High Quality Content by WIKIPEDIA articles! Hierarchical VLAN (HVLAN) is a proposed Ethernet standard that extends the use of enterprise Ethernet VLAN (802.1Q) to carrier networks. A number of developments have emerged in recent years to help bring Ethernet, a flexible and cost-efficient packet transport technology, to carrier networks. These developments include Q-in-Q (802.1ad), PBB (802.1ah), PBT (Provider Backbone Transport), and PBB-TE, which bring a set of features to traditional Ethernet to make it “carrier-grade”, adding to it high-availability, OA M, and more.