CIS 3360 Homework 2
Due Date: September 11(Monday)
Worth: 3%
Q 1. This elementary problem begins to explore propagation delay and transmission
delay, two central concepts in data networking. Consider two hosts, A and B, connected
by a single link of rate R bps. Suppose that the two hosts are separated by m meters, and
suppose the propagation speed along the link is s meters/sec. Host A is to send a packet
of size L bits to Host B.
a. Express the propagation delay, dprop, in terms of m and s.
b. Determine the transmission time of the packet, dtrans, in terms of L and R.
c. Ignoring processing and queuing delays, obtain an expression for the end to-end
delay.
d. Suppose Host A begins to transmit the packet at time t = 0. At time t = dtrans ,
where is the last bit of the packet?
e. Suppose dprop is greater than dtrans,.At time t = dtrans, where is the first bit of the
packet?
f. Suppose dprop is less than dtrans,.At time t = dtrans, where is the first bit of the packet?
g. Suppose s = 2.5 * 108, L = 100 bits, and R = 28 kbps. Find the distance m so that
dprop is equal to dtrans.
Q 2. Suppose two hosts, A and B, are separated by 10,000 kilometers. and are connected
by a direct link of R=l Mbps. Suppose the propagation speed over the link is 2.5 * 108
meters/sec.
a. Calculate the bandwidth-delay product, R * tprop.
b. Consider sending a file of 400,000 bits from Host A to Host B. Suppose the file is
sent continuously as one big message. What is the maximum number of bits that
will be in the link at any given time?
c. Provide an interpretation of the bandwidth-delay product.
d. What is the width (in meters) of a bit in the link? Is it longer than a football field?
e. Derive a general expression for the width of a bit in terms of the propagation
speed s, the transmission rate R, and the length of the link m.