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CSS432 Applications Textbook Ch 9.1

CSS432 Applications Textbook Ch 9.1. Professor: Munehiro Fukuda Augmented by Rob Nash. Protocols and Companions. HTTP defines a GET/PUT protocol For file distribution HTML defines the data format A companion descriptor or protocol SMTP – defines a mail moving protocol

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CSS432 Applications Textbook Ch 9.1

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  1. CSS432 ApplicationsTextbook Ch 9.1 Professor: Munehiro Fukuda Augmented by Rob Nash CSS432: Applications

  2. Protocols and Companions • HTTP defines a GET/PUT protocol • For file distribution • HTML defines the data format • A companion descriptor or protocol • SMTP – defines a mail moving protocol • RFC 822 – companion format description ASCII • MIME – companion to extend ASCII CSS432: Applications

  3. mail/web server outlook browser TCP with buffers, variables TCP with buffers, variables Applications Client Server • Client – Server Paradigm • Client: initiates contact with server • Server: provides client with a response • Applications use their corresponding protocol • Defined in RFC by Internet Engineering Task Force (http://www.ietf.org/) • Implemented on top of TCP or UDP SMTP, HTTP, FTP SMTP, HTTP, FTP socket socket Internet CSS432: Applications

  4. Name Server DNS Name Service • Value • System-provided fixed value • Location dependent • Name • Variable length and mnemonic • Location independent • Hosts cheltenham.cs.princeton.edu 192.12.69.17 192.12.69.17 80:23:A8:33:5B:9F • Files /usr/llp/tmp/foo (server, inode) • Users Larry Peterson llp@cs.princeton.edu (UID + host IP) CSS432: Applications

  5. User 1 2 lpr –Puw1-320-p1 manual.ps uw1-320-p1 Name lpr server program 4 216.186.75.218 216.186.75.218 3 TCP 216.186.75.218 5 IP DNS Name service (cont) • lpr/a2ps commands • Unix system call • struct hostent h = gethostbyname( const char *hostname ); • *(struct in_addr *)*h->h_addr_list; // returns IP list CSS432: Applications

  6. edu com gov mil org net uk fr … … … … … washington mit cisco yahoo nasa nsf arpa navy acm ieee bothell cs u homer goodall uw1-320-00 medusa DNS Domain Naming System • Hierarchy • Name uw1-320-00.bothell.washington.edu CSS432: Applications

  7. administrative unit edu com gov mil org net uk fr … … … … … washington mit cisco yahoo nasa nsf arpa navy acm ieee bothell cs u Root name server homer goodall uw1-320-00 medusa … washington Cisco name server name server … bothell cs name server name server DNS Name Servers Network Information Center manages • Partition hierarchy into zones Managed by UW C&C • Each zone implemented by two or more name servers CSS432: Applications

  8. DNS Resource Records • Each name server maintains a collection of resource records (Name, Value, Type, Class, TTL) • Name/Value: not necessarily host names to IP addresses • Type • A: Value returns IP address • NS: Value returns the corresponding name server’s name • CNAME: Value returns aliases. • MX: Value returnsthe domain name of this host’s mail • Class: IN (Internet class) • TTL: how long the resource record is valid CSS432: Applications

  9. DNS Name Servers From Root to Bottom Level • Find a root name server • dig edu ns • edu a3.nstld.com NS IN • a3.nstld.com 192.5.6.32 A IN • Find uwb.edu’s name servers • dig @192.5.6.32 uwb.edu ns • uwb.edu, DNS1.uwb.edu NS IN • uwb.edu, DNS2.uwb.edu NS IN • DNS1.uwb.edu 216.186.73.6 A • DNS2.uwb.edu 216.186.73.7 A • Find mercury.uwb.edu • dig @216.186.73.6 mercury.uwb.edu A • mercury.uwb.edu 216.186.72.15 A CSS432: Applications

  10. Root 2 name server cicada.cs.princeton.edu 3 princeton.edu, 128.196.128.233 4 1 Local Princeton cicada.cs.princeton.edu cicada.cs.princeton.edu name name Client server server cs.princeton.edu, 192.12.69.5 192.12.69.60 8 5 cicada.cs.princeton.edu 192.12.69.60 cicada.cs.princeton.edu, 6 CS name server 7 DNS Name Resolution • Client • Initialized with its local name server’s address • appends its domain name to a given name before a submission. • Local server • needs to know root at only one place (not each host). • caches recent responses from remote servers. CSS432: Applications

  11. mail server mail server mail server outgoing mail queue outgoing mail queue outgoing mail queue user agent user agent user agent user agent user agent user agent User mailbox User mailbox SMTP/TCP SMTP/TCP Email Electronic Mail (SMTP, MIME, IMAP) • user agents (client) • a.k.a. “mail reader” • composing, editing, reading mail messages • e.g., Eudora, Outlook, elm, Netscape Messenger, Thunderbird • mail servers (server) • outgoing, incoming messages stored on server SMTP IMAP CSS432: Applications

  12. Email SMTP • TCP port 25 – Persistent connection • Email sending protocol • From User agent to his/her local mail server • From a local to an intermediate/destination mail server (direct transfer) • From an intermediate to a destination server (relay) • Three phases of transfer • Handshaking: HELO • Transfer of messages: MAIL FROM, RCPT TO, and DATA • Closure: QUIT • Command/response interaction • Commands: ASCII text • Response: status code and phrase CSS432: Applications

  13. Email SMTP Example [mfukuda@uw1-320-20]$ telnet smtp.washington.edu 25 Trying 140.142.33.9… Connected to smpt.washington.edu (140.142.33.9). Escape character is ‘^]’. 220 smtp.washington.edu ESMTP Sendmail 8.12.11+UW04.02/8.12.11+UW04.02; Sat, 21 Feb 2004 20:00:56 -0800 HELO mfukuda 250 smtp.washington.edu Hello UW1-320-20.bothell.washington.edu [216.186.75.195] , pleased to meet you MAIL FROM:mfukuda@u.washington.edu 250 2.1.0 <mfukuda@u.washington.edu>... Sender ok RCPT TO:MunehiroFukuda@yahoo.net 250 2.1.5 MunehiroFukuda@yahoo.net... Recipient ok DATA 354 Enter mail, end with “.” on a line by iteself Blah blah blah… …etc. etc. etc. . 250 2.0.0 i1M40uc3013699 Message accepted fro delivery QUIT 221 2.0.0 smtp.washington.edu closing connection Connection closed by foreign host. [mfukuda@uw1-320-20]$ _ CSS432: Applications

  14. Header To: Subject: Date: From: Received: A blank line Body Email RFC 822 Message Format • Header • A series of line<crlf>s • Body • ASCII characters only. • Then, what about multimedia information? CSS432: Applications

  15. Email MIME MIME-Version: 1.0 Content-Type: multipart/mixed; boundary=“-------417CA6E2DE4ABCAFBC5” From: mfukuda@u.washington.edu To: css432a_au04@u.washington.edu Subject: promised material Date: Mon, 01 Apr 2004 12:34:56 -0800 -------417CA6E2DE4ABCAFBC5 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Dear CSS432 students, Here is the jpeg image and draft report I promised. -- Fukuda -------417CA6E2DE4ABCAFBC5 Content-Type: image/jpeg Content-Transfer-Encoding: base64 … Unreadable encoding of a jpeg figure -------417CA6E2DE4ABCAFBC5 Content-Type: application/postscript; name=“draft.ps” Content-Transfer-Encoding: 7bit … Readable encoding of a postscript document • MIME: multimedia mail extension, RFC 2045, 2056 • Additional lines in msg header declare MIME content type Carry more than one data type Type of the data How the data is encoded Definitions for content types 3bytes = 3 * 8bits = 24bits = 4 * 6bit-chars, each mapped onto one of 64 ASCII chars (A~Z,a~z,0~9,+,/) CSS432: Applications

  16. Email Mail Reader - IMAP TCP to 143 Connection established Server greeting Server: OK Server: PREAUTH Server: BYE Not authenticated Client LOGOUT Client: LOGIN or AUTHENTICATE Authenticated Client: CLOSE Client LOGOUT Client SELECT or EXAMINE Selected Client: FETCH, STORE, DELETE, EXPUNGE Client LOGOUT Logout Both sides close the connection CSS432: Applications

  17. FTP user interface FTP client FTP server TCP port 21 for control (persistent) TCP port 20 for data transfer (not persistent) local file system remote file system FTP File Transfer Protocol • Transfer file to/from remote host • Client/server model • Client:initiates a control TCP connection to a server on port 21. • Client:sends a user ID and password as part of FTP commands. • Server:authorizes the client • Client:opens a data TCP connection to a server on port 20. • Server:maintains state: current directory, earlier authentication. • A ftp client is allowed to initiate a transfer between two ftp servers. CSS432: Applications

  18. FTP FTP Commands • <CRLF>delimits each command (and reply). • Commands consist of four uppercase ASCII characters, some with optional arguments: • USER username : sendsa user identification to server. • PASS password : sends the user password to the server. • PASV: requests the server to send back its IP and port on which it listens to a data TCP connection from the user. • LIST :ask the server to send back itscurrent directory contents through the data connection. • RETR filename : gets a file from the current remote directory. • STOR filename : stores a file into the current remote directory. • Each command is followed by a reply: • 331 Username OK, password required • 125 Data connection already open; transfer starting • 425 Can't open data connection • 452 Error writing file CSS432: Applications

  19. FTP FTP Example [mfukuda@uw1-320-20]$ telnet ftp.tripod.com 21 Trying 209.202.240.80… Connected to ftp.tripod.com (209.202.240.80). Escape character is ‘^]’. 220 Welcome to Tripod FTP. USER css432 331 Username set to css432. Now enter your password. PASS ******** 230 User ‘css432’ logged on. LIST 425 Can’t open data connection for LIST. PASV 227 Entering Passiv Mode (209,202,240,80,195,210) // Open another xterm and telnet 209.202.240.80 50130 (=195*256+210) // Trying 209.202.240.80… // Connected to ftp.tripod.com (209.202.240.80). // Escape character is ‘^]’. // drwxr-xr-x 1 css432 Tripod 0 Sep 15 21:22 cgi-bin // -rw-r--r-- 1 css432 Tripod 26169 Sep 16 18:28 ttcp.c // -rw-r--r-- 1 css432 Tripod 8236 Sep 15 21:22 index.htm // drwxr-xr-x 1 css432 Tripod 0 Sep 16 18:33 project // Connection closed by foreign host. LIST 150 Opening ASCII mode data connection for LIST. 226 Transfer complete. QUIT 221 Goodbye Connection closed by foreign host. [mfukuda@uw1-320-20]$ _ CSS432: Applications

  20. FTP passive mode FTP client FTP server TCP port 21 for control (persistent) Client request: connect( ), USER, PASS, LIST Server Reply: 220 server ready, 331 send password, 230 login ok, 425 connection timeout TCP port 20 for data transfer (one time) FTP client FTP server TCP port 21 for control (persistent) Client request: connect( ), USER, PASS, PASV, LIST Server Reply: 220 server ready, 331 send password, 230 login ok, 227 Entering Passive Mode (140,142,12,173,195,54), 226 complete TCP port 195*256 + 54 = 49974 for data transfer (one time) data CSS432: Applications

  21. FTP proxy command (3’) 227 Entering Passive Mode (140,142,12,173,195,54) FTP client (1) USER, PASS, SYST (2) USER, PASS, SYST (3) TYPE I, PASV (4) TYPE I, PORT (140,142,12,173,195,54), STOR file (5) RETR file ftp> open server1 ftp> proxy open server2 ftp> proxy get file …(1) …(2) …(3)~(5) FTP Server 1 FTP Server 2 TCP port 195*256 + 54 = 49974 for data transfer (one time) data CSS432: Applications

  22. Netscape HTTP server TCP port 80 (one-time connection) HTTP request HTTP response TCP port 80 (one-time connection) /public_html IE Web World Wide Web - HTTP • Hypertext Transfer Protocol: one-time TCP port 80 connection for each response/reply • client: Browser requests, receives, and displays Web objects • server: Web server sends objects in response to the request CSS432: Applications

  23. Web HTTP Commands • Client • Initiates a TCP connection to a server on port 80. • Sends an HTTP request over this TCP connection • OPTIONS: request information about available options • GET: retrieve document identified in URL • HEAD: retrieve document metainformation in URL • POST: give inofrmation (annotation, servlet invocation) to server • PUT: store document under specified URL • DELETE, TRACE, CONNECT • Receives an HTTP response • Server • Accepts a TCP connection from a client on port 80. • Receives an HTTP request • Returns an HTTP response and disconnects the connection. • 1xx: Informational • 2xx: success • 3xx: Redirection • 4xx: Client error • 5xx: Server error CSS432: Applications

  24. Web HTTP Example [mfukuda@uw1-320-20]$ telnet www.uwb.edu 80 Trying 216.186.72.12… Connected to jupiter.uwb.edu (216.186.72.12). Escape character is ‘^]’. GET HTTP/1.1 200 OK Date: Sun, 22 Feb 2004 09:06:17 GMT Server: Apache/1.3.28 (Unix) PHP/4.3.3 mod_perl/1.29 mod_backhand/1.2.2 Connection: close Content-type: text/html <!doctype html public “-//W3C/DTD HTML 4.0 Transitional//EN”> <html><head> … </body></html> Connection closed by foreign host. [mfukuda@uw1-320-20]$ _ CSS432: Applications

  25. Web Performance Improvement in Web • Persistent TCP connections • Advantages • Eliminate the connection setup overhead • Eliminate repetitions of slow start phase • Disadvantages • Need to know the time period of connection – server times out the connection. • Caching • Recently access pages can be cached at browsers and ISPs • Advantages • Reduce the number of HTTP accesses • Disadvantages • Need to purge out-of-date version of pages – use expiration date and cache directives to cache or not to cache a given page CSS432: Applications

  26. Reviews • RFC • Naming service: DNS • Email: SMTP, MIME, and IMAP • File transfer: FTP • WWW: HTTP • Exercises: try the following examples by yourself. • Slide p8 (DNS) • Slide p12 (SMTP) • Slide p18 (FTP) • Slide p21 (HTTP) CSS432: Applications

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