When CFM is the OAM module at the other end, it is required to use any of the following methods (depending on local configuration) to notify the remote peer:
Generating AIS for certain MEP levels
Sending CCM with interface status TLV ‟down”
Stopping CCM transmission
7210 platforms expect that the fault notified using interface status TLV, is cleared explicitly by the remote MEP when the fault is no longer present on the remote node. On the 7210 SAS, use of CCM with interface status TLV Down is not recommended to be configured with a Down MEP, unless it is known that the remote MEP clears the fault explicitly.
User can configure UP MEPs to use Interface Status TLV with fault propagation. Special considerations apply only to Down MEPs.
When a fault is propagated by the service manager, if AIS is enabled on the SAP/SDP-binding, then AIS messages are generated for all the MEPs configured on the SAP/SDP-binding using the configured levels.
Note that the existing AIS procedure still applies even when fault propagation is disabled for the service or the MEP. For example, when a MEP loses connectivity to a configured remote MEP, it generates AIS if it is enabled. The new procedure that is defined in this document introduces a new fault condition for AIS generation, fault propagated from SMGR, that is used when fault propagation is enabled for the service and the MEP.
The transmission of CCM with interface status TLV must be done instantly without waiting for the next CCM transmit interval. This rule applies to CFM fault notification for all services.
Notifications from SMGR to the CFM MEPs for fault propagation should include a direction for the propagation (up or down: up means in the direction of coming into the SAP/SDP-binding; down means in the direction of going out of the SAP/SDP-binding), so that the MEP knows what method to use. For instance, an up fault propagation notification to a down MEP will trigger an AIS, while a down fault propagation to the same MEP can trigger a CCM with interface TLV with status down.
For a specific SAP/SDP-binding, CFM and SMGR can only propagate one single fault to each other for each direction (up or down).
When there are multiple MEPs (at different levels) on a single SAP/SDP-binding, the fault reported from CFM to SMGR will be the logical OR of results from all MEPs. Basically, the first fault from any MEP will be reported, and the fault will not be cleared as long as there is a fault in any local MEP on the SAP/SDP-binding.