This field reports the total number of packets received that were less than 64 octets long (excluding framing bits, but including FCS octets) and were otherwise well formed, exposed here as cienaCesPmExtendedTxRxAllTimeBinUndersizePkts. On this Ciena CES port's PM data, these are frames shorter than the 64-octet Ethernet minimum that were nonetheless well-formed (good FCS, no alignment error), so a nonzero count points at an attached device intentionally or accidentally generating non-standard short frames rather than at wiring damage; and this 'all-time' counter for the extended Tx/Rx PM group has no fixed rollover schedule of its own — it just keeps accumulating from whenever the PM instance was last cleared, so a single reading only tells you the running total, not a rate. For example, a healthy port would sit at 0 for undersized-but-valid frames in this bin; even 48 is enough to warrant a look, since this class of counter isn't supposed to move under normal operation.