Q1.(a) Explain why Companders are required in Pulse Code Modulation and describe the operation and characteristics of a µ law Compander. (6 marks)(b) Using the converter of figure 8.5 from the course notes as a model, design a DAC that can handle 5 bit input codes. Taking 10V as the reference voltage calculate the output voltages for inputs of (i) 00001 and (ii) 10000. Determine the resolution of the DAC and confirm that calculated output voltages are consistent with the binary input values. (10 marks) (c) Figure 1(c)The summing amplifier in Figure 1(c) needs to be configured as a 3 input code DAC. Determine the appropriate resistor values and the equation for Vo if 1 kΩ is smallest resistor used. (4 marks)(Total 20 marks)Q2 (a) Describe in detail the operation of a semiconductor laser source. How does it compare to a LED? (9 marks) (b) A single mode 50k fibre link is powered from a laser source with a spectral width of 1nm. and a response time of 1ns, the photodiode receiver has a response time of .3 ns and the dispersion coefficient of the fibre is 50 psnm-1 km-1. Calculate the overall response time of the link. (6 marks)Note: Modal dispersion does not feature in Single Mode Fibre dispersion calculations. (Total 15 marks)Q 3 (a) Asynchronous, Synchronous and Isochronous are formats used to transfer data streams. Compare and contrast the three formats. (8 marks) (b) Compare, using diagrams where appropriate, the operation of the Selective Repeat and Go-Back N flow control protocols. (5 marks)(c) (i) Under what circumstances is the control field of a HDLC frame set at 16 bits? (ii) What adjustment should be applied to the following information string to prevent a HDLC receiver misinterpreting the information string? (4 marks) 110110011111110111011011010110(Total 17 marks)Q4. (a) Explain what is meant by each of the following terms as they relate to teletraffic engineering: (3 marks) (i) Busy Hour (ii) Erlang (iii) Grade of Service(b) During the busy hour at an exchange the average call duration is 2 minutes, 45 calls are lost from offered traffic of 250 erlangs. Calculate (i) the grade of service (ii) the actual traffic intensity