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. 

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. 

Q2 (a) Describe in detail the operation of a semiconductor laser source. How does it compare to a LED? 

 (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.  

Q 3 (a) Asynchronous, Synchronous and Isochronous are formats used to transfer data streams. Compare and contrast the three formats.    

 (b) Compare, using diagrams where appropriate, the operation of the Selective Repeat and Go-Back N flow control protocols. 

(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 HDLCreceiver misinterpreting the information string? 

Q4.(a)Explain what is meant by each of the following terms as they relate to teletraffic engineering: 

(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      

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