15). CFM/OAM assumes there may be multiple levels of customer-provider
relationships involved in providing Carrier Ethernet services. An operator in a city may
run a Q-in-Q network. An end-to-end provider may contract with Q-in-Q networks in
several cities and with a MAC-in-MAC backbone provider to create the end-to-end service
required by a customer. The customer, in turn, may be offering services to clients
internally to an enterprise.
In this kind of layered environment, it is important to hide information. For example, if
a customer initiates a linktrace operation, the provider does not want each bridge in his
network to be visible as a waypoint to that customer??™s linktrace. This is especially true if
that ???customer??? is a rival provider that is subcontracting services. The various frame encapsulations
(Q-in-Q, MAC-in-MAC) often ensure that a CFM/OAM message at a higher
level cannot be detected as such by a lower level device. Where business relationships add
additional layers not reflected in the actual data frames themselves, CFM/OAM provides
a ???Maintenance Domain Level (802.1ag)??? or ???Maintenance Entity Group Level (Y.
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