# Computer Networks - Data Communication & Network Security

76:

Phase shift keying (PSK.) method is used to modulate digital signals at 9600 bps using 16 levels. The line signals speed (i.e. modulation rate) will be

 A. 2400 bands B. 1200 bands C. 4800 bands D. 9600 bands Answer Report Discuss Option: A Explanation : 9600 corresponds to bits per second and the level is 16. For a 16-PSK, given the baud rate N, the bit rate would be 4N. Here bps is provided which is 9600. In order to calculate the baud rate we have to divide bps/4, because the signal level is 16.So the answer would be 9600/4=2400 baud. Option is (A). Click on Discuss to view users comments. Write your comments here:
77:

Television channels are 6 MHz. How many bits can be sent if four level digital signals are used (assume a noiseless channel)?

 A. 24 Mbps B. 12 Mbps C. 6 Mbps D. 36 Mbps Answer Report Discuss Option: A Explanation : Click on Discuss to view users comments. Write your comments here:
78:

What is the maximum burst length on an 155.52 Mbps ATM ABR connection whose PCR value 200,000 and whose L value is 25 msec ?

 A. 9 cells B. 12 cells C. 15 cells D. 18 cells Answer Report Discuss Option: B Explanation : Given : T = 5 μ sec              L = 25 μ sec              d = 2.73 μ sec.            N = (1 + L) /  (T - δ) = 12.01 i.e. 12 cells.  Click on Discuss to view users comments. Write your comments here:
79:

Poll/select line discipline requires what to identify the packet recipient ?

 A. Timer B. Buffer C. Address D. Dedicated line Answer Report Discuss Option: C Explanation : In Poll / select method, every device on a link has an address that can be used for identification Click on Discuss to view users comments. Write your comments here:
80:

In sliding window flow control, if window size is 63, what is the range of sequence numbers ?

 A. 0 to 63 B. 0 to 64 C. 1 to 63 D. 1 to 64 Answer Report Discuss Option: A Explanation : In sliding window flow control the window size is 63, the range of sequence numbers are 0 to 63 { 0.....63}. Click on Discuss to view users comments. Write your comments here: