This feature is supported on VPLS and VLL service where the end-to-end solution is built using two node solutions (requiring SDP connections between the nodes).
In VLAN swapping, only the VLAN ID value is copied to the inner VLAN position. Ethertype of the inner tag is preserved and all consecutive nodes work with that value. Similarly, the dot1p bits value of the outer tag is not preserved.
Figure 1 describes the network where, at user access side (DSLAM facing SAPs), every subscriber is represented by several QinQ SAPs with inner-tag encoding service and outer-tag encoding subscriber (DSL line). The aggregation side (BRAS or PE-facing SAPs) is represented by a DSL line number (inner VLAN tag) and DSLAM (outer VLAN tag). The effective operation on the VLAN tag is to drop the inner tag at the access side and push another tag at the aggregation side.