Cal Amp VIPER SC+ 100 series User Manual - page 203
Viper SC+™ IP Router for Licensed Spectrum PN 001-5008-000 Rev. C
| Page 193
Summary of Connected or Unconnected Operation
With the Connected option selected and polling interval between messages for the same remote CIP connection is
longer than the UnconnectedTimeout (default 30 seconds), CIP Forward Open and CIP Forward Close messages add 4
extra on-air messages (includes message reply) for each unit polled. If each poll is 2 messages (message and reply), the
4 extra messages increase the message load (on air) by 200 %.
Therefore the Connected checkbox should be unchecked (Unconnected) to avoid sending CIP Forward Open and CIP
Forward Close messages. If Connected is required, then increase the UnconnectedTimeout and ConnectionRate
timeout to a value greater than the polling interval per remote (use precaution with this).
Timeouts used for message responses over Ethernet /IP Connected or Unconnected should not be too short, and
therefore should not be set shorter than 15 seconds (normally) in the event it is required to be lower than 30 seconds
for application-level retransmission. The TCP/IP communication driver does its own retransmissions and will not
require application retransmissions of messages since a TCP connection will not lose a message unless the connection
terminates normally or due to a problem. Therefore with TCP longer timeouts within reason are okay. Longer timeouts
(for example, 30 seconds) are okay since they minimize duplicated messages being buffered by TCP in the event of
network congestion or communication problems with the remote unit.
With future releases of PLC software and firmware, the described operation could change. It is always recommended to
be informed on PLC release changes from your PLC provider or manufacturer or Allen-Bradley or Rockwell Automation
support.
ALLEN-BRADLEY COMPACTLOGIX OR CONTROLLOGIX SERIES PLCS SEND MANY TCP/IP KEEP-ALIVE
MESSAGES
The CompactLogix and ControlLogix series PLCs send TCP/IP keep-alive messages every 8 seconds in both directions for
each TCP connection. When several PLCs do the same, it is possible that a good part of the on-air bandwidth is used up
by the keep-alive traffic.
We recommend that the Viper be configured in router mode and that the TCP Proxy is enabled. The Viper TCP Proxy
feature will filter-out the TCP/IP keep-alive messages.
The PLCs TCP keep-alive cannot be disabled nor adjusted. It has been recommended to Allen-Bradley and Rockwell
Automation to have an option in the PLC settings to disable keep-alive and have user-selectable keep-alive intervals.
This could potentially become available in future releases of PLC firmware.
Also please refer to Viper General Setup With PLCs, earlier in this appendix.