Data Communication Class Note

1. Data Communication lecture note
Abul Kalam Robin
September 10, 2021
Contents
1 Class 1 2
1.1 Data Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Type of internet connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Data Transmission modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 Network types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.5 Network devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.6 Network addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Class 2 6
2.1 OSI Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 TCP/IP model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Class 3 9
3.1 Digital modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4 Class 4 11
4.1 Difference between Broadband and Baseband . . . . . . . . . . . . . . . . . . . . 11
4.2 Transmission Impairment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5 Class 5 13
5.1 Line Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2 Encapsulation/De-capsulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2. 1 Class 1
1.1 Data Communication
Data communications refers to the transmission of this digital data between two or more computers
and a computer network or data network is a telecommunications network that allows computers
to exchange data. The physical connection between networked computing devices is established
using either cable media or wireless media. The best-known computer network is the Internet.
1.2 Type of internet connection
• Internet: The Internet is a globally-connected network of computers that enables people to
share information and communicate with each other.
• Intranet: An intranet, on the other hand, is a local or restricted network that enables people
to store, organize, and share information within an organization.
1.3 Data Transmission modes
• Simplex: In simplex transmission mode, the communication between sender and receiver
occurs in only one direction. The sender can only send the data, and the receiver can only
receive the data. The receiver cannot reply to the sender. Simplex transmission can be
thought of as a one-way road in which the traffic travels only in one direction—no vehicle
coming from the opposite direction is allowed to drive through. To take a keyboard / monitor
relationship as an example, the keyboard can only send the input to the monitor, and the
monitor can only receive the input and display it on the screen. The monitor cannot reply, or
send any feedback, to the keyboard.
• Half-duplex: The communication between sender and receiver occurs in both directions in
half duplex transmission, but only one at a time. The sender and receiver can both send and
receive the information, but only one is allowed to send at any given time. Half duplex is
still considered a one-way road, in which a vehicle traveling in the opposite direction of the
traffic has to wait till the road is empty before it can pass through. For example, in walkie-
talkies, the speakers at both ends can speak, but they have to speak one by one. They cannot
speak simultaneously.
• Full-duplex: In full duplex transmission mode, the communication between sender and re-
ceiver can occur simultaneously. The sender and receiver can both transmit and receive at the
same time. Full duplex transmission mode is like a two-way road, in which traffic can flow
in both directions at the same time. For example, in a telephone conversation, two people
communicate, and both are free to speak and listen at the same time.
Reference: https://techcomputerscience.com/simplex-half-duplex-full-duplex

3. 1.4 Network types
• Personal Area Network(PAN)
The smallest and most basic type of network, a PAN (Personal Area Network) is made up
of a wireless modem, a computer or two, phones, printers, tablets, etc., and revolves around
one person in one building. These types of networks are typically found in small offices or
residences, and are managed by one person or organization from a single device.
• Local Area Network(LAN)
A LAN (local area network) is a group of computers and network devices connected together,
usually within the same building. By definition, the connections must be high speed and
relatively inexpensive. Most Indiana University Bloomington departments are on LANs.
• Metropolitan Area Network(MAN)
A MAN (metropolitan area network) is a larger network that usually spans several buildings
in the same city or town. The IUB network is an example of a MAN.
• Wide Area Network(WAN)
A WAN (wide area network), in comparison to a MAN, is not restricted to a geographical
location, although it might be confined within the bounds of a state or country. A WAN
connects several LANs, and may be limited to an enterprise or accessible to the public. The
technology is high speed and relatively expensive. The Internet is an example of a worldwide
public WAN.
Reference: https://www.belden.com/blogs/network-types
1.5 Network devices
Network devices, or networking hardware, are physical devices that are required for communica-
tion and interaction between hardware on a computer network.
1. Hub
Hubs connect multiple computer networking devices together. A hub also acts as a repeater
in that it amplifies signals that deteriorate after traveling long distances over connecting ca-
bles. A hub is the simplest in the family of network connecting devices because it connects
LAN components with identical protocols.
A hub can be used with both digital and analog data, provided its settings have been config-
ured to prepare for the formatting of the incoming data. For example, if the incoming data is
in digital format, the hub must pass it on as packets; however, if the incoming data is analog,
then the hub passes it on in signal form
2. Switch
Switches generally have a more intelligent role than hubs. A switch is a multiport device that
improves network efficiency. The switch maintains limited routing information about nodes
in the internal network, and it allows connections to systems like hubs or routers. Strands
of LANs are usually connected using switches. Generally, switches can read the hardware

4. addresses of incoming packets to transmit them to the appropriate destination.
Using switches improves network efficiency over hubs or routers because of the virtual cir-
cuit capability. Switches also improve network security because the virtual circuits are more
difficult to examine with network monitors. You can think of a switch as a device that has
some of the best capabilities of routers and hubs combined. A switch can work at either
the Data Link layer or the Network layer of the OSI model. A multilayer switch is one that
can operate at both layers, which means that it can operate as both a switch and a router. A
multilayer switch is a high-performance device that supports the same routing protocols as
routers.
3. Router
Routers help transmit packets to their destinations by charting a path through the sea of in-
terconnected networking devices using different network topologies. Routers are intelligent
devices, and they store information about the networks they’re connected to. Most routers
can be configured to operate as packet-filtering firewalls and use access control lists (ACLs).
Routers, in conjunction with a channel service unit/data service unit (CSU/DSU), are also
used to translate from LAN framing to WAN framing. This is needed because LANs and
WANs use different network protocols. Such routers are known as border routers. They
serve as the outside connection of a LAN to a WAN, and they operate at the border of your
network.
4. Repeater
A repeater is an electronic device that amplifies the signal it receives. You can think of
repeater as a device which receives a signal and retransmits it at a higher level or higher
power so that the signal can cover longer distances, more than 100 meters for standard LAN
cables. Repeaters work on the Physical layer.
Reference: https://blog.netwrix.com/2019/01/08/network-devices-explained
1.6 Network addressing
A network address is any logical or physical address that uniquely distinguishes a network node
or device over a computer or telecommunications network. It is a numeric/symbolic number or
address that is assigned to any device that seeks access to or is part of a network.
• Types of network addressing
1. Physical address/MAC address (48 bit): MAC address is the physical address, which
uniquely identifies each device on a given network. To make communication between
two networked devices, we need two addresses: IP address and MAC address. It is
assigned to the NIC (Network Interface card) of each device that can be connected to
the internet.
2. Logical address/IP address (32 bit): An IP address is the identifier that enables your
device to send or receive data packets across the internet. It holds information related
to your location and therefore making devices available for two-way communication.
The internet requires a process to distinguish between different networks, routers, and

5. websites. Therefore, IP addresses provide the mechanism of doing so, and it forms an
indispensable part in the working of the internet. You will notice that most of the IP
addresses are essentially numerical. Still, as the world is witnessing a colossal growth
of network users, the network developers had to add letters and some addresses as
internet usage grows.
• IP address class
An IP (Internet Protocol) address is a numerical label assigned to the devices connected to
a computer network that uses the IP for communication. IP address act as an identifier for
a specific machine on a particular network. It also helps you to develop a virtual connec-
tion between a destination and a source. The IP address is also called IP number or internet
address. It helps you to specify the technical format of the addressing and packets scheme.
Most networks combine TCP with IP.
IP Class
1 - 126 A
128 - 191 B
192 - 223 C
224 - 239 D
240 - 255 E
ipv4 classes
Reference: https://study-ccna.com/classes-of-ip-addresses

6. 2 Class 2
2.1 OSI Model
1. Physical: The lowest layer of the OSI Model is concerned with electrically or optically
transmitting raw unstructured data bits across the network from the physical layer of the
sending device to the physical layer of the receiving device. It can include specifications
such as voltages, pin layout, cabling, and radio frequencies. At the physical layer, one
might find “physical” resources such as network hubs, cabling, repeaters, network adapters
or modems.
2. Data link: At the data link layer, directly connected nodes are used to perform node-to-node
data transfer where data is packaged into frames. The data link layer also corrects errors that
may have occurred at the physical layer.
The data link layer encompasses two sub-layers of its own. The first, media access control
(MAC), provides flow control and multiplexing for device transmissions over a network.
The second, the logical link control (LLC), provides flow and error control over the physical
medium as well as identifies line protocols.
3. Network: The network layer is responsible for receiving frames from the data link layer,
and delivering them to their intended destinations among based on the addresses contained
inside the frame. The network layer finds the destination by using logical addresses, such as
IP (internet protocol). At this layer, routers are a crucial component used to quite literally
route information where it needs to go between networks.
4. Transport: The transport layer manages the delivery and error checking of data packets. It
regulates the size, sequencing, and ultimately the transfer of data between systems and hosts.
One of the most common examples of the transport layer is TCP or the Transmission Control
Protocol.
5. Session: The session layer controls the conversations between different computers. A ses-
sion or connection between machines is set up, managed, and termined at layer 5. Session
layer services also include authentication and reconnections.
6. Presentation: The presentation layer formats or translates data for the application layer
based on the syntax or semantics that the application accepts. Because of this, it at times also
called the syntax layer. This layer can also handle the encryption and decryption required by
the application layer.
7. Application: At this layer, both the end user and the application layer interact directly with
the software application. This layer sees network services provided to end-user applica-
tions such as a web browser or Office 365. The application layer identifies communication
partners, resource availability, and synchronizes communication.
Reference: https://www.forcepoint.com/cyber-edu/osi-model

7. 2.2 TCP/IP model
1. Physical Layer
This layer corresponds to the combination of Data Link Layer and Physical Layer of the OSI
model. It looks out for hardware addressing and the protocols present in this layer allows for
the physical transmission of data.
We just talked about ARP being a protocol of Internet layer, but there is a conflict about
declaring it as a protocol of Internet Layer or Network access layer. It is described as residing
in layer 3, being encapsulated by layer 2 protocols.
2. Network Layer
This layer parallels the functions of OSI’s Network layer. It defines the protocols which
are responsible for logical transmission of data over the entire network. The main protocols
residing at this layer are :
(a) IP – stands for Internet Protocol and it is responsible for delivering packets from the
source host to the destination host by looking at the IP addresses in the packet headers.
IP has 2 versions:
IPv4 and IPv6. IPv4 is the one that most of the websites are using currently. But IPv6
is growing as the number of IPv4 addresses are limited in number when compared to
the number of users.
(b) ICMP – stands for Internet Control Message Protocol. It is encapsulated within IP
datagrams and is responsible for providing hosts with information about network prob-
lems.
(c) ARP – stands for Address Resolution Protocol. Its job is to find the hardware address
of a host from a known IP address. ARP has several types: Reverse ARP, Proxy ARP,
Gratuitous ARP and Inverse ARP.
3. Transport Layer
This layer is analogous to the transport layer of the OSI model. It is responsible for end-to-
end communication and error-free delivery of data. It shields the upper-layer applications
from the complexities of data. The two main protocols present in this layer are :
(a) Transmission Control Protocol (TCP) – It is known to provide reliable and error-
free communication between end systems. It performs sequencing and segmentation
of data. It also has acknowledgment feature and controls the flow of the data through
flow control mechanism. It is a very effective protocol but has a lot of overhead due to
such features. Increased overhead leads to increased cost.
(b) User Datagram Protocol (UDP) – On the other hand does not provide any such fea-
tures. It is the go-to protocol if your application does not require reliable transport as
it is very cost-effective. Unlike TCP, which is connection-oriented protocol, UDP is
connectionless.

8. 4. Application Layer
This layer performs the functions of top three layers of the OSI model: Application, Pre-
sentation and Session Layer. It is responsible for node-to-node communication and controls
user-interface specifications. Some of the protocols present in this layer are: HTTP, HTTPS,
FTP, TFTP, Telnet, SSH, SMTP, SNMP, NTP, DNS, DHCP, NFS, X Window, LPD. Have a
look at Protocols in Application Layer for some information about these protocols. Protocols
other than those present in the linked article are :
(a) HTTP and HTTPS – HTTP stands for Hypertext transfer protocol. It is used by
the World Wide Web to manage communications between web browsers and servers.
HTTPS stands for HTTP-Secure. It is a combination of HTTP with SSL(Secure Socket
Layer). It is efficient in cases where the browser need to fill out forms, sign in, authen-
ticate and carry out bank transactions.
(b) SSH – SSH stands for Secure Shell. It is a terminal emulations software similar to
Telnet. The reason SSH is more preferred is because of its ability to maintain the
encrypted connection. It sets up a secure session over a TCP/IP connection.
(c) NTP – NTP stands for Network Time Protocol. It is used to synchronize the clocks
on our computer to one standard time source. It is very useful in situations like bank
transactions. Assume the following situation without the presence of NTP. Suppose
you carry out a transaction, where your computer reads the time at 2:30 PM while the
server records it at 2:28 PM. The server can crash very badly if it’s out of sync.
Reference: https://www.geeksforgeeks.org/tcp-ip-model/

9. 3 Class 3
3.1 Digital modulation
Digital-to-Analog signals is the next conversion we will discuss in this chapter. These techniques
are also called as Digital Modulation techniques.
Digital Modulation provides more information capacity, high data security, quicker system avail-
ability with great quality communication. Hence, digital modulation techniques have a greater
demand, for their capacity to convey larger amounts of data than analog modulation techniques.
1. ASK(Amplified 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.
• Signal on = 1
• Signal off = 0
2. FSK(Frequency Shift Keying): The frequency of the output signal will be either high or
low, depending upon the input data applied.
• 1 — High Frequency
• 0 — Low Frequency
3. 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 BPSK and
Quadrature Phase Shift Keying QPSK, according to the number of phase shifts. The other
one is Differential Phase Shift Keying DPSK which changes the phase according to the
previous value. Router or Brouter
• BPSK(Binary Phase Shift Keying): Two face data communication. 0-180/180-0 de-
gree.
• QPSK(Quadrature Phase Shift Keying): Four face data communication. 0/90/180/270
degree.
Reference: https://www.tutorialspoint.com/digitalmodulationtechniques.htm
3.2 Signals
A signal is an electromagnetic or electrical current that carries data from one system or network to
another. In electronics, a signal is often a time-varying voltage that is also an electromagnetic wave
carrying information, though it can take on other forms, such as current. There are two main types
of signals used in electronics: analog and digital signals. This article discusses the corresponding
characteristics, uses, advantages and disadvantages, and typical applications of analog vs. digital
signals.

10. 1. 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.
Analog signal
2. 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. With
digital signals, the physical quantity representing the information can be many things:
(a) Variable electric current or voltage
(b) Phase or polarization of an electromagnetic field
(c) Acoustic pressure
(d) The magnetization of a magnetic storage media
Digital signal

11. 4 Class 4
4.1 Difference between Broadband and Baseband
1. Baseband
• Baseband technology uses digital signals in data transmission.
• It sends binary values directly as pulses of different voltage levels.
• Support the bidirectional communication, this technology uses two separate electric
circuits together; one for sending and another for receiving.
• Frequency division multiplexing is not possible.
• Example: Ethernet is using Baseband for LAN.
2. Broadband
• Broadband technology uses wave signal (ASK, FSK, PSK).
• Broadband has more speed than Baseband.
• It transfers data as frequency division multiplexing.
• Signal traveling distance is long.
• Simultaneous transmission of multiple signals over different frequencies.
• Example: Used to transmit cable TV to premises.
4.2 Transmission Impairment
1. Attenuation
Here attenuation Means loss of energy that is the weaker signal. Whenever a signal trans-
mitted through a medium it loses its energy, so that it can overcome by the resistance of the
medium.
• That is why a wire carrying electrical signals gets warm, if not hot, after a while. Some
of the electrical energy is converted to heat in the signal.
• Amplifiers are used to amplify the signals to compensate for this loss.
• A signal has lost or gained its strength, for this purpose engineers use the concept of
decibel(dB).
• Decibel is used to measure the relative strengths of two signals or a signal at two dif-
ferent points.
• If a signal is attenuated then dB is negative and if a signal is amplified so the db is
positive.
Attenuation(dB) = 10log10(P2/P1)
where P2 and P1 are the power of a signal at points1 and 2.

12. 2. Distortion
If a signal changes its form or shape, it is referred to as distortion. Signals made up of
different frequencies are composite signals. Distortion occurs in these composite signals.
• Each component of frequency has its propagation speed traveling through a medium
and therefore, different components have different delay in arriving at the final destina-
tion.
• It means that signals have different phases at the receiver than they did at the source.
3. Noise
Noise is another problem. There are some random or unwanted signals mix up with the
original signal is called noise. Noises can corrupt the signals in many ways along with the
distortion introduced by the transmission media.
Different types of noises are:
(a) Thermal noise
(b) Inter-modulation noise
(c) Crosstalk
(d) Impulse noise
Reference: https://www.includehelp.com/computer-networks/transmission-impairment.aspx

13. 5 Class 5
5.1 Line Coding
In telecommunication, a line code (also called baseband modulation also called digital baseband
transmission method) is a code chosen for use within a communication system for baseband trans-
mission purposes. Line coding is often used for digital data transport. Binary 1’s and 0’s, such as
in PCM signaling, may be represented in various serial-bit signaling formats called line codes.
1. Polar NRZ: Also called NRZ-L where L denotes the normal logic level assignment.
2. Bipolar RZ: Also called RZ-AMI, where AMI denotes alternate mark (binary 1) inversion.
3. Bipolar NRZ: also called NRZ-M, where M denotes inversion on mark (binary 1).
4. Unipolar signaling: In positive-logic unipolar signaling, the binary 1 is represented by a high
level (+A volts) and a binary 0 by a zero level. This type of signaling is also called on-off
keying (OOK).
5.2 Encapsulation/De-capsulation
• Encapsulation: Data Encapsulation is the process in which some extra information is added
to the data item to add some features to it. We use either the OSI or the TCP/IP model in
our network, and the data transmission takes place through various layers in these models.
Data encapsulation adds the protocol information to the data so that data transmission can
take place in a proper way. This information can either be added in the header or the footer
of the data.
• De-capsulation: Data De-encapsulation is the reverse process of data encapsulation. The
encapsulated information is removed from the received data to obtain the original data. This
process takes place at the receiver’s end. The data is de-encapsulated at the same layer at
the receiver’s end to the encapsulated layer at the sender’s end. The added header and trailer
information are removed from the data in this process.

14. Reference: https://www.tutorialspoint.com/digitalcommunication/digitalcommunicationlinecodes.htm
Reference: https://afteracademy.com/blog/what-is-data-encapsulation-and-de-encapsulation