Department of Computer Science Southern Illinois University Edwardsville Spring, 2008 Dr. Hiroshi Fujinoki FTP Protocol Programming (Part I) Application_Level_Protocol (1)/000 CS 447 Network and Data Communication, Project Phase 2

App_Protocol_1/ What is “application level protocols”? Why we need them? Presentation Agenda 2. Major application level protocols: HTTP,FTP,POP, Telnet SMTP, 3. Protocol details for HTTP, FTP, POP, SMTP CS 447 Network and Data Communication, Project Phase 2

What are the application level protocols? Protocols that are implemented in the top three layers in the OSI model App_Protocol_1/002 CS 447 Network and Data Communication, Project Phase 2

Application Layer NFS (Network File Server) Presentation Layer Session Layer XDR (External Data Rep.) RPC (Remote Proc. Call) Transport Layer Physical Layer Datalink Layer Network Layer Network Hardware TCP UDP IP ARP RARP Telnet, FTP, SMTP, rlogin, DNS, HTTP, rcp, finger, etc. Application- layer protocol Transport- layer protocol Network- layer protocol App_Protocol_1/003 CS 447 Network and Data Communication, Project Phase 2

FTP Fundamental operations in FTP:Get and Send files from/to a remote host FTP Server (FTP Daemon) FTP Client FTP GET FTP SEND FTP Server (FTP Daemon) FTP Client GET Command SEND Command Download File Local Disk Remote Disk Upload File App_Protocol_1/004 CS 447 Network and Data Communication, Project Phase 2

FTP Server (FTP Daemon) FTP Client FTP Architecture PI = Protocol Interpreter DTP = Data Transfer Process Client PI GUI Client DTP FTP Client Disk Server PI Server DTP Disk FTP Server Port #21 Commands Files Port #20 App_Protocol_1/005 CS 447 Network and Data Communication, Project Phase 2

FTP Commands Commands Semantics USER Transmit a login name of a user to the FTP server Transmit the password of a user to the FTP server PASS RETR Download a file from the FTP server STOR Upload a file to the FTP server TYPE Set ASCII/Binary transmission mode SYST Display FTP server information LISTList (display) the directory contents PWD List the current directory path DELE Delete a remote file QUITClose the current FTP session (Most essential FTP commands) App_Protocol_1/006 CS 447 Network and Data Communication, Project Phase 2

FTP Return Codes Code # Meaning 200Previous command successfully completed 220FTP server ready 230 User login in progress (not login completed) 331 User login name identified but password required 500FTP command syntax error 550 Requested file/directory doe not exist 503 Login not successful (session not established) (Major return codes) 221Current FTP session is now closed 226 File Transfer Completed 150 Transmission change acknowledgement App_Protocol_1/007 CS 447 Network and Data Communication, Project Phase 2

FTP Procedures  USER ABC  PASS *** 230 Login in progress  CLIENT SERVER Time  Connection to port # (Server Ready)  331 (Password Required)  215 Login completed  Phase 1: FTP login App_Protocol_1/008 Welcome Message CS 447 Network and Data Communication, Project Phase 2

FTP Procedures CLIENT SERVER Time  RETR command 226 (Transmission Complete)  Phase 2-(1): FTP file transfers (GET) FTP file transfer (port #20)  App_Protocol_1/009 CS 447 Network and Data Communication, Project Phase 2

FTP Procedures CLIENT SERVER Time  RETR command 550 (No such file or directory)  Phase 2-(1): FTP file transfers (GET) If the requested file does not exist in the remote FTP server App_Protocol_1/010 CS 447 Network and Data Communication, Project Phase 2

FTP Procedures CLIENT SERVER Time  STOR command 226 (Transmission Complete)  Phase 2-(2): FTP file transfers (SEND)  FTP file transfer (port #20) App_Protocol_1/011 CS 447 Network and Data Communication, Project Phase 2

FTP Procedures CLIENT SERVER Time (11) QUIT Command 221 (FTP Session Closed) (12) Phase 3: Closing Session If you need more details about FTP protocols, what can you do? App_Protocol_1/012 CS 447 Network and Data Communication, Project Phase 2

App_Protocol_1/ RFC for FTP 2. Other FTP related RFCs RFC 959: The core RFC for FTP RFC 607: Passive and active FTP transmission modes RFC 614: Auxiliary information for RFC 607 RFC 624: Auxiliary information for RFC 607 Documentations for FTP CS 447 Network and Data Communication, Project Phase 2