This PerfCounter64 counter reports a count of bytes received on the flow, in the upstream (subscriber-to-network) direction in the upstream (subscriber-to-network) direction, tallied over the current interval. An admin uses it for precise usage accounting on one specific subscriber flow, separate from the aggregate totals on the physical port it rides. If cmFlowStatsBytesInA2N on flow entry 5 totals roughly 500 MB for the interval while the flow's rate-limited counterpart is far lower, an operator can tell how much of that subscriber's offered traffic is actually being shaped away rather than delivered.