Viper SC+™ IP Router for Licensed Spectrum PN 001-5008-000 Rev. C
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Summary On TCP Connection Timeout (Inactivity Setting)
Since the longest inactivity timeout per TCP connection with a remote unit (PLC/RTU) is 120 seconds (based on
message inactivity for maximum of 120 seconds), it is important that each remote (PLC/RTU) is polled with the 120
second period to avoid extra traffic resulting from additional TCP/IP open and close connection messages. For systems
where polling is done infrequently (> 120 seconds), the additional TCP traffic needs to be considered for the system
traffic plan.
For normal operation
the inactivity timeout does not need to be specified in the Path setting. Master and remotes
should be set this way, especially if remote PLCs send unsolicited messages or initiate communication with other
remotes. If a system has a mix of PLCs (CompactLogix or ControlLogix with MicroLogix or SLC), then also refer to
information earlier in this appendix regarding the Allen-Bradley Micrologix 1100 or 1400 (may also apply to SLC 5) and
Allen-Bradley PLC for Viper System information, which precedes it.
ALLEN-BRADLEY COMPACTLOGIX OR CONTROLLOGIX SERIES PLCS SENDS TOO MANY CIP FORWARD
OPEN AND CIP FORWARD CLOSE
When using the Ethernet/IP with CIP communications protocol with Allen-Bradley CompactLogix or ControlLogix PLCs
(and with other Logix series PLCs), the option to use Connected or Unconnected is available in the Message
Configuration. By default the Connected checkbox is selected and therefore it will add additional messages (CIP
Forward Open and CIP Forward Close) for each read-write operation when the next message is sent outside the
message timeout period. The default setting is 30 seconds.
To lower the on-air traffic, the Connected checkbox should be unchecked (Unconnected).
Connected or Unconnected operation description for CIP
When the Connected checkbox is checked (Connected)
, if there is not a CIP connection already established, then
the controller sends an Open Forward CIP Connection command and waits for the Good response before
transmitting the read or write command. The CIP connection remains open as long as there is activity before the
timeout (default = 30 seconds). Any message instruction sending commands to the same device can use the same
CIP and TCP connection. If this timeout is reached, a close CIP connection is sent.
When the Connected checkbox is unchecked (Unconnected)
, the controller uses the Unconnected CIP service to
transmit the read or write command so there is less overhead.
The
Connection timeout
is on a per-message instruction basis as shown below – this is with regards to the CIP
connection, which is only controlled by the Inactivity timeout.