The Subscriber or customer equipment is typically a router or a switch
(an IEEE 802.1Q bridge).
A MEN itself consists of physical components (e.g., network elements, ports, etc.)
and logical components (e.g., meters, policers, shapers, virtual switches, links, etc.).
It can be owned and operated by multiple Service Providers and provides the underlying
transport (SONET, WDM, RPR, etc.) to carry the Ethernet frames. It essentially
connects geographically separated enterprise LANs across the MAN and WAN.
The Carrier Ethernet service is actually provided by the Service Provider owning
the MEN over an Ethernet Virtual Connection (or EVC, which is defined in a later
section).
The MEF has more formally defined a three-layered model (also shown in Figure 2.5)
for the MEN; the Application services (APP) layer supports end-user applications carried
over Ethernet connectivity services provided at the Ethernet services (ETH) layer,
and these connectivity services in turn are delivered over various transport/networking
technologies in the Transport services (TRAN) layer. The key focus of the MEF and
other standards bodies is the ETH layer; Carrier Ethernet is defined in this layer.
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