This controls the LAPB frame window size (1-127), which determines how many frames can remain unacknowledged before the sender must wait. If set above 7, it uses modulo-128 sequencing for longer sequence numbers; values of 7 or below use modulo-8 sequencing. Network engineers adjust this to balance throughput against buffer memory availability and link latency. Example: setting to 4 allows only 4 frames outstanding at once, while 64 permits 64 simultaneous unacknowledged frames for higher-speed links.