User`s manual

EDS-828 Series Featured Functions
3-36
Configuration Limits of RSTP/STP
The Spanning Tree Algorithm places limits on three of the configuration items described above:
[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-828’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.
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 EDS-828’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-828 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-828’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.