Инструкции По Установке для 3com S7906E

 

1-4 

Figure 1-4 Levels of MPs 

 

A MEP list is a collection of local MEPs allowed to be configured in an MA and the remote MEPs to be 

monitored. It lists all the MEPs configured on different devices in the same MA. The MEPs all have 

unique MEP IDs. When a MEP receives from a remote device a continuity check message (CCM) that 

carries a MEP ID not included in the MEP list of the MA, it drops the message.  

CFD works effectively only in properly-configured networks. Its functions, which are implemented 

through the MPs, include: 

z 

Continuity check (CC); 

z 

Loopback (LB) 

z 

Linktrace (LT) 

Continuity check is responsible for checking the connectivity between MEPs. Connectivity faults are 

usually caused by device faults or configuration errors. This function is implemented through periodic 

sending of continuity check messages (CCMs) by the MEPs. As a multicast message, a CCM sent by 

one MEP is intended to be received by all the other MEPs in the same MA. If a MEP fails to receive the 

CCMs within 3.5 sending periods, the link is regarded as faulty and a corresponding log is generated. 

When multiple MEPs send CCMs at the same time, the multipoint-to-multipoint link check is achieved.  

Similar to ping at the IP layer, loopback is responsible for verifying the connectivity between a local 

device and a remote device. To implement this function, the local MEP sends loopback messages 

(LBMs) to the remote MEP. Depending on whether the local MEP can receive a loopback reply 

message (LBR) from the remote MEP, the link state between the two can be verified. LBMs and LBRs 

are unicast messages. They are used to verify the connectivity between two points.