NETWORKING Suppose two hosts A and B are separated by 40000

NETWORKING

Suppose two hosts, A and B are separated by 40,000 kilometers and are connected by a direct link of R=1 Mbps. Suppose the propagation speed over the link is 2*108 meters/sec. Consider sending a file of 4,000,000 bits from Host A to Host B.

a. Suppose the file is sent continuously as one big message. How long does it take to send the file, assuming it is sent continuously?

b. Suppose now the file is broken up into 1000 packets with each packet containing 4,000 bits. Suppose that each packet is acknowledged by the receiver and the transmission time of an acknowledgement 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?

c. Calculate the bandwidth-delay product, R*tprop. What does it mean? (Provide an interpretation of the bandwidth-delay product.)

d. If there are two routers between Host A and B (rather than a direct link), and all three links have 1 Mbps links, how long does it take to send the file? (use the assumptions in 1.b)

Solution

a) t trans= 4000000/1M= 4sec

to send file continuously= t trans + tprop= 4 + 0.2 = 4.2 sec (tprop calculation is done under c) )

b) total delay to transmit 1000 packets is = 1000(t trans + 2 tprop) = 1000 (4m +  0.4) = 404 sec

c) tprop= 40000*10^3/(2*10^8) =  0.2 sec

bandwidth relay product r*tprop = 1M * 0.2 = 200000 bits

The bandwidth-delay product of a link is the maximum number of bits that can be in the link.