)[2 marks] What is half-duplex transmission and what flow control is needed for half-duplex transmission? 5) [1 mark] How many signal levels will be required to encode 4 bits in a single symbol? =) [3 marks] In general, how is it that faster speeds can be achieved over the same optical fibre as technology improves? H) [4 marks] Describe controlled access and contention-based access to a physical medium? Which is centralized and which is distributed?