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20 Description of the Ring Protocol
link non-monitoring ring placed at both ends of the shared link. Of the two ring ports, these
health check frames are sent from the ring port that is not a shared link. This means that
when a fault occurs on a shared link, even though the master node of the shared link
non-monitoring ring can no longer receive the health check frames it sent itself, fault
detection can be prevented while health check frames can be received from the terminal
nodes (shared nodes) of the shared link non-monitoring ring.
Figure 20-11 Normal operation for shared link non-monitoring rings
(a) Master node operation
To prevent fault misdetection due to one-way link faults, health check frames (HC(M)s) are
sent from two ring ports. Monitoring is performed to check that HC(M)s in both directions
are received within the pre-determined time. Aside from the HC(M)s sent from the master
node, reception is also monitored for health check frames (HC(S)s) sent from the terminal
nodes (shared nodes) of the shared link non-monitoring ring placed at both ends of a
shared link. Data frame transfer is performed on the primary port. Because the secondary
port is logically blocked, data frame transfer and MAC address learning are not performed.
(b) Transit node operation
Transit node operation is the same as for single rings. Transit nodes do not monitor HC(M)s
and HC(S)s. When an HC(M) or HC(S) is received, it is transferred to the next node in the
ring. Data frame transfer is performed on both ring ports.
(c) Terminal node operation for shared link non-monitoring rings
Terminal nodes (shared nodes) for shared link non-monitoring rings send HC(S)s to the
master node in shared link non-monitoring rings. Of the two ring ports, these HC(S)s are
sent from the one that is not a shared link. The HC(M)s sent and data frames transferred by
master nodes are the same as for transit nodes.
(2) Shared link monitoring rings
Like single rings, shared link monitoring rings consist of one master node and multiple
transit nodes. The nodes placed at both ends of a shared link run the same as for a single
ring, as master nodes or transit nodes.
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