PT-7728 User’s Manual
Featured Functions
3-34
Port Status
Indicates the current Spanning Tree status of this port.
Forwarding
indicates normal transmission
and
Blocking
indicates blocked transmission.
Configuration Limits of RSTP/STP
The Spanning Tree Algorithm places limits on three of the configuration items:
[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 * (Forwardin
≦
≦
g Delay – 1 sec)
The PT-7728’s firmware will alert you immediately if any of these restrictions are violated. For
example, suppose Hello Time = 5 sec, Max. Age = 20 sec, and Forwarding Delay = 4 sec. This
does not violate Eqs. 1 through 3, but it violates Eq. 4:
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 seconds.
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 PT-7728’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 PT-7728 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 PT-7728’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:
y
Improve network performance by controlling a wide variety of traffic and managing
congestion.
y
Assign priorities to different categories of traffic. For example, set higher priorities for
time-critical or business-critical applications.
