In the specification document MEF 12.2, CEN is described as "a network from a Service Provider or Operator supporting the MEF service and architecture models".
The connection between the Subscriber's sites and the Carrier Ethernet Network (CEN) is achieved by connecting a switch/router at the end-user premises denoted as CE (Customer Equipment) to one or more switches/routers of the Service Provider (SP). The interface between the Customer Edge (CE) and the CEN is referred to as the User Network Interface (UNI).
Note that a CEN can be composed of two or more internal CENs. For instance, a Service Provider network can consistof a number of independent Carrier Ethernet networks interconnected over a wide-area Ethernet network acting as a backbone.
Carrier Ethernet Network is often used interchangeably with Metro Ethernet Network (MEN). It is also referred to as MEN Operator or MEN Service Provider.
A Carrier Ethernet Network (CEN) is the entity used for the backhaul service for a Mobile Operator (see MEF 22.2 - MBH)