Computer Networks

Identify the ONE CORRECT matching between
the
OSI
layers
and
their
corresponding
functionalities as shown.

• (a)
• (a)-(I), (b)-(II), (c)-(III)
• (b)
• (a)-(I), (b)-(III), (c)-(II)
• (c)
• (a)-(II), (b)-(III), (c)-(I)
• (d)
• (a)-(III), (b)-(II), (c)-(I)

In the following pairs of OSI protocol layer/sub-
layer and its functionality, the INCORRECT pair is

• (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

Assume that source S and destination D are
connected through two intermediate routers labeled
R. Determine how many times each packet must
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
• (c)Network layer - 4 times and Data link layer - 6 times
• (d)Network layer - 2 times and Data link layer - 6 times

In Ethernet, when Manchester encoding is used, the
bit rate is:

• (a)Half the baud rate
• (b)Twice the baud rate
• (c)Same as the baud rate
• (d)None of the above

Consider a file of size 4 million bytes being
transferred between two hosts connected via a path
consisting of three consecutive links of bandwidth
2 Mbps, 500 kbps, and 1 Mbps, respectively.

All processing delays and propagation delays are
negligible. Assume there is no other background
traffic over the path and no additional overhead to
transfer the file.

Which one of the following is the total time

(in seconds) to transfer the file?

Note: 1M = 106, 1k = 103

• (a)731
• (b)64
• (c)8
• (d)16

Consider the implementation of a sliding window
protocol over a lossless link, with a window size of
W frames, where each frame is of size 1000 bits
(including header).

The bandwidth of the link is 100 kbps (1k = 103)
and the one-way propagation delay is 100
milliseconds. Assume that processing times at the
sender and receiver are zero and the transmission
time of acknowledgements is also zero.

Which one of the following options gives the
minimum size of W (in number of frames) required
to achieve 100% link utilization?

• (a)10
• (b)21
• (c)20
• (d)11

Suppose we are transmitting frames between two
nodes
using
Stop-and-Wait
protocol.
The frame size is 3000 bits. The transmission rate of
the channel is 2000 bps (bits per second) and the
propagation delay between the two nodes is 100
milliseconds. Assume that the processing times at the
source and destination are negligible. Also, assume
that the size of the acknowledgment packet is
negligible. Which ONE of the following most
accurately gives the channel utilization for the above
scenario in percentage?

• (a)88.23
• (b)93.75
• (c)85.44
• (d)66.67

Consider an Ethernet segment with a transmission
speed of 108 bits/sec and a maximum segment length
of 500 meters. If the maximum speed of propagation
of the signal in the medium is 2×108 meters/sec, then
the minimum frame size (in bits) required for
collision detection is __________.

Suppose two hosts are connected by a point-to-point
link and they are configured to use Stop-and-Wait
protocol for reliable data transfer. Identify in which
one of the following scenarios, the utilization of the
link is the lowest.

• (a)Longer link length and lower transmission rate
• (b)Longer link length and higher transmission rate
• (c)Shorter link length and lower transmission rate
• (d)Shorter link length and higher transmission rate

Consider a 100 Mbps link between an earth station
(sender) and a satellite (receiver) at an altitude of

COMPUTER NETWORK
2100 km. The signal propagates at a speed of 3×108
m/s. The time taken (in milliseconds, rounded off
to two decimal places) for the receiver to
completely receive a packet of 1000 bytes
transmitted by the sender is: ________

Consider the cyclic redundancy check (CRC) based
error detecting scheme having the generator
polynomial
x3+x+1.
Suppose
the
message
m4m3m2m1m0=11000 is to be transmitted. Check
bits c2c1c0 are appended at the end of the message
by the transmitter using the above CRC scheme.
The transmitted bit string is denoted by
m4m3m2m1m0c2c1c0. The value of the check bit
sequence c2c1c0 is:

• (a)110
• (b)111
• (c)100
• (d)101

Assume that a 12-bit Hamming codeword
consisting of 8-bit data and 4 check bits is
d8d7d6d5c8d4d3d2c4d1c2c1, where the data
bits and the check bits are given in the
following tables:

Data Bits d8 d7 d6 d5 d4 d3 d2 d1

1
1
0
x
0
1
0
1

Check Bits
c8
c4
c2
c1

y
0
1
0

Which one of the following choices gives the
correct values of x and y?

• (a)x is 0 and y is 0
• (b)x is 0 and y is 1
• (c)x is 1 and y is 0
• (d)x is 1 and y is 1

Consider the sliding window flow-control protocol
operating between a sender and a receiver over a full-
duplex error-free link.

Assume the following:
 The time taken for processing the data frame by
the receiver is negligible.
 The
time
taken
for
processing
the
acknowledgement frame by the sender is
negligible.
 The sender has an infinite number of frames
available for transmission.
 The size of the data frame is 2000 bits, and the size
of the acknowledgement frame is 10 bits.
 The link data rate in each direction is 1 Mbps (=
106 bits per second).
 One-way propagation delay of the link is 100
milliseconds.

The minimum value of the sender's window size in
terms of the number of frames, (rounded to the
nearest integer) needed to achieve a link utilization of
50% is _______.

Consider a network using the pure ALOHA medium
access control protocol, where each frame is of length
1,000 bits. The channel transmission rate is
1Mbps(= 106 bits per second). The aggregate
number of transmissions across all the nodes
(including new frame transmissions and retransmitted
frames due to collisions) is modelled as a Poisson
process with a rate of 1,000 frames per second.
Throughput is defined as the average number of
frames successfully transmitted per second. The
throughput of the network (rounded to the nearest
integer) is ____________

Consider a simple communication system where
multiple nodes are connected by a shared broadcast
medium (like Ethernet or wireless).

The nodes in the system use the following carrier-
sense based medium access protocol.

A node that receives a packet to transmit will carrier-
sense the medium for 5 units of time.

COMPUTER NETWORK

If the node does not detect any other transmission
in this duration, it starts transmitting its packet in
the next time unit.

If the node detects another transmission, it waits
until this other transmission finishes and then
begins to carrier-sense for 5 time units again.

Once they start to transmit, nodes do not perform
any collision detection and continue transmission
even if a collision occurs.

All transmissions last for 20 units of time.

Assume that the transmission signal travels at the
speed of 10 meters per unit time in the medium.

Assume that the system has two nodes P and Q,
located at a distance d meter from each other.

P starts transmitting a packet at time t=0 after
successfully completing its carrier-sense phase.
Node Q has a packet to transmit at time t=0 and
begins to carrier-sense the medium.

The maximum distance d (in meters, rounded to the
closest integer) that allows Q to avoid a collision
between its proposed transmission and P's ongoing
transmission is _______.

Consider a binary code that consists of only four
valid
codewords
as
given
below:
00000, 01011, 10101, 11110.

Let the minimum Hamming distance of the code be
p and the maximum number of erroneous bits that
can be corrected by the code be q. Then the values
of p and q are:

• (a)p=3 and q=1
• (b)p=3 and q=2
• (c)p=4 and q=1
• (d)p=4 and q=2

A computer network uses polynomials over GF(2)
for error checking with 8 bits as information bits
and uses x3+x+1 as the generator polynomial to
generate the check bits. In this network, the
message 01011011 is transmitted as:

• (a)01011011010
• (b)01011011011
• (c)01011011101
• (d)01011011100

The values 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.
 Time to process a frame = 0.25 ms.
 Number of bytes in the information frame = 1980.
 Number of bytes in the acknowledge frame = 20.
 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).

Consider two hosts X and Y ,connected by a single
direct link of rate 106 bits /sec .The distance
between the two hosts is 10,000 km and the
propagation speed along the link is 2 × 108 m/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 value of p and q are:

• (a)p = 50 and q = 100
• (b)p = 50 and q = 400
• (c)p = 100 and q = 50
• (d)p = 400 and q = 50

Consider
a
128×103
bits/second
satellite
communication link with one-way propagation delay
of 150 milliseconds. Selective retransmission (repeat)
protocol is used on this link to send data with a frame
size of 1 kilobyte. Neglect the transmission time of
acknowledgment. The minimum number of bits
required for the sequence number field to achieve
100% utilization is ______.

COMPUTER NETWORK

A sender uses the Stop-and-Wait ARQ protocol for
reliable transmission of frames. Frames are of size
1000 bytes and the transmission rate at the sender
is 80 Kbps (1 Kbps = 1000 bits/second). Size of an
acknowledgment is 100 bytes and the transmission
rate at the receiver is 8 Kbps. The one-way
propagation delay is 100 milliseconds. Assuming
no frame is lost, the sender throughput is
__________ bytes/second.

A network has a data transmission bandwidth of
20×106 bits per second. It uses CSMA/CD in the
MAC layer. The maximum signal propagation time
from one node to another node is 40 microseconds.
The minimum size of a frame in the network is
______ bytes.

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 backoff mechanism reduces the probability of collision on retransmissions

Consider a CSMA/CD network that transmits data
at a rate of 100 Mbps (108 bits per 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?

• (a)8000
• (b)10000
• (c)16000
• (d)20000

Consider a LAN with four nodes S1,S2,S3,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 transmits 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
__________.

A link has a transmission speed of 106 bits/sec. It uses
data packets of size 1000 bytes each. Assume that the
acknowledgment 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 this setup is exactly 25%.
The value of the one-way propagation delay (in
milliseconds) is:

Two hosts are connected via a packet switch with 107
bits per second links. Each link has a propagation
delay of 20 microseconds. The switch begins
forwarding a packet 35 microseconds after it receives
the same. If 10000 bits of data are to be transmitted
between the two hosts using a packet size of 5000
bits, the time elapsed between the transmission of the
first bit of data and the reception of the last bit of the
data in microseconds is:

COMPUTER NETWORK

Consider a network connecting 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

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: __________

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 ____ .

A bit-stuffing based framing protocol uses an 8-bit
delimiter pattern of 01111110. If the output bit-
string after stuffing is 011111100101, then the
input bit-string is:

• (a)0111110100
• (b)0111110101
• (c)0111111101
• (d)0111111111

Consider the store and forward packet switched
network given below. Assume that the bandwidth of
each link is 10^6 bytes/sec. A user on host A sends a
file of size 10^3 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 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?

• (a)T1 < T2 < T3
• (b)T1 > T2 > T3
• (c)T2 = T3, T3 < T1
• (d)T1 = T3, T3 > T2

Determine the maximum length of the cable (in km)
for transmitting data at a rate of 500 Mbps in an
Ethernet LAN with frames of size 10,000 bits.
Assume the signal speed in the cable to be 2,00,000
km/s.

• (a)1
• (b)2
• (c)2.5
• (d)5

Consider a source computer (S) transmitting a file of
size 106 bits to a destination computer (D) over a
network of two routers (R1 and R2) and three links
(L1, L2, and L3).

COMPUTER NETWORK

L1 connects S to R1; L2 connects R1 to R2; and L3
connects R2 to D. Let each link be of length 100
km.

Assume signals travel over each link at a speed of
108meters per second.

Assume that the link bandwidth on each link is 1
Mbps. Let the file be broken down into 1000
packets, each of size 1000 bits.

Find the total sum of transmission and propagation
delays in transmitting the file from S to D?

• (a)1005 ms
• (b)1010 ms
• (c)3000 ms
• (d)3003 ms

Frames of 1000 bits are sent over a 106 bps duplex
link between two hosts. The propagation time is 25
ms. Frames are to be transmitted into this link to
maximally pack them in transit (within the link).

What is the minimum number of bits (l) required to
represent the sequence numbers distinctly? Assume
that no time gap needs to be given between
transmission of two frames.

• (a)I = 2
• (b)I = 3
• (c)I = 4
• (d)I = 5

Suppose that the sliding window protocol is used
with the sender window size of 2l, where l is the
number of bits identified in the earlier part and
acknowledgements are always piggybacked. After
sending 2l frames, what is the minimum time the
sender will have to wait before starting
transmission of the next frame? (Ignore frame
processing time.)

• (a)16 ms
• (b)18 ms
• (c)20 ms
• (d)22 ms

Let G(x) be the generator polynomial used for CRC
checking. What is the condition that should be
satisfied by G(x) to detect odd number of bits in
error?

• (a)G(x) contains more than two terms
• (b)G(x) does not divide 1 + xk, for any k not exceeding the frame length
• (c)1 + x is a factor of G(x)
• (d)G(x) has an odd number of terms.

The distance between two stations M and N is L
kilometers. All frames are K bits long. The
propagation delay per kilometer is t seconds. Let R
bits/second be the channel capacity. Assuming that
processing delay is negligible, the minimum number
of bits for the sequence number field in a frame for
maximum utilization, when the sliding window
protocol is used, is:

• (a)⌈log2 (2LtR+2K) K ⌉
• (b)⌈log2 ( 2LtR K)⌉
• (c)⌈log2(( 2LtR + K) K )⌉
• (d)⌈log2( (2LtR + K) (2K) )⌉

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:

• (a)11001001000
• (b)11001001011
• (c)11001010
• (d)110010010011 COMPUTER NETWORK

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:

• (a)500 metres of cable
• (b)200 metres of cable
• (c)20 metres of cable
• (d)50 metres of cable

There are n 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?

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

Station A uses 32 byte packets to transmit messages
to Station B using a sliding window protocol. The
round trip delay between A and B is 80
milliseconds and the bottleneck bandwidth on the
path between A and B is 128 kbps. What is the
optimal window size that A should use?

• (a)20
• (b)40
• (c)160
• (d)320

Station A needs to send a message consisting of 9
packets of Station B using sliding window (window
size 3) and go-back-n error control strategy. All
packets are ready and immediately available for
transmission. If every 5th packet that A transmits
gets lost (but no ACKs from B ever get lost), then
what is the number of packets that A will transmit for
sending the message to B?

• (a)12
• (b)14
• (c)16
• (d)18

Consider the diagram shown below where a number
of LANs are connected by (transparent) bridges. In
order to avoid packets looping through circuits in the
graph, the bridges organize themselves in a spanning
tree. First, the root bridge is identified as the bridge
with the least serial number. Next, the root sends out
(one or more) data units to enable the setting up of the
spanning tree of shortest paths from the root bridge to
each bridge.

Each bridge identifies a port (the root port) through
which it will forward frames to the root bridge. Port
conflicts are always resolved in favour of the port
with the lower index value. When there is a
possibility of multiple bridges forwarding to the same
LAN (but not through the root port), ties are broken
as follows: bridges closest to the root get preference
and between such bridges, the one with the lowest
serial number is preferred.

For the given connection of LANs by bridges, which
one of the following choices represents the depth first
traversal of the spanning tree of bridges?

COMPUTER NETWORK

• (a)B1, B5, B3, B4, B2
• (b)B1, B3, B5, B2, B4
• (c)B1, B5, B2, B3, B4
• (d)B1, B3, B4, B5, B2

Consider the correct spanning tree for the previous
question. Let host H1 send out a broadcast ping
packet. Which of the following options represents

the correct forwarding table on B3?

• (a)
• (b)
• (c)
• (d)

The maximum window size for data transmission
using the selective reject protocol with n-bit frame
sequence numbers is:

• (a)2n
• (b)2n-1
• (c)2n -1
• (d)2n-2

In a network of LANs 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

Suppose the round trip propagation delay for a 10
Mbps Ethernet having 48-bit jamming signal is 46.4
μs. The minimum frame size is:

• (a)94
• (b)416
• (c)464
• (d)512

If an IP network uses a subnet mask of
255.255.240.0, the maximum number of IP
addresses that can be assigned to network interfaces
is ______. (answer in integer)

An ISP having an address block 202.16.0.0/15
assigns a block of 6000 IP addresses to a client
using the Classless Internet Domain Routing
(CIDR) supernetting approach.

Which of the following address blocks can be
assigned by the ISP?

• (a)202.16.0.0/19
• (b)202.17.64.0/19
• (c)202.16.32.0/19
• (d)202.17.24.0/19

A TCP sender successfully establishes a connection
with a TCP receiver and starts the transmission of
segments.
The
TCP
congestion
control
mechanism's slow-start threshold is set to 10000
segments. Assume that the round-trip time is fixed
at 1 millisecond. Assume that the sender always has
data to send, the segments are numbered from 1,
and no segment is lost.

Let t denote the time (in milliseconds) at which the
transmission of segment number 2000 starts.

Which one of the following options is correct?

• (a)9 ≤ t < 10
• (b)10 ≤ t < 11
• (c)11 ≤ t < 12
• (d)12 ≤ t < 13

With respect to a TCP connection between a client
and a server, which one of the following statements is
true?

• (a)The client and server use a two-way handshake mechanism before the start of data transmission
• (b)The server cannot initiate closing of the connection before the client initiates closing of the connection
• (c)The TCP connection is half-duplex
• (d)The client and server can initiate closing of the connection at the same time

It is necessary to design a link-layer protocol between
two hosts that are directly connected over a lossless
link of length 3000 km. The link bandwidth is 108 bits
per second, and the propagation delay is 5 ns per
meter. Every transmitted data byte is assigned a
unique sequence number.

Let N be the minimum number of bits needed for the
sequence number field such that:

i. the sequence numbers do not wrap around before
60 seconds, and
ii. the maximum utilization of the link is achieved.

Find N. (answer in integer)

Consider a new TCP connection between a sender
and a receiver. The receiver advertised window is
constant at 48 KB, the maximum segment size (MSS)
is 2 KB, and the slow start threshold (ssthresh) is 16
KB.

Assume there are no timeouts or duplicate
acknowledgements. The number of rounds of
transmission required for the congestion control

COMPUTER NETWORK
algorithm to reach the congestion avoidance phase
is ______.

Note: 1K = 210

Consider a network that uses Ethernet and IPv4.
Assume that IPv4 headers do not use any options
field. Each Ethernet frame can carry a maximum of
1500 bytes in its data field. A UDP segment is
transmitted. The payload (data) in the UDP
segment
is
7488
bytes.
Which ONE of the following choices has the
CORRECT total number of fragments transmitted
and the size of the last fragment including IPv4
header?

• (a)5 fragments, 1488 bytes
• (b)6 fragments, 88 bytes
• (c)6 fragments, 108 bytes
• (d)6 fragments, 116 bytes

Consider the following statements:
 (i) Address Resolution Protocol (ARP) provides
a mapping from an IP address to the
corresponding hardware (link-layer) address.
 (ii) A single TCP segment from a sender S to a
receiver R cannot carry both data from S to R
and acknowledgment for a segment from R to S.

Which ONE of the following is CORRECT?

• (a)Both (i) and (ii) are TRUE
• (b)(i) is TRUE and (ii) is FALSE
• (c)(i) is FALSE and (ii) is TRUE
• (d)Both (i) and (ii) are FALSE

Suppose a message of size 15000 bytes is
transmitted from a source to a destination using
IPv4 protocol via two routers as shown in the
figure. Each router has a defined maximum
transmission unit (MTU) as shown in the figure,
including the IP header. The number of fragments
that will be delivered to the destination is ________.

A
packet
with
the
destination
IP
address
145.36.109.70 arrives at a router whose routing table
is shown. Which interface will the packet be
forwarded to?

Subnet
Address
Subnet Mask
(in
CIDR
notation)
Interface
145.36.0.0
/16
E1
145.36.128.0
/17
E2
145.36.64.0
/18
E3
145.36.255.0
/24
E4
Default
--
E5

• (a)E3
• (b)E1
• (c)E2
• (d)E5

Consider the routing protocols given in List-I and the
names given in List-II:

List-I
List-II
(i) Distance vector routing (a) Bellman-Ford
(ii) Link state routing
(b) Dijkstra

For matching of items in List-I with those in List-II,
which ONE of the following options is CORRECT?

• (a)(i) - (a) and (ii) - (b)
• (b)(i) - (a) and (ii) - (a)
• (c)(i) - (b) and (ii) - (a)
• (d)(i) - (b) and (ii) - (b) COMPUTER NETWORK

A machine receives an IPv4 datagram. The
protocol field of the IPv4 header has the protocol
number of a protocol X.
Which ONE of the following is NOT a possible
candidate for X?

• (a)Internet Control Message Protocol (ICMP)
• (b)Internet Group Management Protocol (IGMP)
• (c)Open Shortest Path First (OSPF)
• (d)Routing Information Protocol (RIP)

Consider the 3-way handshaking protocol for TCP
connection establishment. Let the three packets
exchanged during the connection establishment be
denoted as P1, P2, and P3, in order. Which of the
following option(s) is/are TRUE with respect to
TCP header flags that are set in the packets?

• (a)P3: SYN = 1, ACK = 1
• (b)P2: SYN = 1, ACK = 1
• (c)P2: SYN = 0, ACK = 1
• (d)P1: SYN = 1

Consider a network path P → Q → R between
nodes P and R via router Q. Node P sends a file of
size 106 bytes to R via this path, splitting the file
into chunks one after the other, each of size 103
bytes. Node P sends these chunks without any wait
time between the successive chunk transmissions.
Assume that the size of the extra headers added to
these chunks is negligible, and that the chunk size
is less than the MTU. Each of the links P → Q and
Q → R has a bandwidth of 106 bits/sec, and
negligible
propagation
latency.
Router
Q
immediately transmits every packet it receives
from P to R, with negligible processing and
queuing delays.

Assume P starts transmitting the chunks at time t =
0. Which one of the following options gives the
time (in seconds, rounded off to 3 decimal places)
at which R receives all the chunks of the file?

• (a)16.000
• (b)8.000
• (c)8.008
• (d)15.992

Which one of the following CIDR prefixes exactly
represents the range of IP address 10.12.2.0 to
10.12.3.255?

• (a)10.12.2.0/24
• (b)10.12.2.0/22
• (c)10.12.0.0/22
• (d)10.12.2.0/23

Consider a TCP connection operating at a point of
time with the congestion window of size 12 MSS
(Maximum Segment Size), when a timeout occurs
due to packet loss. Assuming that all the segments
transmitted in the next two RTTs (Round Trip Time)
are acknowledged correctly, the congestion window
size (in MSS) during the third RTT will be
___________.

Consider the entries shown below in the forwarding
table of an IP router. Each entry consists of an IP
prefix and the corresponding next hop router for
packets whose destination IP address matches the
prefix. The notation "/N" in a prefix indicates a
subnet mask with the most significant N bits set to 1.

Prefix
Next hop router
10.1.1.0/24
R1
10.1.1.128/25 R2
10.1.1.64/26
R3
10.1.1.192/26 R4

This router forwards 20 packets each to 5 hosts. The
IP addresses of the hosts are 10.1.1.16, 10.1.1.72,
10.1.1.132,
10.1.1.191,
and
10.1.1.205.
The number of packets forwarded via the next hop
router R2 is ________.

COMPUTER NETWORK

Consider sending an IP datagram of size 1420 bytes
(including 20 bytes of IP header) from a sender to
a receiver over a path of two links with a router
between them. The first link (sender to router) has
an MTU (Maximum Transmission Unit) size of 542
bytes, while the second link (router to receiver) has
an MTU size of 360 bytes. The number of
fragments that would be delivered at the receiver is
______.

Which of the following statements about IPv4
fragmentation is/are TRUE?

• (a)The fragmentation of an IP datagram is performed only at the source of the datagram.
• (b)The reassembly of fragments is performed at all intermediate routers along the path from the source to the destination.
• (c)The reassembly of fragments is performed only at the destination of the datagram.
• (d)The fragmentation of an IP datagram is performed at any IP router which finds that the size of the datagram to be transmitted exceeds the MTU.

Which of the following fields of an IP header is/are
always modified by any router before it forwards
the IP packet?

• (a)Time to Live (TTL)
• (b)Header Checksum
• (c)Protocol
• (d)Source IP Address

Which of the following fields is/are modified in the
IP header of a packet going out of a network address
translation (NAT) device from an internal network to
an external network?

• (a)Total Length
• (b)Source IP
• (c)Destination IP
• (d)Header Checksum

TCP client P successfully establishes a connection to
TCP server Q. Let NP denote the sequence number in
the SYN sent from P to Q. Let NQ denote the
acknowledgment number in the SYN ACK from Q to
P. Which of the following statements is/are
CORRECT?

• (a)The acknowledgment number NQ is equal to NP
• (b)The sequence number NP is always 0 for a new connection
• (c)The acknowledgment number NQ is equal to NP + 1
• (d)The sequence number NP is chosen randomly by P

Node X has a TCP connection open to node Y. The
packets from X to Y go through an intermediate IP
router R. Ethernet switch S is the first switch on the
network path between X and R. Consider a packet
sent
from
X
to
Y
over
this
connection.
Which of the following statements is/are TRUE about
the destination IP and MAC addresses on this packet
at the time it leaves X?

• (a)The destination IP address is the IP address of Y
• (b)The destination MAC address is the MAC address of Y
• (c)The destination MAC address is the MAC address of S
• (d)The destination IP address is the IP address of R COMPUTER NETWORK

Which
of
the
following
statements
is/are
INCORRECT about the OSPF (Open Shortest Path
First) routing protocol used in the Internet?

• (a)OSPF implements Bellman-Ford algorithm to find shortest paths.
• (b)OSPF uses Dijkstra's shortest path algorithm to implement least-cost path routing.
• (c)OSPF is used as an inter-domain routing protocol.
• (d)OSPF implements hierarchical routing.

The forwarding table of a router is shown below:

Subnet
Number
Subnet mask
Interface
ID
200.150.0.0
255.250.0.0
1
200.150.64.0
255.255.224.0
2
200.150.68.0
255.255.255.0
3
200.150.68.64 255.255.255.224 4
Default

0

A packet addressed to a destination address
200.150.68.118

arrives at the router. It will be forwarded to the
interface

with ID ________.

Suppose You are asked to design a new reliable
byte-stream transport protocol like TCP, named
myTCP, which runs over a 100 Mbps network
with a Round Trip Time (RTT) of 150
milliseconds and a maximum segment lifetime of
2 minutes.
Which of the following is/are valid lengths of the
Sequence Number field in the myTCP header?

• (a)30 bits
• (b)32 bits
• (c)34 bits
• (d)36 bits

Consider a network with three routers P, Q, R shown
in the figure below. All the links have cost of unity.

The routers exchange distance vector routing
information and have converged on the routing tables,
after which the link Q-R fails. Assume that P and Q
send out routing updates at random times, each at the
same average rate. The probability of a routing loop
formation (rounded off to one decimal place) between
P and Q, leading to the count-to-infinity problem, is
___________.

Consider the routing table of an organization's router
shown below:

Subnet number
Subnet mask
Next hop
12.20.164.0
255.255.252.0
R1
12.20.170.0
255.255.254.0
R2
12.20.168.0
255.255.254.0
Interface 0
12.20.166.0
255.255.254.0
Interface 1
default

R3

Which of the following prefixes in CIDR notation can
be collectively used to correctly aggregate all of the
subnets in the routing table?

• (a)12.20.164.0/20
• (b)12.20.164.0/22
• (c)12.20.164.0/21
• (d)12.20.168.0/22

Consider an enterprise network with two Ethernet
segments, a web server and a firewall, connected via

COMPUTER NETWORK
three routers as shown below:

What is the number of subnets inside the enterprise
network?

• (a)3
• (b)12
• (c)6
• (d)8

Consider the data transfer using TCP over a 1 Gbps
link. Assuming that the maximum segment lifetime
(MSL) is set to 60 seconds, the minimum number
of bits required for the sequence number field of the
TCP header, to prevent the sequence number space
from wrapping around during the MSL is
___________.

Consider a computer network using the distance
vector routing algorithm in its network layer. The
partial topology of the network is as shown below.

The objective is to find the shortest-cost path from
the router R to routers P and Q.

Assume that R does not initially know the shortest
routes to P and Q.

Assume that R has three neighbouring routers
denoted as X, Y, and Z.

During one iteration, R measures its distance to its
neighbours X, Y, and Z as 3, 2, and 5, respectively.
Router R gets routing vectors from its neighbours
that indicate that the distance to router P from
routers X, Y, and Z are 7, 6, and 5, respectively.
The routing vector also indicates that the distance
to router Q from routers X, Y, and Z are 4, 6, and 8,
respectively. Which of the following statement(s)
is/are correct with respect to the new routing table of
R, after update during this iteration?

• (a)The distance from R to Q will be stored as 7.
• (b)The distance from R to P will be stored as 10.
• (c)The next hop router for a packet from R to Q is Z.
• (d)The next hop router for a packet from R to P is Y.

Consider two hosts P and Q connected through a
router R. The maximum transfer unit (MTU) value of
the link between P and R is 1500 bytes, and between
R and Q is 820 bytes.

A TCP segment of size 1400 bytes was transferred
from P to Q through R, with IP identification value as
0x1234. Assume that the IP header size is 20 bytes.
Further, the packet is allowed to be fragmented, i.e.,
Don't Fragment (DF) flag in the IP header is not set
by P.

Which of the following statements is/are correct?

• (a)Two fragments are created at R and the IP datagram size carrying the second fragment is 620 bytes.
• (b)If the second fragment is lost, P is required to resend the whole TCP segment.
• (c)TCP destination port can be determined by analyzing only the second fragment.
• (d)If the second fragment is lost, R will resend the fragment with the IP identification value 0x1234. COMPUTER NETWORK

A TCP server application is programmed to listen
on port number P on host S. A TCP client is
connected to the TCP server over the network.
Consider that while the TCP connection was active,
the server machine S crashed and rebooted.
Assume that the client does not use the TCP
keepalive timer.

Which of the following behaviors is/are possible?

• (a)If the client sends a packet after the server reboot, it will receive a FIN segment.
• (b)If the client was waiting to receive a packet, it may wait indefinitely.
• (c)The TCP server application on S can listen on P after reboot.
• (d)If the client sends a packet after the server reboot, it will receive a RST segment.

Consider the three-way handshake mechanism
followed during TCP connection establishment
between hosts P and Q. Let X and Y be two random
32-bit starting sequence numbers chosen by P and
Q respectively. Suppose P sends a TCP connection
request message to Q with a TCP segment having
SYN bit = 1, SEQ number = X, and ACK bit = 0.
Suppose Q accepts the connection request. Which
one of the following choices represents the
information present in the TCP segment header that
is sent by Q to P?

• (a)SYN bit = 1, SEQ number = Y, ACK bit = 1, ACK number = X + 1, FIN bit = 0
• (b)SYN bit = 1, SEQ number = Y, ACK bit = 1, ACK number = X, FIN bit = 0
• (c)SYN bit = 0, SEQ number = X + 1, ACK bit = 0, ACK number = Y, FIN bit = 1
• (d)SYN bit = 1, SEQ number = X + 1, ACK bit = 1, ACK number = Y, FIN bit = 0

Consider the following two statements:
 S1: Destination MAC address of an ARP reply is
a broadcast address.
 S2: Destination MAC address of an ARP request
is a broadcast address.

Which one of the following choices is correct?

• (a)S1 is false and S2 is true.
• (b)Both S1 and S2 are false.
• (c)Both S1 and S2 are true.
• (d)S1 is true and S2 is false.

Consider the following statements about the
functionality of an IP-based router.
I. A router does not modify the IP packets during
forwarding.
II. It is not necessary for a router to implement any
routing protocol.
III. A router should reassemble IP fragments if the
MTU of the outgoing link is larger than the size of
the incoming IP packet.

Which of the above statements is/are TRUE?

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

Consider a TCP connection between a client and a
server with the following specifications: the round
trip time is 6 ms, the size of the receiver advertised
window is 50 KB, slow-start threshold at the client is
32 KB, and the maximum segment size is 2 KB. The
connection is established at time t = 0. Assume that
there are no timeouts and errors during transmission.
Then the size of the congestion window (in KB) at
time t + 60 ms after all acknowledgments are
processed is __________.

COMPUTER NETWORK

An organization requires a range of IP addresses to
assign one to each of its 1500 computers. The
organization has approached an Internet Service
Provider (ISP) for this task. The ISP uses CIDR and
serves the requests from the available IP address
space 202.61.0.0/17. The ISP wants to assign an
address space to the organization which will
minimize the number of routing entries in the ISP's
router using route aggregation. Which of the
following address spaces are potential candidates
from which the ISP can allot any one to the
organization?

I. 202.61.84.0/21
II. 202.61.104.0/21
III. 202.61.64.0/21
IV. 202.61.144.0/21

• (a)I and IV only
• (b)III and IV only
• (c)I and II only
• (d)II and III only

Suppose that in an IP-over-Ethernet network, a
machine X wishes to find the MAC address of
another machine Y in its subnet. Which one of the
following techniques can be used for this?

• (a)X sends an ARP request packet with broadcast IP address in its local subnet
• (b)X sends an ARP request packet to the local gateway's MAC address which then finds the MAC address of Y and sends to X
• (c)X sends an ARP request packet with broadcast MAC address in its local subnet
• (d)X sends an ARP request packet to the local gateway's IP address which then finds the MAC address of Y and sends to X

Consider that 15 machines need to be connected in
a LAN using 8-port Ethernet switches. Assume that
these switches do not have any separate uplink
ports. The minimum number of switches needed is
_______.

Consider three machines M, N, and P with IP
addresses 100.10.5.2, 100.10.5.5, and 100.10.5.6
respectively.
The
subnet
mask
is
set
to
255.255.255.252 for all the three machines. Which
one of the following is true?

• (a)M, N and P all belong to the same subnet
• (b)Only N and P belong to the same subnet
• (c)M, N, and P belong to three different subnets
• (d)Only M and N belong to the same subnet

Consider an IP packet with a length of 4500 bytes that
includes a 20-byte IPv4 header and a 40-byte TCP
header. The packet is forwarded to an IPv4 router that
supports a Maximum Transmission Unit (MTU) of
600 bytes. Assume that the length of the IP header in
all the outgoing fragments of this packet is 20 bytes.
Assume that the fragmentation offset value stored in
the first fragment is 0.

The fragmentation offset value stored in the third
fragment is __________.

Consider a long-lived TCP session with an end-to-end
bandwidth of 1 Gbps = (109 bits per second). The
session starts with a sequence number of 1234. The
minimum time (in seconds, rounded to the closest
integer) before this sequence number can be used
again is

Match the following:

Field
Length (bits)
P. UDP Header's Port Number
i. 48
Q. Ethernet MAC Address
ii. 8
R. IPv6 Next Header
iii. 32
S. TCP Header's Sequence Number iv. 16

COMPUTER NETWORK

• (a)P-III, Q-IV, R-II, S-I
• (b)P-II, Q-I, R-IV, S-III
• (c)P-IV, Q-I, R-II, S-III
• (d)P-IV, Q-I, R-III, S-II

Consider the following statements regarding the
slow start phase of the TCP congestion control
algorithm. Note the cwnd stands for the TCP
congestion window and MSS denotes the
Maximum Segment Size.

(i) The cwnd increases by 2 MSS on every
successful acknowledgment.
(ii) The cwnd approximately doubles on every
successful acknowledgment.
(iii) The cwnd increases by 1 MSS every round
trip time.
(iv) The cwnd approximately doubles every round
trip time.

Which one of the following is correct?

• (a)Only (ii) and (iii) are true
• (b)Only (i) and (iii) are true
• (c)Only (iv) is true
• (d)Only (i) and (iv) are true

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?

• (a)LAST-ACK
• (b)TIME-WAIT
• (c)FIN-WAIT-1
• (d)FIN-WAIT-2

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
protocol

Which of the statements above are CORRECT?

• (a)I and IV only
• (b)I, II and III only
• (c)I, II and IV only
• (d)II, III and IV only

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
statements is/are CORRECT?

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

The maximum number of IPv4 router addresses that
can be listed in the record route (RR) option field of
an IPv4 header is __________.

For a host machine that uses the token bucket
algorithm for congestion control, the token bucket has
a capacity of 1 megabyte and the maximum output
rate is 20 megabytes per second. Tokens arrive at a
rate to sustain output at a rate of 10 megabytes per
second. The token bucket is currently full and the
machine needs to send 12 megabytes of data. The

COMPUTER NETWORK
minimum time required to transmit the data is
______ seconds.

An IP datagram of size 1000 bytes arrives at a
router. The router has to forward this packet on a
link whose MTU (maximum transmission unit) is
100 bytes. Assume that the size of the IP header is
20 bytes. The number of fragments that the IP
datagram will be divided into for transmission is
______.

Which one of the following protocols is NOT used
to resolve one form of address to another one?

• (a)DNS
• (b)ARP
• (c)DHCP
• (d)RARP

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 ______.

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 header is 20 bytes. There is no
option field in the IP header. How many total
number of IP fragments will be transmitted and
what will be the contents of the offset field in the
last fragment?

• (a)6 and 925
• (b)6 and 7400
• (c)7 and 1110
• (d)7 and 8880

Assume that the bandwidth for a TCP connection is
1048560 bits/sec. Let α be the value of RTT in
milliseconds (rounded off to the nearest integer) after
which the TCP window scale option is needed. Let β
be the maximum possible window size with window
scale option. Then the values of α and β are:

• (a)63 milliseconds 65535 × 214
• (b)63 milliseconds 65535 × 216
• (c)500 milliseconds 65535 × 214
• (d)500 milliseconds 65535 × 216

Consider the following statements:
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 II are correct
• (c)Only II and III are correct
• (d)All of I, II, and III are correct

Which one of the following fields of an IP header is
NOT modified by a typical IP router?

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

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

• (a)listen, accept, bind, recv
• (b)bind, listen, accept, recv
• (c)bind, accept, listen, recv
• (d)accept, listen, bind, recv COMPUTER NETWORK

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?
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)3 only
• (b)1 and 3 only
• (c)1 and 4 only
• (d)2 and 4 only

Consider the following routing table at an IP
router:
Network No
Net Mask
Next Hop
128.96 .170 .0
255.255 .254 .0
Interface 0
128.96 .168 .0
255.255 .254 .0
Interface 1
128.96 .166 .0
255.255 .254 .0
R2
128.96 .164 .0
255.255 .252 .0
R3
0.0 .0 .0
Default
R4

For each IP address in Group I Identify the
correct choice of the next hop from Group II
using the entries from the routing table above.

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 .164 .121
• (d)R3 e) R4 A. i-a, ii-c, iii-e, iv-d B. i-a, ii-d, iii-b, iv-e c, j-b, ii-c, iii-d, iv-e D. j-b, ij-c, iii-e. iv-d

Which one of the following is TRUE about the
interior gateway routing protocols - Routing
Information Protocol (RIP) and Open Shortest Path
First (OSPF)?

• (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.

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 COMPUTER NETWORK

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:

• (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

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 links within each ISP and across the
two ISPs, are all point-to-point optical links. The
initial value of the TTL field is 32. The maximum
possible value of the TTL field when R receives the
datagram is __________.

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

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

Which one of the following socket API functions
converts an unconnected active TCP socket into a
passive socket?

• (a)connect
• (b)bind
• (c)listen
• (d)accept

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?

An IP router implementing Classless Interdomain
Routing (CIDR) receives a packet with address
131.23.151.76. The router's routing table has the
following entries:

Prefix
Output Interface Identifier
131.16.0/12
3
131.28.0.0/4
5
131.19.0.0/16
2
131.22.0.0/15
1

The identifier of the output interface on which this
packet will be forwarded is ______.

COMPUTER NETWORK

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 __________.

Let the size of the 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 __________.

In an IPv4 datagram, the M bit is 0, the value of
HLEN is 10, the value of total length is 400 and the
fragment offset value is 300. The position of the
first fragment in the datagram, the sequence
numbers of the payload, and the last bytes of the
payload, respectively, are

• (a)Last fragment, 2400 and 2789
• (b)First fragment, 2400 and 2759
• (c)Last fragment, 2400 and 2759
• (d)Middle fragment, 300 and 689

Consider an instance of TCP's Additive Increase
Multiplicative Decrease (AIMD) algorithm where
the windows size at the start of the slow start phase
is 2 MSS and the threshold at the start of the first
transmission is 8 MSS. Assume that a time-out
occurs during the fifth transmission. Find the
congestion window size at the end of the tenth
transmission.

• (a)8 MSS
• (b)14 MSS
• (c)7 MSS
• (d)12 MSS

An Internet Service Provider (ISP) has the following
chunk of CIDR-based IP addresses available with it:
245.248.128.0/20. The ISP wants to give half of this
chunk of addresses to Organization A, and a quarter
to Organization B, while retaining the remaining with
itself. Which of the following is a valid allocation of
addresses to A and B?

• (a)245.248.136.0/21 and 245.248.128.0/22
• (b)245.248.128.0/21 and 245.248.128.0/22
• (c)245.248.136.0/22 and 245.248.132.0/21
• (d)245.248.136.0/24 and 245.248.132.0/21

In the IPv4 addressing format, the number of
networks allowed under Class C addresses is

• (a)214
• (b)27
• (c)221
• (d)224

Consider a network with five nodes, N1 to N5, as
shown as below.

The network uses a Distance Vector Routing
protocol. Once the routes have been stabilized, the
distance vectors at different nodes are as follows.
N1: ( 0,1,7,8,4 )
N2: ( 1,0,6,7,3 )
N3: (7,6,0,2,6)
N4: (8, 7, 2, 0,4)
N5: (4, 3, 6, 4, 0)
Each distance vector is the distance of the best
known path at that instance to nodes, N1 to N5,

COMPUTER NETWORK
where the distance to itself is 0 . Also, all links are
symmetric and the cost is identical in both
directions. In each round, all nodes exchange their
distance vectors with their respective neighbors.
Then all nodes update their distance vectors. In
between two rounds, any change in cost of a link
will cause the two incident nodes to change only
that entry in their distance vectors.
The cost of link N2 -N3 reduces to 2 (in both
directions). After the next round of updates, what
will be the new distance vector at node, N3 ?

• (a)(3,2,0,2,5)
• (b)(3,2,0,2,6)
• (c)(7,2,0,2,5)
• (d)(7,2,0,2,6)

Consider a network with five nodes, N1 to
                     N5, as shown as below.

The network uses a Distance Vector Routing
protocol. Once the routes have been stabilized, the
distance vectors at different nodes are as follows.

N1: ( 0,1,7,8,4 )

N2: (1,0,6,7,3)

N3: (7,6,0,2,6)

N4: (8,7,2,0,4)

N5: (4, 3, 6, 4, 0)
Each distance vector is the distance of the best
known path at that instance to nodes, N1 to N5,
where the distance to itself is 0 . Also, all links
are symmetric and the cost is identical in both
directions. In each round, all nodes exchange
their distance vectors with their respective
neighbors. Then all nodes update their distance
vectors. In between two rounds, any change in
cost of a link will cause the two incident nodes
to change only that entry in their distance
vectors.
The cost of link N2 -N3 reduces to 2 (in both
directions). After the next round of updates, the
link N1 -N2 goes down. N2 will reflect this
change immediately in its distance vector as cost,
∞. After the NEXT ROUND of update, what will
be the cost to N1 in the distance vector of N3 ?

• (a)3
• (b)9
• (c)10
• (d)∞

Consider a network with 6 routers R1 to R6
connected with links having weights as shown
in the following diagram.

All the routers use the distance vector based
routing algorithm to update their routing
tables. Each router starts with its routing table
initialized to contain an entry for each
neighbor with the weight of the respective
connecting link. After all the routing tables
stabilize, how many links in the network will
never be used for carrying any data?

• (a)4
• (b)3
• (c)2
• (d)1

Consider a network with 6 routers R1 to R6
connected with links having weights as shown in
the following diagram.

COMPUTER NETWORK

Suppose the weights of all unused links are
changed to 2 and the distance vector algorithm is
used again until all routing tables stabilize. How
many links will now remain unused?

• (a)0
• (b)1
• (c)2
• (d)3

Suppose computers A and B have IP addresses
10.105.1.113 and 10.105.1.91 respectively. They
both use the same netmask N. Which of the values
of N given below should not be used if A and B
should belong to the same network?

• (a)255.255.255.0
• (b)255.255.255.128
• (c)255.255.255.192
• (d)255.255.255.224

One of the header fields in an IP datagram is the
Time-to-Live (TTL) field. Which of the following
statements best explains the need for this field?

• (a)It can be used to prioritize packets
• (b)It can be used to reduce delays
• (c)It can be used to optimize throughput
• (d)It can be used to prevent packet looping

While opening a TCP connection, the initial
sequence number is to be derived using a time-of-
day (ToD) clock that keeps running even when the
host is down. The low order 32 bits of the counter of
the ToD clock is to be used for the initial sequence
numbers. The clock counter increments once per
millisecond. The maximum packet lifetime is given
to be 64 s.

Which one of the choices given below is closest to the
minimum permissible rate at which sequence
numbers used for packets of a connection can
increase?

• (a)0.015/s
• (b)0.064/s
• (c)0.135/s
• (d)0.327/s

In the slow start phase of the TCP congestion control
algorithm, the size of the congestion window

• (a)does not increase
• (b)increases linearly
• (c)increases quadratically
• (d)increases exponentially

If a class B network on the Internet has a subnet mask
of 255.255.248.0, what is the maximum number of
hosts per subnet?

• (a)1022
• (b)1023
• (c)2046
• (d)2047

A computer on a 10 Mbps network is regulated by a
token bucket. The token bucket is filled at a rate of 2
Mbps. It is initially filled to capacity with 16
Megabits. What is the maximum duration for which
the computer can transmit at the full 10 Mbps?

• (a)1.6 seconds
• (b)2 seconds
• (c)5 seconds
• (d)8 seconds COMPUTER NETWORK

A client process P needs to make a TCP connection
to a server process S. Consider the following
situation: the server process S executes a socket(),
a bind() and a listen() system call in that order,
following which it is preempted. Subsequently, the
client process P executes a socket() system call
followed by connect() system call to connect to the
server process S. The server process has not
executed any accept() system call. Which one of the
following events could take place?

• (a)connect() system call returns successfully
• (b)connect() system call blocks
• (c)connect() system call returns an error
• (d)connect() system call results in a core dump

Which of the following system calls results in the
sending of SYN packets?

• (a)socket
• (b)bind
• (c)listen
• (d)connect

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?

• (a)62 subnets and 262142 hosts
• (b)64 subnets and 262142 hosts
• (c)62 subnets and 1022 hosts
• (d)64 subnets and 1024 hosts

For which one of the following reasons does
Internet Protocol (IP) use the time-to-live (TTL)
field in the IP datagram header?

• (a)Ensure packets reach destination within that time
• (b)Discard packets that reach later than that time
• (c)Prevent packets from looping indefinitely
• (d)Limit the time for which a packet gets queued in intermediate routers

Two computers C1 and C2 are configured as follows:
C1 → IP: 203.197.2.53, Mask: 255.255.128.0
C2 → IP: 203.197.75.201, Mask: 255.255.192.0

Which statement is true?

• (a)C1 and C2 both assume they are on the same network
• (b)C2 assumes C1 is on same network, but C1 assumes C2 is on a different network
• (c)C1 assumes C2 is on same network, but C2 assumes C1 is on a different network
• (d)C1 and C2 both assume they are on different networks

Packets of the same session may be routed through
different paths in:

• (a)TCP, but not UDP
• (b)TCP and UDP
• (c)UDP, but not TCP
• (d)Neither TCP nor UDP

An organization has a class B network and wishes to
form subnets for 64 departments. The subnet mask
would be:

• (a)255.255.0.0
• (b)255.255.64.0
• (c)255.255.128.0
• (d)255.255.252.0 COMPUTER NETWORK

In a packet switching network, packets are routed
from source to destination along a single path
having two intermediate nodes. If the message size
is 24 bytes and each packet contains a header of 3
bytes, then the optimum packet size is:

• (a)4
• (b)6
• (c)7
• (d)9

The address resolution protocol (ARP) is used for:

• (a)Finding the IP address from the DNS
• (b)Finding the IP address of the default gateway
• (c)Finding the IP address that corresponds to a MAC address
• (d)Finding the MAC address that corresponds to an IP address

Which of the following statements is/are true with
respect to the interaction of a web browser with a
web server using HTTP 1.1?

• (a)HTTP 1.1 facilitates downloading multiple objects of the same webpage over the same TCP connection, if the objects are stored in the same server
• (b)HTTP 1.1 facilitates downloading multiple objects of the same webpage over the same TCP connection, even if they are stored in different servers
• (c)HTTP 1.1 facilitates sending a request for downloading one object without waiting for a previously requested object to be downloaded completely
• (d)HTTP 1.1 facilitates downloading multiple webpages on the same server to be downloaded over a single TCP connection

Which one of the following protocols may need to
broadcast some of its messages?

• (a)SMTP
• (b)FTP
• (c)DHCP
• (d)HTTP

A user starts browsing a webpage hosted at a
remote server. The browser opens a single
connection to fetch the entire webpage from the
server. The webpage consists of a top-level index
page with multiple embedded image objects.
Assume that all caches (e.g., DNS cache, browser
cache) are all initially empty. The following packets
leave the user's computer in some order.

(i) HTTP GET request for the index page.
(ii) DNS request to resolve the web server's name to
its IP address.
(iii) HTTP GET request for an image object.
(iv) TCP SYN to open a connection to the web
server.

Which one of the following is the CORRECT
chronological order (earliest in time to latest) of the
packets leaving the computer?

• (a)(iv), (ii), (iii), (i)
• (b)(iv), (ii), (i), (iii)
• (c)(ii), (iv), (i), (iii)
• (d)(ii), (iv), (iii), (i)

Suppose in a web browser, you click on the www .
gate-2023 . in URL. The browser cache is empty.
The IP address for this URL is not cached in your
local host, so a DNS lookup is triggered (by the local
DNS server deployed on your local host) over the 3-
tier DNS hierarchy in an iterative mode. No resource
records are cached anywhere across all DNS servers.
Let RTT denote the round trip time between your
local host and DNS servers in the DNS hierarchy.
The round trip time between the local host and the
web server hosting www.gate-2023.in is also equal
to RTT. The HTML file associated with the URL is
small enough to have negligible transmission time
and negligible rendering time by your web browser,
which references 10 equally small objects on the
same web server.
Which of the following statements is/are CORRECT
about the minimum elapsed time between clicking
on the URL and your browser fully rendering it?

• (a)7 RTTs, in case of non-persistent HTTP with 5 parallel TCP connections.
• (b)5 RTTs, in case of persistent HTTP with pipelining.
• (c)9 RTTs, in case of non-persistent HTTP with 5 parallel TCP connections.
• (d)6 RTTs, in case of persistent HTTP with pipelining. COMPUTER NETWORK

Consider the resolution of the domain name
www.gate.org.in by a DNS resolver. Assume that
no resource records are cached anywhere across the
DNS servers and that iterative query mechanism is
used in the resolution. The number of DNS query-
response pairs involved in completely resolving the
domain name is ___________.

Assume that you have made a request for a web
page through your web browser to a web server.
Initially, the browser cache is empty. Further, the
browser is configured to send HTTP requests in
non-persistent mode. The web page contains text
and five very small images. The minimum number
of TCP connections required to display the web
page completely in your browser is _________.

Which of the following protocol pairs can be used
to send and retrieve e-mails (in that order)?

• (a)IMAP, SMTP
• (b)IMAP, POP3
• (c)SMTP, MIME
• (d)SMTP, POP3

Which of the following is/are examples of stateful
application layer protocols?
(i) HTTP
(ii) FTP
(iii) TCP
(iv) POP3

• (a)(i) and (ii) only
• (b)(ii) and (iii) only
• (c)(ii) and (iv) only
• (d)(iv) only

Identify the correct sequence in which the
following packets are transmitted on the network
by a host when a browser requests a webpage from
a remote server, assuming that the host has just been
restarted.

• (a)HTTP GET request, DNS query, TCP SYN
• (b)DNS query, HTTP GET request, TCP SYN
• (c)DNS query, TCP SYN, HTTP GET request
• (d)TCP SYN, DNS query, HTTP GET request

In one of the pairs of protocols given below, both the
protocols can use multiple TCP connections between
the same client and the server. Which one is that?

• (a)HTTP, FTP
• (b)HTTP, TELNET
• (c)FTP, SMTP
• (d)HTTP, SMTP

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:
[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 I1
• (c)Only I2 and I3
• (d)Only I3 and I4

The transport layer protocols used for real-time
multimedia,
file
transfer,
DNS,
and
email
respectively are:

COMPUTER NETWORK

• (a)TCP, UDP, TCP, and TCP
• (b)UDP, TCP, TCP, and UDP
• (c)UDP, TCP, UDP, and TCP
• (d)TCP, UDP, TCP, and UDP

The Protocol Data Unit (PDU) for the application
layer in the Internet stack is

• (a)Segment
• (b)Datagram
• (c)Message
• (d)Frame

Which of the following transport layer protocols is
used to support electronic mail?

• (a)SMTP
• (b)IP
• (c)TCP
• (d)UDP

A layer-4 firewall (a device that can look at all
protocol headers up to the transport layer)
CANNOT

• (a)block entire HTTP traffic during 9:00 pm and 5:00 am
• (b)block all ICMP traffic
• (c)stop incoming traffic from a specific IP address but allow outgoing traffic to the same IP address
• (d)block TCP traffic from a specific user on a multi-user system during 9:00 pm and 5:00 am

Consider the different activities related to email.

ml : Send an email from mail client to mail
server

m 2 : Download an email from mailbox server
to a mail client

m3 ; Checking email in a web browser

Which is the application level protocol used in each
activity?

• (a)m1: HTTP m2: SMTP m3: POP
• (b)m1 : SMTP m2 : FTP m3 : HTTP
• (c)m1: SMTP m2: POP m3: HTTP
• (d)m1 : POP m2 : SMTP m 3 : IMAP

Which one of the following is not a client-server
application?

• (a)Internet chat
• (b)Web browsing
• (c)E-mail
• (d)Ping

What is the maximum size of data that the application
layer can pass on to the TCP layer below?

• (a)Any size
• (b)216 bytes - size of TCP header
• (c)216 bytes
• (d)1500 bytes

Which one of the following uses UDP as the transport
protocol?

• (a)HTTP
• (b)Telnet
• (c)DNS
• (d)SMTP COMPUTER NETWORK

Match the following:

• (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