Control Connection; Data Connection - HP jetdirect 175x Administrator's Manual

Control Connection

Using standard FTP, a control connection is opened by the client
to the FTP server on the HP Jetdirect print server. FTP control
connections are used to exchange commands between the client
and the FTP server. The HP Jetdirect print server supports up to
four control connections (or FTP sessions) simultaneously. If the
number of allowed connections is exceeded, a message indicating
that service is not available will be displayed.
FTP control connections use TCP port 21.

Data Connection

A second connection, a data connection, is created each time a file
is transferred between the client and the FTP server. The client
controls the creation of a data connection by issuing the commands
that require a data connection (such as FTP ls, dir or put
commands).
Although the ls and dir commands are always accepted, the
HP Jetdirect FTP server supports a single data connection for
printing at a time.
The transmission mode for an FTP data connection with the
HP Jetdirect print server is always in stream mode, which marks
the end-of-file by closing the data connection.
Once a data connection is established, the file transfer type (ASCII
or binary) can be specified. Clients may attempt to autonegotiate a
transfer type, and the default transfer type depends on the client
system (for example, Windows NT may default to ASCII, while
UNIX may default to binary). To specify the transfer type, enter
the bin or ascii command at the FTP prompt.
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