EXAM TDDI07 Distributed Embedded Software and Networks

Department of Computer and Information Science
Distributed Embedded Software and Networks
(Distribuerad inbyggd mjukvara och nätverk)
2012-12-21 14-18
On-call (jour):
Mikael Asplund, +46 707 481462,
Massimiliano Raciti, +46 762 388815
Admitted material:
Pocket calculator
General instructions:
The assignments are not ordered according to difficulty.
You may answer in either English or Swedish.
Read all assignments carefully and completely before you begin.
Use a new sheet for each assignment and use only one side.
Before you hand in, order the sheets according to assignment, number each sheet, and fill
in AID-number, date, course code and exam code at the top of the page.
Write clearly. Unreadable text will be ignored.
Be precise in your statements.
Motivate clearly all statements and reasoning.
Explain calculations and solution procedures.
If in doubt about the question, write down your interpretation and assumptions.
Grading: U, 3, 4, 5. The preliminary grading thresholds are:
U: 0-20p
3: 21-27p
4: 28-34p
5: 35-40p
Good Luck!
TDDI07, Distributed Embedded Software and Networks
Department of Computer and Information Science
1. Fundamentals (6p)
a) When designing a wireless sensor network, there are several ways of structuring it with
regards to the network topology, for example whether to use a single-hop or a multi-hop
network layout. Describe the implications of these two options in terms of coverage,
installation cost, capacity, and power consumption of the nodes. (4p)
b) Describe two realistic examples of where a WSN/WSAN could be used for monitoring
and/or control. (2p)
2. Medium Access Control (4p)
a) Describe the RTS/CTS mechanism. Give an example of a situation where this
mechanism prevents collisions. (2p)
b) The IEEE 802.15.4 MAC protocol uses CSMA/CA to control medium access in the
contention-access periods in the superframe. What does CA stand for and how can it be
implemented? (2p)
3. Routing and Data Collection (7p)
a) Routing protocols can be categorised as flat, hierarchical or location-based. Explain each
of these categories and for each category describe one problem/limitation with that
approach. (6p)
b) The Collection Tree Protocol (CTP) builds a tree structure on top of the wireless
network. What is special about trees that makes them desirable in this context? (1p)
4. Cellular Networks (4p)
a) In the M2M terminology, sensors are categorised as direct or indirect. Which of these
two sensor types is likely to have a lower power consumption? Why? (2p)
b) Explain why the lack of mobility for some types of sensor nodes is an important aspect
for cellular M2M protocols. (2p)
5. Clock Synchronisation and Positioning (6p)
a) Explain how often a set of clocks need to be synchronised if they required clock
precision should be at most p. (2p)
b) The delivery time of a time synchronisation packet is composed of a number of subdelays. Which of these delays is the most significant? Why? (2p)
c) Describe two ways for a mobile device to determine its position assuming that it has no
sensors except a radio device. (2p)
6. Resource Management (5p)
a) Describe one method for traffic shaping. Comment on the advantages and disadvantages
of this method. (3p)
b) Consider a distributed sensor system designed to detect pollutants and impurities in
underground water pipes. Describe the two most important quality-of-service parameters
for such a system and why these are more important than other parameters. (2p)
TDDI07, Distributed Embedded Software and Networks
Department of Computer and Information Science
7. Dependability and Security (5p)
a) The consensus problem appears in some form in most distributed system applications
(including wireless sensor networks). Explain why clock synchronisation can make it
easier to reach agreement among a set of nodes assuming that some nodes might crash.
b) Consider a car-parking system where a number of parking meters are connected to the
Internet with the help of GSM and communicating with a central server. Explain how
misuse detection can be used to detect malicious faults (attacks) against the system. (2p)
8. Energy Management (3p)
a) Explain the difference between the proactive and reactive power management strategies,
and explain in which category dynamic voltage scaling (DVS) belongs. (3p)
TDDI07, Distributed Embedded Software and Networks
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