This is the historical byte-count counterpart to cpwVcPerfIntervalInHCPackets, recording total bytes received from the PSN during one completed 15-minute interval for the pseudowire. It's used together with the packet count from the same interval to reconstruct average frame size after the fact, which helps when investigating a reported quality issue from hours earlier. A historical interval showing a sharp bytes-to-packets ratio drop compared to neighboring intervals would suggest the VC was carrying smaller, likely control-plane-heavy traffic during that specific quarter-hour.