Assume you wish to transfer an n-B file along a path composed of the source, the destination, seven point-to-point links, and five switches.

Suppose each link has a propagation delay of 2 ms, a bandwidth of 4 Mbps, and that the switches support both circuit and packet switching. Thus you can either break the file up into 1-kB packets or set up a circuit through the switches and send the file as one contiguous bitstream. Suppose packets have 24 B of packet header infor-

mation and 1000 B of payload, that store-and-forward packet processing at each switch incurs a 1-ms delay after the packet had been completely received, that packets may be sent continuously without waiting for acknowledgments, and that circuit setup requires a 1-kB message to make one round-trip on the path incurring a 1-ms delay at each switch after the message has been completely received.

Assume switches introduce no delay to data traversing a circuit. You may also assume that file size is a multiple of 1000 B.

(a) For what file size n B is the total number of bytes sent across the network less for circuits than for packets?

(b) For what file size n B is the total latency incurred before the entire file arrives at the destination less for circuits than for packets?

(c) How sensitive are these results to the number of switches along the path? To the bandwidth of the links? To the ratio of packet size to packet header size?

(d) How accurate do you think this model of the relative merits of circuits and packets is? Does it ignore important considerations that discredit one or the other approach? If so, what are they?