Omron CS1W-ETN21 Precautions on High Traffic in Fins Communications, Conditions for High Traffic

Precautions on High Traffic in FINS Communications Section 6-7

nodes, traffic through the Ethernet Unit (e.g., socket servicing, FTP server communications, etc.), and the system configuration.

Example Calculations

The following example shows calculations for receiving 256 words between two PLC nodes using RECV(098). Calculations are shown in the following table:

Conditions
Local node CPU cycle time:			10 ms
Local node CPU processing mode:			Normal
Local node CPU uniform peripheral servicing time: Default (4%)
Remote node CPU cycle time:			15 ms
Remote node CPU processing mode:			Normal
Remote node CPU uniform peripheral servicing time: Default (4%)
Baud rate:			100Base-TX
Item			Calculations
CPU Bus Unit service cycle (local node 1)	10 ms
CPU Bus Unit service processing time (local node 1)	0.4 ms
Transmission processing time (command)	0.550 ms ≈		0.5 ms
Transmission delay (command)	0.0118 ms ≈		0.1 ms
Reception processing time (command)	0.704 ms ≈		0.7 ms
CPU Bus Unit service cycle (remote node)	15 ms
CPU Bus Unit service processing time (remote node)	0.6 ms
Transmission processing time (response)	256 ⋅	0.002 + 0.550 = 1.062 ≈		1.1 ms
Transmission delay (response)	256 ⋅	0.0013 + 0.0118 = 0.3446 ≈ 0.3 ms
Reception processing time (response)	256 ⋅	0.003 + 0.704 = 1.472 ≈		1.5 ms
CPU Bus Unit service cycle (local node 2)	10 ms
CPU Bus Unit service processing time (local node 2)	0.4 ms
Total	10 + 0.4 + 0.5 + 0.1 + 0.7 + 15 + 0.6 + 1.1 + 0.3
	+ 1.5 + 10 + 0.4 = 40.6 ms

6-7 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

High traffic may occur if FINS messages from multiple communicating nodes are concentrated at a single Ethernet Unit. The Ethernet Unit and the CPU Unit may have insufficient processing capacity for the volume of FINS mes- sages (commands) that are coming from the network.

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