FOR EXTERNAL EXAMINER (date of this version: 28/3/2018)
UNIVERSITY OF EDINBURGH COLLEGE OF SCIENCE AND ENGINEERING SCHOOL OF INFORMATICS
INFR11146 INTERNET OF THINGS SYSTEMS, SECURITY, AND THE CLOUD
Tuesday 15 th May 2018 09:30 to 11:30
INSTRUCTIONS TO CANDIDATES
Answer any TWO of the three questions. If more than two questions are answered, only QUESTION 1 and QUESTION 2 will be marked.
All questions carry equal weight. CALCULATORS MAY BE USED IN THIS EXAMINATION
Year 4 Courses
Convener: I. Murray
External Examiners: S. Rogers, A. Donaldson, S. Kalvala
THIS EXAMINATION WILL BE MARKED ANONYMOUSLY
1.
(a) Enumerate and explain the operation of three functions that gateways im- plement in fog computing architectures. Name and explain one limitation of a gateway based IoT architecture.
(b) A microcontroller operates with two phases, which have the following power consumption profiles:
• Phase 1 (sleep): 0.001W • Phase 2 (compute): 0.5W
The microcontroller runs for 5% of the time in the compute phase and spends the rest of the time in the sleep phase. Given that the microcontroller is powered by a battery with a nominal voltage of 3.5V (which does not change over time) and a capacity of 1800mAh, what is the total lifetime of the device?
(c) Assume a Bluetooth classic connection has been established and a slave device has 200 bytes of information to send to the master. A data frame contains 126 bits corresponding to the access code and header, and the maximum payload is 2,744 bits. Knowing that a 250μs settling time is needed for each transmission, the frame is transmitted at 1Mb/s, and no forward error correction (FEC) is employed, how much time will be required to complete the transfer?
(d) Consider an IoT network where the Routing Protocol for Low-Power and Lossy Networks (RPL) constructs the following topology in the form of a destination-oriented directed acyclic graph (DODAG).
If each link has a distance of 1, what is the rank of node H? List the path from G to H if the DODAG is non-storing. List the path from E to I if the DODAG is storing.
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FOR EXTERNAL EXAMINER (date of this version: 28/3/2018)
[7 marks]
[6 marks]
[7 marks]
[5 marks]
2.
(a) Describe the process by which classic Bluetooth devices are discovered, ex- plaining the states which the master and slave undergo.
(b) Consider a 64-bit plaintext block 0xFACCBF0DFEAA001C is enciphered using a Feistel structure with a round function
F(Ri,Ki)=(Ri <<4)⊕Ki,
where << denotes the circular shift left operation, ⊕ the XOR operation, and Ki is the sub-key used at round i. If the sub-keys at rounds 1 and 2 are K0 =0x10101010 and K1 =0xAB2FCE4D, compute the cipher text at the end of these rounds.
(c) Explain how an Application Specific Integrated Circuit (ASIC) might spe- cialise the instruction set of a commodity processor and give two examples of what applications would benefit from these.
(d) CoAP transactions between a client and a server conclude with the reception of a confirmation. Assuming that the packet error rate on a client–server link is p = 0.025 (that is, 2.5% probability to lose a request, 2.5% probability to lose a response), find the average total time required to successfully retrieve an object, if the link round trip time (RTT) is 80ms.
FOR EXTERNAL EXAMINER (date of this version: 28/3/2018)
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[6 marks]
[7 marks]
[7 marks]
[5 marks]
3.
(a) Consider a LoRaWAN node that transmits over 125kHz channel using the spreading factor SF = 8, which corresponds to an effective bit rate of 3.125kb/s. The node sends 20-byte payload packets which carry a 5-byte overhead, and operates with a 1% duty cycle. The entire message is pro- tected with a 4/8 forward error correction code (FEC). Assume packet trans- mission experiences a collision rate p = 0.05, how many bits of information does the node transmit in total during 1 hour?
(b) Describe one mechanism that can ensure the boot code running on an em- bedded device remains protected.
(c) Consider the Qn.m fixed point format.
(i) What do the variables (n) and (m) represent?
(ii) Convert the decimal number ‘19.34765625’ into Q6.10 format, giving your answer in both binary and hexadecimal.
FOR EXTERNAL EXAMINER (date of this version: 28/3/2018)
(d) Briefly describe the utility of MQTT retain functionality.
[7 marks ] [5 marks ]
[3 marks ]
[5 marks] [5 marks]
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