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A4-18 893-741-B
The Port Server and Rotaries
Terminal Server TTY (TSTTY)
TSTTY is a set of independent software modules that allow a host system to connect to Model 5390
serial ports in such a way that users appear as if they are directly connected to the host system. One
module runs in the Model 5390 server and one module runs in the host. A protocol links the two
modules together. When a host wants to talk to a device attached to a port that is in slave or adaptive
mode, it must first establish a connection by connecting to the appropriate TCP port on the Model
5390 server. The Model 5390 server and host can then send messages over this link to exchange
data and commands. (TSTTY runs on top of any reliable byte stream protocol, for example, TCP.)
By providing a standard tty interface to the host, all standard programs can access the ports through
standard serial port devices, and hence perform all of the functions that a standard, directly connected
port can perform.
Many of the standard actions, such as changing the serial port’s baud rate, are passed to the Model
5390 server for execution, while some actions, such as dealing with a Break character, are executed
by the host system. This design optimizes performance by allowing functions to be executed
wherever it is best to do so. Consequently, since all standard system programs can be run on TSTTY
ports, these ports can be used for login sessions (via getty or ttymon), as line printer ports using the
standard spooler connections, for uucp/cu connections to other systems, and for user written
programs.
TSTTY provides several advantages over telnet or rlogin:
• Processes ioctl from a host to change the parameters of the remote port.
• Eliminates the need for special handling required by many terminal servers.
• Enables terminal servers to use standard UNIX utilities.
How TSTTY Interacts with Model 5390 Port Parameters
Because the TSTTY code on the Model 5390 server receives commands from the host to change
the settings of the serial port, there is a degree of unseen interaction between these settings and the
default settings for the port. This interaction is similar to that of the Model 5390 CLI command stty
and the port parameters, in that the settings are reset to their default values when the port is reset.
For TSTTY, a port is reset when the host closes the last session (usually there is only one session)
to the port.