You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 11 Next »

EVCs and OVCs

EVC

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 (discussed in section 5).

There are three types of EVCs:

  1. Point-to-point EVCs (see diagram at right) – A point-to-point EVC contains exactly 2 UNIs. Each of the UNIs may or may not support multiple services depending on the type of service(s) defined at the UNI. Point-to-point EVCs carry Ethernet Line (E-LINE) services.
  2. Multipoint EVCs – Multipoint EVCs contain two or more UNIs. A Multipoint-to-Multipoint EVC with two UNIs is different from a Point-to-Point EVC because one or more additional UNIs can be added to it. Each of the UNIs may or may not support multiple services depending on the type of service(s) defined at the UNI. Point-to-point EVCs carry Ethernet LAN (E-LAN) services.
  3. Rooted Multipoint EVCsA multipoint EVC in which each UNI has either the Root Role or the Leaf Role. Ingress Service Frames at a Root Role UNI can be delivered to one or more of any of the other UNIs in the EVC. Ingress Service Frames at a Leaf Role UNI can be delivered to only one or more Root Role UNIs in the EVC. Each of the UNIs may or may not support multiple services depending on the type of service(s) defined at the UNI. Point-to-point EVCs carry Ethernet Tree (E-TREE) services.

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. 

 

OVC

When 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:

  • 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.

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.

Next Up

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

 

 

Point-to-point EVC

 

 

 

 

 

 

 

 

EVC Comprising Three OVCs

 

 

 

 

 

 

  • No labels