Continuity check (CC) and connectivity verification (CV) are both MPLS-TP functions. CC is used to check loss of continuity defeat (dLOC) between two MEPs in a MEG. CV monitors connectivity between two MEPs within one MEG or in different MEGs.
CC is a proactive OAM operation. It detects LOC faults between any two MEPs in a MEG. A MEP sends CC messages (CCMs) to a remote RMEP at specified intervals. If the RMEP does not receive a CCM for a period 3.5 times provided that; if the specified interval, it considers the connection between the two MEPs faulty. This causes the RMEP to report an alarm and enter the Down state, and the RMEP triggers automatic protection switching (APS) on both MEPs. After receiving a CCM from the MEP, the RMEP will clear the alarm and exit the Down state.
CV is also a proactive OAM operation. It enables a MEP to report alarms when unexpected or error packets are received. For example, if a CV-enabled MEP receives a packet from an LSP and finds that this packet has been transmitted in error along an LSP, the MEP will report an alarm indicating a forwarding error.