Q4. 9 marks) What do the following acronyms and terms represent in connection with reliability for networks a) MTBF b) MTTR c) Unavailability Your answer should supply definitions for each (3 marks). d) An optical fibre undergoes 0.4 cuts/yr on the average. If the MTTR of the cable is 12 hours, calculate the unavailability in minutes per year. (1 mark) e) iD Esplain what the term 1:1 protection means, define all the terms that you use (I mark) ii) A second fibre is used to provide 1:1 protection and it has the same reliability parameters as above. Calculate the unavailability of the two fibre system with 1:1 protection (3 marks) f) Determine what MTTR for a single cable would be needed to achieve the same unavailability as for the two fibre system. (1 mark)