Chapter 2

1. Chapter 2 Making the Connection: The Basics of Networking

2. Networked Computers Change Our Lives • The Connected/Networked Information Age has brought profound changes • Nowhere is remote (True?) • People are interconnected (Everyone?) • Social relationships are changing (How?) • English may be becoming a universal language • Freedom of speech and assembly haveexpanded • Other Issues? Security, Privacy, Oversight?

3. Nowhere Is Remote • Internet is a complete information resource (almost) no matter where you are • Some differences remain because older sources are not yet all online • North Korea? China? Mt. Everest? • Homes are not remote from work • Information workers can telecommute and live long distances from their offices • Working longer hours? 24/7?

4. People Are More Interconnected • Family and friends can stay in closer, more frequent contact via Internet than via telephone or "snail mail" • “Network effect” – People and Computers • WWW lets us meet people passively • People with similar interests find each other through search engines, social media, etc. • Associations can form rapidly • Facebook. Twitter. • Quality? Privacy? Other Issues?

5. Social Interactions Are Changing • Time spent online displaces other in-person social activities (displacement effect) • The effects are complicated. • Pros? Cons? • The Internet is changing social interactions, but we don't (yet) fully understand how

6. Is English Becoming a Universal Language? • Influence of American pop culture since World War II • Dominance of science and technology in English-speaking countries (Even countries such as China and India use English widely in technical fields) • Much software is available only in English • Most web pages are in English. Changing? • Universal or Common? Thoughts?

7. Freedom of Speech and of Assembly Have Expanded • Internet use is unmediated (True or False?) • No editorial oversight or significant restrictions • Allows for political and artistic expression • Blogs record personal, political, artistic thoughts for public viewing (Sourced vs. Social content) • Like-minded people can communicate, even on private topics • Repercussions? “Google” a potential date or employee/employer? Professor?

8. Communication Types • General Communication • Synchronous: sender and receiver are active at the same time (telephone call, IM) • Asynchronous: sending and receiving occur at different times (email, podcast) • Broadcast communication (all) or Multicast (group): single sender and many receivers (Email, Twitter, Feeds, etc.) • Point-to-point communication: single sender and single receiver (Letter, cell call, etc.)

9. Internet's Communication Properties • Internet provides a universal communication “medium" linking all computers connected to it • Can be applied in many ways: • Point-to-point asynchronous • Email is alternative to standardmail • Point-to-point synchronous (virtual) • IM, Skype is alternative to telephone • Multicasting (and conferencing) • Chat rooms are alternatives to magazines • Broadcasting • Web pages are alternatives to radio and television, newspapers and books.

11. The Client/Server Interaction Protocol • Server is the computer that stores information (web page, files, images, email, etc.) or provides services • Client computer & software accesses the information • When you click link, your computer enters the client/server relationship with web server • Once the page is sent to you, the client/server relationship ends. (Stateless communication) • Server can form many brief relationships so it can serve many clients at the same time • Clients may access one or many servers over time, depending on individual needs. May also serve.

13. Computer IP Addresses • Each computer connected to the Internet is given a unique numerical address. • four numbers (0-255, or 00-FF hexadecimal - one byte each) separated by dots • Example: 192.231.231.60 Memorizing? • Billions, but still running out (IPv4 vs. IPv6) • Hostnames: Human-readable symbolic names, based on domain hierarchy • Easier to read and remember • Example: www.iona.edu

15. DNS Servers • The Domain Name Systemtranslates the human-readable names into IP addresses • Internet host knows the IP address of its nearest DNS name server, a computer that keeps a list of domain names and corresponding IP addresses • When you use a hostname to send information, your computer asks the DNS server to look up the IP address (client-server!) • If the DNS server doesn't know the IP address, it asks a authoritative name server (aka Root name server), which keeps the master list of name-to-address relationships

16. Top-level Domains • Domain is a related group of networked computers • Top-level domains appear in the last part of domain name: .edu educational institutions .org organizations .net networks .mil military .gov government agencies Mnemonic two-letter country designators such as .ca (Canada) Long List in book and at: http://en.wikipedia.org/wiki/Internet_country_codes

19. Hierarchy of Domain Names • Example: spiff.cs.washington.edu • The name of the computer is spiff • Which is part of the Computer Science and Engineering Department domain (cs) • Which is part of the University of Washington domain (washington) • Which is part of the educational domain (edu)

20. Following Protocol - TCP • Protocol is how the information is actually sent • TCP/IP (Transmission Control Protocol/Internet Protocol) • Information is broken into a sequence of small fixed-size units called IP packets • Each packet has space for the unit of data, the destination IP address, and a sequence number • The packets are sent over the Internet one at a time using whatever route is available • Because each packet can take a different route, congestion and service interruptions do not delay transmissions

23. Moving Packets: Wires and More • Internet uses electrical, electronic, and fiber optical communication means • Telephone lines, dedicated fiber optic lines, etc. • The technology used to move the packet is independent from the protocol; transmission of a single file may use multiple technologies

24. Far and Near: WAN and LAN • Internet is a collection of Wide Area Networks (WAN), designed to send information between widely separated locations • Local Area Networks (LAN)connect computers usually close enough to be linked by a single cable or wire pair. Can also be bridged (Iona-Rockland) • Ethernet is the main technology for LAN • Often used to connect all the computers in a lab or building • Wireless is also a major LAN technology

25. Ethernet • Channel (wire, wire pair, or optical fiber) that winds past a set of computers • Each computer is connected to the channel, allowing it to send a signal that can be detected by all computers connected to the channel • Decentralized scheme: • Each computer listens to the channel. If it's quiet, it's free. • The computer transmits unless another starts at the same time. • In that case, both stop for a random time and thentry again.

26. Connecting a Computer to the Internet • By ISP (for home users, small busines): • Internet Service Providers (ISP) sell connections to the Internet (like Comcast and Earthlink) • User plugs into telephone system or dedicated connection (DSL, Cable “Modem”) to ISP • Home computer talks to ISP's computer • Modems convert the bits a computer outputs into a form that is compatible with the carrier • ISP's computer is connected to Internet, and relays information for its customers

27. Connecting a Computer to the Internet • By Enterprise Network Connections (LAN): • Large networked organizations such as schools, businesses, or governmental units • The organization creates a LAN or intranet • The intranet connects to the Internet by a gateway • Information from a Web computer is sent across Internet, through gateway, across LAN to user's computer

28. Wireless Networks – Protocol 802.11 • A variation on the LAN connection • A computer (called the hub or router) is physically connected to the Internet • The hub broadcasts and receives radio frequency (rf) signals • Mobile computers also send and receive signals • The hub relays Internet requests for the networked computers

30. The World Wide Web (WWW) • Web servers: Computers programmed to send files (web pages, images, audio, video, etc.) to browsers running on other computers connected to the Internet • Web servers and their files make up the World Wide Web. (Structure + Information) • The World Wide Web is a subset of the Internet, one service out of many. • The Internet is the “road,” the Web is one form of “traffic” on the road

31. Requesting a Web Page • Web request creates a client/server interaction • Uniform Resource Locator (URL) has 3 main parts: http://www.widgets.com/hardware/support/faq.html • Protocol: • http:// ftp:// • Hypertext Transfer Protocol File Transfer Protocol • Tells the computer how to handle the file • Server computer's name: • Server's IP address translated by the domain hierarchy (DNS – Domain Name System) • Page's pathname: • Tells the server which file (page) is requested and where to find it.

32. The Internet, the Web & Domain Names • WWW is just a name; web sites do not have to use it • For DNS to work, user must give the exact domain name. (Server or Browser may insert the "www”) • To help users reach them, organizations can do : • Redirection: Supply the probable address • Register multiple domain names • Example: Museum of Modern Art has registered both "moma.org" and "www.moma.org" to the same IP address

33. Describing a Web Page • Pages are stored as a description of how they should appear on the screen (markup) • Web browser creates and presents the image from the description file (source file) • Browser can adapt the displayed page more easily this way. Most files are smaller. • Menu: View --> Source or Page Source in a browser to see the HTML or other code • Note that code is NOT WYSIWYG!

36. Hypertext – WWW’s Common Language • Hypertext Markup Language (HTML and XHTML) • Markup languages describe layout of a document • Margin width • Font • Text style • Image placement • Etc. • Hypertext provides a way to jump from point to point in documents (non-linear) • Combination of hypertext with markup language lets us build nonlinear documents for the dynamic and interconnected Net and Web

37. Web Sites and File Structure • Web sites are organized collections of HTML files • URL points into this organization to select a file • Directory, or folder, is a named collection of files, other directories, or both • Directory Hierarchy: Directories can contain other directories, which can contain other directories, etc. (like a “tree”) • Down, or lower in the hierarchy, means moving into subdirectories • Up, or higher in the hierarchy, means into enclosing directories

39. File Structure (cont'd) • Part of the directory (folder) hierarchy is shown in the pathnames of URL's. http://www.nasm.si.edu/galleries/ga1100/pioneer.html • The Page name is (often) given by the last part of the pathname: /galleries/ga1100/pioneer.html • Each time we pass a slash (/), we move into a subdirectory or into the file (lower or down in the hierarchy)

41. Organizing the Directory • List or index files in a directory • Because index linking to the files in a directory is common, browsers look for it automatically • When a URL ends in a slash, the browser looks for a file called index.html in that directory • Why are hierarchies important? • People use them to organize information, their thinking and work, etc. • Directories are “free”; there is (almost) no reason not to use plenty of them. Do so!