This field reports the number of packet drop events on this PM instance, exposed here as cienaCesPmExtendedTxRxTotalStatsBinDropEvents. On this Ciena CES port's PM data, this is an RMON-style drop-event counter — it counts the number of times this PM instance had to drop packets due to resource exhaustion (a full buffer or queue), not the number of packets dropped, so one burst of congestion that drops fifty packets in a row can still just register as a single event here; and this is the running grand-total counter for the extended Tx/Rx PM group, tallied since the bin's own StartTime (in practice since the PM instance was created or last reset), so treat it as a lifetime tally rather than a per-interval number. For example, drop events climbing from 0 to just 3 on this port would already be worth a closer look, since a healthy link should hold this counter at zero.