User manual

FL SWITCH LM
4-16
PHOENIX CONTACT 7278_en_01
Switch-Over Time Response to Be Expected for Spanning Tree
Overview of the switch-over time response to be expected for the maximum number of
switches within a Spanning Tree segment.
4.2.2 Configuration Notes for Rapid Spanning Tree
In contrast to the Spanning Tree method, the Rapid Spanning Tree method supports
event-controlled actions that are no longer triggered based on a timer.
If one cable fails (link down), the Rapid Spanning Tree method can respond more quickly
to this failure and thus the switch-over time can be kept low.
– For short switch-over times, structure your network in such a way that a maximum of
seven switches are located in a cascade up to the root switch. The switch-over times
can range from 2 to 8 s.
– Use priority assignment to specify a central switch as the root.
– It is also recommended to assign a switch as the back-up root.
– For short switch-over times, all switches should support the Rapid Spanning Tree
Protocol.
MaxAge Hello Time Forward Delay Maximum Number of Active
STP Switches
Switch-Over Time
10 s 1 s ≥ 6 s 5 22 s
20 s 1 s ≥ 11 s 10 42 s
30 s 1 s ≥ 16 s 15 62 s
40 s 1 s ≥ 21 s 20 82 s
20 s 2 s 15 s 9 50 s
Bold/italic = Default
A link down or link up must be detected at the switch so that the RSTP switches can
detect a line failure and a restored line more quickly. Please take into consideration, in
particular, paths where media converters are used. If required, media converters offer
setting options to transmit the link status of the fiber optic side to the twisted pair side.
If a link down is not detected at the switch, due to the cable interrupt between the media
converters, and if no link down is forced at the switch, timer-based detection is activated,
which may result in longer switch-over times.