This counts Errored Blocks on this SONET/SDH port: the number of error-detected blocks (at whatever block granularity applies to this signal's rate) recorded during the bin, per the MIB's description. EB is the block-based error tally that feeds the G.826-style performance parameters for this port -- because it counts blocks rather than seconds, it can distinguish a bin with a few, heavily-corrupted seconds from one with light errors smeared across many seconds, which plain ES on the same bin cannot; because this specific bin belongs to the completed-interval history table, its value is frozen the moment the interval closes, so re-polling it later will return the same number -- useful for pinpointing exactly which past 15 minutes a problem occurred in. An EB count of 383 for this bin, spread across relatively few ES for the same interval, would suggest a small number of seconds carried a disproportionate share of the errors on this port.