FILE TRANSFER.
Transferring files from one system to another system is one of the biggest tasks in the networking environment.the large volume of data transfer in the internet today is due to the file transfer and the protocol that is responsible for this task of file transferring is File Transfer Protocol.
File transfer protocol is the standard mechanism provided by TCP\IP for copying and transferring the file from one host to another which seems to be simple and straightforward. FTP differs from other client server applications since it establishes 2 connections between hosts.
That is one connection for data transfer and other for control information.This separation of data and commands makes ftp more efficient.Control connection uses very simple rules for communications where only one command or data is transferred at a time.in data connection since it need to transfer different data types uses a bit complex procedure.
FTP uses two well known TCP ports:
PORT 21 is used for the control connection.
PORT 20 is used for data connection.
COMMUNICATION OVER CONTROL CONNECTION.
FTP uses same approach as SMPT to communicate by using 7 bit ASCII character which is very simple .Each command or response is only one short line and hence need not worry about the file format and file structure.
COMMUNICATION OVER DATA CONNECTION.
File transfer occurs over data connection under control of some set of commands which is sent over control connection.
File transfer in FTP means one of the three things i.e.
Retrieving the file -command used is RETR .
Storing a file-command used is STOR.
Listing of files or directories-command used is LIST .
The client has to define type of file ,data structure and transmission mode.
- File type includes ASCII FILE,EBCDIC file,IMAGE file.
- Data structure includes file structure,record structure and page structure.
- Transmission mode includes stream mode,block mode and compressed mode.
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