Schneider Optics Modicon Quantum Ethernet Compatibility, Guidelines for Designing Your Network

Introduction

Ethernet network traffic, message length and routing are all variable and can be unpredictable. This can give rise to congestion and message collisions. When collisions occur, Ethernet uses a variable delay before retransmitting messages. Therefore, absolute determinism -- or totally predictable performance -- cannot be guaranteed on busy Ethernet networks.

1.4.2Compatibility

	Ethernet technology allows devices from different vendors to coexist on the same
	network. These devices include hubs, bridges, routers and gateways. However, for
	these devices to be compatible they must support the same set of protocols.
	Quantum Ethernet modules support Modbus protocol over TCP/IP over Ethernet
	protocol. Systems that wish to communicate with Quantum Ethernet web
	embedded server modules need to support this protocol stack.
Ethernet	The Modbus protocol was chosen for its particular suitability for the real time
Developers Kit	control environment. It is a well-known and widely-adopted protocol and is fully
	described in the Ethernet Developers Kit. This kit (140 EDK 211 00) helps users
	develop Ethernet-based communications to their own host (PC-based) sockets
	applications. It contains a Quantum Ethernet module plus documentation and
	software tools which fully explain the protocols. The Ethernet Developers Kit is
	available from your distributor or local Square D office.
Ethernet and	Ethernet web embedded server modules may be installed in a hot standby system,
Quantum Hot	but they are not supported at switchover. When control shifts from the primary
Standby	controller to the standby, the Ethernet network is not notified. The network
Systems	continues to address the Ethernet web embedded server module in the original
	primary rack, not the module in the new primary rack.
EMBP Gateway	A Quantum Ethernet web embedded server module can exist on the same Ethernet
	network as the EMBP Gateway, but it cannot communicate with the EMBP
	Gateway because of differences in formatting and network addressing. However,
	the MBT Ethernet Bridge can be used with the web embedded server module (refer
	to Modbus Plus to Ethernet Bridge Users Guide, 890 USE 151 00).

1.4.3 Guidelines for Designing Your Network

A typical Ethernet installation carries many different types of traffic. Large data file transfers or World Wide Web graphics files can keep the network busy and cause network congestion and collisions. These collisions cause nodes to wait a variable amount of time before resending their messages. Because the size and frequency of non-control traffic is unpredictable, network performance may not be suitable for control applications. These problems can be greatly reduced by segregating the office and MIS traffic from control data.

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