An Operator Virtual Connection (OVC) is an association of OVC End Points.
When an EVC spans multiple CENs, it is composed of 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.
OVC Endpoints
Roles
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 an egress frame on a Leaf OVC Endpoint can only come from a Root OVC Endpoint or a Trunk OVC Endpoint.
| Roles | ||
|---|---|---|
| OVC Endpoints | at a UNI | at an ENNI |
| Leaf | Yes | Yes |
| Root | Yes | Yes |
| Trunk | No | Yes |
| Frame | ||||
|---|---|---|---|---|
| To | Leaf | Root | Trunk | |
| From | ||||
| Leaf | No | Yes | Yes | |
| Root | Yes | Yes | Yes | |
| Trunk | Yes | Yes | Yes | |
Trunk Role
The Trunk role is unique to the ENNI. It provides a way to extend the concept of Root and Leaf bidirectionally across the ENNI without having to create multiple OVC Endpoints (Leaves and Roots) and hairpinning from one to the other. 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:
- The S-VLAN ID in the Service Frame is the Root S-VLAN ID and the frame ingress was on a Root OVC Endpoint or a Trunk OVC Endpoint that forwarded the Frame.
- The S-VLAN ID in the Service Frame is the Leaf S-VLAN ID and the frame ingress was on a Leaf OVC Endpoint or a Trunk OVC Endpoint that forwarded the Frame.
OVC Topologies
An OVC is point-to-point if it associates exactly two root OVC End Points. An OVC is multipoint-to-multipoint if associates two or more root OVC End Points that have the root role. An OVC is rooted multipoint if associates a root OVC End Point and it associates (or can associate) leaf or trunk OVC End Points.
| OVCs | ||
|---|---|---|
| Point-to-point | Multipoint-to-multipoint | Rooted Multipoint |
Root + Root | Root + Root + (future roots) Root + Root + Root | Root(s) + (future leaves or trunks) Root(s) + Leaves(s) Root(s) + Trunk(s) Root(s) + Leave(s) + Trunk(s) |
Example
The figure below shows an EVC comprising 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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