Ethernet CFM is enabled by configuring MEPs on each individual path under an Ethernet ring. Only down MEPs can be configured on each path and optionally, CCM sessions can be enabled to monitor the liveliness of the path using interval of 10 or 100 msec. Different CCM intervals can be supported on the path a and path b in an Ethernet ring. CFM is optional if hardware supports Loss of Signal (LOS) for example, which is controlled by configuring no-ccm-enable.
Up MEPs on service SAPs which multicast into the service and monitor the active path may be used to monitor services.
When Ethernet ring is configured on two ports located on different cards, the SAP queues and virtual schedulers are created with the actual parameters on each card.
Ethernet ring CC messages transmitted over the SAP queues using the default egress QoS policy use NC (network class) as a forwarding class. If user traffic is assigned to the NC forwarding class, it competes for the same bandwidth resources with the Ethernet CCMs. As CCM loss could lead to unnecessary switching of the Ethernet ring, congestion of the queues associated with the NC traffic should be avoided. The operator must configure different QoS Policies to avoid congestion for the CCM forwarding class by controlling the amount of traffic assigned into the corresponding queue.
Details of the Ethernet ring applicability in the services solution can be found in the respective sections of the 7450 ESS, 7750 SR, 7950 XRS, and VSR Layer 2 Services and EVPN Guide: VLL, VPLS, PBB, and EVPN.