EDS-405A/408A Series User’s Manual
Featured Functions
3-41
Port Cost
Setting
Description
Factory Default
Numerical value
input by user
Input a higher cost to indicate that this
port is less suitable as a node for the
Spanning Tree topology.
200000
Port Status
This indicates the current Spanning Tree status of this port. The status values are
Forwarding
for
normal transmission, and
Blocking
to block transmission.
Configuration Limits of RSTP/STP
The Spanning Tree Algorithm places limits on three of the configuration items previously
described:
[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 a multitude of ways. One solution is simply to increase the
Forwarding Delay to at least 11 sec.
HINT
: Take 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 DS’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 QoS 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.
