Birla Institute of Technology (BIT Mesra) 2007 B.E Data Communication and Network - Question Paper

BITS PILANI

BITS C372: Data Communication and Network

Comprehensive Examination

PartB (Open Book)

Time-: 90 Min Max Marka-: 80 Weightage -: 20% 07-12-2007

(Do not use pencil. Answer to all parts of a question must be in sequence)

1. Refer to the figure given below and answer to the following questions.

(a)     Sketch clearly with proper labeling x(t) for two time periods starting from t = 0.

(b)     Sketch clearly with proper labeling y(t) for two time periods(of x(t)) starting from t = 0.

(c)     Sketch clearly with proper labeling y(n*T) for n = 0, 1, 2, 3, 4 . T is given in fig.

(d)     The above y(n*T) are quantized by a 4 level quantizer and then binary encoded. Assume the quantizer quantizes ranging from 0V to 8V. In this the first quantization interval is 0 to 2V and other quantization intervals you approximate accordingly. Give the binary data in the following format for first 5 samples obtained above:

Binary data for n=0 sample, Binary data for n=1 sample, - - -.

(e)     Find out the maximum possible quantization error that will be introduced in the above process (A/D conversion of y(t) as done in (c)-(d)) of analog to digital conversion.

(f)      The above binary data is to be transmitted through a traditional Ethernet LAN. Sketch the first six binary bits (obtained above) using appropriate encoding scheme so that it can be transmitted through a traditional Ethernet LAN. [5*6=30]

2. (a) A multistage switching system is given below.

1^st Stage 2^nd Stage 3^rdStage

I. What is the maximum number of simultaneous calls that can be supported?

II. Find the number of cross point switches needed in 1^st,2^nd,and 3^rd stage of the above switching system.

III. If we replace the above three stage switch by only one large cross bar switch to support same number of inlets and outlets, how many cross points will be needed? [2+2+2]

(b) The output of a multiplexer, which multiplexes 200 voice channels, is given as input to a TSI switch. The output of TSI switch is demultiplexed to 200 subscriber lines. 8-bit PCM encoding is used to digitalize voice. Answer to the following questions for the TSI switch.

I. Estimate the size of data memory in bits.

II. Estimate the size of control memory in bits.? [2+2]

3. The following information bit stream is to be transmitted through a noisy channel. Correcting burst error is complex using Hamming code. So use a data rearrangement method, so that single bit Hamming error correction method will also correct single busty error of 5 bits. Assume 4^th,5^th ,6^th ,7^th and 8^th bits of transmission stream(combination of information and redundant bits in arranged form) are corrupted during transmission. Show that you are able to correct the 5-bit error introduced in the following bit stream using single bit error correction method.

Information bit stream is : 1 0 1 1 0 1 1 0 1 0 1 0 1 1 0 [10]

4. (a) We need to transmit data from 400 sources using Asynchronous TDM. Statistical analysis shows that in an average only 60 of the sources are active at a time. As the input sources can generate data at different rate, these slots can have variable length of 1n sec to 32 n sec. Calculate the no of overhead bits added in every slot. [5]

(b) A standard Ethernet LAN(100 Base 5) uses a 5-port bridge. In this each station has an effective average data rate of 0.4 Mbps. Calculate the number of stations in the LAN. [5]

5. In the figure given below shows a site with a given network address and mask. The administrator has to divide the site into several sub networks. Chose the appropriate sub network address, host address of A, B, C, D and gateway addresses.

[4+2+2]

6. You want to send music of 10-minute duration to one of your friend using modem. The music contain signal with frequency up to 20 KHz. For this you have to store the same in your PC memory and then transmit. [4+6]

(a)     Find the minimum memory required in bits to store the music if you are using 16 bits/sample encoding scheme.

(b)     You can send the above music by two ways

Case I -: playing music in front of mouthpiece of general telephone

Or

Case II -: Using a 33.6Kbps modem.

Estimate the exact time difference to transmit the same music signal in both of the above cases.

End