User`s manual

TN-5516/5518 Series Featured Functions
3-38
Hello Time (sec.)
Setting Description Factory Default
Numerical value input
by user
This specifies the time interval between “hello” messages
broadcast by the root of the Spanning Tree topology. The
“hello” message is used to check if the topology is healthy.
2
Max. Age (sec.)
Setting Description Factory Default
Numerical value input
by user
This specifies the amount of time to wait for a “hello” message
from the root before the TN-5500 will reconfigure itself as a
root. When two or more devices on the network are recognized
as a root, the devices will renegotiate to set up a new Spanning
Tree topology.
20
Enable STP per Port
Setting Description Factory Default
Enable/Disable This includes the selected port as a node on the Spanning Tree
topology.
Disabled
NOTE We suggest that you disable the Spanning Tree Protocol for ports that are connected directly to a device (PLC,
RTU, etc.) as opposed to network equipment. This will prevent unnecessary negotiation.
Port Priority
Setting Description Factory Default
Numerical value
selected by user
This specifies the port’s priority as a node on the Spanning Tree
topology. Lower values correspond to higher priority.
128
Port Cost
Setting Description Factory Default
Numerical value input
by user
This specifies the port cost. Higher costs correspond to lower
suitability as a node for the Spanning Tree topology.
200000
Port Status
Indicates the current Spanning Tree status of this port. Forwarding indicates normal transmission and
Blocking indicates blocked transmission. Link Down indicates communication link is broken.
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 * (Forwarding Delay – 1 sec)
The TN-5500’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: