Ericsson ECN330, User Manual

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Configuring the ECN330-switch
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frames to pass through that port. There is also a special "Control VLAN" that can
always pass through all ports in the EAPS Domain, including the secondary port
of the master node.
EAPS uses both a polling mechanism and an alert mechanism, described
below, to verify the connectivity of the ring and quickly detect any faults.
Link Down Alert – When a transit node detects a link-down on any of its ports
in the EAPS Domain, that transit node immediately sends a "link down" control
frame on the Control VLAN to the master node.
When the master node receives this "link down" control frame, the master node
moves from the "normal" state to the ring-fault state and unblocks its secondary
port. The master node also flushes its bridging table, and sends a control frame
to all other ring nodes, instructing them to flush their bridging tables as well.
Immediately after flushing its bridging table, each node begins learning the new
topology.
Ring Polling – The master node sends a health-check frame on the Control
VLAN at a user-configurable interval. If the ring is complete, the health-check
frame will be received on its secondary port, and the master node resets its
fail-period timer and continues normal operation.
If the master node does not receive the health-check frame before the fail-period
timer expires, the master node moves from normal state to "ring-fault" state and
unblocks its secondary port. The master node flushes its bridging table and
sends a control frame to all other nodes, instructing them to also flush their
bridging tables. Immediately after flushing its bridge table, each node starts
learning the new topology. This ring polling mechanism provides a backup in the
event that the Link Down Alert frame should get lost for some unforeseen
reason.
Ring Restoration – The master node continues sending periodic health-check
frames out its primary port even when operating in the ring-fault state. Once the
ring is restored, the next health-check frame will be received on the master
node's secondary port. This will cause the master node to transition back to the
normal state, logically block non-control frames on the secondary port, flush its
own bridge table, and send a control frame to the transit nodes, instructing them
to flush their bridging tables and re-learn the topology.
During the time between the transit node detecting that its link is restored and
the master node detecting that the ring is restored, the secondary port of the