Ethernet CFM

The articles in this subcategory describe ECFM and provide an overview of its salient features, such as MD (Maintenance Domain), MA (Maintenance Association), Maintenance Point, and CFM (Connectivity Fault Management) messages.

ECFM provides capabilities useful for detecting, verifying, isolating connectivity failures, and performance monitoring in Virtual Bridged LANs. The fault detection, isolation, and verification are done through CC, LB, and LT protocols. Performance monitoring is done using LM and DM functions. These capabilities can be used in networks operated by multiple independent organizations, each with restricted access to one another’s equipment.

In general, the network administrator is informed about the failure in the connection, based on the reception of CCMs (Continuity Check Messages). The administrator can then initiate LB or LT accordingly to determine and isolate the fault condition.

ECFM also provides performance monitoring functions for the measurement of various performance parameters in Ethernet point-to-point connections. It also supports the measurement of frame loss ratio, frame delay, and frame delay variation performance parameters.

The CFM information is conveyed in protocol frames called CFM PDUs (CFM Protocol Data Units). The CFM PDUs contain the appropriate control and status information used to detect, verify, and isolate faults. It also contains information for path discovery in CFM-enabled links. The CFM PDUs are processed, forwarded, or discarded by the entities configured in the Bridge port, based on the MD (Maintenance Domain) level to which that entity belongs.

• Defines Maintenance Domains, Maintenance Associations, their constituent Maintenance Points, and the managed objects required to create and administer them.
• Describes the protocols and procedures used by Maintenance Points to detect and diagnose connectivity faults within a maintenance domain.

CFM Functions are categorized as follows:

• Fault Detection
• Fault Verification
• Fault Isolation
• Fault Notification
• Performance Management

Fault Detection uses Continuity Check Protocol to detect both connectivity failure and unintended connectivity between service instances. Each MEP (Maintenance End Point) periodically transmits a multicast CCM announcing the identity of the MEP and its MA and tracks the CCM reception from other MEPs.

Fault Verification is an administrative action, typically performed after fault detection. It uses Loop Back Protocol to perform Fault Verification. An MEP is ordered to transmit a unicast LBM message to MEP in an MA, and the receiving MEP replies (if Target MAC (Media Access Control) Address matches) and sends an LBR (Loop Back Reply) message.

Fault Isolation is also an administrative action that uses Link Trace Protocol to isolate the fault location, in which an MEP is ordered to transmit a multicast LTM (Link Trace Message) in an MA. All the receiving entities, of the same MA, reply to it with a unicast LTR (Link Trace Reply) message and failure in expected LTR reception from an ECFM entity finally isolates the fault location.

Fault Notification is achieved by AISs (Alarm Indication Signals), which notify and suppress alarms on fault events, allowing the relevant operators to take appropriate actions.

Performance management is achieved through Frame Loss measurement and Frame Delay measurement.