EDS-508A/505A Series User’s Manual
Featured Functions
3-48
Configuration Limits of RSTP/STP
The Spanning Tree Algorithm places limits on three of the configuration items described
previously:
[Eq. 1]: 1 sec
≦
Hello Time
≦
10 sec
[Eq. 2]: 6 sec
≦
Max. Age
≦
40 sec
[Eq. 3]: 4 sec
≦
Forwarding Delay
≦
30 sec
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)
The EDS’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 many ways. One solution is simply to increase the Forwarding
Delay value to at least 11 sec.
HINT
: Perform the following steps to avoid guessing:
Step 1:
Assign a value to “Hello Time” and then calculate the left most part of Eq. 4 to get the
lower limit of “Max. Age.”
Step 2:
Assign a value to “Forwarding Delay” and then calculate the right most part of Eq. 4 to get
the upper limit for “Max. Age.”
Step 3:
Assign a value to “Forwarding Delay” that satisfies the conditions in Eq. 3 and Eq. 4.
Using Traffic Prioritization
The EDS’s traffic prioritization capability provides Quality of Service (QoS) to your network by
making data delivery more reliable. 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. The EDS can inspect
both IEEE 802.1p/1Q layer 2 CoS tags, and even layer 3 TOS information to provide consistent
classification of the entire network. The EDS’s QoS capability improves the performance and
determinism of industrial networks for mission critical applications.
The Traffic Prioritization Concept
What is Traffic Prioritization?
Traffic prioritization 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:
Improve network performance by controlling a wide variety of traffic and managing congestion.
Assign priorities to different categories of traffic. For example, set higher priorities for
time-critical or business-critical applications.
Provide predictable throughput for multimedia applications, such as video conferencing or
voice over IP, and minimize traffic delay and jitter.
Improve network performance as the amount of traffic grows. This will save cost by reducing
the need to keep adding bandwidth to the network.
