This read-only Counter32 tracks the number of bytes, measured in 64KB blocks, that exceeded the subscriber's configured traffic profile (i.e. was out-of-contract traffic). Admins monitor it to detect subscribers who are consistently going over their allotted rate, which may trigger billing overage charges or throttling policy. For example, a steadily climbing value here for one subscriber while others stay near zero flags that subscriber as a candidate for a rate-plan upgrade.