29.4.1 Normal operation of the ring

The following figure shows normal operation for a multi-ring configuration with shared links.

Figure 29-13: Status when the ring is normal

<Structure of this section>

(1) Shared link non-monitoring ring

A shared link non-monitoring ring consists of one master node and multiple transit nodes. However, to provide assistance because shared link faults are not monitored, health check frames are sent to the master node from the terminal nodes (shared nodes) of the shared 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 29-14: Normal operation in a shared link non-monitoring ring

(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) End-node operation of a shared link non-monitoring ring

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 to 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 ring

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.

Figure 29-15: Normal operation in a shared link monitoring ring

(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. 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 the HC(M)s sent by the master node. When an HC(M) is received, it is transferred to the next node in the ring. Data frame transfer is performed on both ring ports.