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EVCCarrier 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 (discussed in section 5). 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.
OVCWhen an EVC spans multiple CENs, it is composed on segments in each CEN that are concatenated together to form the EVC. These segments are called Operator Virtual Connections or OVCs. An OVC is the association of UNIs and ENNIs within a single CEN where at least one of these external interfaces is an ENNI. Each association of an OVC and an external interface is called an OVC End Point. An OVC Endpoints have roles. An OVC Endpoint at a UNI can either be a Leaf OVC Endpoint or a Root OVC Endpoint. An OVC Endpoint at an ENNI can be a Leaf OVC Endpoint, a Root OVC Endpoint, or a Trunk OVC Endpoint. Leaf and Root OVC Endpoints are similar to UNIs, i.e. an egress frame on an Root OVC Endpoint can come from any type of OVC Endpoint, but a egress frame on a Leaf OVC Endpoint can only come from a Root OVC Endpoint or a Trunk OVC Endpoint. The Trunk role is unique to the ENNI. It provides a way to extend the concept of Root and Leaf bidirectionally across the ENNI. A Trunk OVC Endpoint is configured with two S-VLAN IDs, one for Service Frames that came from a Root OVC Endpoint (or another Trunk OVC Endpoint) and a second one that is for Service Frames that came from a Leaf (or another Trunk OVC Endpoint). A Service Frame can only egress on a Trunk OVC Endpoint if:
An OVC is point-to-point if it associates exactly two OVC End Points. An OVC is multipoint-to-multipoint if can can associate two more OVC End Points that have the root role. An OVC is rooted multipoint if it has at least one leaf or trunk OVC End Point. At right is a diagram of an EVC comprises 3 point-to-point OVCs. OVC1 runs from the first UNI to the ENNI. OVC2 runs from ENNI to ENNI. OVC3 runs from ENNI to the second UNI. Each OVC is managed by the CEN Operator and the EVC is managed by the Service Provider. |
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Congratulations, you have reached the end of section 4. Proceed to the next section: (insert link) Go back to the beginning of this section: 4. Key Components of a Carrier Ethernet Network |
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There are two categories of service connections - Ethernet Virtual Connections and Operator Virtual Connections. Ethernet Virtual Connection (EVC)
Operator Virtual Connection (OVC)
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