This read-write value, 1 to 7, applicable to all PU modes with an SDLC connection, sets the transmitter window size on the SDLC side of this PU's connection. A larger window lets more frames be outstanding, unacknowledged, at once, improving throughput on a link with round-trip delay at the cost of more data at risk if a frame is lost. For example, raising this object toward 7 on a higher-latency SDLC link can improve throughput compared to leaving it at a smaller window size.