STAT-4, STAT-8, AND STAT-24
32
If the DTE cannot recognize the X-ON and X-OFF characters, you must select the Off option. In this case, the
control of data flow between the stat mux and the DTE connected to it is performed via the CTS control line
contained in the RS-232 interface.
Screen selections are as follows:
Code numbers 1 and 2 list the available selections of software flow control status: on or off.
Type
Q
to return to the Local Sub-Channel Configuration screen (8). The Current State line shows the current
status of software flow control used on this sub-channel.
Procedure:
To change the status of software flow control, type the appropriate code number. The new selection appears in
the Current State line.
Type
Q
to return to the Local Sub-Channel Configuration screen (8).
14. End-to-End Software Flow Control Screen
Purpose:
View the current status of end-to-end software flow control used on this sub-channel and select a new
status, if desired.
Description:
In addition to the stat mux-to-DTE control function (13), the stat mux provides a DTE-to-DTE (or end-to-end)
flow-control function. This function allows a receiving DTE to command the remote transmitting DTE to
interrupt data flow, because temporarily it cannot accept new data, and then send a request for continuing data
flow. The stat mux transmits the flow control commands to the other end and simultaneously executes the
required action on the local sub-channel. This avoids problems that could be caused by the link transmission
delay. This is done by selecting the ON option on this screen. The stat mux is then configured to recognize the
two special characters (selected via the screens presented in 3 and 4): X-OFF conveys local DTE “stop flow”
command, and X-ON conveys local DTE “restart flow” command.
The detected X-ON/X-OFF commands are sent to the remote stat mux, which converts them to flow-control
commands for the remote DTE connected to it. When the stat mux receives an X-OFF command from the local
DTE, the local stat mux interrupts immediately the transfer of received data to the local DTE. The additional
data sent by the remote DTE during the time it takes to transfer the X-OFF command accumulates in stat mux
buffers. Similarly, when the stat mux receives an X-ON command from the local DTE, the local stat mux
immediately starts the transfer of received data (accumulated as explained before).
The flow-control commands supplied to the remote DTE depend on the stat mux-to-DTE flow control mode
selected at the remote DTE: the same X-ON/X-OFF characters, or use of CTS line handshaking (see 13).
When the local stat mux does not have software flow control capability, the stat mux “end-to-end software flow
control” must be configured as OFF, to prevent the stat mux from responding to the X-ON and X-OFF
characters. In this case, see also 15.
Screen selections are as follows: Code numbers 1 and 2 list the available selections of end-to-end software flow
control status: on or off. Type
Q
to return to the Local Sub-Channel Configuration screen (8 above). The
Current State line shows the current status of end-to-end software flow control used on this sub-channel.
