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

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 2

3. 3 Applications 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 ApplicationsProtoc ol RFCPort Name serviceDNS103553 EmailSMTP IMAP 82125 143 WebHTTP261680 File transferFTP95921 Remote terminal access telnet85423 TCP with buffers, variables socket TCP with buffers, variables socket Internet mail/web server SMTP, HTTP, FTP outlook browser SMTP, HTTP, FTP ClientServer

4. CSS432: Applications 4 Name Service 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.edullp@cs.princeton.edu (UID + host IP) Name Server Name Variable length and mnemonic Location independent Value System-provided fixed value Location dependent DNS

5. CSS432: Applications 5 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 Name server lpr program User TCP IP 2 uw1-320-p1 216.186.75.218 3 lpr –Puw1-320-p1 manual.ps 1 216.186.75.218 4 5 DNS

6. CSS432: Applications 6 Domain Naming System Hierarchy Name uw1-320-00.bothell.washington.edu educom washington … mit ucs uw1-320-00 medusa bothell cisco … yahoonasa … nsfarpa … navyacm … ieee govmilorgnetukfr homergoodall DNS

7. CSS432: Applications 7 Name Servers Partition hierarchy into zones Root name server washington name server Cisco name server bothell name server cs name server … … Each zone implemented by two or more name servers educom washington … mit ucs uw1-320-00 medusa bothell cisco … yahoonasa … nsfarpa … navyacm … ieee govmilorgnetukfr homergoodall Network Information Center manages Managed by UW C&C administrative unit DNS

8. CSS432: Applications 8 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 returns the domain name of this host’s mail Class: IN (Internet class) TTL: how long the resource record is valid DNS

9. CSS432: Applications 9 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 DNS

10. CSS432: Applications 10 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. Root name server Princeton name server CS name server Local name server Client 1 cicada.cs.princeton.edu 192.12.69.60 8 cicada.cs.princeton.edu princeton.edu, 128.196.128.233 cicada.cs.princeton.edu cicada.cs.princeton.edu, 192.12.69.60 cicada.cs.princeton.edu cs.princeton.edu, 192.12.69.5 2 3 4 5 6 7 DNS

11. CSS432: Applications 11 Electronic Mail (SMTP, MIME, IMAP) Email mail server outgoing mail queue User mailbox user agent user agent mail server outgoing mail queue mail server outgoing mail queue User mailbox user agent user agent user agent user agent SMTP/TCP 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 SMTPIMAP

12. CSS432: Applications 12 SMTP Email 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

13. 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.edumfukuda@u.washington.edu 250 2.1.0... Sender okmfukuda@u.washington.edu RCPT TO:MunehiroFukuda@yahoo.netMunehiroFukuda@yahoo.net 250 2.1.5 MunehiroFukuda@yahoo.net... Recipient okMunehiroFukuda@yahoo.net 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]$ _

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

15. CSS432: Applications 15 MIME MIME: multimedia mail extension, RFC 2045, 2056 Additional lines in msg header declare MIME content type Email 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 Type of the data How the data is encoded Definitions for content types Carry more than one data type 3bytes = 3 * 8bits = 24bits = 4 * 6bit-chars, each mapped onto one of 64 ASCII chars (A~Z,a~z,0~9,+,/)

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

17. CSS432: Applications 17 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. FTP local file system remote file system FTP server FTP client FTP user interface TCP port 20 for data transfer (not persistent) TCP port 21 for control (persistent)

18. CSS432: Applications 18 FTP Commands delimits each command (and reply). Commands consist of four uppercase ASCII characters, some with optional arguments:  USER username : sends a 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 its current 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 FTP

19. CSS432: Applications 19 FTP Example FTP [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]$ _

20. CSS432: Applications 20 FTP passive mode FTP server FTP client 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 server FTP client 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

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

22. CSS432: Applications 22 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 Web /public_html HTTP server Netscape TCP port 80 (one-time connection) IE TCP port 80 (one-time connection) HTTP request HTTP response

23. CSS432: Applications 23 HTTP Commands Web 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

24. CSS432: Applications 24 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 … Connection closed by foreign host. [mfukuda@uw1-320-20]$ _ Web

25. CSS432: Applications 25 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 Web

26. 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)