Download Differences Between Industrial Ethernet Fiber Optic Backbone, Ring

N-TRON Corp.
578 Azalea Road, Suite 105, Mobile,AL 36609
TEL: 251-666-9878; FAX: 251-666-9833
Differences Between Industrial Ethernet
Fiber Optic Backbone, Ring, and Star Topologies
Fiber Optic Backbones
Fiber Optic backbones have been used effectively in industrial Ethernet systems requiring highspeed communications with excellent noise characteristics. Since the fiber optic cable is
impervious to electric and magnetic fields, all conventional electrically generated cross talk and
interference is eliminated.
In the event that great distances (over 100m) separate nodes, fiber optic backbones can realize
very cost effective Ethernet systems. A diagram of an N-TRON fiber optic backbone
implementation is shown in Figure 1.
HMI
CAT5
CAT5
PLC
N-TRON
900B
908TX
902FX-ST
FIBER OPTIC PAIR
N-TRON
405FX-ST
CAT5
DATA
SERVER
CAT5
PLC
FIBER OPTIC PAIR
N-TRON
202MC-ST
CAT5
CAT5
PLC
PLC
Figure 1.
However, the classic fiber-optic backbone has several limitations:
•
•
•
•
A single fiber media failure divides the network into segments that cannot communicate.
A single switch failure divides the network into segments that cannot communicate.
Many single points of failure can render a control system inoperable.
All network traffic is funneled down into the 100Mb/s fiber-optic backbone. Devices must
compete for this party line resource.
N-TRON Corp.
578 Azalea Road, Suite 105, Mobile,AL 36609
TEL: 251-666-9878; FAX 251-666-9833
Industrial Ethernet Ring Topology
To remove the limitation of media failure, Ethernet switches have been used effectively in ring
topology installations where long fiber distances and low bandwidth were requirements. When the
switches are to be located so far apart that it becomes cost prohibitive to make a “home run” for
each switch, ring topology offers a definite cost saving alternative.
In addition, industrial ring topology offers media redundancy. In the event that the fiber link is
broken, the redundancy manager heals the ring by re-directing traffic. For industrial applications,
the traditional spanning tree algorithm is much to slow to use in control and high-speed data
acquisition applications. This has led to the development of the “higher speed” protocols now
being used by prominent leaders in the industrial network arena. Healing speeds of less than
300ms are achievable. A diagram of an N-TRON Fiber-Optic ring implementation is shown in
Figure 2.
PC
MMI
PC
MMI
PC
MMI
CAT5
CAT5
CAT5
CAT5 TO MES
FIBER OPTIC PAIR
608MFX
RING
MANAGER
#7
#8
#8
#7
608MFX
CAT5
PLC
#7
FIBER OPTIC PAIR
CAT5
PC
LAPTOP
#8
608MFX
CAT5
Additional
Ports
N-TRON
405TX
#7
FIBER OPTIC PAIR
CAT5
PLC
608MFX RING TOPOLOGY
Figure 2
Page 2
#8
608MFX
CAT5
PLC
CAT5
DRIVE
N-TRON Corp.
578 Azalea Road, Suite 105, Mobile,AL 36609
TEL: 251-666-9878; FAX 251-666-9833
The Industrial Ring Topology still has several shortcomings:
•
•
•
•
•
•
•
Many single points of failure can still render the control system inoperable.
A failed switch can render a control system inoperable.
The network becomes inoperable with the failure of the redundancy manager.
Implementation requires costly managed switches.
Utilizes proprietary high speed healing algorithms that are not 802.3 compliant. Users cannot
use products from different vendors in the ring due to compatibility issues.
All network traffic is funneled down into the 100Mb/s fiber ring.
All traffic must flow on the ring, thus hard limiting the bandwidth of the installation to
100Mb/s.
Dual Redundant Fiber Optic Rings
To build a fault tolerant network (no single point of failure) requires two rings. The redundancy
manager is operating with a standby master and standby slave to shadow its operation and step in
and direct traffic in the event of a redundancy manager failure.
This also requires that dual Ethernet ports be installed in the PC’s, and PLC’s to fully utilize the
fault tolerance features (still higher costs). This topology is shown implemented with N-TRON
Products in Figure 3.
Drawbacks of the Redundant Ring Topology include:
•
•
Cost
Performance (still limited to 100Mbit Fiber-Optic Loop)
The 100Mbit limitation can become quite severe when users start considering the addition of
security cameras and vision systems to their control networks.
Page 3
N-TRON Corp.
578 Azalea Road, Suite 105, Mobile,AL 36609
TEL: 251-666-9878; FAX 251-666-9833
FIBER OPTIC PAIR
#7
608MFX
RING
MANAGER
#8
ITP Cable
#8
608MFX
#7
#7
FIBER OPTIC PAIR
608MFX
Standby
Master
#8
Cat5E
608MFX
#7
FIBER OPTIC PAIR
#7
FIBER OPTIC PAIR
Cat5E
#1
#8
608MFX
#7
FIBER OPTIC PAIR
#1
FIBER OPTIC PAIR
#7
608MFX
Standby
Slave
#8
#1
#8
608MFX
#1
608MFX
RING
MANAGER
#8
608MFX Network Segment Redundancy
Figure 3
Page 4
#7
N-TRON Corp.
578 Azalea Road, Suite 105, Mobile,AL 36609
TEL: 251-666-9878; FAX 251-666-9833
Star Topology
Star topology networks have been used effectively in data acquisition and control systems.
Because the MTBF of a high quality industrial switch is in excess of 2M hours, the likelihood of a
switch failure, or media failure is indeed remote. All N-TRON switches offer dual power supply
inputs to eliminate the possibility of a single power supply failure bringing the network down.
Star topology also allows for the utilization of lower cost layer 2 switches and an order of
magnitude speed improvement over Ring Topology. N-TRON 900 Series switches utilize a
2.6Gb/s backplane that is over 260 times faster than the 100Mb/s Ring.
Star topology can easily be implemented with fiber or copper, or a combination of both. The
network is also simpler to maintain and troubleshoot, and it is far more open and adheres to 802.3
standards (thus allowing plug and play multi-vendor interoperability). This topology is shown
implemented with N-TRON products in Figure 4.
PC
HMI
Fiber Pair
N-TRON
900B
904FX-ST
Fiber Pair
PLC
Fiber Pair
Fiber Pair
Ethernet
I/O
Drive
Figure 4.
Page 5
N-TRON Corp.
578 Azalea Road, Suite 105, Mobile,AL 36609
TEL: 251-666-9878; FAX 251-666-9833
Limitations of the Star Topology include:
•
•
No Media Redundancy
Many single points of failure can still render the control system inoperable.
Redundant Star Topology
To build a fault tolerant star network (no single point of failure) requires dual Ethernet ports be
installed in the PC’s, and PLC’s. Every node would have a “home run” back to dual central highdensity switches. As long as the fiber distances are under 2km in distances, this topology is
superior in cost performance and reliability when compared to ring.
This topology is shown implemented with N-TRON products in Figure 5.
Duplex Fiber Cable
Duplex Fiber Cable
405FX
405FX
Device
w/dual ethernet
N-TRON
900B
908TX
902FX-ST
Duplex Fiber Cable
Duplex Fiber Cable
405FX
405FX
Device
w/dual ethernet
Device
w/dual ethernet
Device
w/dual ethernet
N-TRON
900B
908TX
902FX-ST
PC with
Dual Ethernet
Figure 5.
In most instances, redundant star with redundant Ethernet devices can be implemented at a lower
cost point than redundant ring topology. This, coupled with an order of magnitude higher
bandwidth, makes it a technically superior (and more open) approach for most industrial
networks. The exception is when the fiber optic runs become very long (> 2km) and the cost of
the fiber (typically $1-2 per foot) is more expensive than the switches.
Page 6