Exactly as described, this counts 128-to-255-byte frames received on this benchmark port. This range corresponds to the "b" (128-byte) EMIX letter, so its received count should closely mirror the transmitted count in the same bucket if the network path preserved frame sizes end-to-end without truncation or padding. For example, a received count in this bucket noticeably lower than the corresponding transmitted count, even with zero total frame loss reported, would suggest frames are being re-sized rather than lost outright somewhere on the path.