# Computer Networks - Data Communication & Network Security

91:

What is the percentage of over head on a T1 carrier (1.544 Mbps) ?

 A. 25% B. 13% C. 20% D. 47% Answer Report Discuss Option: B Explanation : Click on Discuss to view users comments. Write your comments here:
92:

A noiseless 3 kHz channel transmits bits with binary level signals. What is the maximum data rate ?

 A. 3 kbps B. 6 kbps C. 12 kbps D. 24 kbps Answer Report Discuss Option: B Explanation : Click on Discuss to view users comments. Write your comments here:
93:

Given an infinite amount of buffer space. In the text it was stated that a satellite with two uplink and one downlink slotted ALOHA channels can achieve a downlink utilization of

 A. 0.536 B. 0.636 C. 0.736 D. 0.936 Answer Report Discuss Option: C Explanation : The probability of success (i.e. exactly one frame in a slot) = 1 / e  ~ 0.368. Then probability of a failure (no frames or multiple frames) = 0.632. Thus joint probabilities of the two uplink channels are : success on 1 and success on 2 : 0.135 (2 frames sent) success on 1 and failure on 2 : 0.233 (1 frame sent) failure on 1 and success on 2 : 0.233 (1 frame sent) failure on 1 and success on 2 : 0.399 (0 frames sent) Then expected number of success per slot. E = 0.35 * x + 0.233 * 1 + 0.233 * 1 + 0.399 * 0 = 0.270 + 0.233 + 0.233 = 0.736  Click on Discuss to view users comments. Write your comments here:
94:

In time division switches, if each memory access takes 100 ns and one frame period is 125ms, then maximum number of lines that can be supported is

 A. 625 B. 1250 C. 2300 D. 318 Answer Report Discuss Option: A Explanation : In time division switches 2nT = 1 frame period, where T = memory access time. Click on Discuss to view users comments. Write your comments here:
95: