esaProbeHistoryR2PPkts is a 64-bit performance counter counting the number of test packets sent or received from the reflector back to the probe for a completed interval that has already closed and been archived into the rolling history log. Comparing the transmitted-versus-received packet counts is how a technician confirms the SLA test itself is actually exchanging traffic before trusting any of the delay or jitter numbers recorded in the same bin. For example, an archived bin whose packet count is far lower than every neighboring bin tells a technician the probe (or the network path to it) was down for part of that historical interval, even though the bin still closed and got logged.