Networking

1. Networking INFO/CSE 100, Fall 2006 Fluency in Information Technology http://courses.washington.edu/info100/ networks @ university of washington

2. Lab 2 / Homework 2 • Any questions? networks @ university of washington

3. Readings and References • Reading • Fluency with Information Technology • Chapter 3, Making the Connection networks @ university of washington

4. Today’s Objectives • Learn Basics of networks / what they can do • Understand protocols • IP • Routing • HTTP & URL Structure • DNS networks @ university of washington

5. Networks… • Computers are useful alone, but are even more useful when connected (networked) • Access more information and software than is stored locally • Help users to communicate, exchange information .. Changing ideas about social interaction • Perform other services -- printing, audio, video • Immediate access to knowledge: for example, Google networks @ university of washington

6. Networking Changes Life • The Internet is making fundamental changes … the FIT text gives 5 ways • Nowhere is remote -- access to information is no longer bound to a place • Connection with others -- email is great! But what about spam?!? • Revised human relationships -- too much time spent online could be bad • English is becoming a universal language • Enhanced freedom of speech, assembly networks @ university of washington

7. Network Structure • Internet: all of the wires, fibers, switches, routers, etc… connecting named computers • Networks are physically structured differently based (mostly) on how far apart the computers are • Local area network (LAN) • A small area such as a room or building • Wide area networks (WAN) • Large area, e.g. distance is more than 1Km • What do you think a PAN might be?!? networks @ university of washington

8. Local Area Network Mac disk and printers available on the nearby Windows PC Windows disk and printers available on the nearby Mac networks @ university of washington

9. Wide Area Network instant messenger world wide web UW servers Internet router networks @ university of washington

10. Exercise • Our class is the Internet - lets pass some data! networks @ university of washington

11. Transfer Data • Goal: get “data packet” to the named student • Rules: (to replicate internet) • only the person with the packet can ask questions of other students • you can talk to students who physically sit next to you (all 9 directions) (as your aren’t “connected” to the others) • must hand off packet to one of 9 students for them to repeat networks @ university of washington

12. How Did that work? • What didn’t work? • Imagine this more than 1,000,000,000,000 times per day! • What can make this process better? networks @ university of washington

13. What is your IP Address? • IP Address =ROW.COLUMN • Examples: • 10.1 • 8.13 • 2.3 networks @ university of washington

14. Protocols are Important! • To communicate, computers need to know how to set-up the info to be sent and to interpret the info received • Communication rules are a protocol • Example protocols: • Ethernet for physical connection in a LAN • TCP/IP -- transmission control protocol/internet protocol • HTTP -- hypertext transfer protocol (for the WWW) • FTP -- file transfer protocol (for transferring files) • Protocols often rely on or build on other protocols networks @ university of washington

15. LAN in the Lab • Ethernet is a popular LAN protocol Connection to campus network infrastructure Typical MGH or OUGL Lab PC PC PC PC PC PC Ethernet Cable networks @ university of washington

16. Campus & The World • The campus sub-networks interconnect computers of the UW domain which connects to the Internet via a gateway • The protocol used is TCP/IP Switch MGH Homer Gate way Dante Student washington.edu CS Switch networks @ university of washington

17. IP -- Like Using Postcards • Information is sent across the Internet using the Internet Protocol -- postcard analogy • Break message into fixed size units • Form IP Packets with destination address, sequence number, and content • Each makes its way separately to destination, possibly taking different routes • Reassembled at destination forming message • Taking separate routes lets packets by-pass congestion and out-of-service network devices networks @ university of washington

18. IP con’d DEST ADDRESS | SIZE | # | DATA Source Destination networks @ university of washington

19. A Trip to Switzerland • A packet sent from UW to ETH (Swiss Federal Technical University took 21 hops UW Gateway networks @ university of washington

20. Check Internet Hops • There are numerous Trace Route utilities • Windows: tracert, OSX: Network Utility networks @ university of washington

21. What the Internet “looks like” networks @ university of washington

22. Naming Computers • Computers connected to the Internet are part of a network domain • A hierarchical scheme that groups computers • .edu All educational computers • .washington.edu All computers at UW • dante.u.washington.edu A UW computer • .ischool.washington.edu iSchool computers • .cs.washington.edu CSE computers • www.ischool.washington.edu an iSchool computer networks @ university of washington

23. Domains • .edu, .com, .mil, .gov., .org, .net domains are some of the “top level domains” in the USA • Recently added TLD names include: • .biz, .info, .name, .pro, .aero, .coop, .museum, .tv • Each country has a TLD name: .ca (Canada), .es (Spain), .de (Germany), .au (Australia), .uk (England), .us (USA) • The FIT book contains the complete list of country domains networks @ university of washington

24. Naming Computers con’d • Computers are named by IP address, four numbers in the range 0-255 called an octet • dante.u.washington.edu: 140.142.14.67 • live.xbox.com: 65.59.234.169 • Remembering IP address would be brutal for humans, so we use domain names • Computers find the IP address for a domain name from the Domain Name System (DNS) • An IP address-book for the computer networks @ university of washington

25. Logical vs. Physical • There are 2 ways to view the Internet • Humans see a hierarchy of domains relating computers • Logical network • Computers see groups of four-number IP addresses • Physical network • Both are ideal for the “users” needs • Domain Name System (DNS) relates the logical network to the physical network by translating domains to IP addresses networks @ university of washington

26. Anatomy of it All • Domain name: dante . u . washington . edu • IP address: 140.142.14.67 Third-level Second-level Top-level Fourth-level networks @ university of washington

27. Your DNS Name as your name • IP Address =ROW.COLUMN • Examples: • 10.1 = Ima Student • 8.13 = Will Getana • 2.3 = Bob Upndown networks @ university of washington

28. Client/Server Structure • Many internet applications rely on theclient / server model to provide services • Example services: email server, web server, sftp server • UW servers: dante, students, www • Frequently, a “server” is actually many computers acting as one, e.g. dante is a group of more than 50 servers called a cluster or a farm • Protocol governs the communication • Client packages a request and sends it to a server; • Server does the service and sends a reply networks @ university of washington

29. World Wide Web • World Wide Web (WWW) is a collection of web servers on the Internet • Subset of Internet computers • WWW is not the same as the Internet! • They give access to information using the HTTP protocol • The “server” is a web site computer and the “client” is a web browser (like Internet Explorer) • Many Web server’s domain names begin with www by tradition, but any name is OK • Often multiple servers map to the same site:moma.org and www.moma.org networks @ university of washington

30. History of the WWW • Web beginnings • 1989: Tim Berners-Lee • URLs, http, first browser (HTTP 1.0) • 1993: NCSA Mosaic • HTTP 1.1 supported images • Then Netscape, then Mozilla • 1994: World Wide Web Consortium • http://w3.org/ • Standards organization for Web protocols and formats • 1994-5: Web crawlers and search engines • WebCrawler, Lycos, AltaVista, Yahoo • Developed at UW CSE School networks @ university of washington

31. World Wide Web • URL -- uniform resource locator • Web page addresses • HTTP -- hypertext transfer protocol • Client-server communication rules • HTML -- hypertext markup language • A specifal format for making the pages universally readable by all clients networks @ university of washington

32. Dissecting a URL • Web addresses are URLs (uniform resource locator) • A server address and a path to a particular file • http://courses.washington.edu/info100/classwork/calendar/index.html protocol = http:// Web server = courses domain = washington.edu path = /info100/classwork/calendar/ dirs(folders) file = index file extension = .html hypertext markup language networks @ university of washington

33. Server Client Server Server Client Client request Server Client Server Client reply Server Server Client Client Server Client Client/Server Interaction • For Web pages, the client requests a page the server returns it: there’s no permanent connection, just a short conversation • Details of the conversation are specified by HTTP networks @ university of washington

34. Simple HTTP Request request protocol method GET /pub/WWW/TheProject.html HTTP/1.1 Host: www.w3.org host networks @ university of washington

35. A Typical Browser Request GET/pub/WWW/TheProject.htmlHTTP/1.1 Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-powerpoint, application/vnd.ms-excel, application/msword, application/x-shockwave-flash, */* Accept-Language: en-us Accept-Encoding: gzip, dflate User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; APC) Host: www.w3.org Connection: Keep-Alive networks @ university of washington

36. Server Response HTTP/1.1 200 OK Date: Monday, 23 May 2005 22:38:34 GMT Server: Apache/1.3.27 (Unix) (Red-Hat/Linux) Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT Etag: "3f80f-1b6-3e1cv03b" Accept-Ranges: bytes Content-Length: 438 Connection: close Content-Type: text/html <html> <head><title>A Sample Page</title></head> <body> … networks @ university of washington

37. Summary • Networking is changing the world • Internet: named computers using TCP/IP • WWW: servers providing access to information via the HTTP protocol • Principles • Local network of domain names • Physical network of IP address • Protocols rule: LAN, TCP/IP, HTTP • Domain Name System connects the two • Client/Server, relationship on WWW networks @ university of washington