Computer Network Test - 5 - PDF Flipbook

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GATE
CSE

Computer
Network

Test-05Solutions

COMPUTER NETWORK
1. The OSPF protocol

a) is a link-state route discovery protocol
b) has the ability to discover a network's specific topology
c) provides better performance than RIP in large internet-

works
d) all of these
Answer: (d)
2. The threshold efficient in demodulator is
a) exhibited by all demodulator, when the input signal to

noise ratio is low
b) The rapid fall on output signal to noise ratio when the

input signal to noise ratio fall below a particular value.
c) The property exhibited by all A.M. Suppressed carrier

coherent demodulator.
d) The property exhibited by correlation receiver.
Answer: (b)
Solution:
The threshold effect in demodulator is the rapid fall on
output signal to noise ratio when the input signal to noise
ratio fall below a particular value.
3. A clustering technique that permits a convenient graphical
display is:
a) partition-based cluster
b) probabilistic model-based clustering

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c) hierarchical clustering
d) agglomerative clustering
Answer: (c)
Solution:
Hierarchical methods of cluster analysis permit a convenient
graphical display in which the entire sequence of merging
(or splitting) is shown.
4. Optical storages are
a) High-speed direct access storage device.
b) Low-speed direct access storage device.
c) medium-speed direct access storage device
d) high-speed sequential access storage device
Answer: (b)
Solution:
DVD and CD devices have much longer seek time as
compared to magnetic –disk devices Rotational speeds of
DVD and CD drives are lower than that of magnetic disk
drives.
5. 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 nodes are
negligible. The efficiency of the stop-and-wait protocol in

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this setup is exactly 25%. The value of the one-way
propagation delay (in milliseconds) is _____.
Answer: 12
Solution:
Efficiency of stop and wait protocol = 1/(1 +2a)
Where
A = propagation delay/Transmission delay
Transmission delay = L/B = (1000 × 8)/106 = 0.008
Efficiency of stop and wait protocol
1/(1 + 2)× (propagation delay/0.008)) = 0.25
Propagation delay = 12m sec
6. Sending a file from personal computer's primary memory or
disks to another computer is called
a) uploading
b) downloading
c) logging on
d) none of these
Answer: (a)
7. The Register or main memory location which contains the
effective address of the operand is known as:
a) Pointer
b) indexed register
c) Special Locations
d) Scratch Pad
Answer: (a)

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Solution:
The register or memory location that contains the effective
address of the operand is a pointer.
When an execution take place in such mode instruction may
be told to go to specific address once, it Is there, instead of
finding an operand, it finals an address where the oprand is
locatd.
8. What is the routing algorithm used by RIP and IGRP?
a) OSPF
b) Link-state
c) Dynamic
d) Distance vector
Answer: (d)
Solution:
The RIP (routing information protocol) is one of the oldest
distance vector protocols which empty the hop count as a
routing metric RIP prevents routing loops by implementing a
limit on the number of hops allowed in a path from source to
destination.
IGRP (interior gateway routing protocol) is a distance vector
interior routing protocol (IGP) was created in a part to
overcome the limitation or RIP when used within large
networks.

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9. 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?
I. If the sequence number of a segment is m, then the
sequence number of the subsequent segment is always
m+ 1.
II. II. If the estimated round trip time at any given point of
time is t sec, the value of the retransmission time out is
always set to greater than or equal to t sec.
III. The size of the advertised window never changes during
the course of the TCP connection.
IV. 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)
Solution:
First statement IS· FALSE. If sequence number of segment
is 'm', then 'm' is treated as first byte number. So sequence
number of next segment should be (m + n) + 1. Where 'n' is
total data bytes in first segment.
Third statement is FALSE: In every transmission advertised
window size depends on available space at the destination

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and hence changing in every communication. Sometimes it
would be zero also, and leads to silly window syndrome.
10. Everything below the system call interface and above the
physical hardware is known as_____
a) Kernel
b) Bus
c) Shell
d) Stub
Answer: (a)
Solution:
The UNIX OS consists of two separable-parts:
(i) system programs
(ii) the kernel
Consists of everything below the system call interface and
above the physical hardware.
Provides the file system, CPU-scheduling system functions;
a large number of functions for one level.
11. What services does the internet Layer provide?
1. Quality of service
2. Routing
3. addressing
4. connection-oriented delivery
5. framing bits
a) 1, 2, 3
b) 2, 3, 4, 5.

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c) 1, 3, 4,5
d) 2,3, 4,5
Answer: (a)
Solution:
The internet layer is group of networking methods,
protocols, and specifications in the internet protocol suite
that are used to transport datagrams(packets) from the
originating host access network boundaries it does not
provide connection oriented services, it provides only an
unreliable service and best effort delivery.
12. Decryption and encryption of data are the responsibility of
which of the following layer?
a) Physical layer
b) Data Link layer
c) Presentation layer
d) Session layer
Answer: (c)
Solution:
Services by presentation layers:

• Data conversion
• Character code translation
• Comparision
• Encryption and decryption
Services by session layer
• Authentication

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• Authorization
• Session restoration (checking and recovery)
13. After sending a message, the sender should not be able to, at
a later date, deny having sent the message, is referred to as:
a) Authenticity
b) Non_Repudiabitity
c) Auditability
d) Reputability
Answer: (b)
Solution:
Authorization is a process of determining that a requester is
allowed to receive service or perform an operation
Non-repudiation is that someone cannot-repudiation refers to
the ability to ensure that a party to a contact or a
communication cannot deny to a contact or a communication
cannot deny the authenticity of their signature on a document
or the sending of a message that they originated
14. Which provides an interface to the TCP/IP suit protocols in
windows95 and Windows NT?
a) FTP Active-X Control
b) TCP/IP Active-X Control
c) Calin sock Active-X Control
d) HTML Active-X Control
Answer: (b)

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Solution:
TCP/IP active-x control and cailsock Active-X control
provided an interface to TCP/IP protocol suit in window 95
and windows NT.
15. A public key encryption system
a) allows anyone to decode the transmissions
b) allows only the correct sender to decode the data
c) allows only the correct receiver to decode the data
d) does not encode the data before transmitting it
Answer: (c)
Solution:
Public key cryptosystem is a cryptographic system that uses
pairs of keys: Public keys that may be disseminated widely
paired with private keys which are known only to the owner.
The encryption system ensures that only the correct receiver
decodes the data.
16. The device which connects dissimilar LANs of different
topologies using different sets of communication protocols
so that information can flow from one to another is called:
a) Router
b) Bridge
c) Gateway
d) Switch
Answer: (c)

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Solution:
The gateway is the computer that routes the traffic from a
workstation to the outside network that is serving the web
pages the gateway is the ISP that connects the user to the
internet Gateway node often acts as proxy server and
firewall Gateway works on application layer while router
works on layer of OSI model.
17. In an Ethernet local area network, which one of the
following statements is TRUE?
a) A station stops to sense the channel once it starts

transmitting a frame.
b) The purpose of the jamming signal is to pad the frames

that are smaller than the minimum frame size.
c) A station continues to transmit the packet even after the

collision is detected.
d) The exponential back off mechanism reduces the

probability of collision on retransmissions.
Answer: (d)
Solution:
The concept of binary exponential back off algorithm
The exponential back off mechanism reduces the probability
of collision on retransmissions.
18. Data Encryption Techniques are particularly used for___
a) Protecting data in Data Communication System.
b) Reduce Storage Space Requirement.

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c) Enhances Data integrity.
d) Decreases Data integrity.
Answer: (a)
Solution:
Data encryption techniques are particularly used for
protecting data in data commination system
19. Which transport class should be used with a perfect network
layer?
a)TPO and TP2
b) TP1 and TP3
c) TPO, TP1, TP3
d) TPO, TP1, TP2, TP3, TP4
Answer: (a)
Solution:
TP0 and TP2 are perfect network layers, loss or zero
OSI model definite five types of transport classes:
(i) TP0: simple class
(ii) TP1: Basic recover recovery class
(iii) TP2:multiplexing class
(iv) TP3: error recovery and multiplexing class
(v) TP4 Error detection and recovery class
20. The code which uses 7 bits to represent a character is :
a) ASCII
b) BCD
c) EBCDIC

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d) Gray
Answer: (a)
Solution:
ASCII encodes 128 specified characters into 7-bit integers.
21. Contention is
a) one or more conductors that serve as a common

connection for a related group of devices
b) a continuous frequency capable of being modulated or

impressed with a second signal
c) the condition when two or more stations attempt to use

the same channel at the same time
d) a collection of interconnected functional units that

provides a data communications service among stations
attached to the network
Answer: (c)
22. Identify the devices given below with their IC number:
List-I
A. Networked-Controlled Handoff (NCH)
B. Mobile-Assisted Handoff (MAHO)
C. Forward Handoff
D. Hard Handoff
List-II
1. MS connects to BS
2. Process via channel the target BS
3. First Generation Analog cellular system

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4. Second Generation Digital Cellular System
Codes

A BC D
a) 3 4 2 1
b) 2 3 1 4
c) 2 1 4 3
d) 4 3 1 2
Answer: (a)
Solution:
Handoff is very important for managing the different
resources in cellular systems
23. Which layer of OSI reference model uses the ICMP

(internet Control Message Protocol)?
a) Transport layer
b) Data link layer
c) Network layer
d) Application layer
Answer: (c)
Solution:
The internet control message protocol (ICMP) is a
network layer protocol that is used by network devices,
link routers, to send error message and operational
information indicating, for example, that a requesting
service is not available or that a host or router could not
be reached.

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24. Consider the following three statements about link state
and distance vector routing protocols, for a large network
with 500 network nodes and 4000 links.
[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)
Solution:
• Distance vector Routing protocol send periodic update
at every 30 (or) 60 second. Due to this, it has slower
convergence.
Example: RIP, IGRE, BGP
Distance vector protocol uses following mechanism to
avoid the loop
• Max hop count
• Split horizon
• Route poisoning

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• Hold down Timer
In link state protocols, updates are triggered not periodic
so it has fast convergence no loops in link state protocol
In link state protocols, updates are triggered not periodic
so it has fast convergence No loops in link state protocol
Example: S1 and S3 are true but S2 false.
25. More than one word is put in one catch block to
a) Exploit the temporal locality of reference in a Program
b) exploit the spatial locality of reference in a Program
c) reduce the miss penalty
d) None of these
Answer: (b)
Solution:
More than one word is put in one cache block to exploit
the spatial locality of reference in a program. Spatial
locality refers to the use of data element with in relatively
close storage locations.
26. Assume that source S and destination Dare connected
through two intermediate routers labelled R. Determine
how many times each packet has to visit the network layer
and the data link layer during a transmission from S to D.

a) Network layer - 4 times and Data link. layer-4 times
b) Network layer - 4 times and Data link layer -3 times

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c) Network layer - 4 times and Data link layer-6 times
d) Network layer - 2 times and Data link layer-6 times
Answer: (c)
Solution:
Network layer 4 times, Data link: layer 6 times.

27. What is the name of the computer based EMMS that
provides a common forum where users can check it at their
convenience, post message, actively exchange ideas and
participate in ongoing discussions?
a) E-mail
b) Bulletin Board System (BBS)
c) Tele conferencing
d) Video conferencing
Answer: (b)

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28. In a network of LAN s connected by bridges, packets are sent
from one LAN to another through intermediate bridges.
Since more than one path may exist between two LANs,
packets may have to be routed through multiple bridges.
Why is the spanning tree algorithm used for bridge-routing?
a) For shortest path routing between LANs
b) For avoiding loops in the routing paths
c) For fault tolerance
d) For minimizing collisions
Answer: (b)
Solution:
To avoid infinite looping network layer uses TTL. Datalink
layer constructs spanning tree among bridges to avoid
infinite loop in routing paths.

29. The ATM cell is:
a) 48 bytes’ long
b) 53 bytes’ long
c) 64 bytes’ long
d) 69 bytes’ long
Answer: (b)
Solution:
Shortest job first CPU scheduling is advantageous because of
its simplicity and because it minimize the average amount of
time each process has to wait until its execution is complete
So, as per shortest jo b first J3 = 3, J4 = 5, J2 = 6, J1 = 9

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

Answer: 26
Solution:
For each hop, TTL IS reduced by 1 (minimum) and there are
6 hops here.
Hence 32 – 6 = 26

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