ABB EDS500 Series Function Manual page 32

Quality of Service
frames are lost but potentially huge delays may arise for all connections so that the use of
flow control together with QoS is not recommended.
The default value for flow-control is: off.
With the use of QoS (Quality of Service) Ethernet frames get a priority. If an overload
situation occurs at one place in the network then it is decided under consideration of the IEEE
802.1p tag priority which frames should be preferred and which are discarded. Like this, e.g.,
it can be guaranteed to transport critical data traffic and less important connections may be
delayed.
Higher values for priority are better (lower probability of loss) than low ones.
Figure 7: Priorities for data traffic in the network with QoS
To avoid that certain services get compromised, their priority is set to a higher level. In this
example the telecontrol link of the RTUs has priority over all other links, especially the IP
cameras.
EDS500 devices have eight priorities (CoS, Class-of-Service) according to IEEE 802.1p. These
are divided into four non-blocking queues.
The default value for the processing of this queue is: weighted-fair.
This avoids the blocking of lower priorities.
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Ethernet
DSL 1 Mbps
DSL 2 Mbps
Control station
RTU
RTU
Functions
Priority 4
Priority 6
Priority 0
Priority 2
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