Comtrol NS-link Windows NT - Manual (Page 29)

Initial NS-Link Installation 29
Windows 2000: NS-Link Installation
The KeepAlive feature
works in the following
ways:
• During normal
operation the
driver periodically
sends a connection
check to the NS-
Link device, and
the device then
returns a response.
There are two
timers, one in the
driver, and one in
the device. These
timers are reset
when a connection
check signal is
received and goes
to the next signal.
If a connection is
broken, the data is
stored in the
computer and the device. Depending on the amount of time that has
expired since the connection was lost, the following happens:
-
When the computer loses its connection to the device but re-establishes
it before the timeout period expires, any data transmitted during this
period is queued and sent when the connection resumes.
- When the computer loses its connection to the NS-Link device and does
not re-establish it before the timeout period expires; the driver then
purges any pending I/O data for ports on that connection and returns
all pending, and future I/O commands, with the exception of the Close
command, to the application with an error indicating the disconnected
status.
This is similar to the processing which occurs when the computer
receives a notification from the device that a port release request, from
FreePort, was processed on a port it owns with the exception that a
different status is returned. When the connection is re-established, the
computer will attempt to re-acquire the ports that were open when the
connection was lost. If the attempt is successful, normal operations
resume for the port. If any port has been acquired, then the computer
will continue to fail all further I/O operations, with the exception of a
Close request. When the Close request is received, the port can then be
re-opened.
- When the computer loses its connection to the NS-Link device, and the
time period expires, the device places the port into a state from which
another computer can establish a connection, locking out the original
driver when the connection is made. The driver will respond to all I/O
commands, with the exception of the Close command, with an error
indicating the disconnect status.
If you need the ability to reconnect with a port that another server is
currently using, Comtrol includes an utility called FreePort (Page 78) and
its source code which makes the API calls that would force a port closure.
The included source code for FreePort demonstrates the calls an application
would make to perform the same operation.
22. Optionally, set the TCP Timeout Multiplier value.
Use the TCP Multiplier to modify two timers used in TCP/IP socket
communications. The first identifies how long the TCP protocol should wait
before timing out an attempt to open a TCP channel. This timer defaults to
500 ms when the TCP/IP address method is used to communicate with a
device. If the TCP Multiplier is set to 2, the timer would now be 1000 ms, or 1
sec. If the multiplier is 4, the new timeout period would be 2000 ms, or 2 sec.