class notes

1. Class notes
Course code: CSE 313
Course Title: Data communication
Submitted to:
Pranab Bandhu Nath
Senior Lecturer
Department of CSE
City University
Submitted by
Faysal Ahmed
Id:1834902611
batch 49 (B)

3. Data communication :
Data communications means the exchange of data between two devices via
some form of transmission medium such as a wire cable. Data communication is
said to be local if communicating devices are in the same building or a similarly restricted
geographical area.
Components of data communication system
1. Message: It is the information or data to be communicated. It can consist of text,
numbers, pictures, sound or video or any combination of these.
2. Sender: It is the device/computer that generates and sends that message.
3. Receiver: It is the device or computer that receives the message. The location of
receiver computer is generally different from the sender computer. The distance between
sender and receiver depends upon the types of network used in between.
4. Medium: It is the channel or physical path through which the message is carried from
sender to the receiver. The medium can be wired like twisted pair wire, coaxial cable,
fiber-optic cable or wireless like laser, radio waves, and microwaves.
5. Protocol: It is a set of rules that govern the communication between the devices. Both
sender and receiver follow same protocols to communicate with each other.
The effectiveness depends on four fundamental characteristics of data
communications:
1.Delivery: The data must be deliver in correct order with correct destination.
2.Accuracy: The data must be deliver accurately.
3. Timeliness: The data must be deliver in a timely manner. Late delivered Data useless.
4. Jitter: It is the uneven delay in the packet arrival time that cause uneven quality.
References:
https://ecomputernotes.com/computernetworkingnotes/communica
tion-networks/what-is-data-communication

4. Data transmission mode :
Transmission mode means transferring data between two devices.
There are three types of transmission mode:-
1. Simplex Mode –
In Simplex mode, the communication is unidirectional, as on a one-
way street. Only one of the two devices on a link can transmit, the
other can only receive. The simplex mode can use the entire capacity
of the channel to send data in one direction.
Example: Keyboard and traditional monitors. The keyboard can only
introduce input, the monitor can only give the output.
2. Half-Duplex Mode –
In half-duplex mode, each station can both transmit and receive, but not at the
same time. When one device is sending, the other can only receive, and vice
versa. The half-duplex mode is used in cases where there is no need for
communication in both directions at the same time. The entire capacity of the
channel can be utilized for each direction.
Example: Walkie-talkie in which message is sent one at a time and messages
are sent in both directions.

5. 3. Full-Duplex Mode –
In full-duplex mode, both stations can transmit and receive simultaneously. In
full duplex mode, signals going in one direction share the capacity of the link
with signals going in another direction, this sharing can occur in two ways:
Reference :
https://www.google.com/amp/s/www.geeksforgeeks.org/transmissi
on-modes-computer-networks/amp/

6. Data :
Data can be analog or digital.
Digital data: It refers to information that has discrete state.
Analog data: The term refers to information that is continue.
Signals:
There are two types of signals to transfer data.
Analog signal: An analog signal is time-varying and generally bound to a range
(e.g. +12V to -12V), but there is an infinite number of values within that
continuous range. An analog signal uses a given property of the medium to
convey the signal’s information, such as electricity moving through a wire. In an
electrical signal, the voltage, current, or frequency of the signal may be varied to
represent the information. Analog signals are often calculated responses to
changes in light, sound, temperature, position, pressure, or other physical
phenomena.

7. Digital signal: A digital signal is a signal that represents data as a sequence of
discrete values. A digital signal can only take on one value from a finite set of
possible values at a given time.
Reference : https://www.monolithicpower.com/en/analog-vs-digital-signal

8. OSI Model: The Open Systems Interconnection (OSI) model describes seven layers
that computer systems use to communicate over a network. It was the first
standard model for network communications, adopted by all major computer and
telecommunication companies in the early 1980s.
Let’s Study each layer in detail:

9. 7.Aplication
This is the only layer that directly interacts with data from the user. Software applications
like web browsers and email clients rely on the application layer to initiate
communications. But it should be made clear that client software applications are not
part of the application layer; rather the application layer is responsible for the protocols
and data manipulation that the software relies on to present meaningful data to the
user. Application layer protocols include HTTP as well as SMTP (Simple Mail Transfer
Protocol is one of the protocols that enables email communications).
6. The presentation layer
This layer is primarily responsible for preparing data so that it can be used by the
application layer; in other words, layer 6 makes the data presentable for applications to
consume. The presentation layer is responsible for translation, encryption, and
compression of data.
Two communicating devices communicating may be using different encoding methods,
so layer 6 is responsible for translating incoming data into a syntax that the application
layer of the receiving device can understand.
If the devices are communicating over an encrypted connection, layer 6 is responsible
for adding the encryption on the sender’s end as well as decoding the encryption on the
receiver's end so that it can present the application layer with unencrypted, readable
data.
Finally the presentation layer is also responsible for compressing data it receives from
the application layer before delivering it to layer 5. This helps improve the speed and
efficiency of communication by minimizing the amount of data that will be transferred.

10. 5. The session layer
This is the layer responsible for opening and closing communication between the two
devices. The time between when the communication is opened and closed is known as
the session. The session layer ensures that the session stays open long enough to
transfer all the data being exchanged, and then promptly closes the session in order to
avoid wasting resources.
The session layer also synchronizes data transfer with checkpoints. For example, if a 100
megabyte file is being transferred, the session layer could set a checkpoint every 5
megabytes. In the case of a disconnect or a crash after 52 megabytes have been
transferred, the session could be resumed from the last checkpoint, meaning only 50
more megabytes of data need to be transferred. Without the checkpoints, the entire
transfer would have to begin again from scratch.
4. The transport layer
Layer 4 is responsible for end-to-end communication between the two devices. This
includes taking data from the session layer and breaking it up into chunks called
segments before sending it to layer 3. The transport layer on the receiving device is
responsible for reassembling the segments into data the session layer can consume.
The transport layer is also responsible for flow control and error control. Flow control
determines an optimal speed of transmission to ensure that a sender with a fast
connection doesn’t overwhelm a receiver with a slow connection. The transport layer
performs error control on the receiving end by ensuring that the data received is
complete, and requesting a retransmission if it isn’t.

11. 3. The network layer
The network layer is responsible for facilitating data transfer between two different
networks. If the two devices communicating are on the same network, then the network
layer is unnecessary. The network layer breaks up segments from the transport layer into
smaller units, called packets, on the sender’s device, and reassembling these packets on
the receiving device. The network layer also finds the best physical path for the data to
reach its destination; this is known as routing.
2. The data link layer
The data link layer is very similar to the network layer, except the data link layer
facilitates data transfer between two devices on the SAME network. The data link layer
takes packets from the network layer and breaks them into smaller pieces called frames.
Like the network layer, the data link layer is also responsible for flow control and error
control in intra-network communication (The transport layer only does flow control and
error control for inter-network communications).
1.Physical layer
This layer includes the physical equipment involved in the data transfer, such as the cables
and switches. This is also the layer where the data gets converted into a bit stream, which is a
string of 1s and 0s. The physical layer of both devices must also agree on a signal convention so
that the 1s can be distinguished from the 0s on both devices.
Reference : https://www.imperva.com/learn/application-security/osi-model/

12. Tcp/Ip model:
TCP/IP helps you to determine how a specific computer should be connected to
the internet and how you can transmit data between them. It helps you to create a
virtual network when multiple computer networks are connected together.
TCP/IP stands for Transmission Control Protocol/ Internet Protocol. It is specifically
designed as a model to offer highly reliable and end-to-end byte stream over an
unreliable internetwork

13. The 4 layers of the TCP/IP model:
TCP/IP functionality is divided into four layers, each of which includes specific protocols:
1. The application layer provides applications with standardized data
exchange. Its protocols include HTTP, FTP,SMIP and Simple Network
Management Protocol. At the application layer, the payload is the actual
application data.
2. The transport layer is responsible for maintaining end-to-end
communications across the network. TCP handles communications between
hosts and provides flow control, multiplexing and reliability. The transport
protocols include TCP and User datagram protocol, which is sometimes used
instead of TCP for special purposes.
3. The network layer, also called the internet layer, deals with packets and
connects independent networks to transport the packets across network
boundaries. The network layer protocols are IP and Internet Control Message
Protocol, which is used for error reporting.
4. The physical layer, also known as the network interface layer or data link
layer, consists of protocols that operate only on a link -- the network
component that interconnects nodes or hosts in the network. The protocols in
this lowest layer include Ethernet for local area network .
TCP/IP model vs. OSI model:
TCP/IP and OSI are the most widely used communication networking protocols. The
main difference is that OSI is a conceptual model that is not practically used for
communication. Rather, it defines how applications can communicate over a network.
TCP/IP, on the other hand, is widely used to establish links and network interaction.

14. The TCP/IP protocols lay out standards on which the internet was created, while the
OSI model provides guidelines on how communication has to be done. Therefore,
TCP/IP is a more practical model.
The TCP/IP and OSI models have similarities and differences. The main similarity is in
the way they are constructed as both use layers, although TCP/IP consists of just four
layers, while the OSI model consists of the following seven layers:
• Layer 7, the application layer, enables the user -- software or human -- to
interact with the application or network when the user wants to read
messages, transfer files or engage in other network-related activities.
• Layer 6, the presentation layer, translates or formats data for the application
layer based on the semantics or syntax that the app accepts.
• Layer 5, the session layer, sets up, coordinates and terminates
conversations between apps.
• Layer 4, the transport layer, handles transferring data across a network and
providing error-checking mechanisms and data flow controls.
• Layer 3, the network layer, moves data into and through other networks.
• Layer 2, the data link layer, handles problems that occur as a result of bit
transmission errors.
• Layer 1, the physical layer, transports data using electrical, mechanical or
procedural interfaces.
Reference : https://www.guru99.com/difference-tcp-ip-vs-osi-
model.html

15. What is digital Modulation :
Modulation is a process by which some characteristics of a carrier wave is varried i.s. accordance
with a moduling signal.
Digital modulation is the process of encoding a digital information signal into the
amplitude, phase, or frequency of the transmitted signal.
There are many types of digital modulation techniques and also their combinations,
depending upon the need. Of them all, we will discuss the prominent ones.
ASK – Amplitude Shift Keying
The amplitude of the resultant output depends upon the input data whether it should be
a zero level or a variation of positive and negative, depending upon the carrier frequency.
FSK – Frequency Shift Keying
The frequency of the output signal will be either high or low, depending upon the input
data applied.
PSK – Phase Shift Keying
The phase of the output signal gets shifted depending upon the input. These are mainly
of two types, namely Binary Phase Shift Keying BPSKBPSK and Quadrature Phase
Shift Keying QPSKQPSK, according to the number of phase shifts. The other one is
Differential Phase Shift Keying DPSKDPSK which changes the phase according to the
previous value.
Reference:
https://www.tutorialspoint.com/digital_communication/digital_comm
unication_digital_modulation_techniques.htm
Difference Between Baseband vs Broadband

16. Factor Baseband Broadband
The signal used for
transmission.
The baseband
transmits the digital
signal using the
physical medium like
wires.
The broadband
transmits the analog
signals using optical
fibers and twisted
cables as a medium of
transmission.
Transmission
direction
The baseband
signaling is termed as
bidirectional and is
capable of sending
digital signals in both
directions.
The broadband
signaling is termed as
bidirectional and is
capable of sending
digital signals in only
one direction.
Encoding scheme
used
The baseband
signaling used
The broadband
signaling used

17. Manchester encoding
scheme while
transmitting the digital
signals.
Manchester encoding
scheme while
transmitting the analog
signals.
Range of signals The baseband
transmission can
transmit the digital
signals over a short
distance only when
compared to
broadband
transmission. If the
digital signals need to
be transmitted for a
long distance, the
The broadband
transmission can
transmit the analog
signals over a long
distance compared to
baseband transmission,
and for transmitting
the signals, no need for
attenuation technique
is required.

18. attenuation process is
required.
Topology used The baseband
transmission uses the
bus topology as the
application.
The broadband
transmission uses the
tree and bus topology
as the application.
A number of data
streams transmitted.
The baseband
transmission can
transmit the single
data type stream at
one glance and can
send in bidirectional.
The broadband
transmission can
transmit multiple data
streams at the same
time but in one
direction only.
Medium of transfer The baseband signals
used twisted-pair
cables, coaxial cables
The broadband signals
used optical fiber
cables, coaxial cables,

19. and wires as a medium
of transmitting digital
signals.
and radio waves to
transmit the analog
signals.
Application The baseband
transmission is mostly
used for the LAN
networks as the
baseband signaling can
transmit the digital
signal for a short
distance only. And
there is a requirement
of repeaters for
transmitting the
signals.
Broadband
transmission is mostly
used for telephone
networks. The
broadband signaling
can transmit the
analog signals for
long-distance without
using any external
device like a repeater
or attenuator.

20. Transmission Impairment :
Transmission Impairments:
In communication system, analog signals travel through transmission media, which
tends to deteriorate the quality of analog signal, which means that the signal at the
beginning of the medium is not the same as the signal at the end of the medium. The
imperfection causes signal impairment. Below are the causes of the impairment.
There are three types of transmission impairments: attenuation, delay distortion, and
noise.
Attenuation – It means loss of energy. The strength of signal decreases with
increasing distance which causes loss of energy in overcoming resistance of medium.
This is also known as attenuated signal. Amplifiers are used to amplify the attenuated
signal which gives the original signal back and compensate for this loss.
Distortion – It means changes in the form or shape of the signal. This is generally
seen in composite signals made up with different frequencies. Each frequency
component has its own propagation speed travelling through a medium. And thats why
it delay in arriving at the final destination Every component arrive at different time
which leads to distortion. Therefore, they have different phases at receiver end from
what they had at senders end.
Noise – The random or unwanted signal that mixes up with the original signal
is called noise. There are several types of noise such as induced noise,
crosstalk noise, thermal noise and impulse noise which may corrupt the signal.
Reference :
https://www.google.com/amp/s/www.geeksforgeeks.org/transmission-
impairment-in-data-communication/amp/