a byte $-$ oriented sliding window protocol uses selective reject, and carries blocks of $3,968$data bits. the frame header and trailer together add $42$bits to each frame, and acknowledgemnets are also $42$bits$.$ the physical layer has a propagation delay $9\mathrm{.}0$ us$.$ the receiver make an independent decision on each bit, with probability of bit error $0\mathrm{.}000043.$ a throughput of at least $29$ Mbit$/$s is required.