This is the byte-count sibling of cpwVcPerfCurrentInHCPackets, using Counter64 to track total bytes received from the PSN for this pseudowire within the current, still-open 15-minute interval. Comparing bytes to packets received in the same window lets an engineer spot abnormally small or large average frame sizes, which can indicate MTU issues or fragmentation on the VC. If this counter shows 45,000,000 bytes against 30,000 packets in the same partial interval, that works out to roughly 1500-byte average frames, consistent with full-size Ethernet payloads.