Cisco ASR 920 series, Руководство по настройке Ethernet-маршрутизатора

Страница: 145 / 438

larger the domain, the higher the level value. For example, a customer domain would be larger than an operator
domain. The customer domain may have a maintenance level of 7 and the operator domain may have a
maintenance level of 0. Typically, operators would have the smallest domains and customers the largest
domains, with service provider domains between them in size. All levels of the hierarchy must operate together.
Domains should not intersect because intersecting would mean management by more than one entity, which
is not allowed. Domains may nest or touch but when two domains nest, the outer domain must have a higher
maintenance level than the domain nested within it. Nesting maintenance domains is useful in the business
model where a service provider contracts with one or more operators to provide Ethernet service to a customer.
Each operator would have its own maintenance domain and the service provider would define its domain
—
a
superset of the operator domains. Furthermore, the customer has its own end-to-end domain which is in turn
a superset of the service provider domain. Maintenance levels of various nesting domains should be
communicated among the administering organizations. For example, one approach would be to have the
service provider assign maintenance levels to operators.
CFM exchanges messages and performs operations on a per-domain basis. For example, running CFM at the
operator level does not allow discovery of the network by the higher provider and customer levels.
Network designers decide on domains and configurations. The figure below illustrates a hierarchy of operator,
service provider, and customer domains and also illustrates touching, intersecting, and nested domains.
Maintenance Associations and Maintenance Points
A maintenance association (MA) identifies a service that can be uniquely identified within the maintenance
domain. The CFM protocol runs within a maintenance association. A maintenance point is a demarcation
Carrier Ethernet Configuration Guide (Cisco ASR 920 Series)
127
Configuring Ethernet Connectivity Fault Management in a Service Provider Network
Maintenance Associations and Maintenance Points