This Counter32 counts the number of frames the local WDS mesh backhaul link has transmitted at MCS4 since the link was established, one of sixteen per-MCS transmit counters that together profile the link's rate distribution. An admin can compare this counter against the other MCS counters to see whether the backhaul link mostly transmits at this particular rate or only occasionally falls back or ramps up to it. For example, if traffic on a rooftop-to-rooftop bridge is concentrated in the MCS4 counter rather than spread toward the higher MCS indices, that points to a link running well below its potential due to distance, alignment, or interference.