Schneider Optics Web Embedded Server - Manual (Page 23)

Introduction
840 USE 115 00 Version 1.0 13
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.
1.4.2 Compatibility
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
Developers Kit The Modbus protocol was chosen for its particular suitability for the real time
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
Quantum Hot
Standby
Systems Ethernet web embedded server modules may be installed in a hot standby system,
but they are not supported at switchover. When control shifts from the primary
controller to the standby, the Ethernet network is not notified. The network
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.