This read-write value sets the cell-buffer occupancy threshold above which the switch marks the Explicit Forward Congestion Indication bit on cells for this channel, defaulting to three-quarters of the maximum cell count. EFCI marking is how the switch signals downstream congestion to ABR-capable end systems so they can throttle back before cells are actually dropped. If a channel is experiencing repeated cell discards, an admin might lower bbChanEfciThreshold so congestion signaling kicks in earlier, before buffers fill completely.