The SAP encapsulation definition on Ethernet ingress ports defines which VLAN tags are used to determine the service to which the packet belongs:
null encapsulation defined on ingress
Any VLAN tags are ignored and the packet goes to a default service for the SAP.
dot1q encapsulation defined on ingress
Only the first label is considered.
QinQ encapsulation defined on ingress
Both labels are considered. The SAP can be defined with a wildcard for the inner label (for example, ‟100:100.*”). In this situation, all packets with an outer label of 100 are treated as belonging to the SAP. If on the same physical link, there is also an SAP defined with a QinQ encapsulation of 100:100.1, then traffic with 100:1 goes to that SAP and all other traffic with 100 as the first label goes to the SAP with the 100:100.* definition.
In the last two situations above, traffic encapsulated with tags for which there is no definition are discarded.