With every successful transmission of a window's worth of packets without a time-out, the transmit window size is increased by one packet until it reaches the maximum window size that was sent by the other side when the call was connected. As stated earlier, no retransmission is done on a time-out. After a time-out, the transmission resumes with the window starting at one half the size of the transmit window when the time-out occurred and adjusting upward by one each time the transmit window is filled with packets that are all acknowledged without time-outs.