The
demarcation or handoff between the Service Providers is referred to as the Network-to-
Network Interfaces (NNIs). The MEF has defined several NNIs:
?– External Network-to-Network Interface (E-NNI) An open interface used to
interconnect two MEN Service Providers.
?– Internal Network-to-Network Interface (I-NNI) An open interface used to
interconnect network elements from a given MEN Service Provider.
?– Network Interworking Network-to-Network Interface (NI-NNI) An open
interface that supports the extension of transport facilities used to support Ethernet
services and associated EVCs over an external transport network not directly
involved in the end-to-end Ethernet service.
?– Service Interworking Network-to-Network Interface (SI-NNI) An interface
that supports the interworking of an MEF service with services provided via other
service enabling technologies (e.g., Frame Relay, ATM, IP, etc.).
Defining Carrier Ethernet Services
Carrier Ethernet services are essentially connectivity services that employ Ethernet
frames transported over the MEN using a host of different technologies such as SONET,
WDM, MPLS, and so on. As shown in Figure 2.
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