CN |Gate-2007| Previous Year Questions| Set-14

Set-15 GATE-2006 CN

CN |Gate-2007| Computer Networks

1. In Ethernet when Manchester encoding is used, the bit rate is: [GATE – 2007]

a. Half the baud rate.
b. Twice the baud rate.
c. Same as the baud rate.
d. None of the above.

Answer : a)

2. Which one of the following uses UDP as the transport protocol? [GATE – 2007]

b. DNS
d. Telnet

Answer : b)

3. There are stations in a slotted LAN. Each station attempts to transmit with a probability p in each time slot. What is the probability that ONLY one station transmits in a given time slot? [GATE – 2007]

a. np(1-p)n-1
b. (1-p)n-1
c. p(1-p)n-1
d. 1-(1-p)n-1

Answer : a)

4. In a token ring network the transmission speed is 107 bps and the propagation speed is 200 metres/μs. The 1-bit delay in this network is equivalent to: [GATE – 2007]

a. 500 metres of cable.
b. 200 metres of cable.
c. 20 metres of cable.
d. 50 metres of cable.

Answer : c)

5. The address of a class B host is to be split into subnets with a 6-bit subnet number. What is the maximum number of subnets and the maximum number of hosts in each subnet? [GATE – 2007]

a. 62 subnets and 262142 hosts.
b. 64 subnets and 262142 hosts.
c. 64 subnets and 1024 hosts.
d. 62 subnets and 1022 hosts.

Answer : d)

6. The message 11001001 is to be transmitted using the CRC polynomial x3+1 to protect it from errors. The message that should be transmitted is: [GATE – 2007]

a. 11001001011
b. 11001001000
c. 11001010
d. 110010010011

Answer : a)

7. Match the following: [GATE – 2007]

(P) SMTP     (1) Application layer
(Q) BGP      (2) Transport layer
(R) TCP      (3) Data link layer
(S) PPP      (4) Network layer
            (5) Physical layer

a. P – 2 Q – 1 R – 3 S – 5
b. P – 1 Q – 4 R – 2 S – 3
c. P – 1 Q – 4 R – 2 S – 5
d. P – 2 Q – 4 R – 1 S – 3

Answer : b)

8. Consider the following statements about the timeout value used in TCP. i. The timeout value is set to the RTT (Round Trip Time) measured during TCP connection establishment for the entire duration of the connection. ii. Appropriate RTT estimation algorithm is used to set the timeout value of a TCP connection. iii. Timeout value is set to twice the propagation delay from the sender to the receiver. Which of the following choices hold?  [GATE – 2007]

a. (i) is false, but (ii) and (iii) are true
b. (i) and (ii) are false, but (iii) is true
c. (i) and (iii) are false, but (ii) is title
d. (i), (ii) and (iii) are false

Answer : c)

9. Consider a TCP connection in a state where there are no outstanding ACKs. The sender sends two segments back to back. The sequence numbers of the first and second segments are 230 and 290 respectively. The first segment was lost, but the second segment was received correctly by the receiver. Let X be the amount of data carried in the first segment (in bytes), and Y be the ACK number sent by the receiver. The values of X and Y (in that order) are : [GATE – 2007]

a. 60 and 290
b. 230 and 291
c. 60 and 231
d. 60 and 230

Answer : d)

10. Consider the following two statements: i. A hash function (these are often used for computing digital signatures) is an injective function. A. encryption technique such as DES performs a permutation on the elements of its input alphabet. Which one of the following options is valid for the above two statements?  [GATE – 2007]

a. Both are false
b. Statement (i) is true and the other is false
c. Statement (ii) is true and the other is false
d. Both are true

Answer : c)

11. A firewall is to be configured to allow hosts in a private network to freely open TCP connections and send packets on open connections. However, it will only allow external hosts to send packets on existing open TCP connections or connections that are being opened (by internal hosts) but not allow them to open TCP connections to hosts in the private network. To achieve this the minimum capability of the firewall should be that of : [GATE – 2007]

a. A combinational circuit
b. A finite automaton
c. A pushdown automaton with one stack
d. A pushdown automaton with two stacks

Answer : d)

12. An error correcting code has the following code words: 00000000, 00001111, 01010101, 10101010, 11110000. What is the maximum number of bit errors that can be corrected ? [GATE – 2007]

a. 0
b. 1
c. 2
d. 3

Answer  : b)

13. In the waveform (a) given below, a bit stream is encoded by Manchester encoding scheme. The same bit stream is encoded in a different coding scheme in wave form (b). The bit stream and the coding scheme are : [GATE – 2007]

a. 1000010111 and Differential Manchester respectively
b. 1000010111 and Integral Manchester respectively
c. 0111101000 and Differential Manchester respectively
d. 0111101000 and Integral Manchester respectively

Answer : c)

14. Let us consider a statistical time division multiplexing of packets. The number of sources is 10. In a time unit, a source transmits a packet of 1000 bits. The number of sources sending data for the first 20 time units is 6, 9, 3, 7, 2, 2, 2, 3, 4, 6, 1, 10, 7, 5, 8, 3, 6, 2, 9, 5 respectively. The output capacity of multiplexer is 5000 bits per time unit. Then the average number of backlogged of packets per time unit during the given period is : [GATE – 2007]

a. 5.
b. 4.45
c. 3.45
d. 0

Answer : b)

15. A group of 15 routers are interconnected in a centralized complete binary tree with a router at each tree node. Router j communicates with router j by sending a message to the root of the tree. The root then sends the message back down to router j. The mean number of hops per message, assuming all possible router pairs are equally likely is : [GATE – 2007]

a. 3
b. 4.26
c. 4.53
d. 5.26

Answer : c)

16. A broadcast channel has 10 nodes and total capacity of 10 Mbps. It uses polling for medium access. Once a node finishes transmission, there is a polling delay of 80 μs to poll the next node. Whenever a node is polled, it is allowed to transmit a maximum of 1000 bytes. The maximum throughput of the broadcast channel is : [GATE – 2007]

a. 100/11 Mbps
b. 1 Mbps
c. 10 Mbps
d. 100 Mbps

Answer : a)
CN |Gate-2007|

17. Consider the following clauses: i. Not inherently suitable for client authentication. ii. Not a state sensitive protocol. iii. Must be operated with more than one server. iv. Suitable for structured message organization. v. May need two ports on the serve side for proper operation. The option that has the maximum number of correct matches is : [GATE – 2007]

a. IMAP-(i), FTP-(ii), HTTP-(iii), DNS-(iv), POP3-(v)
b. FTP-(i), POP3-(ii), SMTP-(iii), HTTP-(iv), IMAP-(v)
c. POP3-(i), SMTP-(ii), DNS-(iii), IMAP-(iv), HTTP-(v)
d. SMTP-(i), HTTP-(ii), IMAP-(iii), DNS-(iv), FTP-(v)

Answer : d)
CN |Gate-2007|

18. Your are given the following four bytes : 10100011            00110111            11101001            10101011 Which of the following are substrings of the base 64 encoding of the above four bytes ?  [GATE – 2007]

a. zdp
b. fqp
c. qwA
d. oze

Answer : b)
CN |Gate-2007|

19. Consider a token ring topology with N stations (numbered 1 to N) running token ring protocol where the stations are equally spaced. When a station gets the token it is allowed to send one frame of fixed size. Ring latency is tp, while the transmission time of a frame is tt. All other latencies can be neglected. The maximum utilization of the token ring when tt =3 ms, tp = 5 ms, N = 10 is : [GATE – 2007]

a. 0.857
b. 0.6
c. 0.961
d. 0.545

Answer : a)
CN |Gate-2007|

20. Consider a token ring topology with N stations (numbered 1 to N) running token ring protocol where the stations are equally spaced. When a station gets the token it is allowed to send one frame of fixed size. Ring latency is tp, while the transmission time of a frame is tt. All other latencies can be neglected. The maximum utilization of the token ring when tt = 5 ms, tp = 3 ms, N = 15 is : [GATE – 2007]

a. 0.545
b. 0.655
c. 0.9375
d. 0.961

Answer : d)
CN |Gate-2007|


Spread the love

Leave a Comment

Your email address will not be published. Required fields are marked *