This PerfCounter64 counter reports a count of Layer 2 Protocol Tunneling frames transmitted after being de-encapsulated. An admin watches it to confirm that a customer's own Layer 2 control frames (such as spanning-tree BPDUs) are being carried transparently across the provider network instead of being terminated or dropped at this port. A managed-Ethernet customer running their own spanning tree across two sites would expect cmEthernetAccPortHistoryL2PTTxFramesDecap on access port 44 to climb in step with their BPDU interval; a flat cmEthernetAccPortHistoryL2PTTxFramesDecap while the customer reports STP re-convergence issues would point straight at the tunneling feature on this port.