ACKs and NAKs are never in error. C ontinuous RQ Higher link utilization. Larger buffer storage requirements. P sends frames continuously without waiting for ACKs. S transmits an ACK for each correctly received I-frame.
P maintains a retransmission list.
S maintains a receive list. A corrupted frame is detected when a frame with the next sequence number is received. R etransmission List P maintains a list of frames sent and a copy of each frame. Different frames are distinguished by their sequence numbers. S elective Repeat S requests the retransmission of only the corrupted frames.