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Consider a network connecting two systems located $2000$ kilometers apart. The bandwidth of the network is $64 \text{ Mbps}$. The propagation speed of the media is $2/3$ of the speed of light in vacuum. It is needed to design selective repeat sliding window protocol for this network. The average packet size is of $16 Kb$. The network is to be used to its full capacity.

Assume that processing delays at nodes are negligible. Then, the minimum size in bits of the sequence number field has to be __________.
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My answer is coming out to be 8 bits. Please check my approach. Thanks.

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speed of light 2 * 108 m/sec

propagation time=2000*1000/2*108
                           =0.01 sec
in 1 sec --------------------64*106 bits
in 0.01 sec -----------------64*106 *0.01bits
          total bits =640000 bits
frame size =16 kb =16*1000 bits
 no of frames= total bits/ frame size
                           =640000/16000
                          =40 frmaes
so we need 6 bits 
but remember we use here selective repeat window in which SWS<=2m-1

so here m value will be 7 bits. 
 

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