REVIEW MODEL FOR MINOR
COMPUTER NETWORKS
pc
[COMPANY NAME] [Company address]
REVIEW MODEL QUESTIONS & ANSWERS
----------------------------------------------------------------------------------------------------------------QUESTION 1: MATCH [10 marks]
Stands for hybrid fiber coax which is asymmetric link
1
HFC:
A
rate (bits/s) at which bits are being sent from sender to receiver at
Instantaneous
2
B
3
4
Throughput:
A Network
Protocol
Bottleneck link
C
D
given point in time
Set of rules and activities as well as the actions taken on the
transmission and/or receipt of a message or other event
link on end-end path that constrains end-end throughput
packet-switched
networks
circuit-switched
networks
The transmission
delay
The propagation
delay
The processing
delay.
E
10
The queuing
delay
J
The time that a witing packet has to stay in the buffere before getting
sent
11
Quick UDP Internet
Connections (QUIC)
K
12
Base station
L
An application-layer protocol, using UDP as its underlying transportlayer protocol, and is designed to interface above specifically to a
simplified but evolved version of HTTP/2
A major element in infrastructure wireless networks with on anlogy
in wired ones whose function is to connect wireless network side to
the larger network (e.g., the Internet, corporate or home network),.
13
Hand-off/
Handover
M
14
Multipath
propagation
N
15
Bit Error Rate
(BER)
O
The probability that a transmitted bit is received in error at the
receiver side
16
UDP checksum
P
One’s complement sum of segment content.placed into UDP
checksum field to compare both values at sender and receiver side
5
6
7
8
9
F
G
H
I
resources are not reserved but on demand as a consequence, may
have a wait (queue) for access to a communication link
requires reserving the resources needed along a path (buffers,
link,..etc) for the duration of the communication
This is the amount of time required to push all of the packet’s bits
into the link on the order of microseconds to
The time needed once 1st bit of the packet is transmitted out of router
A to router B end with distance
The time required to examine the packet’s header / trailer to direct
the packet to destination and check for bit-level errors in the packet
Refers to the process when a mobile host moves beyond the range of
one base station and into the range of another,(.e., change the base
station with which it is associated)
.A common problem in wireless networks which may be caused due
to moving objects between the sender and receiver which can cause
multipath propagation to change over time
1
17
Pipelining in data
transfer :
Q
sender allows multiple, “in-flight”, yet-to-be-acknowledged packets
thus range of sequence numbers must be increased
buffering at sender and/or receiver
18
Flow control
R
19
Maximum Segment
Size (MSS).)
S
A mechanism to the calamity of a receiver being over-run by a sender
that is sending too fast which enables the RECEIVER to explicitly
control the SENDER so sender won’t overflow receiver’s buffer by
transmitting too much, too fast
In TCP, the CongestionWindow is not allowed to fall below the
size of a single packet,
20
A Trojan horse
T
21
A Spyware
22
Flow control
23
Congestion
24
forwarding
25
Routing:
26
Multipath
propagation
Is a malware that appears, to the user, to perform a desirable function
but, in fact, facilitates unauthorized access to the user's computer
system
Is a malware that is installed surreptitiously on personal computers to
collect information about users, their computer or browsing habits
without their informed consent
A mechanism that allows the RECEIVER to explicitly control
the SENDER so sender won’t overflow receiver’s buffer by
transmitting too much, too fast
Takes palce when too many sources sending too much data too fast
for network to handle
A network layer function which move packets from a router’s input
link to appropriate router output link
A network layer function which determines optimal route taken by
packets from source to destination
A typical wireless communivation problem as radio signal reflects off
objects ground, arriving at destination at slightly different times
QUESTION (2): TRUE & FALSE
FOR EACH OF THE FOLLOWING STATEMENTS, IDENTIFY TRUE OR FALS AND
CORRECT THE FALSE ONES:
1) The smaller SNR makes the easier for the receiver to extract the transmitted signal from the
background noise
FALSE, THE LARGER THE SNR
2
2) Code Devision Multiple Access (CDMA) belongs to the family of random access protocols and it’s
prevalent in wireless LAN and cellular technologies.
FALSE, ITBELONGS TO channel partitioning FAMILY PROTOCOLS
3) UDP is an unreliable service protocol at the transport layer which does not guarantee that data sent by
one process will arrive intact (or at all!) to the destination process.
[ true]
4) In connectionless demultiplexing that takes place in transport layer, the IP/UDP
datagrams with same dest. port #, but different source IP addresses and/or source port numbers will
be directed to same socket at receiving host
[ TRUE]
5) Both Multiplexing, demultiplexing take place in all layers and are based on segment,
datagram header field values [ True]
6) Both UDP and TCP demultiplexing use only destination port number but (only)
[ False] UDP use destination port number only but TCP: demultiplexing using 4-tuple:
source and destination IP addresses, and port numbers
7) Despite the unrialble feature of UDP as compared to TCP, developer mstly favor it for
their applications due to its no connection establishment (which can add RTT delay) and
simplicity but it’s necessary to its enforced congestion control
[FALSE] it’s preferred for simplicity and no delay but it doesn’t require congestion control
8) For reliable data transfer, communication over unreliable channel is TWO-way as sender
and receiver will exchange messages back and forth to enable implement one-way reliable data
transfer
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[ TRUE]
9) Here’s how TCP implement flow control. The basic idea is simple – the receiver informs the
sender how much free buffer space there is, and the sender is limited to send no more than this
amount of data. That the value o RWND in the diagram to the right.
This information is carried from the receiver to the sender in the “receiver advertised
window” (do a PIP of header) in the TCP header, and the value will change as the amount
of free buffer space fluctuates over time.
10) The network limit is estimated using the CongestionWindow parameter whereas the
receiver limit is advertised using the AdvertisedWindow parameter
[TRUE]
11) In TCP congestion control, the Slow start mechanism effectively increases the
congestion window exponentially, rather than linearly.
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1
2
3
4
5
6
7
A packet switch is
A) a device with
B) Its core job is to
C) requires reserving D) A +B
several inputs and
take packets that
the resources needed
outputs leading to
arrive on an input and along
during
the
and from the hosts
forward along the
communication
that the switch
proper route reach
session duration
interconnects.
their destination.
Which of the following media are valid examples of guided link media
A) UTP, & STP
B) RADIO LINKS
C) FIBER OPTICS
D) A+C
Which of the following causes a problem of contention
A) If packets destined
B) If packets destined C) if we have Wire
D) NOT ALL
for a certain output
for a certain output tapping to capture data
arrive at a switch and
arrive at a switch and in a network.
their arrival rate is
their
arrival
rate
slower to fill the
exceeds the capacity
capacity of that output, of that output,
Which of the following attacks are valid examples against AVAILABILITY
A) An asset of the
B) Changing data file
C) Destruction of some D) All of above
system is destroyed or
Altering a program
hardware or jmming
becomes unavailable
and the contents of a
signals
or unusable.
message
The IP protocol is
A) An important
C) It’s a protocol that D) A + B
B) Essential routine
internet protocol
for internet which for
works in the
among the TCP/IP
addressing of network application layer of
protocol stack
and format of the
the OSI
packets
The delay components in the end-to-end delay which are fixed in time are
A) transmission delay
B) propagation delay
C) queuing delay
D) A +B
If there’s no intervention traffic, the throughput can simply be calculated as
D) ALL
A) the minimum
B) depends not only
C) the maximum of
transmission rate
on the transmission
transmission rate
along the path
rates of the links
along the path
between source and
along the path, but
between source and
destination
also on the
destination
intervening traffic. I
In reference to OSI model, following tasks that a layer can perform are
A-) error and flow
B-) segmentation
C-) multiplexing, and D- All
control,
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9
and reassembly
connection setup.
A socket interface
A) specifies how a
B) An encryption
C) An essential SW
program running on
algorithms that include routine for internet
one end system asks
hash algorithms
which specifies the
the Internet
addressing of network
infrastructure to
and format of the
deliver data to a
packets that are sent
specific destination
and received
program running on
another end system.
Which is NOT TRUE of the following statements ?
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D) B + C
A) An asset of the
system when destroyed
or becomes unavailable
is an attack on
availability principles
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B) Destruction of
C) An unauthorized
D) B+ C
some hardware, or and party gains access to an
disabling file
asset is an attack on
management systems
Non-repudiation
is an example of
security principle
static/passive attack
Which of the following statements is TRUE FOR Voie over-IP (VoIP) applications?
B) In addition to
C) It encounters Only
D) A+B
A) It has media
transmission
and
packetization delay, as processing,
queing delays
transmission, and
the sending side must
propagation delays,
first fill a packet with
there’s also
encoded digitized
packetization delay
speech before passing
the packet to the
Internet.
https://webmail.niit.org.pk/src/login.php where 2nd level (.org) is spoofed is an example
A) of email spoofing
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14
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B) URL Spoofing
(phishing)
C) DNS spoofing
Which is aTRUE about Secret key encryption algorithms
A) Are often referred
B) The decryption
C) . One acceptable
D) ALL
to as symmetric
algorithm is the
solution to the problem
encryption algorithms
inverse of the
encountered by secret
encryption algorithm – key encryption is to
(i.e. if the encryption
rely on trusted third
algorithm uses a
party, a key distribution
combination of
center (KDC) where .
addition and
it’s normally a server
multiplication, the
that shares a key with
decrypting algorithm
each user.
would use a
combination of
subtraction and
division
Which of the following statements is valid for Client server architecture
A) No or a minimal
B) Hosts are esktops
C) Cost effective as
D) NOT ALL
dedicated servers
and laptops controlled they don’t require
therefore application
by users, with most of significant server
exploits direct
the peers residing in
infrastructure neither
communication
homes, universities,
server bandwidth
between pairs of
and offices.
connected hosts,
If there’s no intervention traffic, the throughput can simply be calculated as
A) the minimum
B) Depends on both
C) the maximum of
D) ALL
transmission rate along the transmission rates
transmission rate along
the path between
of the links and on the the path between
source and destination
intervening traffic.
source and destination
Datagram switching is done at which layer of OSI model?
A) Network layer
B) Application layer
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C) Transport layer
D) ALL
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Datagram networks mainly refers to _________
A) Connection
oriented networks
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D) NOT ALL
B) Datagram table
C) Routing table
D)NOT ALL
The main contents of the routing table in datagram networks are ___________
A) Source and
Destination address
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C) Telephone
networks
Datagrams are routed to their destinations with the help of ________
A) Switch table
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B) Connection less
networks
B) Destination
address and Output
port
C) Source address
and Output port
D) NOT ALL
ransport layer aggregates data from different applications into a single stream before
passing it to ____________
A) network layer
B) data link layer
C) application layer
D) physical layer
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Which of the following are transport layer protocols used in networking?
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A) TCP and FTP
B) UDP and HTTP
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C) TCP and UDP
D) NOT ALL
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Which is TRUE about the functions of the Network layer data Plane ?
A) Forward datagrams
from their input links
to their output links
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B) Determine the
paths a packet takes
from its source to its
destination
C) Iteroperate
with the link
layer at the
other side of
the incoming
link, and
perform lookup
function at the
input ports.
D) A+C
Which is TRUE about the functions of the Network layer Control Plane ?
A) Forward datagrams
from their input links
to their output links
B) Determine the
paths a packet takes
from its source to its
destination
C) Iteroperate
with the link
layer at the
other side of
the incoming
link, and
perform lookup
function at the
input ports.
D) A+C
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Which of the following is NOT TRUE about components of a router?
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A) Input port,
B)A routing
C) Input port, switching D)
switching fabric, and
processor uses SW for fabric, and output ports
output ports are HW
executing routing
are SW because their
because their
protocols, maintaining datagram-processing
datagram-processing
routing tables router fneeds more control on
functionality is far too
their number and
fast for software
functions and to avoid
implementation.
high cost of HW.
Which of the following are transport layer protocols used in networking?
A) TCP and FTP
B) UDP and HTTP
C) TCP and UDP
D) HTTP and FTP
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Which one of the following is not a function of network layer?
A) routing
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C) congestion
control
D) error control
The network layer protocol for internet is __________
C) hypertext transfer
protocol
A 4 byte IP address consists of __________
A) Ethernet
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B) inter-networking
B) Internet protocol
8
D) file
protocol
transfer
A) only network
address
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B) only host
address
C) network address
& host address
D)
network
address & MAC
address
Suppose two packets arrive to two different input ports of a router at the same time and there
are no other packets anywhere in the router. If the two packets are to be forwarded to two
different output ports. Which of the following is Correct ?
A) No, you can only
transmit one packet
at a time over a
shared bus.
B) It’s possible to
forward the two
packets at the same
time over a shared bus
B) It’s possible to
D) NOT ALL
forward the two packets
at the same time using a
crossbar switching
fabric
ESSAY QUESTIONS
QUESTION(3)
A)Discuss the key Difference between Forwarding and Routing in the Network layer?
B) In reference to the network layer, if R_switch is N times faster than R_line,(e.g. only negligible
queuing will occur at the input ports, even if all the packets are to be forwarded to the same output
port). Now suppose that R_switch = R_line, but all packets are to be forwarded to different output
ports. Let D be the time to transmit a packet. As a function of D, what is the maximum input queuing
delay for a packet for the (i) memory, (ii) bus, and (iii) crossbar switching fabrics?
C) Suppose that a Web server runs in Host C on port 80. and this Web server uses persistent
connections, and is currently receiving requests from two different Hosts, A and B. Discuss and
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explain.
i) Are all of the requests being sent through the same socket at Host C?
ii) If they are being passed through different sockets, do both of the sockets have port 80?
(D) In reference to the TCP :
i) State five of its main features/charchterstics?
ii) Explain briefly the approach taken by TCP for classical congestion control?
iii) Explain briefly the approach taken by TCP forflow control?
(E) Explain briefly the main axioms of classifying wireless networks and state the corresponding main
types?
QUESTION(4): Explain briefly each of the following :
A- Signal to Noise Ratio (SNR)
B- difference between UDP and TCP portocols
C- Multiplexing and demultiplexing at Transport layer
D) Traceout in application layer process
E)EXPLAIN BRIEFLY THE NETWORK LAYER SERVICE MODEL?
QUESTION(5)
A- Explain briefly reliable data transfer mechanisms and indicate use of each of them?
B) Consider a 1 Gbps link with 15 ms prop. Delay and size of packets is 8000 bits, given that
time of RTT (request to transmit) is 30 msec
i) Calculate the time to transmit packet into channel? Corresponding throughput
ii) Calculate the utilization of the channel based on Stop and wait mechanism
iii) What’s meant by pipelined and does it improves utilization of channel
iv) Reclaculate the utilization of the channel based on 3 stage pipelined mechanism(
sending 3 packets )per session
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ANSWER:
QUESTION(3)
A)Discuss the key Difference between Forwarding and Routing in the Network layer?
Answer:
The key differences between routing and forwarding is that forwarding is a router’s local action of
transferring packets from its input interfaces to its output interfaces, and forwarding takes place at very short
timescales (typically a few nanoseconds), and thus is typically implemented in hardware. Routing refers to
the network-wide process that determines the end-to-end paths that packets take from sources to destinations.
Routing takes place on much longer timescales (typically seconds), and is often implemented in software.
B) In reference to the network layer, if R_switch is N times faster than R_line,(e.g. only negligible
queuing will occur at the input ports, even if all the packets are to be forwarded to the same output
port). Now suppose that R_switch = R_line, but all packets are to be forwarded to different output
ports. Let D be the time to transmit a packet. As a function of D, what is the maximum input queuing
delay for a packet for the (i) memory, (ii) bus, and (iii) crossbar switching fabrics
Answer:
i) Maximum queueing delay if a memory = D *( n-1)
ii) Maximum queueing delay if a bus =
iii) Maximum queueing delay if a crossbar = 0
C) Suppose that a Web server runs in Host C on port 80. and this Web server uses persistent
connections, and is currently receiving requests from two different Hosts, A and B. Discuss and
explain.
i) Are all of the requests being sent through the same socket at Host C?
ii) If they are being passed through different sockets, do both of the sockets have port 80?
Answer:
i) No. for each persistent connection, the Web server creates a separate “connection socket”. Each
connection socket is identified with a four-tuple: (source IP address, source port number, destination IP
address, destination port number).
ii) The identifier for both of these sockets has 80 for the destination port; however, the identifiers for
these sockets have different values for source IP addresses.
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(D) In reference to the TCP :
i) State five of its main features/charchterstics?
ii) Explain briefly the approach taken by TCP for classical congestion control?
iii) Explain briefly the approach taken by TCP forflow control?
i) main features and charcterstics of TCP?








point-to-point:one sender, one receiver
reliable, in-order byte steam:no “message boundaries"
full duplex data:bi-directional data flow in same connection
MSS: maximum segment size
cumulative ACKs
pipelining:TCP congestion and flow control set window size
connection-oriented: handshaking (exchange of control messages) initializes sender,
receiver state before data exchange
flow controlled: sender will not overwhelm receiver
ii) Classic Congestion control :
The approach taken by TCP is to have each sender limit the rate at which it sends traffic into its connection
as a function of perceived network congestion.
iii) Here’s how TCP implement flow control.:
The basic idea is simple is the receiver informs the sender how much free buffer space there is, and the
sender is limited to send no more than this amount of data.
E) Explain briefly the main axioms of classifying wireless networks and state the corresponding main
types?

Main axioms for classification are:
•
(i) whether a packet in the wireless network crosses exactly one wireless hop or multiple
wireless hops,
•
(ii) whether there is infrastructure such as a base station in the network:
Corresponding types are summarized as follows:
1-Single-hop, infrastructure-based. :
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•
have a base station that is connected to a larger wired network (e.g., the Internet).
•
all communication is between this base station and a wireless host over a single wireless
hop.
2-Single-hop, infrastructure-less.:
•
there is no base station that is connected to a wireless network.
•
However, as we will see, one of the nodes in this single-hop network may coordinate the
transmissions of the other nodes.
•
Bluetooth networks (that connect small wireless devices such as keyboards, speakers, and
headsets are single-hop, infrastructure-less networks.
3- Multi-hop, infrastructure- based :In these networks, a base station is present that is wired to the larger
network , However, some wireless nodes may have to relay their communication through other wireless
nodes in order to communicate via the base station.

Examples are some wireless sensor networks and so-called wireless mesh networks deployed in
homes fall in this category.
•4-Multi-hop, infrastructure-less.:
•
There is no base station in these networks, and nodes may have to relay messages among
several other nodes in order to reach a destination.
•
Nodes may also be mobile, with connectivity changing among nodes
•
a class of networks known as mobile ad hoc networks (MANETs). If the mobile nodes are
vehicles, the network is a vehicular ad hoc network (VANET).
QUESTION (4) Explain briefly each of the following :
a- Signal to Noise Ratio (SNR)
b- difference between UDP and TCP portocols
c- Multiplexing and demultiplexing at Transport layer
d) Traceout in application layer process
Answer:
a) The signal-to-noise ratio (SNR) is a relative measure of the strength of the received signal (i.e.,
the information being transmitted) as compared to picked up noise and is measured in decibles
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unit . The larger SNR makes the easier for the receiver to extract the transmitted signal from the
background noise
B)
UDP

TCP
Stands for User
Datagram Protocol
•
similarity
TCP:
Transmission 1- both provides integrity
checking by including error
Control Protocol
detection fields in their
segments’ headers.
2-The fundamental
responsibility of UDP and
no-frills extension of “best- It is possible to have TCP is to extend IP’s
congestion therefore needs to delivery service between
effort” IP
two end systems to a
control congestion
delivery service between
two processes running on
the end systems.
unordered delivery
It enables flow control
unreliable,
reliable, in-order delivery

Requires connection setup
C) Multiplexing takes place at the sender side where its process is gathering data chunks at the
source host from different sockets, and encapsulating each data chunk with header information to
create segments .

Demultiplexing. Takes place at the receiver side where the process is to deliver the data in
a transport-layer segment to the correct socket .
D) Traceout?
Traceroute is a simple program that can run in any Internet host. When the user specifies a destination
hostname, the program in the source host sends multiple, special packets toward that destination
passing through a series of routers.
E) Network layer service model:
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
Guaranteed delivery. This service guarantees that a packet sent by a source host will
eventually arrive at the destination host.

Guaranteed delivery with bounded delay. This service not only guarantees delivery of
the packet, but delivery within a specified host-to-host delay bound (for example, within
100 msec).

In-order packet delivery. This service guarantees that packets arrive at the destination in
the order that they were sent.

Guaranteed minimal bandwidth. emulates the behavior of a transmission link of a
specified bit rate (for example, 1 Mbps) between sending and receiving hosts.

Security. The network layer could encrypt all datagrams at the source and decrypt them at
the destination, thereby providing confidentiality to all transport-layer segments
QUESTION(5)
A- Explain briefly reliable data transfer mechanisms and indicate use of each of them?
B) Consider a 1 Gbps link with 15 ms prop. Delay and size of packets is 8000 bits, given that
time of RTT (request to transmit) is 30 msec
i) Calculate the time to transmit packet into channel? Corresponding throughput
ii) Calculate the utilization of the channel based on Stop and wait mechanism
iii) What’s meant by pipelined and does it improves utilization of channel
iv) Reclaculate the utilization of the channel based on 3 stage pipelined mechanism(
sending 3 packets )per session
ANSWER
A) Reliable Data Transfer mechanisms
1
Checksum
Used to detect bit errors in a transmitted packet.
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2
Timer
Used to timeout/retransmit a packet, possibly because the packet (or
its ACK) was lost within the channel.
3
Sequence number
Used for sequential numbering of packets of data flowing from sender
to receiver.
4
Acknowledgment
Used by the receiver to tell the sender that a packet or set of packets
has been received correctly.
5
Negative
acknowledgment
Used by the receiver to tell the sender that a packet has not been
received correctly.
6
Window, pipelining
The sender may be restricted to sending only packets with sequence
numbers that fall within a given range. By allowing multiple packets to
be transmitted but not yet acknowledged, sender utilization can be
increased over a stop-and-wait mode of operation. We’ll see shortly
that the window size may be set on the basis of the receiver’s ability to
receive and buffer messages, or the level of congestion in the network,
or both
B) i) Dtrans = L/ R= 8000 bits/ 109 bits= 8 10 -6 sec= 8 microsecs
ii) Utilization of channel= time used for transmission / wait time (RTT) + time used for
transmission
= Dtrans / RTT + Dtrans = 8 10 -6 / 30 10-3 + 8 10 -6 = 0.008/ 30.008= 0.00027

Which is extremely low utilization indicating that Protocol limits performance of
underlying infrastructure (channel)
iii) In case of pipelined protocol which allows multiple, “in-flight”, yet-to-be-acknowledged
packetswhich means that range of sequence numbers must be increased and implies buffering at
sender and/or receiver , Yes it increases the channel utilization ratio
iv) in case of 3 stage pipeline it means that 3 packets are sent from sender to RX but ACK from
Rec for each received packet however the RTT is counted from time last bit of 1st packet is sent
ACK arrives, send next
packet, t = RTT + L / R
Utilization becomes = 3L/R / RTT + L/R = 0.0024 / 30.008 = 0.00081
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Comment: utilization was improved as compared to first mechanism 81/27= 3 times
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