Contents:
Part One:
Setting up a Remote Port
Facility
Setting
up a Remote Port Facility
Communications Server remote port facility is a feature that allows
UNIX applications to treat the serial ports on a LAN-connected Communications
Server unit as if they were serial ports on the local machine.
This provides a convenient method for using modems, printers and other
serial devices connected to an Communications Server port, as well as
providing the ability to run dedicated applications on these ports.
This section describes how the remote port facility works, how to configure
it, and how to acquire or build the pieces needed to implement it.
Operating system dependencies are dealt with individually at the end
of the document. The remote port facility was previously named
hard TTY and older documentation may still refer to it by this name.
Theory of Operation
This section discusses how the remote port facility works. An
understanding of this is helpful but not mandatory. If you have
trouble with this section you can skip ahead and follow the configuration
'recipes'. The remote port facility is implemented by a UNIX application
call svr_tty and the Telnet Listener capability of the Communications
Server. A block diagram showing the various pieces and their relationships
follows:
Applications talk to the serial ports on an Communications Server unit
via a UNIX pseudo-tty. The actual transfer of data between a pseudo-tty
and Communications Server serial port is done by a svr_tty daemon process.
svr_tty reads data from the master end of the pseudo-tty and passes
it to the Communications Server and vice versa. svr_tty uses a
simple protocol to communicate with the serial ports on an Communications
Server unit via Telnet Listeners (processes that run within the Communications
Server and transfer data between the network and serial ports).
Note: The use of a UNIX pseudo-tty imposes some limitations,
although these are not normally a problem for most applications.
The same limitations occur in other situations where pseudo-ttys are
used, i.e. a remote login connection using telnet or rlogin. The
major difference between a real serial port and the pseudo-tty which
provides a remote port connection, is that hardware-related characteristics
such a baud rate, number of bits per character, hardware flow control,
etc. cannot be set by the application program using the normal UNIX
API (ioctl). These characteristics must be configured in the Communications
Server using the facilities it provides (command line interface, configuration
files, etc.)
Setting
up a Telnet Listener for Remote Port
Each Communications Server serial port that is to be configured for
use with remote ports must be configured with a telnet listener, a process
that runs within the server and transfers data between the serial port
and the network. This section lists the commands required to set
up a telnet listener but does not describe them in detail. For
more information see the EasyServer
II Command Reference Manual, or the online documentation.
The following examples show the commands required to set up telnet
listeners for various devices. These commands are typed at the
Communications Server command line interface (you must be in privileged
mode). Note that each telnet listener is identified by a TCP port
number (2003 in the examples below). We recommend the use of 2001
for serial port 1, 2002 for port 2, etc.
Printers,
Outgoing Modems or getty login ports
CHANGE TELNET LISTENER
2003 CONNECTIONS ENABLED
CHANGE TELNET LISTENER
2003 RAW MODE ENABLED
CHANGE TELNET LISTENER
2003 NOTIFICATION DISABLED
CHANGE TELNET LISTENER
2003 PORT 3 ENABLED
CHANGE PORT 3 ACCESS
REMOTE
Note: The command CHANGE TELNET LISTENER 2003 IDENTIFICATION
'LASER' can be used to attach a comment to a telnet listener for documentation
purposes.
As well as setting up telnet listeners you will also need to set up
appropriate serial port characteristics for the connected devices, i.e.
baud rate (disable autobauding), parity, flow control, etc. See
the Communications Server documentation
for further details.
