Metro Ethernet services can support a wide range of
applications and subscriber needs easily, efficiently
and cost-effectively.  Using standard Ethernet interfaces, 
subscribers can set up secure, private Ethernet Virtual 
Connections, to connect their sites together and connect 
to business partners, suppliers and the Internet.
        
This MIB module defines the managed objects and notifications
describing Ethernet Virtual Connections.
        
Ethernet Virtual Connections (EVC), are defined by the Metro
Ethernet Forum (MEF), as an association between two or more
UNIs.  Frames within an EVC can only be exchanged among the
associated UNIs.  Frames sent into the MEN via a particular
UNI must not be delivered back to the UNI from which it 
originated.  
        
Along an EVC path, there are demarcation flow points on 
associated ingress and egress interface, of every device, 
through which the EVC passes.  A service instance represents
these flow points where a service passes through an interface.  
        
From an operational perspective, a service instance serves 
three purposes: 
    1.  Defines the instance of a particular EVC service on
        a specific interface and identifies all frames that
        belongs to that particular service/flow.
    2.  To provide the capability of applying the configured 
        features to those frames belonging to the service.
    3.  To optionally define how to forward those frames in
        the data-path.  
        
The association of a service instance to an EVC depicts
an instance of an Ethernet flow on a particular interface
for an end-to-end (UNI-to-UNI) Ethernet service for a 
subscriber.
        
The following diagram illustrates the association of
EVC, UNIs and service instances.  UNI physical ports
are depicted as 'U', and service instances as 'x'.
        
    CE             MEN            MEN            CE
  -------        -------        -------        -------
  |     |        |     |   ()   |     |        |     |
  |     |--------Ux   x|--(  )--|x   xU--------|     |
  |     |        |     |   ()   |     |        |     |
  -------        -------        -------        -------
                 ^                    ^
                 |                    |
                 -------- EVC ---------
        
This MIB module addresses the functional areas of network
management for EVC, including:
        
    The operational mode for interfaces that are providing
    Ethernet service(s).
        
    The service attributes regarding an interface behaving
    as UNI, such as CE-VLAN mapping and layer 2 control 
    protocol (eg. stp, vtp, cdp) processing.
        
    The provisioning of service instances to define flow 
    points for an Ethernet service.
        
    The operational status of EVCs for notifications
    of status changes, and EVC creation and deletion.
        
Definition of terms and acronyms:
        
    B-Tag: Backbone Tag field in Ethernet 802.1ah frame
        
    CE: Customer Edge
        
    CE-VLAN: Customer Edge VLAN
        
    CoS: Class Of Service
        
    EVC: Ethernet Virtual Connection
        
    I-SID: Service Instance Identifier field in Ethernet 
    802.1ah frame
        
    MAC: Media Access Control
        
    MEN: Metro Ethernet Network 
        
    NNI: Network to Network Interface
        
    OAM: Operations Administration and Management
        
    PPPoE: Point-to-Point Protocol over Ethernet
        
    Service frame: An Ethernet frame transmitted across the 
    UNI toward the service provider or an Ethernet frame 
    transmitted across the UNI toward the Subscriber.
        
    Service Instance: A flow point of an Ethernet service
        
    Service provider: The organization providing Ethernet
    service(s).
        
    Subscriber: The organization purchasing and/or using 
    Ethernet service(s).
        
    UNI: User Network Interface
         The physical demarcation point between the 
         responsibility of the service provider and 
         the responsibility of the Subscriber.
        
    UNI-C: User Network Interface, subscriber side
        
    UNI-N: User Network Interface, service provider side
        
    VLAN: Virtual Local Area Network