This Counter64 is the number of unicast packets received on this endpoint just since the previous poll. It matters on the live receive-side counter set UCS Manager keeps for one Ethernet endpoint (a blade's vNIC adapter port, an I/O Module uplink, or a fabric-interconnect server port) inside a UCS domain because a sudden drop in this delta while totalPacketsDelta stays flat would point to a broadcast/multicast flood displacing normal unicast traffic rather than a general slowdown. unicastPacketsDelta falling from 50,000 to 500 between polls on this interface, with totalPacketsDelta unchanged, is the kind of signature an admin would use to spot an active broadcast storm.