This is a running count of all packets received across every port on this card. Dividing the byte counter delta of cardInOctets by this packet counter's delta over the same interval gives the admin the average packet size arriving on the card, which helps distinguish a voice or small-packet traffic mix from a bulk-data or large-packet mix without needing a separate traffic analyzer. For example, a sudden spike in cardInPkts with only a modest rise in cardInOctets suggests an influx of small packets, such as a burst of TCP SYN or keepalive traffic, rather than bulk data transfer.