Tripp Lite NGI-S04C2 Owner's Manual page 37

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formation of a closed loop due to the RPL owner node applying an outdated remote MS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.
Instance:
For ERPS version 2, the instance is a profile specifies a control vlan and a data vlan or
multiple data vlans for the ERPS. In ERPS, it can separate the control packets and data
packets in different vlans. The control packets are in the Control VLAN and the data
packets can be in one or multiple data vlan. And then user can assign an instance to an
ERPS ring easily.
In ERPS version 1, if a port is blocked by ERPS, all packets are blocked.
In ERPS version 2, if a port is blocked by a ring of ERPS, only the packets belong to the
vlans in the instance are blocked.
Notice:
Control VLAN and Instance:
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,
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