you wanted to  Then, if your machine were known as xxx.yyy.com, someone on the Internet could connect to your server with the URL The ":918" explicitly specifies the port number  When no port is specified, the browser simply assumes that the server is using the well-known port 80

© Prentice-Hall, Inc HTTP Protocol  Every Web server on the Internet conforms to the HTTP protocol, summarized nicely in The Original HTTP as defined in 1991 The Original HTTP as defined in 1991The Original HTTP as defined in 1991  The most basic form of the protocol understood by an HTTP server involves just one command: GET  "GET filename," the server will respond by sending you the contents of the named file and then disconnecting  telnet 80

© Prentice-Hall, Inc Putting It All Together   The browser breaks the URL into three parts: The protocol ("http") The protocol ("http") The server name (" The server name (" The file name (“athletics/schedules.html") The file name (“athletics/schedules.html")  The browser communicates with a name server to translate the server name, " into an IP address, which it uses to connect to that server machine

© Prentice-Hall, Inc Putting It All Together  The browser then forms a connection to the Web server at that IP address on port 80  Following the HTTP protocol, the browser sends a GET request to the server, asking for the file  The server sends the HTML text for the Web page to the browser  The browser reads the HTML tags and formats the page onto your screen

Static document

Dynamic document using CGI

Dynamic document using server-site script

Active document using Java applet

Active document using client-site script

Electronic Mail ( )  is sending messages via computer  Business is using more and fax  To access you must have a mail server and software  Each person has a username and password  All mail programs allow you to Send, Compose, Reply and Forward, Delete

Internet Address Username Host Computer Next-level domain Highest-level domain A valid Internet Address must contain symbol

Protocols POP Client --Post Office Protocol Mail is read composed and stored locally Can work off-line IMAP --Messages stored remotely Stored on a server Download for local storage SMTP --Simple Mail Transfer Protocol The protocol required to send mail messages through the Internet