Chapter 13
| Basic Administration Protocols
Connectivity Fault Management
– 489 –
◆ A Maintenance Level allows maintenance domains to be nested in a
hierarchical fashion, providing access to the specific network portions required
by each operator. Domains at lower levels may be either hidden or exposed to
operators managing domains at a higher level, allowing either course or fine
fault resolution.
◆ Maintenance End Points (MEPs) which provide full CFM access to a Service
Instance (i.e., a specific MA), and Maintenance Intermediate Points (MIPs) which
are passive entities that merely validate received CFM messages, or respond to
link trace and loop back requests. MIPs are the interconnection points that
make up all possible paths between the DSAPs within an MA, and may also
include interconnection points in lower-level domains if exposed by CFM
settings.
The following figure shows a single Maintenance Domain, with DSAPs located on
the domain boundary, and Internal Service Access Points (ISAPs) inside the domain
through which frames may pass between the DSAPs.
Figure 302: Single CFM Maintenance Domain
The figure below shows four maintenance associations contained within a
hierarchical structure of maintenance domains. At the innermost level, there are
two operator domains which include access points marked “O
1
” and “O
2
”
respectively. The users of these domains can see their respective MEPs as well as all
the MIPs within their domains. There is a service provider domain at the second
level in the hierarchy. From the service provider’s view, the access points marked
“P” are visible, and all access points within the operator domains have also been
made visible as MIPs according to common practice. And finally, there is a customer
domain at the top of the hierarchy. Users at this level can only see the access points
marked “C” on the outer domain boundary. Again, normal practice is to hide the
internal structure of the network from outsiders to reduce security risks.
Maintenance Domain
Bridge
DSAP
ISAP
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