FILE TRANSFER WITH FILE TRANSFER PROTOCOL ( FTP ) PART-1 - Cyber security & Technology

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Monday, June 4, 2018

FILE TRANSFER WITH FILE TRANSFER PROTOCOL ( FTP ) PART-1


FILE TRANSFER

·      Transferring files from one computer to another is one of the most common tasks in a networking and internetworking environment.

·      File transfer is accomplishFTed using a protocol known as FTP.

File Transfer Protocol (FTP)

·      FTP is a part of TCP/IP protocol suite.

·      It is a protocol that enables files to be transferred between the computers.

·      FTP does not actually transfer a file from one computer to another rather it copies it. Hense , the original files exists and a copy of it is transferred.

·      FTP works on the client/server principle. A client program enables the user to interact with a server in order to access information and services on the server computer.

Features of FTP

1.   Data representation

·      FTP handles three types of data representations- ASCII(7bit), EBCDIC(8 bit) and 8 binary data.

·      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 transform the ASCII character to its own representation.

·      The image file is the default format for transferring binary files.

·      The file is sent as continous streams of bits without any interpretation or encoding.

2.   File organization and data structures

·      FTP supports both unstructured and structured file.

·      An unstructured file contains string of bytes and is end – marked by EOF (end of file).

·      The data structure that corresponds to such a file is called file structure.

·      A structured file contains a list of records and each record is delimited by EDR (end of record).

·      The data structure of such  file is called record structure i.e. file is divided into records.

·      Another structured file contains pages , with each page having a page number and a page header .

·      The pages can be stored and accessed randomly or sequently the corresponding data structure is called page structure i.e. file is divided into pages.

3.   Transmission modes

·      FTP can transfer a file by using one of the following three modes:

Stream mode

·      It is the default mode

·      File is transmitted as continous stream of bytes to TCP.

·      TCP is responsible for copying data into segments of  appropriate size.

·      If data is simply a stream of bytes (file structure), no end – of – file is needed. EOF in this case is the closing of the data connection by the sender .

·      If data is divided into records( record structure), each record has a 1-byte EOR (end – of - record), character and the end of the file has a 1-byte EOF (end – of – five ) character.

Black mode

·      Data is delivered from FTP to TCP in blocks.

·      Each block is preceeded by three bytes header.

·      The first bytes is called the block descriptor .

·      The second the third byte define the size of the block in bytes.

Compressed mode

·      Data is usually compressed if the file to be transmitted very big.

·      The comparison method normally used in run – length and encoding.

·      In a text file , usually spaces (blanks are removed).

·      In a binary file , null characters are compressed.

4.   Error control

·      Since TCP is used for data transfer no additional error recovery mechanism is required.

5.   Access control

·      File access protection is done using login procedure with login name and password.
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