What do you mean by data communication? Write shortly about the five main components of a data communication system.

What is switching in data communication? Briefly describe the virtual circuit networks including its stages, advantages, disadvantages and real application scenarios.

 What is OSI model? Differentiate between OSI and TCP/IP model in details.

 What is a composite signal? How can we decompose it into its components? Explain it briefly

 What is the bit rate for the signal in following Figure?

 What is the frequency of the signal in following Figure?

(i) What is the way to measure attenuation? [2]

(ii) The loss in a cable is usually defined in decibels per kilometer (dB/km). If the signal at the beginning of a cable with -0.4 dB/km has a power of 3mW, what is the power of the signal at 20 km? [3]

Why do we need to know about the following terms in data communication course? Briefly explain. Baseline Wandering, DC components and self-synchronization.

 Please do the following analog to digital (ADC) conversion process of the following sampled signal using pulse code modulation (PCM) method and find out the digital data.

 What is QAM? Differentiate between 4-QAM and 8-QAM. Draw an 8-QAM signal of the following bit stream-

000 001 111 100 101 010 001 110 011 101

What is line encoding scheme? [1+7]

Draw the digital signal of the following bit stream by the following schemes: unipolar NRZ, polar NRZ-I, polar RZ, polar biphase (Manchester and differential Manchester), bipolar-AMI and pseudo-ternary and multilevel 2B1Q

01100111001

Mention your logic about which analog conversion technique is the most susceptible to noise.

 What will be the problem if we don't follow the Nyquist theorem during sampling an analog signal. Explain with a proper illustration.

 Explain IP spoofing and packet sniffing?

 In a noisy channel, Selective Repeat ARQ protocol can solve the problems what other ARQ protocols (stop and Wait ARQ, Go-back-N ARQ) may face. What is that problem and how it can solve this? and explain this selective repeat ARQ protocol with a proper diagram and examples.

 Why do we need to apply multiplexing technique in data communication? Mention three multiplexing techniques and differentiate them.

Explain briefly two-dimensional parity-check code. How many bits can be checked if there has been any error occurred or not?

Assume, A sender sends the data 111001011. Now, using C(13, 5) and the divisor 11101, Show how the codeword is generated by CRC method. If the receiver receives the codeword 111001101, how to decide whether an error has occurred or not.

What is Media Access Control (MAC)? How many protocols are there? Name all of them.

 Prove that in CDMA a receiving station can get the data sent by a specific sender if it multiplies the entire data on the channel by the sender's chip code and then divides it by the number of stations.

 Alice and Bob are experimenting with CSMA using a W2 Walsh table (see the following Figure). Alice uses the code [+1, +1] and Bob uses 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 the other person has sent.

Write short notes on the following topics: [ 3 * 4 = 12]

(i) Piggybacking

(ii) Satellite communication and Categories of Satellite

(iii) WiMAX vs Wi-Fi

(iv) Cellular telephony