Tanenbaum

Question

 Imagine a sliding window protocol using so many bits for sequence numbers that wraparound never occurs. What relations must hold among the four window edges and the window size, which is constant and the same for both the sender and the receiver.?

Answer 1

S1: sender’s lower edge

S2: sender’s upper edge

R1: receiver’s lower edge

R2: receiver’s upper edge

W: window size

There are three main conditions that must hold among the four window edges and the

window size:

1. The sender must keep track of 0 to w frames that have currently been sent but

have no acknowledgment i.e outstanding.

0 <= S2 – S1 + 1 <= W

2. The receiver will expect up to w frames.

R2 – R1 + 1 = W

3

3. The receiver’s sequence number must be within the sender’s window

S1 <= R1 <= S2 + 1