Consider sending a file/message of F bytes over a path of Q links. Each link tra

Question

Consider sending a file/message of F bytes over a path of Q links. Each link transmits at R bps. The network is lightly loaded so that there are no queuing delays. Propagation delay on each link is Tp on average.

a. Suppose the network is a packet-switched virtual-circuit (VC) network. Denote the VC setup time by Ts seconds. Suppose the sending layers add a total of h bits of header to each packet. How long does it take to send the file from source to destination? Assuming the length of a packet is L.

b. Suppose the network is a packet-switched datagram network, and a connectionless service is used. Now suppose each packet has 2h bits of header. How long does it take to send the file? Assuming the length of a packet is L.

c. Finally, suppose that the network is a circuit-switched network. Further suppose that the transmission rate of the circuit between source and destination is R bps. Assuming Ts setup time and h bits of header appended to the message, how long does it take to send the message over Q links?

Explanation / Answer

a) The time to transmit one packet onto a link is (L + h) / R. The total latency is,
T= ts + M(L+h)/R +( L + h)(Q-1)/R.
b) Packet switched datagram service does not require a VC setup. Therefore, the total
latency is T = M(L+2h)/R +( L +2 h)(Q-1)/R.
c) Message switched datagram service does not require a VC, hence the total
latency is T = (F+2h)/R +( F+2h)(Q-1)/R.
d) The network is assumed to be light loaded, with no queuing delay at the link. Therefore,
there are no store-and-forward delays at the links. Consequently, the total delay is,
T = ts+ (h +F)/R.

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