Fundamental to both Carrier Ethernet and LAN Ethernet is the fact that data is
carried in an Ethernet frame. What this means is, in effect, an Ethernet frame originating
at a device in the LAN, now continues to traverse across one or more Service
Provider networks,3 largely unaltered, and terminates at a device in a remote LAN.
One way to look at this transformation is that it essentially creates one larger Ethernet,
spanning LANs, MANs, and may be even the WAN, albeit delivered as a service to the
customer. This transformation is shown in Figure 2.2, courtesy of the MEF, and illustrates
the remarkable potential of Carrier Ethernet. The terms UNI and NNI in the
figure denote standardized interface hand-offs between the enterprise customer and
1 MEF is the preeminent nonprofit industry body focused solely on enabling Carrier Ethernet. The ???Metro???
reference in MEF is now a misnomer, however, and does not accurately reflect its charter and focus, which
has long extended beyond the metro.
2 Because it can, as will be seen later, also support non-Ethernet services (albeit over an Ethernet layer).
3 The Service Provider networks could encompass both the MAN and the WAN.
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