Chapter 3, Problem P22P

a.

Explanation of Solution

Sequence numbers inside the sender’s window:

Given:

Window size = Size = 4

Range = 1024

Case 1:

Let’s consider the receiver is “K” and acknowledged all the “k-1” data packets. The sender side window’s range will be of $\text{[ k , k+ Size - 1 ] }$ sequence numbers

b.

Explanation of Solution

Values of ACK field:

Suppose the receiver is waiting for the packet “k”, then it has been received and acknowledged “k-1” packet and the “Size-1” packets before that. If NACKs of those packets have not been received by the sender, then the values of ACK field is $\text{[ k - size , k - 1 ]}$ may propagate back.

• Because the sender has sent packets $\text{k - 1}$, it states that the sender had already received an acknowledgement for $\text{k - Size -1}$