Classical

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%

 
 

Option: B

Explanation :


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

 
 

Option: B

Explanation :


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

 
 

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 


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

 
 

Option: A

Explanation :

In time division switches 2nT = 1 frame period, where T = memory access time.


95:  

A bridge has access to which address of a station on the same network ?

A.

Physical

B.

Network

C.

Service access point

D.

All of these

 
 

Option: A

Explanation :

A bridge operates at the data link layer, giving it access to the physical address of all stations connected to it. Answer is physical addresses.




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