SYSC 3303 E

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Systems and Computer Engineering
SYSC 3303
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Carleton University Department of Systems and Computer Engineering SYSC 3303 A RealTime Concurrent Systems Summer 2012 Midterm Exam thTuesday July 24Sample Solutions This exam is 1 hour 15 minutes 75 min long There are 5 questions worth 70 marks on 9 pagesAnswer all questions in the space provided You may use the back of each page for rough workIf you continue an answer on the back of a page indicate that on the front of the page and circle what should be markedEnsure that your answers fully demonstrate your understanding of the material coveredDo not ask questions during the exam unless you believe that you have found an errorIf you think something about a question is unclear or ambiguous make a reasonable assumption and answer the question Question 1 11 marks 92 for each partHere is a definition of realtime systems studied in the lectures A realtime system must respond to unpredictable stimuli from its environment in a timely fashion while operating reliably and continuously in the presence of failures in its own perhaps distributed components and connections and uncertainty about the state of its environment a Give the name and short description of a specific realtime system and clearly identify how your system meets the definition above ensuring that how your system deals with the three underlined terms is included in your answer Example Telephone Switch NetworkA network of telephone switches allowing phone calls to be connected across the country or around the world 1 or 2 marks deducted if this is not clearA telephone switch must be able to deal with inputs arriving at any time unpredictable stimuliIn fact statistics are gathered to determine the busiest times of day and days of the yearSwitches are rated for a maximum BHCA busyhour call attemptsHowever even if the peaks number of calls exceeds that they will continue to function on a besteffort basis3 marks For telephony systems 99999 reliability is required by the standardsThis means that a telephone system is allowed 2 hours of downtime in 40 years including scheduled downtimeThus all the hardware is duplicated to allow a switch to the new parts if problems are detected and the network has many paths through it so that the network can still function if one node is downThis is how reliable and continuous operation is guaranteed even if there are failures 3 marks Telephone systems must be able to function even when there is uncertainty in the environment ie no matter what is going on in the outside world eg hot cold power outage ice storm earthquake fire etcThere is battery backup and switches are built to be as earthquake and fireproof as possibleWhen a natural disaster occurs the local switch will likely be very busy with people phoning to see if their friends are ok but unless it is totally destroyed it will continue to function on a besteffort basis and this part of the network will be avoided by phonecalls to and from other parts of the network 3 marksbIs your system a hard realtime system or a soft realtime systemBriefly explain why In a hard realtime system death or destruction will result if a deadline is missedIn soft realtime systems the occasional deadline can be missed with few issues1 mark for answer 1 for explanation Page 1 of 8
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