CN |Gate-2015| Previous Year Questions| Set-6

Set-15 GATE-2006 CN

CN |Gate-2015| Computer Networks

1. Suppose two hosts use a TCP connection to transfer a large file. Which of the following statements is/are False with respect to the TCP connection? [GATE – 2015]

1. If the sequence number of a segment is m, then the sequence

   number of the subsequent segment is always m+1.

2. If the estimated round trip time at any given point of time

   is t sec, the value of the retransmission timeout is always

   set to greater than or equal to t sec.

3. The size of the advertised window never changes during the

   course of the TCP connection.

4. The number of unacknowledged bytes at the sender is always

   less than or equal to the advertised window

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

Answer : b)


2. Which one of the following fields of an IP header is NOT modified by a typical IP router? [GATE – 2015]

a. Checksum
b. Time to Live (TTL)
c. Source address
d. Length

Answer : c)


3. Consider  a LAN with four nodes S1, S2, S3 and S4. Time is divided into fixed-size slots, and a node can begin its transmission only at the beginning of a slot. A collision is said to have occurred if more than one node transmit in the same slot. The probabilities of generation of a frame in a time slot by S1, S2, S3 and S4 are 0.1, 0.2, 0.3 and 0.4, respectively. The probability of sending a frame in the first slot without any collision by any of these four stations is _________.  [GATE – 2015]

a. 0.4404
b. 0.463
c. 0.464
d. 0.465

Answer : a)
CN |Gate-2015|


4. Suppose that the stop-and-wait protocol is used on a link with a bit rate of 64 kilobits per second and 20 milliseconds propagation delay. Assume that the transmission time for the acknowledgment and the processing time at nodes are negligible. Then the minimum frame size in bytes to achieve a link utilization of at least 50% is _________.  [GATE – 2015]

a. 320
b. 321
c. 322
d. 323

Answer : a)


5. Identify the correct order in which a server process must invoke the function calls accept, bind, listen, and recv according to UNIX socket API.   [GATE – 2015]

a. listen, accept, bind recv
b. bind, accept, listen, recv
c. accept, listen, bind recv
d. bind, listen, accept, recv

Answer : d)


6. Which one of the following statements is NOT correct about HTTP cookies? [GATE – 2015]

a. A cookie is a piece of code that has the potential to compromise the security of an internet user
b. A cookie gains entry to the user’s work area through an HTTP header
c. A cookie has an expiry date and time
d. Cookies can be used to track the browsing pattern of a user at a particular site

Answer : a)


7. A link has a transmission speed of 106 bits/sec. It uses data packets of size 1000 bytes each. Assume that the acknowledgement has negligible transmission delay, and that its propagation delay is the same as the data propagation delay. Also assume that the processing delays at the nodes are negligible. The efficiency of the stop-and-wait protocol in this setup is exactly 25%. The value of the one-way propagation delay (in milliseconds) is ___________.  [GATE – 2015]

a. 12
b. 13
c. 14
d. 15

Answer : a)


8. Host A sends a UDP datagram containing 8880 bytes of user data to host B over an Ethernet LAN. Ethernet frames may carry data up to 1500 bytes (i.e. MTU = 1500 bytes). Size of UDP header is 8 bytes and size of IP heard is 20 bytes. There is no option field in IP header. How many total number of IP fragments will be transmitted and what will be the contents of offset field in the last fragment? [GATE – 2015]

a. 6 and 925
b. 6 and 7400
c. 7 and 1110
d. 7 and 8880

Answer : c)
CN |Gate-2015|


9. Consider the following routing table at an IP router:

Network No.Net MaskNext Hop
128.96.170.0255.255.254.0Interface 0
128.96.168.0255.255.254.0Interface 1
128.96.166.0255.255.254.0R2
128.96.164.0255.255.252.0R3
0.0.0.0DefaultR4

 For each IP address in Group I identify the correct of the next hop from Group II using the entries from the routing table above. [GATE – 2015]

Group I                                Group II                                               

i) 128.96.171.92                   a) Interface 0

ii) 128.96.167.151               b)  Interface 1                               

iii) 128.96.163.151              c) R2

iv) 128.96.165.121              d) R3

                                             e) R4

a. i-a, ii-c, iii-e, iv-d
b. i-a, ii-d, iii-b, iv-e
c. i-b, ii-c, iii-d, iv-e
d. i-b, ii-c, iii-e, iv-d

Answer : a)


10. Consider the following statements. [GATE – 2015]

I. TCP connections are full duplex.
II. TCP has no option for selective acknowledgment
III. TCP connections are message streams.

a. Only I is correct
b. Only I and III are correct
c. Only II and III are correct
d. All of I, II and III are correct

Answer : a)
CN |Gate-2015|


11. Consider a CSMA/CD network that transmits data at a rate of 100 Mbps (108 bits second) over a 1 km (kilometer) cable with no repeaters. If the minimum frame size required for this network is 1250 bytes, what is the signal speed (km/sec) in the cable?   [GATE – 2015]

a. 8000
b. 10000
c. 16000
d. 20000

Answer : d)


12. Consider a network connected two systems located 8000 kilometers apart. The bandwidth of the network is 500 × 106 bits per second. The propagation speed of the media is 4 × 106 meters per second. It is needed to design a Go-Back-N sliding window protocol for this network. The average packet size is 107 bits. The network is to be used to its full capacity. Assume that processing delays at nodes are negligible. Then the minimum size in bits of the sequence number field has to be ___________.  [GATE – 2015]

a. 5
b. 7
c. 8
d. 6

Answer : c)


13. In the network 200.10.11.144/27, the fourth octet (in decimal) of the last IP address of the network which can be assigned to a host is ____________. [GATE – 2015]

a. 155
b. 158
c.156
d. 157

Answer : b)


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