UNIVERSITY OF EDINBURGH COLLEGE OF SCIENCE AND ENGINEERING SCHOOL OF INFORMATICS
INFR11146 INTERNET OF THINGS SYSTEMS, SECURITY, AND THE CLOUD
Tuesday 14 th May 2019 14:30 to 16:30
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: H.Sun
External Examiners: S. Rogers, S. Kalvala , H.Vandierendonck
THIS EXAMINATION WILL BE MARKED ANONYMOUSLY
1. (a)
(b)
Explain the principle of Over-the-air (OTA) programming, discussing ad- vantages and drawbacks of this technique. Explain how risks facing OTA programming can be circumvented and at what cost.
Consider a LoRaWAN deployment operating over a channel with 250kHz bandwidth. The end devices are configured to transmit packets using the chirp spread spectrum modulation with spread factor SF = 7. An end device is configured to transmit maximum 190 bytes of information (payload) in a single packet, which is preceded by a 14-byte frame header and 1-byte frame port. Additional 5-bytes accounting for the MAC header and message in- tegrity check (MIC) are added to the payload and a forward error correction (FEC) with rate 4/5 is applied before transmission. The Gateway transmits a beacon every 120 seconds and a 1% duty cycle is imposed by regulation on end devices.
i. Assume the transmissions of an end device experiences no collisions or losses, and no packet fragmentation is allowed, how much time would be required to send 1,900 bytes of information to the gateway?
ii. If instead on average 20% of frame transmissions collide with those of other nodes or are corrupted by channel noise, how many bytes of information are delivered to the gateway in 10 minutes?
Describe the ‘topic’ concept with which the MQTT protocol operates, ex- plaining how this enables services to gather information from sensors and commenting on the scalability of this approach.
Consider two parties A and B that wish to communicate securely using the RSA algorithm. Assume A picks two prime numbers p = 3 and q = 11 to generate an encryption key e.
i. What is the highest feasible value e can take and, if that is chosen, what will constitute the public key?
ii. Assume e = 13 is used as the encryption key. What will be the private key that A will use to decipher messages B encrypts with A’s advertised public key?
[7 marks ]
(c)
(d)
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2. (a)
Explain what protocol features were introduced in the Bluetooth Low En- ergy specification in order to reduce the power consumption characteristic to Bluetooth Classic.
(b) Consider a Wi-Fi access point serving a three client stations, which contend for the channel using the parameter CWmin = CWmax = 16 (no back-off). The stations always have packets of size L = 1,200 bytes to transmit and send a single frame upon each channel access. The channel must be sensed idle for AIFS = 34 μs to trigger the access procedure and the duration of an empty slot is σ = 9μs. The RTS/CTS mechanism is not employed. Each transmission is preceded by a 20 μs preamble and the data rate is 24 Mbit/s. Successfully received packets are acknowledged within 16μs, and the total duration of an acknowledgment frame is 24 μs.
i. What is the total throughput that a station can achieve?
ii. Assume a frame transmission of any station may also be corrupted with probability p = 0.05 by a frame transmitted by a hidden terminal at- tached to a different BSSID that is not carrier sensed. How long will it take on average for a station to successfully transmit a data frame?
(Assume the duration of a failed and successful transmission, including ac- knowledgment, is the same.)
(c) Explain the different types of header compression techniques that enable IPv6 to operate over low power networks wireless personal area networks (6LoWPAN), discussing how much information can be omitted/compressed in each scenario.
(d) Consider a microcontroller that operates with two phases. The first one is devoted to computing tasks and has a power consumption profile of 0.25W. The microcontroller sleeps in the second phase in order to reduce its energy consumption. The circuitry is not completely switched off during this second phase, but the microcontroller consumes only 0.002W.
The device spends only 1% of the time in the compute phase and is powered by a miniature cell battery with a nominal voltage of 1.2V and a capacity of 600mAh. What is the total lifetime of the device?
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[5 marks ]
3. (a)
Describe briefly the two main approaches to cloud virtualisation, explaining the advantages and disadvantages of each approach.
(b) Consider a 16-bit number representation in the Qn.m fixed point format, with 9 bits used to represent the sign and integer part.
i. What is the range of numbers that can be covered with this format?
ii. Convert the decimal number ‘23.671875’ into Qn.m format, giving your answer in both binary and hexadecimal.
iii. What would be the advantage of increasing the number of bits used to represent the fractional part?
(c) Discuss the main differences between the Wi-Fi and NB-IoT wireless tech- nologies, commenting on the advantages, shortcomings, and applications of each solution.
(d) Consider an encryption routine based on a Feistel structure that employs the following round function
F(Ri,Ki)=Ki ⊕(Ri >>4),
where >> denotes the circular shift right operation and ⊕ represents an XOR operation. Ki is the sub-key used at round i. Assume the sub-keys at rounds 1 and 2 are K0 =0x2A2A2A2A and K1 =0xFBFCFEFD.
If a 64-bit plaintext block 0xC0BC1FD75D5ABB99 is provided as input to this Feistel network, what is the cipher text obtained after the first two rounds are completed?
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