University of Cincinnati
COPY of ECECS 0688 Final Examination
Part of chapter 8 is included!
Q.1 Answer any 12 of the following questions:
a)Why do you need three different identification numbers: ESN, SID and MIN?
b)What kind of communication technique used in transmitting information in Bluetooth?
c)What is meant by satellite path diversity?
d)What are the relative advanteges of reactive and proactive protocols in ad hoc networks?
e)Is there soft handoff in FDMA and TDMA mobile cellular systems?
f)What do a public key and a private key mean?
g)What are the advantages of power control in CDMA based system?
h)How does HomeRF enable different appliances to be controlled by the internet?
i)Why do you use random number in authentication process?
j)How do you achieve transmission of packets in Ricochet?
k)What is the function of a hierarchical approach in a sensor network?
l)Why do you need to have a higher priority to handoff calls?
m)Why do you have errors in triangulation technique?
n)What is the role of an earth station in satellite communication systems?
Q.2 Write a brief notes on any 12 of the following questions:
a)A Homing MSC and a Serving MSC
b)Differences between simplex and duplex
c)Use Walsh code for CDMA
d)Authentication and encryption
e)Ping-pong effect
f)Footprint
g)Soft and hard handoff
h)Beacon Signals in registration process
i)Orbital and elevation angles
j)Bi-directional tunneling
k)Data-centric concept useful in sensor network
l)Security threats in wireless networks
m)Guard band and guard time
Q.3 Answer the following questions:
a)Consider the word 'wireless' comprised of 8 symbols, each symbol being a letter of the English alphabet. This word is encrypted by first applying a permutation function and then a substitution function. The permutation function is applied on a 4 symbol half word as follows:
(1 2 3 4) => (4 1 3 2)
i.e., every half word with input symbols 1234 is transformed to an output half word, which is 4132.
This word is interpreted as a sequence of 2 half words. The substitution function is as follows:
Input symbol: w i r e l s
Output symbol: i r e l s w
q
1) What is the final output in 'wireless'
2) What would be the output is the substitution function were applied before the permutation function instead of after it?
b)Consider an ad hoc network where communication (message of packet transfer) is to take place from node X to node Y. The route has already been established and a data packet is to be transferred over n hops. To transfer the packet, the kth node uses the following medium access protocol:
- It waits for time t(k) after which the channel becomes free. t(k) = k A time units.
- It transfers the data packet to the next hop. This takes 'A' time units.
- It receives an acknowledgement. This takes another 'A/2' time units.
1)Find an expression for time taken for the data to cover 'n' hops, i.e., from node 1 to nodfe n+1.
2)If the time taken to traverse 'n' hops is T = 2n sqrt (nA), what is the value of 'n'