This object counts the number of Layer 2 Protocol Tunneling (L2PT) encapsulated Spanning Tree Protocol Topology Change Notification (STP TCN) Bridge Protocol Data Units received on a Service Access Point on a Nokia SROS router. L2PT is a mechanism that allows carrier-grade systems to transparently carry customer Ethernet frames while preserving embedded control protocols, and this counter tracks one specific protocol message type. Network operators use this statistic to monitor the health of customer STP topology, verify that network control messages are passing through the service transparently, and diagnose spanning tree convergence issues.