This counts total octets received in DXI2 heartbeat poll frames on this interface, the byte-level inbound counterpart to lportSmdsCntInFrDxi2HbPolls. An admin uses it the same way as the outbound byte counter, mainly to validate heartbeat frame sizes are consistent and as expected rather than to track any meaningful traffic volume trend. For example, an unexpectedly large jump in this byte counter without a matching jump in the frame counter would suggest incoming heartbeat frames have grown larger than the standard fixed size, worth investigating as a possible CPE firmware anomaly.