CANOGA PERKINS 9145E NID Software Version 3.0 - Manual (Page 126)

9145E NID Software User’s Manual Service OAM
Service OAM
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11.1.3 SOAM Protocols
SOAM Connectivity Fault Management provides the following protocols:
• Continuity Check Protocol: The continuity check message (CCM) is used to detect con-
nectivity failures in an MA/MEG. Each MEP can be configured to periodically transmit a
CCM. CCMs are sent to all MEPs associated with a given MA/MEG. Use of a multicast
destination address allows the discovery of remote MEP MAC addresses and the detec-
tion of leaks between MAs/MEGs. Every active MEP maintains a CCM database. As a
MEP receives CCMs, it updates the record in the database. If no CCM frames from a
peer MEP are received within the defined interval (3.5 times the CCM transmission
period), loss of continuity defect is detected.
• Loopback Protocols: A loopback message (LBM) is used to identify the specific fault
location. The MEP generates a loopback message addressed to a specific maintenance
point within an MA/MEG. The destination MIP or MEP must respond with a loopback reply
(LBR).
A single, multicast LBM is generated by a MEP, and every far end MEP in the MA/MEG responds
with a loopback reply; hence, the originating MEP will know all the far end MEPs that have
connectivity.
A sweep loopback procedure is used to detect the maximum transmission unit (MTU) size for a
given end-to-end connection. Loopback messages are sent continuously, incrementing the MTU
size for each new request (by increasing the size of the data type-length-value (TLV) component).
The network will drop frames above a certain unsupported MTU, hence the originating MEP will
not receive the expected responses.
• Linktrace Protocol: The linktrace message (LTM) traces the path from a source MEP to
a destination MP in the same MA or MEG. All intermediate MIPs respond with a linktrace
reply (LTR) to the source MEP. Only the MIPs in the path between the source and desti-
nation will respond. LTM procedures are executed on demand and are initiated by admin-
istrators.
• Alarm Indication Signal (AIS): AIS is a fault isolation method, applicable only to Y.1731
procedures. Using AIS messages, a lower level domain notifies a higher level domain of
connectivity errors detected at that particular lower level. Upon detecting an AIS mes-
sage, a higher level MEP will suppress all other defects detected at its level; the AIS indi-
cates that there is a defect at an underlaying level, hence that defect has to be solved
first.
• Remote Defect Indication (RDI): A MEP can indicate to its peers, through an RDI flag,
that it has encountered a defect, either local or remote. This information is advertised via
CCM messages to all MEPs in the MA/MEG. The RDI flag is set for as long as the error
condition is active.
The differences between 802.1ag and Y.1731 SOAM protocol support are shown in Table 11-1.