1. Jan.2001C.Watters1 World Wide Web Basics

2. Jan.2001C.Watters2 What is an internet anyway? 2 or more networks that can communicate

3. Jan.2001C.Watters3 Historical View: Internet 1969 - Telnet 1970 - 4 computers –Stanford, UCLA, UC Santa Barbara, U Utah 1971 - FTP 1983 - 562 computers on the internet 1993 - 1.2 million computers on the internet 1999 - ?? Kazillions

4. Jan.2001C.Watters4 What is the World Wide Web ? Hypertext connectivity of “documents”

5. Jan.2001C.Watters5 Size of the Internet

6. Jan.2001C.Watters6

7. Jan.2001C.Watters7 The web The Web is protocol that uses the internet as the communication structure links documents stored in computers communicating with the internet main authority: W3 consortium www.w3.com

8. Jan.2001C.Watters8 Historical View: WWW 1989 - Berners Lee - web doc proposal 1990 - Berners Lee - text browser (physicists) 1992 - public access to web docs at CERN 1993 - 60 web servers & Mosaic (graphics) – (500 servers by year end) 1995 - more Internet email than US post 1999 - x million docs & y million servers

9. Jan.2001C.Watters9 http://www.lexis-nexis.com

10. Jan.2001C.Watters10 Basics Web server - machine that services internet request Web client - machine that initiates internet request Browser - software to interact with internet data at the client TCP/IP - internet data protocol FTP - internet file transfer protocol HTTP - hypertext transfer protocol HTML - hypertext markup language

11. Jan.2001C.Watters11 Client-Server Model

12. Jan.2001C.Watters12 Looking in the Cloud /opt/sbin/traceroute

13. Jan.2001C.Watters13 CA*net2 layer 2 links

14. Jan.2001C.Watters14 CA*net3 Physical Links

15. Jan.2001C.Watters15 1. Client-Server & Web Cloud model TCP/IP HTTP and MIME types FTP protocol stacks

16. Jan.2001C.Watters16 Servers and Clients Servers - computer systems at the end of a network that store files and provide other services Clients - computer systems that are end points for users of the data

17. Jan.2001C.Watters17 Network Architectures ISO’s OSI model 1970’s International Organization for Standards Open Systems Interconnection reference Model 7 layer architecture

18. Jan.2001C.Watters18 ISO - OSI Model Application layer presentation layer session layer transport layer network layer data link layer physical layer Ftp, telnet, etc data compression, format set up connections end-to-end trans of packets guide packets along links send packet between nodes deliver bits between nodes

19. Jan.2001C.Watters19 ISO OSI model

20. Jan.2001C.Watters20 INTERNET MODEL 4 layers Application layer –communication services (ftp, telnet, email) transport layer –transmission of messages end-to-end network layer –transmission of messages sequence of links link layer –transmission of packet across one link

21. Jan.2001C.Watters21 Internet layers

22. Jan.2001C.Watters22 Application Layer FTP HTTP SMTP telnet etc

23. Jan.2001C.Watters23 TCP/IP Suite of protocols made the standard for the Internet facilitates communication between heterogeneous and similar networks that are connected together reliable, connection oriented, byte stream protocol

24. Jan.2001C.Watters24 Transport layer: TCP and UDP TCP –transmission control protocol –full duplex byte stream –virtual path (connected) –error free –uses acknowledgements –16 bit address of ports UDP –user datagram protocol –connectionless –no acknowledgements –no flow control –no resending of erroroneous packets –some error detection –16 bit port addresses

25. Jan.2001C.Watters25 TCP/IP Transport Control Protocol Internet Protocol

26. Jan.2001C.Watters26 TCP and IP

27. Jan.2001C.Watters27 Network Layer: IP Delivers packets up to 64kbytes, 1 at a time Each packet has a header –sending host and intended host network addresses –32 bit addresses IP layer (like UDP) – unreliable –connectionless

28. Jan.2001C.Watters28 Link Layer: links Connect computer to Internet SLIP –serial line IP (asynchronous, 1 char at a time) –move IP packets to common link (phone line) PPP –point-to-point protocol –also synchronous transfer for packets

29. Jan.2001C.Watters29 Data encapsulation using TCP on Ethernet

30. Jan.2001C.Watters30 TCP/IP apps TCP/IP software usually includes: –remote terminal client using TELNET protocol for remote login –electronic mail client using SMTP protocol to transfer e-mail to remote system –file transfer client using FTP protocol to transfer files between 2 machines

31. Jan.2001C.Watters31 HTTP HyperText Transport Protocol Native protocol for WWW sits on top of internet’s TCP/IP protocol HTTP is a 4 step process per transaction uses a predefined set of document formats from MIME

32. Jan.2001C.Watters32 MIME MIME - multipurpose internet mail extensions –defines file formats (images, video, text, etc) –e.g. Content-type: text/html – Data type/subtype » text/html » text/plain » image/gif » video/mpeg » application/msword »etc!!!

33. Jan.2001C.Watters33 HTTP Connection 1. Client –makes an HTTP request for a web page –makes a TCP/IP connection 2. Server accepts request –sends page as HTTP 3. Client downloads page 4. Server breaks the connection

34. Jan.2001C.Watters34 HTTP is Stateless!!!! Each operation or transaction makes a new connection each operation is unaware of any other connection each click is a new connection So how do they do those shopping carts??

35. Jan.2001C.Watters35 What does it look like? Header + object file Header –plain text –info about the object (MIME etc) –methods allowed –etc –browser sends a header to server each time you ask for information –server sends a header and possibly content

36. Jan.2001C.Watters36 HTTP Transaction Example GET /catalog/ip/ip.htm HTTP 1.0 Accept: text/plain Accept: text/html Referer: http://www.june.com/catalog.html User-Agent: Mozilla/2.0

37. Jan.2001C.Watters37 HTTP REQUEST PROTOCOL Request = Simple | Full Simple = GET CRLF Full = Method URI ProtVersion CRLF [ *] [CRLF ] Method = GET | POST | HEAD | …. = : CRLF = MIME conforming message www.w3.org/Protocols/HTTP/

38. Jan.2001C.Watters38 HTTP Header fields General-header fields –used for both requests and responses Request-header fields –used for responses –extra client information for use by server –optional

39. Jan.2001C.Watters39 General-header fields Date: mon,11, Jan 1999 08:14:32 GMT MIME-version: 1.0 Pragma: no cache –directives

40. Jan.2001C.Watters40 Request-header fields acceptable MIME types for response –Accept:text/html – Accept:*.* 401 response from client –Authorization: Basic abcdef (uuencoded username and password) From:client-email-addr

41. Jan.2001C.Watters41 More Request-header fields If-Modified-Since:date –conditional get source of current requested Url –Referer:URL robot/browser identification –User-Agent:Mozilla/2.0

42. Jan.2001C.Watters42 Looking at the HTTP Header Values In Perl –$ENV{“From”} In Netscape –www.cs.dal.ca/~watters/cgi-bin/webcourse/env.html

43. Jan.2001C.Watters43 HTTP Methods Client requests either –simple request –full request Request-line= method Request-URI HTTP-version CRLF GET /catalog/ip.html HTTP/1.0

44. Jan.2001C.Watters44 Simple requests Only for HTTP 0.9 only uses Get method causes the server to locate and transfer the object specified client responsible for handling the object GET CRLF

45. Jan.2001C.Watters45 Full Request Uses HTTP version and more methods method tells server what to do to the resource requested Methods –GET –POST –HEAD

46. Jan.2001C.Watters46 GET Method Request server to retrieve object specified conditional GET –request message includes –If-Modified-Since in header

47. Jan.2001C.Watters47 HEAD Method Like GET but does not return the object returns a header about the resource requested (metainformation) good way to test link validity

48. Jan.2001C.Watters48 POST Method Include an object in the request server should use that object in processing the request must include a Content-Length in header

49. Jan.2001C.Watters49 HTTP Response Message HTTP protocol version 3 digit status code reason phrase CRLF optional header fields CRLF

50. Jan.2001C.Watters50 HTTP Response Header Fields Additional information about the server such as: –LOCATION: exact URI address –SERVER: server software (CERN/3.0) –WWW-AUTHENTICATE: status 401 responses (unauthorized request) server challenges client client may use to send authorization info to server

51. Jan.2001C.Watters51 Understanding STATUS Codes 1xx - not yet in use 2xx - action successful 3xx - further action needed 4xx - client request error 5xx - server error

52. Jan.2001C.Watters52 HTTP Transaction 1. Client and server establish a connection 2. Client makes a request 3. Server makes a response 4. Server terminates connection

53. Jan.2001C.Watters53 Step 1 establish connection –TCP/IP connection set up –uses a port number as application reference –usually port 80 –ports 1024 are open) Step 2 client request –Http message sent with a request line –request-line = method URL HTTP version

54. Jan.2001C.Watters54 Web Port Assignments 21FTP 23 Telnet 25 smtp (mail) 70 gopher 79 finger 80 HTTP

55. Jan.2001C.Watters55 Step 3 Server response –server sends Http message and optionally requested data –resp-message = HTTP version statuscode reason-phrase [optional stuff] Step 4 connection terminated –usually the server –sometimes the client “stops” it –anything else, whoever notices terminates