FILE TRANSFER PROTOCOL (FTP)

FILE TRANSFER PROTOCOL (FTP)
Dr R Jegadeesan Prof-CSE
Jyothishmathi Institute of Technology and Science,
karimnagar

FILE TRANSFER PROTOCOL
Transferring files from one computer to another is one
of the most common tasks expected from a networking
or internetworking environment. In reality, the greatest
volume of data exchange in the Internet today is due to
file transfer.
File Transfer Protocol (FTP)
Topics discussed in this section:

◼ File Transfer Protocol (FTP) is the standard
mechanism provided by TCP/IP for copying a
file from one host to another
◼ Although transferring files from one system
to another seems simple and straightforward,
some problems must be dealed.

◼ Two systems may use different file name
conventions.
◼ Two systems may have different ways to represent
text and data.
◼ Two systems may have different directory
structures.
◼ All these problems have been solved by FTP in a
very simple and elegant approach.

◼ FTP differs from other client/server
applications in that it establishes two
connections between the hosts.
◼ One connection is used for data transfer and
the other connection for control information
(commands and responses)
◼ Separation of commands and data transfer
makes FTP more efficient.

◼ FTP uses the services of TCP. It needs two
TCP connections.
◼ The well-known port number 21 is used for
the control connection and the well-known
port number 20 for the data connection.

◼ Figure shows the basic model of FTP.
◼ The client has three components: user
interface, client control process, and the
client data transfer process.
◼ The server has two components: the server
control process and the server data transfer
process.
◼ The control connection is made between the
control processes.
◼ The data connection is made between the
data transfer processes.
26.8

◼ The control connection remains connected
during the entire interactive FTP session.
◼ The data connection is opened and then
closed for each file transferred.
◼ It opens each time commands that involve
transferring files are used, and it closes when
the file is transferred.

Communication over Control Connection
◼ It uses the 7-bit ASCII character set.
◼ Communication is achieved through commands and responses.
◼ This simple method is enough for the control connection
because we send one command (or response) at a time.
◼ Each command or response is only one short line.
◼ Each line is terminated with a two-character (carriage return
and line feed) end-of-line token.

Figure 26.22 Using the control connection

Communication over Data Connection
◼ We want to transfer files through the data
connection.
◼ File transfer occurs over the data connection
under the control of the commands sent over
the control connection.
◼ file transfer in FTP means one of three
things:

◼ A file is to be copied from the server to the
client. This is called retrieving file. It is done
under the supervision of the RETR command
◼ A file is to be copied from the client to the
server. This is called storing file. It is done
under the supervision of the STOR command.
◼ A list of directory or file names is to be sent
from the server to the client. This is done
under the supervision of the LIST command.

Figure 26.23 Using the data connection

◼ In FTP the following three attributes of
communication must be defined by client
➢ the type of file to be transferred
➢ the structure of the data
➢ the transmission mode

File type
◼ Three types of files can be transferred over
the data connection in FTP. They are
➢ ASCII file(American Standard Code for
Information Interexchange)
➢ EBCDIC file (Extended Binary Coded
Decimal Interchange Code)
➢ Binary/image file.

ASCII
◼ The ASCII file is the default format for
transferring text files.
◼ Each character is encoded using 7-bit ASCII.
◼ The sender transforms the file from its own
representation into ASCII characters, and the
receiver transforms the ASCII characters to
its own representation.

EBCDIC
◼ The sender transforms the file from its own
representation into EBCDIC characters, and
the receiver transforms the EBCDIC
characters to its own representation.
Image file
◼ The image file is the default format that is
transferred in binary files.
◼ The file is sent as continuous streams of bits
without any interpretation or encoding

Data Structure
◼ FTP can transfer a file across the data
connection by using one of the following
➢ file structure
➢ record structure
➢ page structure.

◼ In the file structure format, the file is a
continuous stream of bytes.
◼ In the record structure, the file is divided into
records. This can be used only with text files.
◼ In the page structure, the file is divided into
pages, with each page having a page number
and a page header. The pages can be stored
and accessed randomly or sequentially.

Transmission Mode
◼ FTP can transfer a file across the data
connection by using one of the following
three transmission modes:
➢ Block mode
➢ Stream mode
➢ Compressed mode.

Block mode
◼ The incoming data is broken down into
several blocks which are then forwarded over
the TCP connection.
Stream mode
◼ If the data are simply a stream of bytes (file
structure), no end-of-file is needed.
◼ End-of-file in this case is the closing of the
data connection by the sender

Compressed mode
◼ The compression method normally used is
run-length encoding.
◼ In this method, consecutive appearances of a
data unit are replaced by one occurrence and
the number of repetitions.

ASCII (American Standard Code
for Information Interchange)
ASCII is a code for representing
English characters as numbers, with each letter
assigned a number. For example, the ASCII code
for uppercase A is 65 .
Most computers use ASCII codes
to represent text, which makes it possible to
transfer data from one computer to another.

FILE TRANSFER PROTOCOL (FTP)

More Related Content

What's hot (20)

Similar to FILE TRANSFER PROTOCOL (FTP) (20)

More from Jyothishmathi Institute of Technology and Science Karimnagar (20)

Recently uploaded (20)

FILE TRANSFER PROTOCOL (FTP)