CN |Gate-2014| Previous Year Questions| Set-7

Set-15 GATE-2006 CN

CN |Gate-2014| Computer Networks

1. Consider the following three statements about link state and distance vector routing protocols, for a large network with 500 network nodes and 4000 links. [GATE – 2014]

[S1] The computational overhead in link state protocols
     is higher than in distance vector protocols.
[S2] A distance vector protocol (with split horizon)
     avoids persistent routing loops, but not a link
     state protocol.
[S3] After a topology change, a link state protocol
     will converge faster than a distance vector
     protocol.

Which one of the following is correct about S1, S2, and S3 ?

a. S1, S2, and S3 are all true.
b. S1, S2, and S3 are all false.
c. S1 and S2 are true, but S3 is false.
d. S1 and S3 are true, but S2 is false.

Answer : d)


2. Which of the following are used to generate a message digest by the network security protocols? [GATE – 2014]

(P) RSA
(Q) SHA-1
(R) DES
(S) MD5

a. P and R only
b. Q and R only
c. Q and S only
d. R and S only

Answer : c)


3. Identify the correct order in which the following actions take place in an interaction between a web browser and a web server. [GATE – 2014]

1. The web browser requests a webpage using HTTP.
2. The web browser establishes a TCP connection with the web server.
3. The web server sends the requested webpage using HTTP.
4. The web browser resolves the domain name using DNS.

a. 4,2,1,3
b. 1,2,3,4
c. 4,1,2,3
d. 2,4,1,3

Answer : a)


5. Consider a token ring network with a length of 2 km having 10 stations including a monitoring station. The propagation speed of the signal is 2×108 m/s and the token transmission time is ignored. If each station is allowed to hold the token for 2 µsec, the minimum time for which the monitoring station should wait (in µsec) before assuming that the token is lost is _______. [GATE – 2014]

a. 28μs to 30 μs
b. 29μs to 31 μs
c. 30μs to 32 μs
d. 31μs to 33 μs

Answer : a)


6. Let the size of congestion window of a TCP connection be 32 KB when a timeout occurs. The round trip time of the connection is 100 msec and the maximum segment size used is 2 KB. The time taken (in msec) by the TCP connection to get back to 32 KB congestion window is _________. [GATE – 2014]

a. 1101 to 1301
b. 1100 to 1300
c. 1102 to 1302
d. 1103 to 1303

Answer : b)


7. Consider a selective repeat sliding window protocol that uses a frame size of 1 KB to send data on a 1.5 Mbps link with a one-way latency of 50 msec. To achieve a link utilization of 60%, the minimum number of bits required to represent the sequence number field is ________. [GATE – 2014]

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

Answer : a)


8. Which one of the following is TRUE about the interior gateway routing protocols – Routing Information Protocol (RIP) and Open Shortest Path First (OSPF)? [GATE – 2014]

a. RIP uses distance vector routing and OSPF uses link state routing
b. OSPF uses distance vector routing and RIP uses link state routing
c. Both RIP and OSPF use link state routing
d. Both RIP and OSPF use distance vector routing

Answer : a)


9. Which one of the following socket API functions converts an unconnected active TCP socket into a passive socket? [GATE – 2014]

a. connect
b. bind
c. listen
d. accept

Answer : c)


10. In the diagram shown below L1 is an Ethernet LAN and L2 is a Token-Ring LAN. An IP packet originates from sender S and traverses to R, as shown. The link within each ISP, and across two ISPs, are all point to point optical links. The initial value of TTL is 32. The maximum possible value of TTL field when R receives the datagram

is : [GATE – 2014]

a. 29
b. 28
c. 27
d. 26

Answer : d)


11. Consider the store and forward packet switched network given below. Assume that the bandwidth of each link is 106 bytes / sec. A user on host A sends a file of size 103 bytes to host B through routers R1 and R2 in three different ways. In the first case a single packet containing the complete file is transmitted from A to B, In the second case, the file is split into 10 equal parts, and these packets are transmitted from A to B. In the third case, the file is split into 20 equal parts and these packets are sent from A to B. Each packet contains 100 bytes of header information along with the user data. Consider only transmission time and ignore processing, queuing and propagation delays. Also assume that there are no errors during transmission. Let T1, T2 and T3 be the times taken to transmit the file in the first, second and third case respectively. Which one of the following is CORRECT? [GATE – 2014]

a. T1 < T2 < T3
b. T1 > T2 > T3
c. T1 = T3, T3 > T2
d. T2 = T3, T3 < T1

Answer : c)
CN |Gate-2014|


12. An IP machine Q has a path to another IP machine H via three IP routers R1, R2, and R3.

Q—R1—R2—R3—H

H acts as an HTTP server, and Q connects to H via HTTP and downloads a file. Session layer encryption is used, with DES as the shared key encryption protocol. Consider the following four pieces of information: [GATE – 2014]

[I1] The URL of the file downloaded by Q
[I2] The TCP port numbers at Q and H
[I3] The IP addresses of Q and H
[I4] The link layer addresses of Q and H

Which of I1, I2, I3, and I4 can an intruder learn through sniffing at R2 alone?

a. Only I1 and I2
b. Only I2 and I3
c. Only I
d. Only I3 and I4

Answer : b)
CN |Gate-2014|


13. In the following pairs of OSI protocol layer/sub-layer and its functionality, the INCORRECT pair is : [GATE – 2014]

a. Network layer and Routing
b. Data Link Layer and Bit synchronization
c. Transport layer and End-to-end process communication
d. Medium Access Control sub-layer and Channel sharing

Answer : b)


14. A bit-stuffing based framing protocol uses an 8-bit delimiter pattern of 01111110. If the output bit-string after stuffing is 01111100101, then the input bit-string is : [GATE – 2014]

a. 0111110100
b. 011111110
c. 0111110101
d. 0111111111

Answer : c)


15. Host A (on TCP/IP v4 network A) sends an IP datagram D to host B (also on TCP/IP v4 network B). Assume that no error occurred during the transmission of D. When D reaches B, which of the following IP header field(s) may be different from that of the original datagram D? (i) TTL                   (ii) Checksum                 (iii) Fragment Offset : [GATE – 2014]

a. (i) only
b. (i) and (ii) only
c. (i) and (ii) only
d. (i), (ii) and (iii)

Answer : d)
CN |Gate-2014|


16. An IP router implementing Classless Inter-domain Routing (CIDR) receives a packet with address 131.23.151.76. The router’s routing table has the following entries:  

PrefixOutput Interface 
Identifier 
  
131.16.0.0/ 123 
131.28.0.0/ 145 
131.19.0.0/ 162 
131.22.0.0/ 151 

  The identifier of the output interface on which this packet will be forwarded is ______. [GATE – 2014]

a. 1
b. 2
c. 3
d. 4

Answer : a)
CN |Gate-2014|


17. Every host in an IPv4 network has a 1-second resolution real-time clock with battery backup. Each host needs to generate up to 1000 unique identifiers per second. Assume that each host has a globally unique IPv4 address. Design a 50-bit globally unique ID for this purpose. After what period (in seconds) will the identifiers generated by a host wrap around? [GATE – 2014]

a. 256
b. 257
c. 258
d. 259

Answer : a)


18. An IP router with a Maximum Transmission Unit (MTU) of 1500 bytes has received an IP packet of size 4404 bytes with an IP header of length 20 bytes. The values of the relevant fields in the header of the third IP fragment generated by the router for this packet are : [GATE – 2014]

a. MF bit: 0, Datagram Length: 1444; Offset: 370
b. MF bit: 1, Datagram Length: 1424; Offset: 185
c. MF bit: 1, Datagram Length: 1500; Offset: 370
d. MF bit: 0, Datagram Length: 1424; Offset: 2960

Answer : a)


19. Consider the transactions T1, T2, and T3 and the schedules S1 and S2 given below. T1: r1(X); r1(Z); w1(X); w1(Z) T2: r2(Y); r2(Z); w2(Z) T3: r3(Y); r3(X); w3(Y) S1: r1(X); r3(Y); r3(X); r2(Y); r2(Z); w3(Y); w2(Z); r1(Z); w1(X); w1(Z) S2: r1(X); r3(Y); r2(Y); r3(X); r1(Z); r2(Z); w3(Y); w1(X); w2(Z); w1(Z) Which one of the following statements about the schedules is TRUE? [GATE – 2014]

a. Only S1 is conflict-serializable.
b. Only S2 is conflict-serializable.
c. Both S1 and S2 are conflict-serializable
d. Neither S1 nor S2 is conflict-serializable.

Answer : a)
CN |Gate-2014|


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