Chapter 13
| Basic Administration Protocols
Connectivity Fault Management
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Figure 301: Blocking an ERPS Ring Port
Connectivity Fault Management
Connectivity Fault Management (CFM) is an OAM protocol that includes proactive
connectivity monitoring using continuity check messages, fault verification
through loop back messages, and fault isolation by examining end-to-end
connections between provider edge devices or between customer edge devices.
CFM is implemented as a service level protocol based on service instances which
encompass only that portion of the metropolitan area network supporting a
specific customer. CFM can also provide controlled management access to a
hierarchy of maintenance domains (such as the customer, service provider, and
equipment operator).
This switch supports functions for defining the CFM structure, including domains,
maintenance associations, and maintenance access points. It also supports fault
detection through continuity check messages for all known maintenance points,
and cross-check messages which are used to verify a static list of remote
maintenance points located on other devices (in the same maintenance
association) against those found through continuity check messages. Fault
verification is supported using loop back messages, and fault isolation with link
trace messages. Fault notification is also provided by SNMP alarms which are
automatically generated by maintenance points when connectivity faults or
configuration errors are detected in the local maintenance domain.
Key Components of CFM
CFM provides restricted management access to each Service Instance using a
structured conceptual network based on these components:
â—† A Maintenance Domain defines a part of the network controlled by a single
operator, and supports management access to the domain through Domain
Service Access Points (DSAPs) configured on the domain boundary, as well as
connectivity testing between these DSAPs.
â—† A Maintenance Association (MA) contains the DSAPs for an individual Service
Instance. DSAPs are the primary maintenance points used to monitor
connectivity across a maintenance domain, and are the entry points to the
paths which interconnect the access points allocated to a service instance.
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