This is a cumulative count of packets sent from this specific station since the last reset (the MIB description refers to it generically as 'the port,' but this object is scoped per station). This gives an admin the transmit-side packet count for one specific device sharing a multi-drop line, the counterpart to cdx6500allstationsPktInTot. For example, a station that stops incrementing PktOutTot while its PktInTot keeps rising has likely stopped responding on that shared line even though it's still receiving polls.