EE317 – DCN
Assignment Number 1 (Solution)
EE317 – Data Communication and Networks
Assignment Number 1 (Solution)
Fall 2020
Maximum Marks: 50
Due Date: 18 September 2020
Instructions:
• Partially or fully copied assignments will be marked as zero.
• Only handwritten solution on A4 page will be accepted.
• Use the title page provided with this assignment.
• Late submissions are not allowed.
CLO No.
1
CLO Statement
Domain
Taxonomy
Level
Explain the fundamental concepts of data communication
and networks including elements of a protocol and OSI Cognitive
Model.
Question Number 1
(CLO 1)
2
(2 + 2 + 4 + 2 = 10 marks)
Explain the difference between:
• Bandwidth, Data Rate and throughput
• Internet and World Wide Web
• Malware, Virus, Worm and Botnet
• Bandwidth flooding and connection flooding
Bandwidth
Data Rate
Throughput
Throughput refers to the overall
effective
transmission
rate,
The maximum amount of The actual amount of data
considering
things
like
data that can be transferred transferred between two
transmission overhead, protocol
per second on a link.
devices is called data rate.
inefficiencies and perhaps even
competing traffic.
For Example: if the bandwidth of a link is 100 Mbps, the data can be 50 Mbps and throughput
can be 40 Mbps. It means that the link can send 100 Mbit per second, but the devices are
sending at a rate of 50 Mbit per second and after all the delays the overall effective
transmission rate is 40 Mbit per second.
Internet
World Wide Web
It is a network of networks in which several
computers are connected and provide
services to each other by using TCP/IP
protocol.
It is an information space where documents
and other web resources are identified by
URLs and can be accessed via the Internet
using HTTP protocol.
National University of Computer and Emerging Sciences – FAST, CFD Campus
1
EE317 – DCN
Assignment Number 1 (Solution)
Malware
Malware is a
malicious software
that is used to
disturb the normal
working of a
computer.
Virus
Viruses are malware
that require some
form of user
interaction to infect
the user’s device.
Worm
Worms are
malware that can
enter a device
without any
explicit user
interaction.
Botnet
a network of thousands
of similarly
compromised devices
which is used to attack
the server or network.
Bandwidth Flooding
Connection Flooding
In bandwidth flooding, the attacker sends a
deluge of packets to the targeted host—so
many packets that the target’s access link
becomes clogged, preventing legitimate
packets from reaching the server.
In connection flooding, the attacker
establishes many half-open or fully open
TCP connections at the target host. The host
can become so bogged down with these
bogus connections that it stops accepting
legitimate connections.
Question Number 2
i)
(CLO 1)
(6 + 4 = 10 marks)
Consider the following network in which source is sending 3 packets to the
destination and the router is using store-and-forward transmission. Find the amount
of time that elapses from when the source begins to send the first packet until the
destination has received all three packets. The link speed from source to router is R
bps and from router to destination is 2R bps.
The source started to transmit at t = 0 seconds
First packet will be transmitted at t = L/R + L/2R seconds
First packet will reach at destination at t = L/R + L/2R = 3L/2R
2nd packet will reach at destination at t = 3L/R + (L/R+L/R) = 5L/R
3rd packet will reach at destination at t = 5L/R + (L/R+L/R) = 7L/R
ii)
Consider the following network in which a source and destination are connected
through N – 1 routers and the source is sending P packets to the destination. Find
the amount of time that elapses from when the source begins to send the first packet
until the destination has received all P packets. The link speed for all the links is R
bps.
First packet will reach at destination at t = NL/R
Second packet will reach at destination at t = NL/R + L/R
Pth packet will reach at destination at t = (N + P – 1) / R
National University of Computer and Emerging Sciences – FAST, CFD Campus
2
EE317 – DCN
Assignment Number 1 (Solution)
Question Number 3
(CLO 1)
(5 marks)
Explain some disadvantages of Layered Network Architecture.
Some of the disadvantages of the layered network architecture are:
1) It doesn’t define any particular protocol.
2) It may find sometimes difficult to fit a new protocol in this model. This is because
this model was created before the invention of any of these protocols.
3) There might be a negative impact on the performance as we have the extra header of
passing through layers instead of calling a component directly. It will provide
encapsulation but the complexity increases.
4) There is some duplication of services at various layers. Such as, both transport and
data link layer have error control mechanisms.
5) There is also interdependence among the layers. These layers cannot work in parallel.
They must be in wait to receive data from its predecessor.
Question Number 4
(CLO 1)
(2 + 8 = 10 marks)
Explain the difference between Denial of Service (DoS) and Distributed Denial of Service
(DDoS) attacks and outline some methods to prevents these attacks.
Denial of Service (DoS)
Distributed Denial of Service (DDoS)
A DoS attack renders a network, host, or
other piece of infrastructure unusable by
legitimate users. In DoS attack a single
attacker
cause
bandwidth
flooding,
connection flooding or vulnerability attack.
A DoS attack is not a DDoS.
In a distributed DoS (DDoS) attack, the
attacker controls multiple sources and has
each source blast traffic at the target. The
purpose of DDoS attack is same as DoS
attack, but it is more severe than DoS attack.
All the DDoS attack are DoS.
DoS Attack
DDoS Attack
Here are some suggestions to prevent DoS and DDoS attacks.
1) Buy more bandwidth.
2) Build redundancy into your infrastructure.
3) Configure your network hardware against DDoS attacks.
4) Deploy anti-DDoS hardware and software modules.
5) Deploy a DDoS protection appliance.
6) Protect your DNS servers.
National University of Computer and Emerging Sciences – FAST, CFD Campus
3
EE317 – DCN
Question Number 5
Assignment Number 1 (Solution)
(CLO 1)
(5 + 5 = 10 marks)
Consider the following network in which hosts A and B are sending some data to host C. The
link between host A and the router can send 5 packets per second and that of host B is 7 packets
per second. And the link speed from router 1 to router 2 is 200bps. If host A is sending 5 packets
and host B is sending 6 packets to host C, then:
i) Find the number of packets that will wait in the buffer of router 1
ii) Find the minimum link speed required between router 1 and router 2 to avoid queuing
delay.
(Consider that each packet consists of 32 bits)
i) The router is receiving 5 + 6 = 11 packets at the input link.
The router can send (200/32) = 6.25  6 packets per second in the output link.
Thus 5 packets will wait in the buffer.
ii) The router may receive a maximum of 12 packets (384 bits) per second at the input.
So, the minimum link speed between router 1 and router 2 should be 384bps to avoid
queuing delay.
Question Number 6
(CLO 1)
(1 + 4 = 5 marks)
Consider there are 10 hosts in a network that are sending the data to a destination. Suddenly a
single host starts to transmit 1000 packets (each packet with 1000 bits) and the remaining 9
hosts become idle. The link between hosts and destination has a speed of 1Mbps. Find the time
required by ignoring all the delays to send the data to the destination if
i) Packet switching is used
ii) Circuit switching with TDM is used
i) In packet switching all the available bandwidth will be allocated to the transmitting
host. So the host will need [(1000 x 1000) / (1 x 106)] = 1 second.
ii) In circuit switching every host will get 1 second to transmit the data regarding of
available traffic in the link. So in this case the time required to transmit the data will
be
t = (10 x 1000 x 1000) / (1x106) = 10 seconds.
National University of Computer and Emerging Sciences – FAST, CFD Campus
4