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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
                9  TCP/IP General File Transfer Protocols (FTP and TFTP)
                     9  File Transfer Protocol (FTP)
                          9  FTP Concepts and General Operation

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FTP General Data Communication and Transmission Modes
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FTP Commands and Replies
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FTP Data Representation: Data Types, Data Structures and Format Control
(Page 3 of 3)

FTP Format Control

For the ASCII and EBCDIC types, FTP defines an optional parameter called format control. This allows a user to specify a particular representation for how vertical formatting is used to describe a file. The three options are:

  • Non Print: The default, indicating no vertical formatting.

  • Telnet Format: Indicates that vertical format control characters, as specified in the Telnet protocol, are used in this file.

  • Carriage Control / FORTRAN: The file uses format control characters given as the first character of each line, as specified for the FORTRAN programming language.

The format control option was created for the particular purpose of properly handling files transferred from host devices to printers. It is not used today, to my knowledge (or if it is used, it is only in special applications.)

FTP Data Structures

In addition to specifying a file's data type, it is also possible to specify the file's data structure. There are three possibilities:

  • File Structure: The file is a contiguous stream of bytes with no internal structure.

  • Record Structure: The file consists of a set of sequential records, each of which is delimited by an end-of-record marker.

  • Page Structure: The file contains a set of special indexed data pages.

The file structure is the default and is used for most types of files. The record structure can be used for ASCII text files, but these are more commonly sent with the regular file structure using the ASCII data type. The page structure is not commonly used; I believe it was initially created for a now archaic type of computer used in the early ARPAnet.


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FTP General Data Communication and Transmission Modes
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Version 3.0 - Version Date: September 20, 2005

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