This counter tallies error-free Ethernet frames sized between 256 and 511 bytes (counting FCS octets, excluding framing bits) received across all ports in a group, one bin of a standard frame-size histogram. It helps an admin see whether a group's traffic mix leans toward small control-style frames or larger data frames, which affects how collisions and utilization behave on that shared segment. On group 4, a sudden dominance of this 256-511-byte bin over the other size bins would tell an admin the traffic pattern there has shifted, for example toward more frequent small polling packets.