Download JNTUA M.Tech 1st Sem 2018 Aug-Sept 9D06104 Advanced Data Communications Question Paper

M.Tech I Semester Supplementary Examinations August/September 2018

ADVANCED DATA COMMUNICATIONS

(Digital Systems & Computer Electronics)

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(For students admitted in 2013, 2014, 2015 & 2016 only)

Time: 3 hours

Max. Marks: 60

Answer any FIVE questions

All questions carry equal marks

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1. 1. With neat diagram, explain the following modulation schemes: (i) PSK. (ii) QAM.
   2. Find out the minimum bandwidth, baud and bandwidth efficiency for the following bit rates and modulation schemes are 8-QAM and 16-QAM.
      1. f_b = 2400 bps.
      2. f_b = 4800 bps.
      3. f_b = 9600 bps.

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2. 1. In home two computers are connected by an Ethernet hub. In this a LAN or a WAN? Explain the reason.
   2. Assume 8 devices are arranged in a mesh topology. How many cables are needed? How many parts are needed for each device?
3. 1. Performance is inversely related to delay. When we use the internet, which of the following are more sensitive to delay: (i) Sending an e-mail. (ii) Copying a file. (iii) Surfing the internet. Explain in detail.

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   2. How many point-to-point WAN's are needed to connect 'n' LAN's, if each LAN should be able to directly communicate with any other LAN.
4. The parity check bit of (8, 4) block code are generated by C₅ = d₁ + d₂ + d₄, C₆ = d₁ + d₂ + d₃, C₇ = d₁ + d₃ + d₄, & C₈ = d₂ + d₃ + d₄, where d₁, d₂, d₃ and d₄ are message bits. Find:
   1. G and H.
   2. Minimum weight of code.
   3. Error correcting capacity.

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   4. Show that through 2 examples that the code can detect and correct errors.
5. 1. Compare and contract byte-stuffing and bit stuffing.
   2. Assume the only computer in the residence user PPP to communicate with the ISP. If the user sends 10 network-layer packets to ISP, how many frames are exchanged in each of the following cases:
      1. Using no authentication.
      2. Using PAP for authentication.

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      3. Using CHAP for authentication.
6. 1. Consider a space division switch with 100 inputs and outputs. What is the total number of cross points in each of the following cases: (i) Using a single crossbar. (ii) Using a multi-stage switch based on the Clos criteria.
   2. Consider nXk crossbar switch with 'n' inputs and 'k' outputs.
      1. Can we say that the switch acts as a multiplexer if n>k?

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      2. Can we say that the switch acts as a demultiplexer if n<k? Give reason.
7. We have defined the parameter 'a' as the number of frames that can fit the medium between two stations, or a = (T_p)/(T_fr). Another way to define the parameter is a = L_b/F_b, in which L_b in the bit length of the medium and F_b is the frame length of the medium. Show that two definitions are equivalent.
8. Alice and Bob are experimenting with CSMA using a W2 Walsh table. Alice use the code (+1, -1) and Bob user the code (+1, -1). Assume that they simultaneously send a hexadecimal digit to each other. Alice sends (6)₁₆ and Bob sends (B)₁₆. Show how they can detect what are other person has sent.

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