27-Oct-03 Application Layer

File Transfer Protocol (FTP)

The standard mechanism provided by the Internet for copying a file from one host to another.

The needs: - Different file name conventions Different representation of text and

data Different directory structures

27-Oct-03 Application Layer

FTP (Continued…)

Differs from other client-server applications in that it establishes two connections between the client and the server. They are: - Data connection

Used for data transfer Consists of complex rules due to the variety

of data being transferred Control connection

Used for information control (commands and responses)

Uses very simple rules of one line command or response at a time

27-Oct-03 Application Layer

FTP Model

FTP client has three components User interface Client control process Client data transfer process

FTP server has two components Server control process Server data transfer process

Figure 26.12 FTP

27-Oct-03 Application Layer

FTP Connections

Control connection Maintained during the entire FTP

session Uses port 21 Involves interactive connection

between user and server Data connection

Maintained only during a file transfer Uses port 20

27-Oct-03 Application Layer

FTP Communications

Communication over control connection Uses ASCII character set, similar to

SMTP

Communication over data connection File type Data structure Transmission mode

Figure 26.13 Using the control connection

Figure 26.14 Using the data connection

27-Oct-03 Application Layer

File Transfer

File transfer in FTP can mean one of the following three: - Storing a file Retrieving a file Retrieving a list

Most operating systems provide user interface to access the services of FTP where the chosen activity is automatically converted by the interface to the corresponding FTP commands.

Figure 26.15 File transfer

Figure 26.16 Example 1

List of FTP commands in DOSList of FTP commands in DOS

List of FTP commands in UNIXList of FTP commands in UNIX

Commands

!, $, account, append, ascii, bell, binary, bye, case, cd, cdup, close, cr, delete, debug, dir, discount, form, get, glob, hash, help, lcd, ls, macdef, mdelete, mdir, mget, mkdir, mls, mode, mput, nmap, ntrans, open, prompt, proxy, sendport, put, pwd, quit, quote, recv, remotehelp, rename, reset, rmdir, runique, send, status, struct, sunique, tenex, trace, type, user, verbose,?

27-Oct-03 Application Layer

FTP Connection Example

27-Oct-03 Application Layer

GUI FTP Example