Edge-Core ECS4660-28F, Руководство по управлению, Страница: 549 / 2020

C
HAPTER
14
| Basic Administration Protocols
Connectivity Fault Management
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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 299: 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