Suppose a store-and-forward system is used at an intermediate router B to relay communication between end-host A and end-host C. The (bidirectional) link from A to B has transmission capacity 8 Mbps and propagation delay 3 ms, and those of link from B to C are 2 Mbps and 8 ms respectively. Finally suppose that packets sent from A are all 1000 bytes long.
(a) Assuming lossless transmission and negligible queuing delay at B, find and expression for the time taken to send N packets from A to B, from the time the first bit of the first packet commences transmission at A to the time that the last bit of the last packet is completely received at C. Justify your answer by drawing a time-rails diagram for the events at A, B, C.
(b) For (a), further suppose that every k received packets require an acknowledgement form C (of negligible size) before the next k packet can be transmitted by A (i.e., a transmission window of fixed size k). Find the total transmission time assuming N is divisible by k.
(c) How would the answer to (a) and (b) differ if B was merely a bitwise relay rather than a (completely) store than forward device?