The Continuity Check Message (CCM) provides a means to detect hard and soft faults such as software failure, memory corruption, or misconfiguration. The failure detection is achieved by each Maintenance End Point (MEP) transmitting a CCM periodically within its associated Service Instance.
As a result, MEPs also receive CCMs periodically from other MEPs. If a MEP on local Bridge stops receiving the periodic CCMs from peer MEP on a remote Bridge, it can assume that either the remote Bridge has failed or failure in the continuity of the path has occurred. The Bridge can subsequently notify the network management application about the failure and initiate the fault verification and fault isolation steps either automatically or through operator command.
A CCM requires only N transmissions within its member group, where N is the number of members within the member group. In other words, if a Virtual Bridge LAN Service has N members, only N CCMs need to be transmitted periodically, one from each.
Each MEP transmits periodic multicast CCM towards other MEPs. For each MEP, there is 1 transmission and N-1 receptions per time period. Each MEP has remote MEP database. It records the Mac address of remote MEPs.
Continuity Check (CC) messages are periodic hello messages multicast by a MEP within the maintenance domain, at the rate of X; X can be 3 milliseconds (ms), 10ms, 100ms, 1 second or 10 seconds. All Maintenance association Intermediate Points (MIPs) and MEPs in that domain will receive it but will not respond to it. The receiving MEPs will build a MEP database that has entities of the format. MEPs receiving this CC message will catalog it and know that the various maintenance associations (MAs) are functional, including all intermediate MIPs.
CCMs are not directed towards any specific; rather they are multicast across the entire point-to- point or multipoint service on a regular basis. Accordingly, one or more service flows, including the determination of MAC address reachability across a multipoint network, are monitored for connectivity status with IEEE 802.1ag.