Consider sending a file of F bits over a path of Q links. Each link transmits at

Question

Consider sending a file of F bits over a path of Q links. Each link transmits at R bits per second (bps). The
network is lightly loaded so that there are no queueing delays. When a form of packet switching is used, the F
bits are broken up into packets, each packet with L bits, of which h bits of it are header. Propagation delay is
negligible. Let F = 5x104, Q = 20, R = 1 Mbps, L = 1000, and h = 10.
a. Suppose that the network is a circuit-switched network. Further, suppose that the transmission rate of the
circuit between the source and destination is R bps. Assuming ts = 10 milliseconds set-up time and h bits of
header appended to the entire file, how long does it take to send the file? (5 pts)
b. Suppose the network is a packet-switched datagram network and a connectionless service is used. How
long does it take to send the file? (5 pts)
c. Suppose the network is a packet-switched virtual circuit network. Denote the VC set-up time by ts = 250
milliseconds. How long does it take to send the file from source to destination? (5 pts)

Explanation / Answer

a) The time to transmit one packet onto a link is (L + h) / R . The time to deliver the first of the M packets to the destination is Q(L + h) / R . Every (L + h) / R seconds a new packet from the M 1 remaining packets arrives at the destination. Thus the total latency is
ts+( Q+ M- 1)(L+ h)/ R
b) (Q + M 1)(L + 2h) / R
c) Because there is no store-and-forward delays at the links, the total delay is
ts+( h+ ML)/ R

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