TROUBLESHOOTING
SNAP PAC S-Series User’s Guide
40
based on recent network traffic. If the network becomes busier, for example, the stack automatically adjusts
the RTO to a higher value.
If the TCP/IP stack times out while trying to transmit data, it doubles the current RTO and tries again. This
process continues for five retries; after that, the controller stops trying and sends a timeout message.
If you are receiving frequent timeout messages from the SNAP PAC S-series controller, you can change the TCP
parameters in PAC Manager.
1.
Choose Start
Programs
Opto 22
PAC Project Software
PAC Manager.
2.
In the PAC Manager main window, click the Inspect icon
.
3.
In the IP Address field, type the IP address of the controller. Click Status Write.
CAUTION:
Note the following recommended settings:
If you set these fields too low, you may not be able to communicate with the controller at all, even though PAC
Manager, to fix the settings. Then you would have to reset the controller to factory defaults.
4.
Change these four fields as necessary:
TCP Minimum Retransmission Timeout
sets an absolute minimum value for the RTO. The controller’s
calculated RTO will never go below this value.
TCP Initial Retransmission Timeout
sets the RTO for the first communication try. Be careful: since all
future tries are based on this value, if you set it too low for network conditions, a connection will never be
made.
TCP Retransmission Attempts
sets the number of times the controller retries communication. Larger,
busier networks need a higher number of retransmits than smaller networks with less traffic.
TCP Idle Session Timeout
sets how long (in milliseconds) the controller allows a session to remain
open without any activity. After this time, the controller closes the unused session. The default is 240,000
milliseconds, or four minutes.
5.
Click the Apply button to write your changes to the controller.
6.
In the Operation Commands list, highlight Store configuration to flash. Click Send Command.
7.
In the Operation Commands list, highlight Restart I/O Unit from powerup. Click Send Command.
The new TCP parameters are set.
TCP Minimum Retransmission Timeout (msec):
250
TCP Initial Retransmission Timeout (msec):
3000
TCP Retransmission Attempts:
5
TCP Idle Session Timeout (msec):
240,000
