User guide

Introduction
840 USE 115 00 Version 1.0
13
Ethernet network traffic, messa
g
e len
g
th and routin
g
are all variable and can be
unpredictable. This can
g
ive rise to con
g
estion and messa
g
e collisions. When
collisions occur, Ethernet uses a variable dela
y
before retransmittin
g
messa
g
es.
Therefore, absolute determinism -- or totall
y
predictable performance -- cannot be
g
uaranteed on bus
y
Ethernet networks.
1.4.2 Compatibility
Ethernet technolo
gy
allows devices from different vendors to coexist on the same
network. These devices include hubs, brid
g
es, routers and
g
atewa
y
s. However, for
these devices to be compatible the
y
must support the same set of protocols.
Quantum Ethernet modules support Modbus protocol over TCP/IP over Ethernet
protocol. S
y
stems 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 suitabilit
y
for the real time
control environment. It is a well-known and widel
y
-adopted protocol and is full
y
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 full
y
explain the protocols. The Ethernet Developers Kit is
available from
y
our distributor or local S
q
uare D office.
Ethernet and
Quantum Hot
Standby
Systems
Ethernet web embedded server modules ma
y
be installed in a hot standb
y
s
y
stem,
but the
y
are not supported at switchover. When control shifts from the primar
y
controller to the standb
y
, the Ethernet network is not notified. The network
continues to address the Ethernet web embedded server module in the ori
g
inal
primar
y
rack, not the module in the new primar
y
rack.
EMBP Gateway
A Quantum Ethernet web embedded server module can exist on the same Ethernet
network as the EMBP Gatewa
y
, but it cannot communicate with the EMBP
Gatewa
y
because of differences in formattin
g
and network addressin
g
. However,
the MBT Ethernet Brid
g
e 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 t
y
pical Ethernet installation carries man
y
different t
y
pes of traffic. Lar
g
e data file
transfers or World Wide Web
g
raphics files can keep the network bus
y
and cause
network con
g
estion and collisions. These collisions cause nodes to wait a variable
amount of time before resendin
g
their messa
g
es. Because the size and fre
q
uenc
y
of non-control traffic is unpredictable, network performance ma
y
not be suitable for
control applications. These problems can be
g
reatl
y
reduced b
y
se
g
re
g
atin
g
the
office and MIS traffic from control data.