C
HAPTER
14
| Basic Administration Protocols
Connectivity Fault Management
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Figure 293: 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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