Linear regression
1. 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, 𝑑, in terms of m and s.
(b) Determine the transmission time of the packet, 𝑑௧௦,, 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 = 𝑑௧௦, where
is the last bit of the packet?
(e) Suppose 𝑑 is greater than 𝑑௧௦. At time t = 𝑑௧௦s, where is the first bit of the
packet?
(f) Suppose 𝑑 is less than 𝑑௧௦. At time t = 𝑑௧௦, where is the first bit of the
packet?
(g) Suppose s = 2.5×108
meters/sec, L = 100 bits, and R = 28 kbps. Find the distance m so
that 𝑑=𝑑௧௦.
2. A computer system has a 7-layer protocol hierarchy. Applications generate messages of
length 500 bytes. At the data link layer, a 30-byte header and 4-byte trailer are added. At
the remaining 6 layers, a 20-byte header is added. What fraction of the network
bandwidth is filled with headers?
3. In traditional telephone systems, local loop (i.e., between a telephone set and its
nearest telephone switch) link bandwidth is about 3KHz.
(a) What are the maximum achievable baud rates and data rates (assume noiseless
channel) if BPSK and 64-QAM are used?
(b) If the signal-to-noise ratio imposed by the system between two remote telephone
sets is about 30dB, what is the maximum achievable data rate?
(c) In a few sentences, please explain how to improve data rate.
4. Answer the following questions of OSI reference model:
(a) Which layer is responsible for converting data packets from the Data Link layer into
electrical signals?
(b) At which layer is routing implemented, enabling connections and path selection
between two end systems?
(c) Which layer defines how data is formatted, presented, encoded, and converted for
use on the network?
(d) Which layer is responsible for creating, managing and terminating sessions between
applications?
(e) Which layer provides logical addressing that routers will use for path determination?
(f) Which layer specifies voltage, wire speed, and moves bits between devices?
(g) Which layer combines bits into bytes and bytes into frames, uses MAC addressing,
and provide error detection?
(h) Which layer segments and resembles data into a data stream?
(i) Which layer provides interface for users to communicate with applications?
(j) What are the differences between OSI and TCP/IP model?
5. Describe the following line codes:
(a) Non-Return to Zero (NRZ)
(b) Manchester
(c) Bipolar encoding
For each of the line codes listed above give the code for the bit sequence 101001111010.
6. A CDMA receiver gets the following chip sequence: (-1 +1 -3 +3 +1 -1 -1 +1). Assuming
the chip sequences used by four users are A=(-1 -1 -1 +1 +1 -1 +1 +1), B=(-1 -1 +1 -1 +1
+1 +1 -1), C=(-1 +1 -1 +1 +1 +1 -1 -1), and D=(-1 +1 -1 -1 -1 -1 +1 -1). Decide which
stations transmit, and which bits did each one send.
