IEEE 802.1ah (PBB) standard provides a dedicated bit for DE indication in both the backbone VLAN ID (BVID) and the ITAG.
The BVID is a regular 802.1ad S-TAG. Its DE bit may be used to convey the related tunnel QoS throughout an Ethernet backbone.
The ITAG header offers also an I-DEI bit that may be used to indicate the service drop eligibility associated with this frame.
These bits must follow the same rules as described in DEI in IEEE 802.1ad.