Tripp Lite NGI-M08C4POE8-2 Owner's Manual page 146

Wait to Restore (WTR) Timer
The RPL owner uses the WTR timer. The WTR timer applies to the revertive mode to prevent
frequent triggering of the protection switching due to port flapping or intermittent signal failure
defects. When this timer expires, the RPL owner sends a R-APS (NR, RB) through the ring.
Wait to Block (WTB) Timers
This wait-to-block timer is activated on the RPL owner. The RPL owner uses WTB timers before
initiating an RPL block and then reverting to the idle state after operator-initiated commands,
such as for FS or MS conditions, are entered. Because multiple FS commands are allowed to co-
exist in a ring, the WTB timer ensures that the clearing of a single FS command does not trigger
the re-blocking of the RPL. The WTB timer is defined to be 5 seconds longer than the guard
timer, which is enough time to allow a reporting ERN to transmit two R-APS messages and allow
the ring to identify the latent condition. When clearing a MS command, the WTB timer prevents
the formation of a closed loop due to the RPL owner node applying an outdated remote MS
request during the recovery process.
Hold-off timer -- Each ERN uses a hold-off timer to delay reporting a port failure. When the
timer expires, the ERN checks the port status. If the issue still exists, the failure is reported. If
the issue does not exist, nothing is reported.
ERPS Revertive and Non-Revertive Switching
ERPS considers revertive and non-revertive operation. In revertive operation, after the condition
(s) causing a switch has cleared, the traffic channel is restored to the working transport entity, i.e.
blocked on the RPL. In the case of clearing of a defect, the traffic channel reverts after the expiry
of a WTR timer, which is used to avoid toggling protection states in case of intermittent defects.
In non-revertive operation, the traffic channel continues to use the RPL, if it is not failed, after a
switch condition has cleared.
Control VLAN
The pure ERPS control packets domain only, no other packets are transmitted in this vlan to
guarantee no delay for the ERPS. So when you configure a Control VLAN for a ring, the vlan
should be a new one. The ERPS will create this control vlan and its member ports automatically.
The member port should have the Left and Right ports only.
In ERPS, the control packets and data packets are separated in different vlans.
The control packets are transmitted in a vlan which is called the Control VLAN.
Notice:
Control VLAN and Instance
In CLI or Web configurations, there are the Control VLAN and the Instance settings.
If the Control VLAN is configured for a ring and you want to configure an instance for the ring.
The control vlan of the instance must be same as the Control VLAN; otherwise, you will get an
error. If you still want to use this instance, you can change the Control VLAN to same as the
control vlan of the instance first. And then configures the instance.
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