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EDS-508 Series User’s Manual Featured Functions
3-30
These three variables are further restricted by the following two inequalities:
[Eq. 4]: 2 * (Hello Time + 1 sec) ≦ Max. Age ≦ 2 * (Forwarding Delay – 1 sec)
MOXA EtherDevice Switch’s firmware will alert you immediately if any of these restrictions are
violated. For example, setting
Hello Time = 5 sec, Max. Age = 20 sec, and Forwarding Delay = 4 sec does not violate Eqs. 1
through 3, but does violate Eq. 4, since in this case,
2 * (Hello Time + 1 sec) = 12 sec, and 2 * (Forwarding Delay – 1 sec) = 6 sec.
You can remedy the situation in any number of ways. One solution is simply to increase the
Forwarding Delay value to at least 11 sec.
Using Traffic Prioritization
Using the traffic prioritization capabilities of your EDS provides Quality of Service (QoS) to your
network through increased reliability of data delivery. You can prioritize traffic on your network
to ensure that high priority data is transmitted with minimum delay. Traffic can be controlled by a
set of rules to obtain the required Quality of Service for your network. The rules define different
types of traffic and specify how each type should be treated as it passes through the Switch.
MOXA EtherDevice Switch can inspect both IEEE 802.1p/1Q layer 2 CoS tag, and even layer 3
TOS information to provide consistent classification of the entire network. MOXA EtherDevice
Switch Series’ QoS capability improves the performance and determinism of industrial networks
for mission critical applications.
The Concept of Traffic Prioritization
What is Traffic Prioritization?
Today’s application traffic consists of different types of data. When these different types of data
compete for the same bandwidth, a network can quickly become overloaded, resulting in slow
response times (long latency), and application time-outs. Traffic prioritization is a mechanism that
allows you to prioritize data so that time-sensitive and system-critical data can be transferred
smoothly and with minimal delay over a network. The benefits of using traffic prioritization are:
# You can control a wide variety of traffic and manage congestion on your network, therefore
improving performance.
# You can assign priorities to traffic. For example, set higher priorities for time-critical or
business-critical applications.
# You can provide predictable throughput for multimedia applications such as video
conferencing or voice over IP, as well as minimize traffic delay and jitter.
# You can improve network performance as the amount of traffic grows, which also reduces
the need to constantly add bandwidth to the network, therefore saving cost.
How Traffic Prioritization Works
Traffic prioritization uses the four traffic queues that are present in your EDS to ensure that high
priority traffic is forwarded on a different queue from lower priority traffic. This is what provides
Quality of Service (QoS) to your network.
EDS traffic prioritization depends on two industry-standard methods:
# IEEE 802.1D—a layer 2 marking scheme.