If computer B is connected to computer A and C by two pointt

If computer B is connected to computer A and C by two point-to-point links, then it is possible to send messages from A to C by sending them first from A to B, then from B to C. This is called store and forward transmission. A store and forward transmission from A to C is more efficient if the transmission from B to C can start before that from A to B is completed.

A. Suppose A wants to send a long message to C and that transmission of that message on a direct link takes one minute. How long would it take for the message to be fully transmitted from A to C?

B. Now suppose that the long message in (a) is decomposed into 60 packets that take one second each to be transmitted on a direct link. How long would it take for the message to be fully transmitted (as packets) from A to C?

Solution

The actual time taken from A to first packet switch  8*10^6 / 2*10^6 = 4 sec

With store-and-forward switching, the total time to move message from source host to destination host = 4 sec× 3 hops = 12 sec

As the information given here that says it takes one minute via direct link i.e 60secs

According to this information:

With store-and-forward switching, the total time to move message from source host to destination host = 60 sec× 3 hops = 180 sec

b) If the message is decomposed into 60 packets that takes 1 second each to be transmitted on a direct link, then during the first second packet 1 is sent from A to B , during the next second packet 2 is sent from A to B and packet 1 is sent from B to C , and so on. After 1 minute and 1 second, the complete message is received by C .