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

CSS432: Applications 1

CSS432 ApplicationsTextbook Ch 9.1

Professor: Munehiro Fukuda

Augmented by Rob Nash

Protocols and Companions

HTTP defines a GET/PUT protocolFor file distribution

HTML defines the data formatA companion descriptor or protocol

SMTP – defines a mail moving protocolRFC 822 – companion format description ASCIIMIME – companion to extend ASCII



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

Applications Protocol

RFC Port

Name service DNS 1035 53

Email SMTP

IMAP

821 25

143

Web HTTP 2616 80

File transfer FTP 959 21

Remote terminal access

telnet 854 23

TCP withbuffers,variables

socket

TCP withbuffers,variables

socket

Internet

mail/webserver

SMTP, HTTP, FTP

outlookbrowser

SMTP, HTTP, FTP

Client Server


Name Service

Hostscheltenham.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 [email protected]

(UID + host IP)

Name ServerName• Variable length and mnemonic• Location independent

Value• System-provided fixed value• Location dependent

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

Nameserver

lprprogram

User

TCP

IP

2uw1-320-p1

216.186.75.218

3

lpr –Puw1-320-p1 manual.ps1

216.186.75.218 4

216.186.75.218 5

DNS


Domain Naming System Hierarchy

Nameuw1-320-00.bothell.washington.edu

edu com

washington … mit

ucs

uw1-320-00 medusa

bothell

cisco … yahoo nasa … nsf arpa … navy acm … ieee

gov mil org net uk fr

homer goodall

DNS


Name Servers Partition hierarchy into zones

Rootname server

washingtonname server

Cisconame server

bothellname server

csname server

…

…

Each zone implemented by two or more name servers

edu com

washington … mit

ucs

uw1-320-00 medusa

bothell

cisco … yahoo nasa … nsf arpa … navy acm … ieee

gov mil org net uk fr

homer goodall

Network Information Center manages

Managed by UW C&C

administrativeunit

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 returns the domain name of this host’s mail

Class: IN (Internet class) TTL: how long the resource record is valid

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

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.

Rootnameserver

Princetonnameserver

CSnameserver

Localnameserver

Client

1cicada.cs.princeton.edu

192.12.69.608

cicada.cs.princeton.edu

princeton.edu, 128.196.128.233


cicada.cs.princeton.edu,

192.12.69.60


cs.princeton.edu, 192.12.69.5

2

3

4

5

6

7

DNS


Electronic Mail (SMTP, MIME, IMAP)Email

mail server

outgoingmail queue

User mailbox

useragent

useragent

mail server

outgoingmail queue

mail server

outgoingmail queue

User mailbox

useragent

useragent

useragent

useragent

SMTP/TCP 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

SMTP IMAP


SMTPEmail

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


Email

SMTP Example[mfukuda@uw1-320-20]$ telnet smtp.washington.edu 25Trying 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, 21Feb 2004 20:00:56 -0800HELO mfukuda250 smtp.washington.edu Hello UW1-320-20.bothell.washington.edu [216.186.75.195], pleased to meet youMAIL FROM:[email protected] 2.1.0 <[email protected]>... Sender okRCPT TO:[email protected] 2.1.5 [email protected]... Recipient okDATA354 Enter mail, end with “.” on a line by iteselfBlah blah blah……etc. etc. etc..250 2.0.0 i1M40uc3013699 Message accepted fro deliveryQUIT221 2.0.0 smtp.washington.edu closing connectionConnection closed by foreign host.[mfukuda@uw1-320-20]$ _


RFC 822 Message Format

Header A series of line<crlf>s

Body ASCII characters only.

Then, what about multimedia information?

Email

HeaderTo:Subject:Date:From:Received:

Body

A blank line


MIME MIME: multimedia mail extension, RFC 2045, 2056 Additional lines in msg header declare MIME content type

Email

MIME-Version: 1.0Content-Type: multipart/mixed; boundary=“-------417CA6E2DE4ABCAFBC5”From: [email protected]: [email protected]: promised materialDate: Mon, 01 Apr 2004 12:34:56 -0800

-------417CA6E2DE4ABCAFBC5Content-Type: text/plain; charset=us-asciiContent-Transfer-Encoding: 7bit

Dear CSS432 students,Here is the jpeg image and draft report I promised.-- Fukuda

-------417CA6E2DE4ABCAFBC5Content-Type: image/jpegContent-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,+,/)


Mail Reader - IMAPEmail

Connection established

Server greeting

Not authenticated

Authenticated

Selected

Logout

Both sides close the connection

TCP to 143

Server: OK Server: PREAUTH Server: BYE

Client: LOGIN or AUTHENTICATEClient LOGOUT

Client LOGOUT

Client LOGOUT

Client SELECT or EXAMINE

Client: CLOSE

Client: FETCH, STORE, DELETE, EXPUNGE


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

localfile

system

remotefile

system

FTPserver

FTPclient

FTPuser

interface TCP port 20 for data transfer(not persistent)

TCP port 21 for control (persistent)


FTP Commands <CRLF> 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


FTP ExampleFTP

[mfukuda@uw1-320-20]$ telnet ftp.tripod.com 21Trying 209.202.240.80…Connected to ftp.tripod.com (209.202.240.80).Escape character is ‘^]’.220 Welcome to Tripod FTP.USER css432331 Username set to css432. Now enter your password.PASS ********230 User ‘css432’ logged on.LIST425 Can’t open data connection for LIST.PASV227 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.LIST150 Opening ASCII mode data connection for LIST.226 Transfer complete.QUIT221 GoodbyeConnection closed by foreign host.[mfukuda@uw1-320-20]$ _


FTP passive mode

FTPserver

FTPclient


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)

FTPserver

FTPclient


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


FTP proxy command

FTPServer

2

FTPServer

1

FTPclient

(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 server1ftp> proxy open server2ftp> proxy get file

…(1)…(2)…(3)~(5)


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

HTTPserver

NetscapeTCP port 80 (one-time connection)

IE

TCP port 80 (one-tim

e connection)HTTP requestHTTP response


HTTP CommandsWeb

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


HTTP Example

[mfukuda@uw1-320-20]$ telnet www.uwb.edu 80Trying 216.186.72.12…Connected to jupiter.uwb.edu (216.186.72.12).Escape character is ‘^]’.GETHTTP/1.1 200 OKDate: Sun, 22 Feb 2004 09:06:17 GMTServer: Apache/1.3.28 (Unix) PHP/4.3.3 mod_perl/1.29 mod_backhand/1.2.2Connection: closeContent-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]$ _

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

Web


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)

Documents

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