Question

Suppose now the file is broken up into 20 packets with each packet containing 40,000 bits. suppose that each packet is acknowledged by the receiver and the transmission time of an acknowledgment packet is negligible. finally, assume that the sender cannot send a packet until the preceding one is acknowledged. how long does it take to send the file?

Answer 1

The delay to send each packet will be ttrans + tprop. However there is an  additional tprop delay for the acknowledgement packet to arrive at the sender, prior  to which the next packet can be transmitted. Hence the total delay to transmit 10  packet is = 10 * (ttrans + 2 tprop) = 10*(40 msec + 80 msec) = 1.2 sec