7
3. OPTE9 ethernet board technical data
Dual port ethernet option board installation manual
MN032004EN October 2017 www.eaton.com
4.4.1 Topology: Star
In star network, all the devices are connected to the same
switch(es). This topology reduces the damage caused by single
cable failure. It would affect only to a single drive instead of
them all. In this setup, a drive will receive only broadcast/
multicast messages and messages directed to this drive.
Only one port from the OPTE9 can be connected to a
switch in the star topology. Connecting both ports to
switch(es) will cause an involuntary Ethernet ring which,
in this setup, will break the network.
Figure 5. Star topology
4.4.2 Topology: Daisy chain
The daisy-chaining allows you to reduce the costs for cabling
and networking equipment such as switches. The maximum
number of daisy-chained boards is 32. This restriction comes
from the average latency (20 to 40 microseconds) per Ethernet
switch. The drawback in the daisy chain topology is that it
increases traffic in all except the last drive. The first drive in the
daisy chain sees all the traffic in the chain. Also damage to a
single cable will drop all drives behind it from the network.
Both in daisy chain topology and in star topology, the last
drive’s port must not be connected back to the same line.
This would cause an involuntary Ethernet ring which will
break the network.
Figure 6. Daisy chain topology
4.4.3 Topology: Ring
It is possible to use the OPTE9 option board in a ring
topology by adding a managed Ethernet switch that
supports the RSTP protocol. This topology gains the same
reduced cabling cost as the daisy chain topology, but
decreases the damage caused by a single cable failure.
If a single link is broken, the RSTP switch will notice this
and start sending data from the PLC to both directions
effectively creating two daisy chains. When the link has
been repaired, the switch will notice this too and reverts
back to normal operating mode. Compared to the star
topology, the ring topology adds more network traffic to
almost all drives. Damage to two cables will always create
an isolated subnetwork.
In the RSTP configuration, one of the ports in the switch
is “Designated Port” (DP) and the other “Alternative Port”
(AP). When the network is functioning properly, the traffic
flows through the designated port. Only the BPDU (Bridge
Protocol Data Unit) packets are transferred through the
AP port. The BPDU packets are used by the switch to
determine if the network is working properly. If it detects
that the BPDU packets do not go through the ring, it will
change the alternative port to a second designated port.
Now the switch will send packets to both directions in the
broken ring (see Figure 8).
Each designated port has a list of MAC addresses which
are behind that port. Only frames directed to the device
in the MAC list are forwarded into that designated port.
The broadcast and multicast frames are sent to all
designated ports.
Figure 7. Ring topology