4) Store-and-forward Consider a packet of length L which begins at Host A and travels over three links to Host B. These three links are connected by two store-and-forward packet switches. Let di, si, Ri denote the length, propagation speed, and the transmission rate of link i, for i = 1, 2, 3. The packet switch delays each packet by dproc.

a) Assuming no queuing delays, in terms of di, si, Ri (i = 1, 2, 3), and L, what is the total end-to-end delay for the packet? (5 points)

b) Now suppose R1 = R2 = R3 = R and dproc = 0. Further suppose the packet switches do not store-and-forward but instead immediately transmit each bit they receive before waiting for the entire packet to arrive. What is the end-to-end delay? (5 points)