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Precautions on High Traffic in FINS Communications Section 8-7
8-7 Precautions on High Traffic in FINS Communications
When applications are constructed using FINS communications services,
communications errors (from multiple response timeouts) may occasionally
occur due to high traffic, depending on the system configuration and the appli-
cation programs. This section describes precautions for systems with high
traffic in FINS communications.
■ Conditions for High Traffic
A heavy communications load may occur at an EtherNet/IP Unit or built-in
EtherNet/IP port if FINS messages and CIP messages from multiple nodes
are concentrated on that EtherNet/IP Unit or built-in EtherNet/IP port. The
EtherNet/IP Unit or built-in EtherNet/IP port and the CPU Unit may have insuf-
ficient processing capacity for the volume of FINS messages (commands)
that are coming from the network.
For example, suppose that approximately 20 ms are required to process a sin-
gle FINS frame (i.e., 20 ms from the time that the command is received at the
EtherNet/IP Unit or built-in EtherNet/IP port until a response is sent). If 100 or
more FINS frames (commands) are received at once from multiple communi-
cating nodes, it will take approximately 2 seconds to send a response to the
last command. If a timeout is set at the remote node for 2 seconds or less,
then a timeout will be generated. A retry will begin due to the timeout, and the
traffic to the EtherNet/IP Unit or built-in EtherNet/IP port will thus be increased
even further, until ultimately the responses to all the nodes will be too slow. At
this point, the system is overloaded.
■ Avoiding Errors due to High Traffic
To avoid high traffic from FINS communications, the communications load
must be kept down to a reasonable level. To accomplish this, follow the proce-
dure below.
1. Specify the node where FINS frames seem to be concentrated.
2. Estimate the total processing time for all of the FINS frames processed at
that node. (For details, refer to 10-5-1 Maximum Transmission Delays (Ex-
cluding Delays in the Network).)
3. Set the timeout value for all of the SEND(090), RECV(098), and
CMND(490) FINS commands at all the remote nodes to at least 1.5 times
the total processing time for all of the FINS frames.
4. As much as possible, implement communications traffic testing up to the
point of actual system operation. If any problem occurs, adjust the traffic.
5. If a commercially-available protocol analyzer can be used, then the actual
FINS frame processing time (i.e., the time from when a command is re-
ceived at the EtherNet/IP Unit or built-in EtherNet/IP port until a response
is sent) can be measured under high traffic conditions and the communi-
cations traffic can be further adjusted as required.