Computer Networks (Test 2)

Gate Exam : Cs Computer Science And Information Technology

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Computer Networks

Computer Networks
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Q.1
Assume that the bandwidth for a TCP connection is 1048560 bits/sec. Let α be the value of RTT in milliseconds. (rounded off to the nearest integer) after which the TCP window scale option is needed. Let β be the maximum possible window size the window scale option. Then the values of α and β are
A. 63 milliseconds, 65535 × 214
B. 63 milliseconds, 65535 × 216
C. 500 milliseconds, 65535 × 214
D. 500 milliseconds, 65535 × 216
Answer : Option C
Explaination / Solution:
No Explaination.


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Q.2
Which one of the following protocols is NOT used to resolve one form of address to another one?
A. DNS
B. ARP
C. DHCP
D. RARP
Answer : Option C
Explaination / Solution:

Except DHCP, remaining all the protocols are used to resolve one form of address to another one.

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Q.3
Which of the following is/are example(s) of stateful application layer protocols? (i) HTTP (ii) FTP (iii) TCP (iv) POP3
A. (i) and (ii) only
B. (ii) and (iii) only
C. (ii) and (iv) only
D. (iv) only
Answer : Option C
Explaination / Solution:

FTP and POP 3are stateful application layer protocols

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Q.4
Consider the following two phase locking protocol. Suppose a transaction T accesses (for read or write operations), a certain set of objects {O1, . . . , OK}. This is done in the following manner:
Step 1. T acquires exclusive locks to O1, . . . , Ok in increasing order of their addresses. 
Step 2. The required operations are performed. 
Step 3. All locks are released. 
This protocol will
A. guarantee serializability and deadlock-freedom
B. guarantee neither serializability nor deadlock-freedom
C. guarantee serializability but not deadlock-freedom
D. guarantee deadlock-freedom but not serializability
Answer : Option A
Explaination / Solution:

2PL ensures serializability and here as we are following linear order in acquiring the locks there will not be any deadlock.

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Q.5
Consider that B wants to send a message m that is digitally signed to A. Let the pair of private and public keys for A and B be denoted by  for x = A, B, respectively. Let Kx(m) represent the operation of encrypting m with a key Kx and H (m) represent the message digest. Which one of the following indicates the CORRECT way of sending the message m along with the digital signature to A?
A.
B.
C.
D.
Answer : Option B
Explaination / Solution:



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Q.6
A sender S sends a message m to receiver R, which is digitally signed by S with its private key. In this scenario, one or more of the following security violations can take place. 
I. S can launch a birthday attack to replace m with a fraudulent message.
II. A third party attacker can launch a birthday attack to replace m with a fraudulent message.
III. R can launch a birthday attack to replace m with a fraudulent message.
Which of the following are possible security violations? 
A. I and II only
B. I only
C. II only
D. II and III only
Answer : Option B
Explaination / Solution:

Sender can launch a Birthday Attack to replace with fraudulent message, because he has the signature and he can decrypt the signature by his own public key and gets the hash value. With that same hash value, he can create another message and can be sent instead of original. Hence option(B) is correct.

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Q.7
In the IPv4 addressing format, the number of networks allowed under Class C addresses is
A. 214
B. 27
C. 221
D. 224
Answer : Option C
Explaination / Solution:

For class C address, size of network field is 24 bits. But first 3 bits are fixed as 110; hence total number of networks possible is 221

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Q.8
Which of the following transport layer protocols is used to support electronic mail?
A. SMTP
B. IP
C. TCP
D. UDP
Answer : Option C
Explaination / Solution:

E-mail uses SMTP, application layer protocol which intern uses TCP transport layer protocol.

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Q.9
Consider a TCP client and a TCP server running on two different machines. After completing data transfer, the TCP client calls close to terminate the connectional and a FIN segment is sent to the TCP server. Server-side TCP responds by sending an ACK which is received by the client-side TCP. As per the TCP connections state diagram (RFC 793), in which state does the client-side TCP connection wait for the FIN from the sever-side TCP?
A. LAST-ACK
B. TIME-WAIT
C. FIN-WAIT-1
D. FIN-WAIT-2
Answer : Option D
Explaination / Solution:
No Explaination.


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Q.10
The protocol data unit (PDU) for the application layer in the Internet stack is
A. Segment
B. Datagram
C. Message
D. Frame
Answer : Option C
Explaination / Solution:

The PDU for Datalink layer, Network layer , Transport layer and Application layer are frame, datagram, segment and message respectively.

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CS Computer Science and Information Technology