This is a 64-bit high-capacity counter tracking the total number of packets received over the VSL, avoiding 32-bit wraparound on a busy link. An admin cares because comparing this with the peer chassis's transmitted high-capacity counter gives an accurate long-term view of packet delivery across the VSL without wraparound distorting the comparison. For example, over a long monitoring window, comparing this counter against the peer's transmitted total gives a reliable estimate of any cumulative packet loss on the VSL.