Topologies
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System approach
Industrial Ethernet Cabling System
Different network topologies
Next there is a description of some of the available network topologies.
Star topology
DTE
DTE
DTE
DTE
In a star topology, all devices are connected though an intermediate device.
Ethernet Star
In an Ethernet star the intermediate device may be a hub or a switch. Star is the
commonly used topology in corporate networks and as of today is adopted in almost
every automation application. As mentioned previously, for industrial Ethernet
applications the use of full duplex switches as central device rather than hubs is
strongly recommended.
2
Deploying Star topologies with ConneXium
With any of the hubs and switches offered by the ConneXium offer, star topologies
can be implemented.
Bus topology
DTE
DTE
The bus is one of the most adopted topologies in traditional industrial automation
networks. A single trunk cable connects all the devices on the network usually via
passive or active T-connectors, or directly chained (daisy chain). Devices usually can
be installed anywhere along the bus.
DTE
Ethernet Bus
An Ethernet bus can be deployed by interconnecting hubs and/or switches in line
and considering every one of them as the connection for a drop device. A limited
number of hubs and an unlimited number of switches can be interconnected to
achieve this purpose.
Deploying Bus topologies with ConneXium
With any of the hubs and switches offered by the ConneXium offer bus topologies
can be implemented. Specially suitable for this purpose are the switches with 1 or 2
fiber optic ports. The 2 fiber optic ports switches could be for connection of inline
devices while the single fiber optic port switches could be used for the connection of
end line devices.
Daisy chain topology
Daisy chain -along bus- is the other most adopted topology in traditional industrial
automation networks. Cable segments interconnect multiple devices, being the
devices “part ” of the network cable.
DTE
DTE
DTE
Ethernet daisy chain
Daisy chain is not today a very common Ethernet topology, but it will soon become
one of the most popular ones when enough quantity of devices is made available.
In Ethernet daisy chain the devices have 2 Ethernet ports and an embedded
switch.
Schneider Electric is releasing to the Industrial market Industrial Ethernet devices to
be connected in daisy chain architectures.
Deploying daisy chain topologies
To deploy daisy chain topologies, no hubs or switches are required. All devices have
an embedded switch.
Dual port Ethernet at the device level is an absolute integral component for
daisy chain topologies. Each device in the network has at least two Ethernet ports.
One port of the device connects to one port of the neighboring device on either side
of the device. These neighboring connections make up the daisy chain.
Ethernet switches can be employed in a daisy chain topology when multiple scan
chains are in use by the controlling device. It is expected that the Ethernet switch will
be located near the controlling device with the different scan chains emanating from
the switch.
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2.4
Topologies (continued),
characteristics
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System approach
Industrial Ethernet Cabling System
Daisy chain topology (continued)
Limitations of daisy chain:
Limitations of daisy chain to insure the operational integrity of the network and meet
performance metrics, are:
b Dual port Ethernet devices only support 10 Mbit/s and/or 100 Mbit/s operational
speeds and must use one or the other.
b The network will operate only as fast as the slowest device that is connected to the
network
b In order to improve network traffic latency the numbers of devices in a single scan
chain, has been limited to 32 devices.
b Limiting a single scan chain to 32 devices the time for a round trip of a packet
through the daisy Chain is expected less than 5 milliseconds (with 32 devices
plugged on a scan daisy chain.
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The maximum packet latency of a packet passing through any device in a scan chain
is no more than 10 µs.
The first Schneider Electric device with Ethernet daisy chain capabilities is the
Lexium 17D servodrive, see page 3/7.
Ring topology
DTE
In a ring topology, all devices or network infrastructure components are connected in
a loop with no beginning or end. Through these types of topologies a type of network
redundancy is achieved.
DTE
2.4
Ethernet Ring
Ethernet rings are usually the backbones of applications in which high availability is
required. If ring topology is required then switches that support this feature should be
ordered.
DTE
DTE
DTE
DTE
Deploying Ring topologies using ConneXium.
The ConneXium line offers hubs and switches that allow the deployment of single
and coupled self-healing rings. There is additional information about this topic in the
redundancy segment.
Distance limits and number of devices per segment
Based upon the 802.3, the distance limits and the numbers of devices in cascade are
the following:
Type
10BASE-T
100BASE-TX
1000BASE-T
10BASE-FL
100BASE-FX
1000BASE-SX
Maximum segment
length (1)
100 m
100 m
100 m
2000 m
412 m/2000 m
275 m
Maximum segment
length (offered by
ConneXium devices)
100 m
100 m
100 m
3100 m (2)
4000 mwith multimode,
32.500 m with
monomode (3)
–
Maximum number of Maximum number of
hubs in cascade
switches in cascade
4
2
–
11 (fiber ring)
–
Unlimited
Unlimited
Unlimited
–
Unlimited
–
Unlimited
(1) Based on 802.3, full duplex/half duplex.
(2) Depends on the optical budget and fiber attenuation.
(3) Depends on the optical fiber budget and fiber attenuation, typical specification is 2 km for
multimode and 15 km from monomode.
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