Classical

Computer Networks - Data Communication & Network Security

51:  

 What signal-to-noise ratio is needed to put a T1 carrier on a T0-kHz line ?

A.

63 db

B.

73 db

C.

83 db

D.

 93 db 

 
 

Option: D

Explanation :

 

To send a T1 signal we need
Hlog2, (1 + S / N ) = 1.544 x 106 with 50,000.  
S / N = 230 -1,48 ~  93 db. 


52:  

In which ARQ, when a NAK is received, all frame sent since the last frame acknowledged an retransmitted

A.

stop-and-wait

B.

go-back-n

C.

selective-reject

D.

both (a) and (b) 

 
 

Option: B

Explanation :

In the case of go-back-n protocol, when a NAK is received, all the frames sent since the last frame acknowledged are retransmitted. Go ----> Back ----> n.


53:  

PURE ALOHA

A.

Does not require global time synchronization

B.

does require global time synchronization

C.

both (a) and (b)

D.

none of these

 
 

Option: A

Explanation :


54:  

Manchester code is a

A.

non-return to zero code

B.

polar code

C.

both (a) and (b)

D.

none of these

 
 

Option: C

Explanation :

In bipolar code, the singal varies among three levels. In non-return to zero code, the signal remains the same through-out the bit cell. In unipolar code, there will be no signal either below zero or above zero. In Manchester code, the signal level will not vary in the middle and is unipolar.


55:  

Non-polling system is

A.

TDMA

B.

stop and wait

C.

continuous ARQ

D.

none of these

 
 

Option: A

Explanation :




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