This read-write value represents the estimated percentage of the trunk's configured bandwidth, lportDataRate, consumed by headers and internal control messages rather than actual user payload. An admin sets or reviews this to get a realistic picture of usable trunk capacity, since a trunk quoted at 1.5 Mbps that reserves 10% for overhead effectively leaves less for customer PVCs. For example, setting lportTrkOverhead to 8 means the switch accounts for roughly 8% of trunk capacity as control-plane overhead when computing available bandwidth for user traffic.