On the ingress label-edge router (LER), the final EXP value for the VC label is not dependant on the CoS value in the VC-peer configuration.
By default, for traffic flowing from a CE device to a PE device, 3 bits of the PCP field from the incoming Ethernet frame header are extracted and mapped to an internal CoS value by way of an ingress CoS map. This internal value is then mapped to an outgoing CoS value by way of an egress CoS map. The outgoing CoS value is then inserted into the EXP field in the outgoing VC label. When incoming traffic does not have VLAN tag, the default PCP value that is configured on a port is used.
In the case of traffic received from the network core side, by default the EXP field from the incoming VC label is mapped to an internal CoS value by way of an ingress CoS map. This internal value is then mapped to an outgoing CoS value by way of an egress CoS map. The outgoing CoS value is then inserted into the PCP field in the Ethernet frame header going out to the CE device.
On the egress LER, the CoS value for the VC-peer configuration is not dependant on the final EXP value for the VC label.
The following table shows ingress and egress behavior for different global, tunnel and PW configuration combinations.
| Global | Tunnel | PW | AC to PW (per path) | PW to AC (per PW) |
|---|---|---|---|---|
| Uniform | No CoS | No CoS | Uniform | Uniform |
| Uniform | CoS | No CoS | Pipe | Uniform |
| Uniform | No CoS | CoS | Uniform | Pipe |
| Uniform | CoS | CoS | Pipe | Pipe |
| Pipe | No CoS | No CoS | Pipe | Pipe |
| Pipe | CoS | No CoS | Pipe | Pipe |
| Pipe | No CoS | CoS | Pipe | Pipe |
| Pipe | CoS | CoS | Pipe | Pipe |