BW = 30Mbps, Distance = 3000Km, Speed = 3*10^8 m/s, Data Length = 12*10^3*8bits
Transmission Delay (Tt) = Data Length / BW
= (12 * 10^3* 8) / (30 * 10^6) = 3.2 ms
Propagation Delay (Tp) = Distance / Speed
= (3000 * 10^3) / (3 * 10^8) = 10 ms
Efficiency = N / (1 + 2a), where N = Window Size, and a = Tp / Tt = 10 / 3.2 = 3.125
1 = N / (1 + 2 *3.125)
N = ceil(7.25) = 8
For GB-N, N should be 8(Sender) + 1(Receiver) = 9, No. of bits required is 4
For Selective Repeat, N should be 8(Sender) +8(Receiver) = 16, No. of bits required is 4
Please Correct me if I am wrong