CN |Gate-2017| Previous Year Questions| Set-4

Set-15 GATE-2006 CN

CN |Gate-2017| Computer Networks

1. 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 connection 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 connection state diagram (RFC 793), in which state does the client-side TCP connection wait for the FIN from the server-side TCP? [GATE – 2017]

a. LAST-ACK
b. FIN-WAIT-1
c. TIME-WAIT
d. FIN-WAIT-2

Answer : d)


2. 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? [GATE – 2017]

a. (I) and (II) only
b. (I) only
c. (II) only
d. (II) and (III) only

Answer : b)


3. A computer network uses polynomials over GF(2) for error checking with 8 bits as information bits and uses x+ x + 1 as the generator polynomial to generate the check bits. In this network, the message 01011011 is transmitted as : [GATE – 2017]

a. 01011011010
b. 01011011011
c. 01011011101
d. 01011011100

Answer : c)


4. In a RSA cryptosystem, a participant A uses two prime numbers p = 13 and q = 17 to generate her public and private keys. If the public key of A is 35, then the private key of A is _________. [GATE – 2017]

a. 11
b. 12
c. 13
d. 14

Answer : a
CN |Gate-2017|


5. The value of parameters for the Stop-and-Wait ARQ protocol are as given below:

          Bit rate of the transmission channel = 1 Mbps.
          Propagation delay from sender to receiver = 0.75 ms.
Number of bytes in the acknowledge frame = 20.
          Time to process a frame = 0.25 ms.
          Number of bytes in the information frame = 1980.
          Number of overhead bytes in the information frame = 20.

Assume that there are no transmission errors. Then, the transmission efficiency (expressed in percentage) of the Stop-and-Wait ARQ protocol for the above parameters is _________ (correct to 2 decimal places). [GATE – 2017]

a. 89.33%
b. 89.34%
c. 89.35%
d. 89.36%

Answer : a)


6. Consider the following statements about the routing protocols, Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) in an IPv4 network.

I: RIP uses distance vector routing
II: RIP packets are sent using UDP
III: OSPF packets are sent using TCP
IV: OSPF operation is based on link-state routing

Which of the statements above are CORRECT? [GATE – 2017]

a. I and IV only
b. II, III and IV only
c. I, II and IV only
d. I, II and III only

Answer : c)


7. Consider socket API on a Linux machine that supports connected UDP sockets. A connected UDP socket is a UDP socket on which connect function has already been called. Which of the following statement is/are CORRECT? [GATE – 2017]

I. A connected UDP socket can be used to communicate with multiple peers simultaneously.
II. A process can successfully call connect function again for an already connected UDP socket.

a. I only
b. II only
c. Both I and II
d. Neither I nor II

Answer : b)
CN |Gate-2017|


8. The maximum number of IPv4 router addresses that can be listed in the record route (RR) option field of an IPv4 header is _________. [GATE – 2017]

a. 9
b. 10
c. 11
d. 12

Answer : a)


9. Consider two hosts X and Y, connected by a single direct link of rate 106bits/sec. The distance between the two hosts is 10,000 km and the propagation speed along the link is 2 × 108m/sec. Host X sends a file of 50,000 bytes as one large message to host Y continuously. Let the transmission and propagation delays be p milliseconds and q milliseconds, respectively. Then the values of p and q are : [GATE – 2017]

a. p=50 and q=100
b. p=100 and q=50
c. p=50 and q=400
d. p=400 and q=50

Answer : d)


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