The ASCII character set is as defined in the ARPA-Internet
Protocol Handbook. In FTP, ASCII characters are defined to be
the lower half of an eight-bit code set (i.e., the most
significant bit is zero).
- access controls
Access controls define users' access privileges to the use of a
system, and to the files in that system. Access controls are
necessary to prevent unauthorized or accidental use of files.
It is the prerogative of a server-FTP process to invoke access
- byte size
There are two byte sizes of interest in FTP: the logical byte
size of the file, and the transfer byte size used for the
transmission of the data. The transfer byte size is always 8
bits. The transfer byte size is not necessarily the byte size
in which data is to be stored in a system, nor the logical byte
size for interpretation of the structure of the data.
- control connection
The communication path between the USER-PI and SERVER-PI for
the exchange of commands and replies. This connection follows
the Telnet Protocol.
- data connection
A full duplex connection over which data is transferred, in a
specified mode and type. The data transferred may be a part of
a file, an entire file or a number of files. The path may be
between a server-DTP and a user-DTP, or between two
- data port
The passive data transfer process "listens" on the data port
for a connection from the active transfer process in order to
open the data connection.
The data transfer process establishes and manages the data
connection. The DTP can be passive or active.
The end-of-line sequence defines the separation of printing
lines. The sequence is Carriage Return, followed by Line Feed.
The end-of-file condition that defines the end of a file being
The end-of-record condition that defines the end of a record
- error recovery
A procedure that allows a user to recover from certain errors
such as failure of either host system or transfer process. In
FTP, error recovery may involve restarting a file transfer at a
- FTP commands
A set of commands that comprise the control information flowing
from the user-FTP to the server-FTP process.
An ordered set of computer data (including programs), of
arbitrary length, uniquely identified by a pathname.
The mode in which data is to be transferred via the data
connection. The mode defines the data format during transfer
including EOR and EOF. The transfer modes defined in FTP are
described in the Section on Transmission Modes.
The Network Virtual Terminal as defined in the Telnet Protocol.
The Network Virtual File System. A concept which defines a
standard network file system with standard commands and
A file may be structured as a set of independent parts called
pages. FTP supports the transmission of discontinuous files as
independent indexed pages.
Pathname is defined to be the character string which must be
input to a file system by a user in order to identify a file.
Pathname normally contains device and/or directory names, and
file name specification. FTP does not yet specify a standard
pathname convention. Each user must follow the file naming
conventions of the file systems involved in the transfer.
The protocol interpreter. The user and server sides of the
protocol have distinct roles implemented in a user-PI and a
A sequential file may be structured as a number of contiguous
parts called records. Record structures are supported by FTP
but a file need not have record structure.
A reply is an acknowledgment (positive or negative) sent from
server to user via the control connection in response to FTP
commands. The general form of a reply is a completion code
(including error codes) followed by a text string. The codes
are for use by programs and the text is usually intended for
The data transfer process, in its normal "active" state,
establishes the data connection with the "listening" data port.
It sets up parameters for transfer and storage, and transfers
data on command from its PI. The DTP can be placed in a
"passive" state to listen for, rather than initiate a
connection on the data port.
- server-FTP process
A process or set of processes which perform the function of
file transfer in cooperation with a user-FTP process and,
possibly, another server. The functions consist of a protocol
interpreter (PI) and a data transfer process (DTP).
The server protocol interpreter "listens" on Port L for a
connection from a user-PI and establishes a control
communication connection. It receives standard FTP commands
from the user-PI, sends replies, and governs the server-DTP.
The data representation type used for data transfer and
storage. Type implies certain transformations between the time
of data storage and data transfer. The representation types
defined in FTP are described in the Section on Establishing
A person or a process on behalf of a person wishing to obtain
file transfer service. The human user may interact directly
with a server-FTP process, but use of a user-FTP process is
preferred since the protocol design is weighted towards
The data transfer process "listens" on the data port for a
connection from a server-FTP process. If two servers are
transferring data between them, the user-DTP is inactive.
- user-FTP process
A set of functions including a protocol interpreter, a data
transfer process and a user interface which together perform
the function of file transfer in cooperation with one or more
server-FTP processes. The user interface allows a local
language to be used in the command-reply dialogue with the
The user protocol interpreter initiates the control connection
from its port U to the server-FTP process, initiates FTP
commands, and governs the user-DTP if that process is part of
the file transfer.