Dell PowerConnect 7048P User Manual - Page 762

How Does Dot1ag Work Across a Carrier Network? A typical metropolitan area network comprises operator, service provider, and customer networks. To suit this business model, CFM relies on a functional model of hierarchical maintenance domains (MDs). These domains are assigned a unique MD level. There is a maximum of 8 levels, which can be nested but cannot overlap. Each organization can have its own maintenance domain. The MD level limits administrator access to the appropriate domain. Figure 26-1 depicts three domains: the customer subscribes to the services of a provider, who, in turn, subscribes to the services of two operators. This scenario is a likely one, since no operator has complete coverage of a large region. A service instance would span the provider network covering one or more operators. Every domain has its own network management system. Dot1ag defines OAM services that operate across these domains (the vertical arrow) and within them (the horizontal arrow) Figure 26-1. Organization of Domains Customer Site 1 Access Links, 802.3ah Customer Site 2 Customer 802.1ag Provider Operator 1 Operator 3 Operator 2 Entities at different levels have different responsibilities. For example, the lower level (operator) overlooks a subset of the network in detail and provides information about its status to its higher levels such as the provider level). Higher levels have a broader, but less detailed, view of the network. As a result, a provider could include multiple operators, provided that the domains 762 Configuring Connectivity Fault Management