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Web Basics and Protocols CS 502 – 20020129 Carl Lagoze

Web Basics and Protocols CS 502 – 20020129 Carl Lagoze. Acks to McCracken Syracuse Univ . In the beginning…. In the beginning…. ARPANET. DoD funded through leadership of Licklider Inspired by move from batch to timesharing Allowed remote login. Packet Switching.

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Web Basics and Protocols CS 502 – 20020129 Carl Lagoze

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  1. Web Basics and ProtocolsCS 502 – 20020129Carl Lagoze Acks to McCrackenSyracuse Univ.

  2. In the beginning….

  3. In the beginning…

  4. ARPANET • DoD funded through leadership of Licklider • Inspired by move from batch to timesharing • Allowed remote login

  5. Packet Switching • Invented in early 1960’s by Baran, Davies, Kleinrock • digital, redundant, efficient, upgradeable (software) • 1969 ARPANET first network implementation

  6. Packet Switching • Network messages broken up into packets • Each pocket has a destination address • Pass and forward model – router gets packet, examine, decides where to send next • Message reassembled on other end

  7. Layered Protocol Model

  8. TCP/IP Protocol Suite • IP – packet delivery • TCP – virtual circuits, packet reassembly • ARP/RARP – address resolution

  9. Protocol Layers

  10. Internet Issues (Internet 2) • Demands of multimedia applications • Virtual circuit reservations – bandwidth and quality of service guarantees • Real time streaming protocols • State saving

  11. Internet Governance • Internet Society (ISOC) – Evolution, social & political issues • Internet Architecture Board (IAB) – Oversees standards process • Internet Engineering Task Force (IETF) – standards development • Internet Assigned Names Authority (IANA) – protocol # assignment • Internet Corporation for Assigned Names and Numbers (ICANN) – IP and DNS addresses • World Wide Web Consortium (W3C) – web standards and evolution

  12. Internet Documents • STD’s – Official IETF Internet standards • http://www.rfc-editor.org/rfcxx00.html • RFC’s – “Requests for Comments” to IETF community for information, standardization • http://www.ietf.org/rfc.html • Internet Drafts – IETF working documents • http://www.ietf.org/ID.html • W3C Reports (recommendations, drafts, notes) • http://www.w3.org/TR/

  13. Well-Known Protocols • Telnet – external terminal interface, RFC 854 (1983) • FTP – file transfer, RFC 959 (1985) • SMTP – mail transport, RFC 821 (1982) • HTTP – distributed, collaborative hypermedia systems, RFC 1945 (1.0 1996), RFC 2616 (1.1 1999)

  14. Daemons and Ports telnetd Socket (Virtual Circuit) 23 httpd 80 ftpd 21

  15. Basic Socket ServerProgramming

  16. HTTP • HTTP is… • Designed for document transfer • Generic • not tied to web browsers exclusively • can serve any data type • Stateless • no persistent client/server connection

  17. HTTP Session • An HTTP session consists of a client request followed by a server response • Requests and responses: • are sent in plain text • conform to the HTTP syntax • consist of start line, headers, blank line, and message body

  18. HTTP Request • Start line • Consists of method, URL, version GET index.html HTTP/1.1 • Valid methods include: • GET, POST, HEAD, PUT, DELETE • Headers • HTTP/1.1 requires a Host: header • Body content

  19. HTTP Request Methods • Methods include • GET: retrieve information identified by the URL • HEAD: same as get but don't get message body (content) • POST: accept the request content and send it to the URL • PUT: store the request content as the given URL

  20. HTTP Response • Start line • consists of HTTP version, status code, and description HTTP/1.1 200 OK HTTP/1.1 404 Not Found • Headers Content-type: text/html • Content

  21. HTTP Response Codes • Respose coded by first digit • 1xx: informational, request received • 2xx: success, request accepted • 3xx: redirection • 4xx: client error • 5xx: server error

  22. HTTP Content Body • Header fields can affect content interpretation • required header field: Content-type • others: Content-Encoding, Content-Length, Expires, Last-Modified • added by web server - we will configure some of these later

  23. Serving a Page • User of client machine types in a URL

  24. Serving a Page • Server name is translated to an IP address via DNS

  25. Serving a Page • Client connects to server using IP address and port number

  26. Serving a Page • Client determines path and file to request

  27. Serving a Page • Client sends HTTP request to server

  28. Serving a Page • Server determines which file to send

  29. Serving a Page • Server sends response code and the document

  30. Serving a Page • Connection is broken

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