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Carrier Ethernet Services operate over Ethernet Virtual Connections or EVCs. An EVC is an association of two or more UNIs. These UNIs are said to be in the EVC. A given UNI can support more than one EVC via the Service Multiplexing attribute. There are three types of EVCs:
An ingress Service Frame that is mapped to an EVC can be delivered to one or more of the UNIs in the EVC other than the ingress UNI. It MUST NOT be delivered back to the ingress UNI (note that this limitation is only for service frames and does not affect fault management frames like Loopback) It MUST NOT be delivered to a UNI not in the EVC. An EVC is always bi-directional in the sense that ingress Service Frames can originate at any UNI in an EVC. |