Omron CJ1W-ETN21 - 04-2009 Operation Manual page 181

Precautions on High Traffic in FINS Communications
156
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 Unit until a response is sent). If 100 or more FINS frames (com-
mands) are received at once from multiple communicating nodes, it will take
approximately 2 seconds to send a response to the last command. If a time-
out is set at the remote node for 2 seconds or less, then a timeout will be gen-
erated. A retry will begin due to the timeout, and the traffic to the Ethernet Unit
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. Referring to 6-6-6 Transmission Delays, estimate the total processing time
for all of the FINS frames processed at that node.
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 Unit until a response is sent) can be measured un-
der high traffic conditions and the communications traffic can be further
adjusted as required.
Section 6-7