Monitor And Interface Dependencies; Switching And Spanning Tree; Virtual Local Networks (Vlans) - ABB EDS500 Series Manual

Functions overview
Serial protocols that use the RS-232 interface can be transported via IP networks with the
help of EDS500 devices. The serial data stream gets converted into individual packets and
sent to one or more counter parts that re-assemble the packets into a serial data stream. To
avoid data loss due to packet loss, a error correcting protocol can be activated.
3.3.2

Monitor and interface dependencies

The EDS500 devices support the monitoring of an arbitrary device when the IP address is
known. Alternatively, entries in the routing table can be monitored.
This function is called monitor.
The monitor checks periodically the availability of a certain IP address on the basis of the
response to ICMP echo request packages (ping). The query interval can be set.
With the help of the interface dependency function port states can be linked or reversely
linked to other port states or the monitor (Link Fault Pass Through). If e.g. the primary
connection should fail, then a secondary connection can be established with a dial-up
modem.
3.3.3

Switching and Spanning Tree

The primary application of EDS500 devices is that of a (Layer 2) switch. As the devices not
only operate on the layer 2 of the OSI layer model but can also deal with data of the routing
layer 3 they are also called multilayer switches.
In the operation mode of a layer 2 switch the device handles incoming Ethernet frames by
forwarding them to certain ports in correlation to a target address. While doing so, the so-
called MAC table of the device learns the sender address. Ethernet frames with known target
addresses are forwarded only to those ports for which is known that the target address
can be found beyond them. Such a network can be expanded in a self-learning way. An
automatic aging process makes sure that once learned network structures can be modified
and removed.
To avoid that invalid replication of Ethernet frames brings the network to a standstill (so-
called broadcast storms), it has to be taken care of a loop-free operation without active
parallel routes. For this the EDS500 devices implement the Spanning-Tree-, Rapid-Spanning-
Tree-, Multiple-Spanning-Tree-Protocol (IEEE 802.1D-2004 and IEEE 802.Q-2011) and ERPS
protocol (ITU-T G.8032). These protocols are capable to enable or disable redundant paths if
required as they create one or more logical trees so that only one route leads to each target.
3.3.4

Virtual local Networks (VLANs)

VLANs are the option to split one physical network into several logical networks. Using this
feature it is possible to create network segments without additional hardware.
The EDS500 devices support VLANs according to standard IEEE 802.1Q.
For example, two networks can be connected isolated from each other using the same
infrastructure: RTUs and IP telephones can't see each other. Access ports and trunk ports
have to be differentiated. Access ports form the outer edge of the VLAN infrastructure
whereas the trunk ports connect the VLAN components (switches).
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System concept
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