This document provides an overview of data communication and computer networks. It discusses various topics related to transmission media and switching, including guided transmission media like twisted pair cable and coaxial cable, unguided transmission media like radio waves and infrared, and multiplexing and switching techniques. Specifically, it describes the characteristics of twisted pair cable, coaxial cable, and fiber optic cable. It provides details on the core components and propagation modes of fiber optic cable. Overall, the document presents information on different types of transmission media and switching concepts relevant to data communication and computer networks.

1. SEMESTER : IV
SUBJECT : Data Communication & Computer Network
UNIT - II : Transmission Media & Switching
PRESENTED BY: MR. AAKASH YADAV
ARMIET/AN/SEM-4/DCC

2. 2.1 Communication Media: Guided Transmission Media Twisted-
Pair Cable, Coaxial Cable Fiber-Optic Cable
2.2 Unguided Transmission Media: Radio Waves, Microwave,
Infrared Satellite
2.3 Lin-of-Sight Transmission Point to Point, Broadcasting.
2.4 Multiplexing: Frequency-Division Multiplexing, Time –
Division Multiplexing
2.5 Switching: Circuit-switched networks, Packet -switched
networks
Contents :
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Communication Media
•Transmission media means a communication signal is carried from one computer
system to another
•The physical path over which the information flows from transmitter to receiver is
called the transmission medium/communication media
•The transmission medium is usually free space, metallic cable or fiber-optic cable.
Need of Transmission/Communication Media:
1) Transmission media are needed for interacting with the devices.
2) Without transmission media communication cannot take place.
3) Communication media is the middle part of sender and receiver.
4) Transmission media is needed for faster communication.
5) It is needed for reliable delivery of data with efficient methods.
6) Transmission media is needed for secure transmission of data.

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Guided Transmission Media
Guided media are also known as wired or bounded media. These media consist of wires
through which the data is transferred. Guided media is a physical link between
transmitter and recipient devices. Signals are directed in a narrow pathway using
physical links. These media types are used for shorter distances since physical limitation
limits the signal that flows through these transmission media.
Twisted Pair Cable
In this type of transmission media, two insulated conductors of a single circuit are
twisted together to improve electromagnetic compatibility. These are the most widely
used transmission medium cables. These are packed together in protective sheaths. They
reduce electromagnetic radiation from pairs and crosstalk between the neighbouring
pair. Overall, it improves the rejection of external electromagnetic interference. These
are further subdivided into unshielded and shielded twisted pair cables.

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Each of the twisted pairs act as a single communication link. The use of twisted
configuration minimises the effect of electrical interference from similar pairs close by.
Twisted pairs are less expensive and most commonly used in telephone lines and LANs.
These cables are of two types: Unshielded twisted-pair (UTP) and Shielded twisted-pair
(STP)
a. Unshielded Twisted Pair Cable(UTP): These consist of two insulated copper wires
that are coiled around one another. These types of transmission media block interference
without depending on any physical shield. The unshielded twisted pair are very affordable
and are simple to set up. These provide a high-speed link.

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b. Shielded Twisted Pair (STP): This twisted cable consisted of a foil shield to block
external interference. The insulation within these types of the twisted cable allow
greater data transmission rate. These are used in fast-data-rate Ethernet and in data and
voice channels of telephone lines.

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UTP STP
UTP stands for Unshielded Twisted Pair. STP stands for Shielded Twisted Pair.
In UTP grounding cable is not necessary. While in STP grounding cable is required.
Data rate in UTP is slow compared to STP. Data rate in STP is high.
The cost of UTP is less. While STP is costlier than UTP.
In UTP much more maintenance is not needed. While in STP much more maintenance is needed.
In UTP noise is high compared to STP. While in STP noise is less.
In UTP, speed offered is about 10 to up to 1000
Mbps.
While in STP speed offered is about 10 to up to
100 Mbps.
It is used for data transmission within short
distance such as for home and office networks.
Generally used for connecting organizations over
a long distance.
Usage-
•Telephone wiring
•Local Area Networks and more.
Usage-
•Used in frigid temperatures.
•Used in case of lot of heat generation like for
heavy industrial applications.
•Employed under high radiation conditions and
more.

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Coaxial Cable
A coaxial cable is an electrical cable with a copper conductor and an insulator shielding
around it and a braided metal mesh that prevents signal interference and cross talk.
Coaxial cable is also known as coax.
The core copper conductor is used for the transmission of signals and the insulator is
used to provide insulation to the copper conductor and the insulator is surrounded by a
braided metal conductor which helps to prevent the interference of electrical signals and
prevent cross talk. This entire setup is again covered with a protective plastic layer to
provide extra safety to the cable.
Outer jacket Foil shield Center conductor
Braided shield Dielectric medium

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1. Central Conductor: A central conductor, which consists of copper. The conductor is
the point at which data transmits.
2. Dielectric Insulator: Dielectric plastic insulation around the copper conductor. it is
used to maintain the spacing between the center conductor and shield.
3. Braided shield: A braided mesh of copper helps to shield from electromagnetic
interference, The braid provides a barrier against EMI moving into and out of the
coaxial cable.
4. Foil shield: Although not always present on coaxial cables, the foil shield serves to
protect from Radio Frequency Interference (RFI). Foil shields are almost always made
of aluminium foil & simply wrap around the inner parts of cable. Unlike braided
shields, which have a percentage coverage, foil shields always cover 100%
5. Outer Jacket: An external polymer layer, which has a plastic coating. It is used to
protect internal layers from damages.

10. Applications of Coaxial cable
The coaxial cables are used in Ethernet LANs and also used in MANs
Television: Coaxial cable used for television would be 75 Ohm and RG-6 coaxial cable.
Internet: Coaxial cables are also used for carrying internet signals, RG-6 cables are used
for this.
CCTV: The coaxial cables are also used in CCTV systems and both RG-59 AND RG-6
cables can be used.
Video: The coaxial cables are also used in video Transmission the RG-6 is used for better
digital signals and RG-59 for lossless transmission of video signals.
HDTV: The HDTV uses RG-11 as it provides more space for signals to transfer.
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Advantages
•Coaxial cables support high bandwidth.
•It is easy to install coaxial cables.
•coaxial cables have better cut-through resistance so they are more reliable and
durable.
•Less affected by noise or cross-talk or electromagnetic inference.
•Coaxial cables support multiple channels
Disadvantages
•Coaxial cables are expensive.
•The coaxial cable must be grounded in order to prevent any crosstalk.
•As a Coaxial cable has multiple layers it is very bulky.
•There is a chance of breaking the coaxial cable and attaching a “t-joint” by
hackers, this compromises the security of the data.

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Fiber Optics Cable
An Optical Fiber is a cylindrical fiber of glass which is hair thin size or any transparent
dielectric medium. The fiber which is used for optical communication is waveguides
made of transparent dielectrics.
Strengthening Fibers Cladding
Cable jacket Coating Core

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Core: It is the central tube of very thin size made of optically transparent
dielectric medium and carries the light transmitter to receiver and the core
diameter may vary from about 5 micron to 100 micron.
Cladding: It is outer optical material surrounding the core having reflecting
index lower than core and cladding helps to keep the light within the core
throughout the phenomena of total internal reflection.
Coating: This is a layer of plastic that surrounds the core & cladding to
reinforce & protect the fibre core. Coating are the measured in microns & can
range from 250 to 900 microns.
Strengthening Fibres: These components help protect the core against crushing
forces & excessive tension during installation.
Cable Jacket: This is the outer layer of fiber optic cable. Most fibre optic cables
have an orange jacket, although some types can have black or yellow jackets.

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Propagation Modes:
•An optical fiber guides light waves in distinct patterns called modes. Mode describes the
distribution of light energy across the fiber.
•In fiber optics terminology, the word mode simply means "path“. If them is only one
path for light rays to take down a cable, it is called as single mode. If there is more than
one path, it is called as multi mode
•Multi mode can be implemented in two forms i. e. step index or graded-index.
1. Multimode: Multimode is so named because multiple beams from a light source move
through the core in different paths.
Multimode step index fiber, the density of the core remains constant from the center to
the edges. A beam of light moves through this constant density in a straight line until it
reaches the Interface of the core and the cladding. At the interface, there is an abrupt
change due to a lower density; this alters the angle of the beam's motion.
(i) The term step index refers to the suddenness of this change, which contributes to the
distortion of the signal as it passes through the fiber.
(ii) A graded index fiber therefore is one with varying densities. Density is higher at the
center of the core and decreases gradually to its lowest at the edge.
2. Single Mode: Single mode uses step index fiber and a highly focussed source of light
that limits beams to a small range of angles, all close to the horizontal

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Multimode, Step Index
Multimode, Graded Index
Single Mode

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Advantages of Fiber-optic Cable:
1. Higher data rate than TP and coaxial cable.
2. Less signal attenuation.
3. Noise resistance.
4. Light weight.
5. More immune to tapping (or Security).
6. More Reliability.
7. Long distance.
Disadvantages of Fiber-optic Cable:
1. Installation and maintenance need expertise that is not yet available
everywhere.
2. Propagation of light is unidirectional.
3. Fiber-optic cable is more expensive.
4. Limited physical arc of cable of cable.

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Applications of Fiber-optic Cable:
1. Medical: Used as light guides, imaging tools and also as lasers for surgeries.
2. Defence/Government: Used as hydrophones for seismic and SONAR uses,
as wiring in aircraft, submarines and other vehicles and also for field
networking.
3. Data storage: Used for data transmission.
4. Telecommunications: Fiber is laid and used for transmitting and receiving
purposes.
5. Networking: Used to connect users and servers in a variety of network
settings and helpincrease the speed and accuracy of data transmission.
6. Broadcast: Broadcast/cable companies are using fiber optic cables for wiring
CATV, HDTV, internet, video on-demand and other applications.

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Characteristics Twisted pair cable Co-axial cable Optical fiber cable
Signal
transmission
Takes place in the electrical
form over the metallic
conducting wires.
Takes place in the electrical
form over the inner conductor
of the cable.
Takes place in an optical form
over glass fiber.
Consists of
Pair of insulated copper
wires
Requires 4 components from
inner to outer-
•Solid conductor wire
•Layer of insulation
•Grounding conductor
•Layer of exterior insulation.
Bundling of very thin optical
fibers made up of glass or
plastic in a single cable.
Installation and
Implementation
Simple and easy Relatively difficult Difficult

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Characteristics Twisted pair cable Co-axial cable Optical fiber cable
External
magnetic field
Affected due to external
magnetic field.
The external magnetic field is
less affected.
The external magnetic field is
not affected.
Cause of power
Power loss due to conduction
and radiation.
Power loss due to conduction.
power loss due to absorption,
scattering, and bending.
Diameter
Large diameter than Optical
fiber cable.
Large diameter than Optical
fiber cable.
Small diameter
Bandwidth
The twisted-pair cable has
low bandwidth.
Co-axial cable has moderately
high bandwidth.
Optical fiber cable has a very
high bandwidth.
Electro-
-magnetic
interference
(EMI)
EMI can take place. EMI is reduced to shielding. EMI is not present.

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Characteristics Twisted pair cable Co-axial cable Optical fiber cable
Installation Easy installation. Fairly easy installation. Difficult to install.
Attenuation
In twisted pair cable has very
high attenuation.
In coaxial cable has low
attenuation.
In optical fiber cable has very
low attenuation.
Data rate
Twisted pair cable supports a
low data rate.
Moderately high data rate. Very high data rate.
Noise immunity
Twisted pair cable has low
noise immunity.
Co-axial cable has higher noise
immunity.
Optical fiber cable has the
highest noise immunity.
Cost The cost is very low. Cost is moderate Cost is expensive.
Repeater
Spacing
Repeater spacing is 2-10 km. Repeater spacing is 1-10 km. Repeater spacing is 10-100 km.
Security
Security is not guaranteed of
the transmitted signal.
Security is not guaranteed of
the transmitted signal.
Security is guaranteed of the
transmitted signal.

21. Characteristics Twisted pair cable Co-axial cable Optical fiber cable
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Types
•Unshielded Twisted Pair
(UTP)
•Shielded Twisted Pair
(STP)
•RG59
•RG6
•Single mode fiber (SMF)
•Multimode fiber (MMF)
Power loss
Reasons-conduction and
radiation
Reasons- absorption, scattering
dispersion and bending
Reasons-conduction

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UnGuided Transmission
•An unguided transmission transmits the electromagnetic waves without using
any physical medium. Therefore it is also known as wireless transmission.
•In unguided media, air is the media through which the electromagnetic energy
can flow easily.

23. Radio waves
•Radio waves are the electromagnetic waves that are transmitted in all the directions of
free space.
•Radio waves are omnidirectional, i.e., the signals are propagated in all the directions.
•The range in frequencies of radio waves is from 3Khz to 1 khz.
•In the case of radio waves, the sending and receiving antenna are not aligned, i.e., the
wave sent by the sending antenna can be received by any receiving antenna.
•An example of the radio wave is FM radio.
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Applications Of Radio waves:
•A Radio wave is useful for multicasting when there is one sender and many receivers.
•An FM radio, television, cordless phones are examples of a radio wave.
Advantages Of Radio transmission:
•Radio transmission is mainly used for wide area networks and mobile cellular phones.
•Radio waves cover a large area, and they can penetrate the walls.
•Radio transmission provides a higher transmission rate.
Disadvantages Of Radio transmission:
•Travel in a straight line, so repeater stations may be needed.
•Limited number of free frequency bands.
•Greater power consumption
•Limited spectrum of frequency

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Microwaves
Microwaves are of two types:
•Terrestrial microwave
•Satellite microwave communication

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Terrestrial Microwave Transmission
•Terrestrial Microwave transmission is a technology that transmits the focused
beam of a radio signal from one ground-based microwave transmission antenna to
another.
•Microwaves are the electromagnetic waves having the frequency in the range
from 1GHz to 1000 GHz.
•Microwaves are unidirectional as the sending and receiving antenna is to be
aligned, i.e., the waves sent by the sending antenna are narrowly focussed.
•In this case, antennas are mounted on the towers to send a beam to another
antenna which is km away.
•It works on the line of sight transmission, i.e., the antennas mounted on the
towers are the direct sight of each other.

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Characteristics of Microwave:
•Frequency range: The frequency range of terrestrial microwave is from 4-6
GHz to 21-23 GHz.
•Bandwidth: It supports the bandwidth from 1 to 10 Mbps.
•Short distance: It is inexpensive for short distance.
•Long distance: It is expensive as it requires a higher tower for a longer
distance.
•Attenuation: Attenuation means loss of signal. It is affected by environmental
conditions and antenna size.

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Advantages Of Microwave:
•Microwave transmission is cheaper than using cables.
•It is free from land acquisition as it does not require any land for the installation of cables.
•Microwave transmission provides an easy communication in terrains as the installation of
cable in terrain is quite a difficult task.
•Communication over oceans can be achieved by using microwave transmission.
Disadvantages of Microwave transmission:
•Eavesdropping: An eavesdropping creates insecure communication. Any malicious user
can catch the signal in the air by using its own antenna.
•Out of phase signal: A signal can be moved out of phase by using microwave
transmission.
•Susceptible to weather condition: A microwave transmission is susceptible to weather
condition. This means that any environmental change such as rain, wind can distort the
signal.
•Bandwidth limited: Allocation of bandwidth is limited in the case of microwave
transmission.

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Satellite Microwave Communication
•A satellite is a physical object that revolves around the earth at a known height.
•Satellite communication is more reliable nowadays as it offers more flexibility than cable
and fibre optic systems.
•We can communicate with any point on the globe by using satellite communication.
How Does Satellite work?
The satellite accepts the signal that is transmitted from the earth station, and it amplifies the
signal. The amplified signal is retransmitted to another earth station.

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Advantages Of Satellite Microwave Communication:
•The coverage area of a satellite microwave is more than the terrestrial microwave.
•The transmission cost of the satellite is independent of the distance from the centre of the
coverage area.
•Satellite communication is used in mobile and wireless communication applications.
•It is easy to install.
•It is used in a wide variety of applications such as weather forecasting, radio/TV signal
broadcasting, mobile communication, etc.
Disadvantages Of Satellite Microwave Communication:
•Satellite designing and development requires more time and higher cost.
•The Satellite needs to be monitored and controlled on regular periods so that it remains in
orbit.
•The life of the satellite is about 12-15 years. Due to this reason, another launch of the
satellite has to be planned before it becomes non-functional.

31. Infrared
•An infrared transmission is a wireless technology used for communication over short
ranges.
•The frequency of the infrared in the range from 300 GHz to 400 THz.
•It is used for short-range communication such as data transfer between two cell phones,
TV remote operation, data transfer between a computer and cell phone resides in the same
closed area.
Characteristics Of Infrared:
•It supports high bandwidth, and hence the data rate will be very high.
•Infrared waves cannot penetrate the walls. Therefore, the infrared communication in one
room cannot be interrupted by the nearby rooms.
•An infrared communication provides better security with minimum interference.
•Infrared communication is unreliable outside the building because the sun rays will
interfere with the infrared waves.
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Advantages:
1. Simple circuit and cheap in cost.
2. Low power consumption.
3. No licenses needed.
4. Higher security
5. Portable.
Disadvantages:
1. Works only on Line-Of-Sight (LOS) mode.
2. Short range.
3. Blocked by common materials: people, walls, etc.
4. Low bandwidth.
5. Speed is comparatively slow.

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Sr. No. Guided Media Unguided Media
1.
In guided media, the signal energy
communicates via wires.
In unguided media, the signal energy
communicates through the air.
2.
Guided media is generally preferred when we
want to execute direct communication.
Unguided media is generally preferred for radio
broadcasting in all directions.
3.
The guided media formed the different network
topologies.
The unguided media formed the continuous
network topologies.
4.
Here, the signals are in the state of current and
voltage.
Here, the signals are in the state of
electromagnetic waves.
5.
In the case of guided media, the transmission
capacity can be boosted by counting more wires.
In the case of unguided media, it is not feasible to
acquire more capacity.
6.
Open Wire, Twisted Pair, Coaxial Cable, and
Optical Fibre are the different kinds of guided
media.
Microwave Transmission, Radio Transmission,
and Infrared Transmission are the types of
unguided media.

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Line of Sight (LOS) Propagation
Among the modes of propagation, this line-of-sight propagation is the one, which we
commonly notice. In the line-of-sight communication, as the name implies, the wave
travels a minimum distance of sight. Which means it travels to the distance up to which a
naked eye can see. Now what happens after that? We need to employ an amplifier cum
transmitter here to amplify the signal and transmit again.
This is better understood with the help of the following diagram.
The figure depicts this mode of propagation very clearly. The line-of-sight propagation will
not be smooth if there occurs any obstacle in its transmission path. As the signal can travel
only to lesser distances in this mode, this transmission is used for infrared or microwave
transmissions.

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1. Broadcast Networks :
Broadcast networks are also known as terrestrial networks. It is basically a group of radio
stations, television stations, or any other electronic media outlets that simply generate
agreement to air, or broadcast, content generally from a centralized source. Broadcasting
is simply a method of transferring messages to all the recipients simultaneously.
In this network, a message that is sent by a node is received by all the other nodes
connected to the network and share a common medium of communication. Broadcast
networks also avoid procedures of complex routing of switched network by simply
confirming and ensuring that each transmission of nodes is basically received by all the
other nodes in the network. This is the reason why the broadcast network has single
communications channel.
In this network, each receiving station just receives all signals that are sent by
transmitters. Even routing of signals is highly affected passively. These networks
generally have single communication that is shared by all machines present on the
network. Short messages also are known as packets that are sent by any of the machines
present are received by all of the others present over there. Some of the systems of
broadcast also support transmission to subset of machines also known as multicasting. It
just links, in contrast, communication channel that is basically shared by all of machines
in network.

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2.Point-to-PointNetworks:
Point-to-Point Networks or Point-to-Point Connection is type of private data connection
that is connecting securely two or more locations for private data services. It might also be
configured to usually carry voice, internet, and data services together all over same point-
to-point network. It simply refers to type of communication connection among two
endpoints or nodes of communication. It is connection among pairs of machines.
Transmission from point-to-point with one sender and receiver is commonly known as
unicasting.
This network is generally used for two locations that are required to securely send data that
is very sensitive and confidential among each of locations. A point-to-point or P2P (Data
Link) also gives or provides path from one point that is fixed to other point being fixed. It
is very closed network data transport service that does not travel through public Internet.
This network includes various connections among individual pairs of machine. A packet
present on these types of networks might be needed to go through intermediate computers
before they reach desired or destination computer. The packets also need to follow multiple
routes of different length sizes.
Therefore, routing algorithms are very essential and important in point-to-point connection.
This network is generally available in range of bandwidth speeds along with point-to-point
T1, point-to-point Ethernet, or many more.

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Multiplexing is used in cases where the signals of lower bandwidth and the transmitting
media is having higher bandwidth. In this case, the possibility of sending a number of
signals is more. In this, the signals are combined into one and are sent over a link that
has greater bandwidth of media than the communicating nodes.
1. Frequency Division Multiplexing (FDM):
In this, a number of signals are transmitted at the same time, and each source transfers its
signals in the allotted frequency range. There is a suitable frequency gap between the 2
adjacent signals to avoid over-lapping. Since the signals are transmitted in the allotted
frequencies so this decreases the probability of collision. The frequency spectrum is
divided into several logical channels, in which every user feels that they possess a
particular bandwidth. A number of signals are sent simultaneously at the same time
allocating separate frequency bands or channels to each signal. It is used in radio and TV
transmission. Therefore to avoid interference between two successive channels Guard
bands are used.

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Application of FDM:
1.In the first generation of mobile phones, FDM was used.
2.The use of FDM in television broadcasting
3.FDM is used to broadcast FM and AM radio frequencies.

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2. Time Division Multiplexing (TDM):
This happens when the data transmission rate of media is greater than that of the source,
and each signal is allotted a definite amount of time. These slots are so small that all
transmissions appear to be parallel. In frequency division multiplexing all the signals
operate at the same time with different frequencies, but in time-division multiplexing,
all the signals operate with the same frequency at different times.

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It is of the following types:
1. Synchronous TDM:
The time slots are pre-assigned and fixed. This slot is even given if the source is not
ready with data at this time. In this case, the slot is transmitted empty. It is used for
multiplexing digitized voice streams.

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2. Asynchronous (or statistical) TDM:
The slots are allocated dynamically depending on the speed of the source or their ready
state. It dynamically allocates the time slots according to different input channels’
needs, thus saving the channel capacity.

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Circuit Switching Network
In circuit switching network resources (bandwidth) are divided into pieces and bit delay
is constant during a connection. The dedicated path/circuit established between sender
and receiver provides a guaranteed data rate. Data can be transmitted without any delays
once the circuit is established.
Telephone system network is one of the example of Circuit switching. TDM (Time
Division Multiplexing) and FDM (Frequency Division Multiplexing) are two
methods of multiplexing multiple signals into a single carrier.
• Frequency Division Multiplexing : Divides into multiple bands
Frequency Division Multiplexing or FDM is used when multiple data signals are
combined for simultaneous transmission via a shared communication medium. It is a
technique by which the total bandwidth is divided into a series of non-overlapping
frequency sub-bands,where each sub-band carry different signal. Practical use in
radio spectrum & optical fibre to share multiple independent signals.

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• Time Division Multiplexing : Divides into frames
Time-division multiplexing (TDM) is a method of transmitting and receiving
independent signals over a common signal path by means of synchronized switches
at each end of the transmission line. TDM is used for long-distance communication
links and bears heavy data traffic loads from end user.
Time division multiplexing (TDM) is also known as a digital circuit switched.
Advantages of Circuit Switching:
It has the following advantages :
1.The main advantage of circuit switching is that a committed transmission channel is
established between the computers which give a guaranteed data rate.
2.In-circuit switching, there is no delay in data flow because of the dedicated
transmission path.

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Disadvantages of Circuit Switching:
It has the following disadvantages :
1.It takes a long time to establish a connection.
2.More bandwidth is required in setting up dedicated channels.
3.It cannot be used to transmit any other data even if the channel is free as the
connection is dedicated to circuit switching.
Formulas in Circuit Switching :

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Question on Circuit switching –
These questions will help you understand circuit switching
Example 1 : How long it takes to send a file of ‘x bits’ from host A to host B over a
circuit switched network that uses TDM with ‘h slots’ and have a bit rate of ‘R Mbps’,
circuit establish time is k seconds.Find total time?
Explanation :
Transmission rate = Link Rate or Bit rate / no. of slots = R/h bps
Transmission time = size of file/ transmission rate = x / (R/h) = (x*h)/R
Total time = transmission time + circuit setup time = (x*h)/R secs + k secs
Example 2 : If a link transmits F frames/sec and each slot has B bits then find the
transmission rate?
Explanation :
Since it is not mention how many slots in each frame we take one frame has one slot.
The transmission rate is the amount of data sent in 1 second.
Transmission rate = F * B bits/sec

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Packet Switched Network (PSN)
A packet-switched network (PSN) is a kind of computer communications network that
sends data in the form of small packets. It allows the sender to send data or network
packets to the source and destination node over an internet network channel that is
transferred between multiple users and/or applications. A packet-switched is also called a
connectionless network, as it does not create an endless connection between a source and
destination points.
How Packet Switching Works:
In packet switching, the network packet is part of a file. The packet includes one letter of
that email and the path of the email. It also includes a tiny chip of the letter next to it, in
case that letter is lost. The packets are then transferred to the internet. The packets can be
returned to many nodes and switches, going all the way around the world if they have to,
each going their own different ways as internet traffic conditions allow. The data, sent at
nearly the speed of light, makes it to its destination in milliseconds.
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Hop in Networking:
In computer networking, a hop is the duration of the trip of a data packet when a packet
is transferred from a source point to the destination point. Data packets pass via routers
as they cross source and destination. The hop count is defined as the number of network
devices by which the data packets passes from source to destination which is depending
on routing protocol, It may include the source/destination. The first hop is counted as hop
0 or hop 1.

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Network technologies in PSN:
There are many network technologies in PSN. Some of them are given below:
•CS: TDM, PDH, SDH, OTN
•CO: ATM, FR, MPLS, TCP/IP, SCTP/IP
•CL: UDP/IP, IPX, Ethernet, CLNP
Connectionless Forwarding:
A Packet Switched Network is connectionless (CL) for the following reasons:
•When there is no setup is needed before transmitting a packet, each router makes an
independent forwarding decision.
•When Packets are self-describing packets are inserted anywhere and will be properly
forwarded.
•When IP forwarding is detailed in RFC 1812 hundreds of software cycles per packet.

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Circuit Switching Packet Switching
In-circuit switching has there are 3 phases:
i) Connection Establishment.
ii) Data Transfer.
iii) Connection Released.
In Packet switching directly data transfer takes
place.
In-circuit switching, each data unit knows the
entire path address which is provided by the
source.
In Packet switching, each data unit just knows
the final destination address intermediate path
is decided by the routers.
In-Circuit switching, data is processed at the
source system only
In Packet switching, data is processed at all
intermediate nodes including the source
system.
The delay between data units in circuit
switching is uniform.
The delay between data units in packet
switching is not uniform.
Resource reservation is the feature of circuit
switching because the path is fixed for data
transmission.
There is no resource reservation because
bandwidth is shared among users.

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Circuit switching is more reliable. Packet switching is less reliable.
Wastage of resources is more in Circuit
Switching
Less wastage of resources as compared to
Circuit Switching
It is not a store and forward technique. It is a store and forward technique.
Transmission of the data is done by the source.
Transmission of the data is done not only by
the source but also by the intermediate routers.
Congestion can occur during the connection
establishment phase because there might be a
case where a request is being made for a
channel but the channel is already occupied.
Congestion can occur during the data transfer
phase, a large number of packets comes in no
time.
Circuit switching is not convenient for
handling bilateral traffic.
Packet switching is suitable for handling
bilateral traffic.
In-Circuit switching, the charge depends on
time and distance, not on traffic in the network.
In Packet switching, the charge is based on the
number of bytes and connection time.

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Recording of packets is never possible in
circuit switching.
Recording of packets is possible in packet
switching.
In-Circuit Switching there is a physical path
between the source and the destination
In Packet Switching there is no physical path
between the source and the destination
Circuit Switching does not support store and
forward transmission
Packet Switching supports store and forward
transmission
Call setup is required in circuit switching. No call setup is required in packet switching.
In-circuit switching each packet follows the
same route.
In packet switching packets can follow any
route.
The circuit switching network is implemented
at the physical layer.
Packet switching is implemented at the
datalink layer and network layer
Circuit switching requires simple protocols for
delivery.
Packet switching requires complex protocols
for delivery.