User`s manual

PT-G7509 User’s Manual Featured Functions
3-45
Configuration Limits of RSTP/STP
The Spanning Tree Algorithm places limits on three of the configuration items:
[Eq. 1]: 1 sec Hello Time ≦≦2 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 PT-G7509’s firmware will alert you immediately if any of these restrictions are violated. For
example, suppose Hello Time = 2 sec, Max. Age = 6 sec, and Forwarding Delay = 4 sec. This does
not violate Eqs. 1 through 3, but it violates Eq. 4:
2 * (Hello Time + 1 sec) = 6 sec, and 2 * (Forwarding Delay – 1 sec) = 6 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 PT-G7509’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-G7509 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-G7509’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.
y Provide predictable throughput for multimedia applications, such as video conferencing or
voice over IP, and minimize traffic delay and jitter.
y Improve network performance as the amount of traffic grows. This will save cost by reducing
the need to keep adding bandwidth to the network.