Metro Ethernet Forum (MEF) Services
MEF Services Overview
MEF Ethernet Services are defined as connectivity services provided by a Service Provider's Carrier Ethernet Networks (CENs) to Customer Edge (CE) devices. The connectivity service is modeled by an Ethernet Virtual Connection (EVC). The EVC is defined as an association of two or more User Network Interfaces (UNIs) that limits the exchange of Service Frames to UNIs in the EVC. An Ethernet Service   consists of an Ethernet Service Type and is associated with one or more Bandwidth Profile(s) and supports one or more Classes of Service. A service is also associated with a list of Layer Two Control Protocols such as Spanning Tree Protocol or Link Aggregation Control Protocol and a set of actions that specify how they should be handled.
Ethernet Service Types can be used to create a broad range of Subscriber services. The service types are characterized by their required connectivity . The following service types have been defined to date: Ethernet Line Service (E-Line Service) uses a Point-to-Point EVC. The Ethernet LAN Service (E-LAN Service) uses a Multipoint-to-Multipoint EVC.The Ethernet Tree Service (E-TREE Service) uses a Rooted-Multipoint EVC.
MEF E-Line Service
E-Line service types require Point-to-Point (P2P) connectivity, as illustrated in Figure 2. In a Point-to-Point EVC, exactly two UNIs must be associated with one another. Ingress Service Frame to the EVC at one UNI can only result in an egress Service Frame at the associated UNI.
Figure 2 - Point-to-Point EVC.
MEF E-LAN Service
E-LAN service types require Multipoint-to-Multipoint (MP2MP) connectivity, as illustrated in Figure 3. In a Multipoint EVC, two or more UNIs are associated with one another. An ingress Service Frame mapped to the EVC at one of the UNIs can only result in an egress Service Frame at one or more of the associated UNIs.
Figure 3 - Multipoint-to-Multipoint EVC.
MEF E-Tree Service
E-Tree service types require Rooted-Multipoint (RMP) connectivity, as illustrated in Figure 4. In a Rooted-Multipoint EVC, one or more of the UNIs must be designated as a Root and each of the other UNIs must be designated as a Leaf. A single root has connectivity to all the leaves. An ingress Service Frame mapped to the EVC at a Root UNI may be delivered to one or more of the associated UNIs (either Root or Leaf) in the EVC. An ingress Service Frame mapped to the EVC at a Leaf UNI can only result in an egress Service Frame at one, some or all of the Root UNIs.
Figure 4 - Rooted-Multipoint EVC.