Introduction to Data

Communications and Networks

 Introduction to Data Communications
• - What is Data Communication?
• - Importance of Networking
• - Basic Components: Sender, Receiver,
Transmission Medium, Message, Protocol
 Network Types
• - Local Area Network (LAN)
• - Wide Area Network (WAN)
• - Metropolitan Area Network (MAN)
• - Personal Area Network (PAN)
 LAN
• LAN (Local Area Network): A LAN covers a
small geographic area, like a single building or
a campus. It's used for connecting devices
within a limited area, such as computers,
printers, and servers, allowing them to share
resources and information quickly.
 MAN (Metropolitan Area Network):
• MAN (Metropolitan Area Network): A MAN
spans a city or a large campus. It connects
multiple LANs within a city and provides high-
speed data transfer over a larger area than a
LAN. It's commonly used by organizations or
service providers to interconnect various
buildings or branches.
 WAN
• WAN (Wide Area Network): A WAN covers a
broad area, often a country or even global
distances. It connects multiple MANs or LANs
across long distances. The Internet is the most
prominent example of a WAN. WANs typically
use public or leased communication lines.
 PAN
• PAN (Personal Area Network): A PAN is used
for connecting devices within the range of a
person, typically up to 10 meters. It includes
connections between personal devices like
smartphones, tablets, and laptops, often using
technologies like Bluetooth or infrared.
 Network Models
• - Importance of Network Models
• - Overview of Protocol Layering
 Importance of Network Models
• Standardization: Network models provide a framework and set standards for designing and implementing
networks. This ensures interoperability between different systems and devices from various manufacturers.
• Simplification: By breaking down complex network operations into manageable layers, network models simplify
troubleshooting, development, and understanding. Each layer focuses on specific functions, making it easier to
handle and fix issues.
• Modularity: Network models, such as the OSI (Open Systems Interconnection) model, promote modularity by
dividing network processes into distinct layers. This modularity allows for easier upgrades and changes to one
layer without affecting others.
• Interoperability: Models ensure that different types of network hardware and software can work together
seamlessly. This is particularly important in heterogeneous environments where various technologies and
protocols need to interact.
• Communication Protocols: They provide a structured approach to designing and implementing communication
protocols. Each layer of the model defines specific protocols and functions, which helps in creating efficient and
reliable communication systems.
• Educational Tool: Network models serve as an educational framework, helping students and professionals
understand complex networking concepts by breaking them down into simpler, more digestible layers.
• Performance Optimization: By isolating different network functions into layers, models help in optimizing
network performance. Issues can be pinpointed to specific layers, facilitating targeted improvements and
adjustments.
• Documentation and Design: They assist in documenting network architecture and designing new networks by
providing a clear and organized representation of how different components interact.
 Overview of Protocol Layering
• Key Concepts of Protocol Layering
• Layered Architecture:
– Layering involves dividing network protocols into separate layers, each responsible for specific aspects of
communication. The most well-known layered model is the OSI (Open Systems Interconnection) model,
which has seven layers. Another widely used model is the TCP/IP model, which has four layers.
• Encapsulation:
– In layering, each layer adds its own header (or sometimes trailer) to the data from the layer above, a process
known as encapsulation. The resulting package of data is passed down to the next layer. Each layer removes
the headers (or trailers) added by the layer above it as it processes the data.
• Separation of Concerns:
– Each layer has a specific responsibility and interacts with the layers directly above and below it. This
separation of concerns simplifies troubleshooting, development, and understanding of network systems.
• Standard Interfaces:
– Layers communicate with each other through well-defined interfaces, which allows different layers to interact
without needing to know the details of other layers. This modularity ensures that changes in one layer don’t
necessarily affect others.
• Interoperability:
– By standardizing the functions of each layer, protocol layering promotes interoperability between different
systems and devices. It allows different hardware and software to work together by adhering to the same
layer-specific protocols.
 TCP/IP Protocol Suite
• - Layers of TCP/IP
• - Application Layer
• - Transport Layer
• - Internet Layer
• - Network Interface Layer
• TCP/IP Model Layers
• Network Interface Layer: Combines the OSI’s Physical and
Data Link layers, handling the transmission of data over
physical networks.
• Internet Layer: Corresponds to the OSI’s Network layer,
focusing on routing and addressing (e.g., IP).
• Transport Layer: Similar to the OSI’s Transport layer, managing
end-to-end communication and data integrity (e.g., TCP/UDP).
• Application Layer: Encompasses the OSI’s Application,
Presentation, and Session layers, providing services directly to
applications (e.g., HTTP, FTP).
 The OSI Model
• - Layers of the OSI Model
• - Application
• - Presentation
• - Session
• - Transport
• - Network
• - Data Link
• - Physical
 Application Layer
• Key Functions of the Application Layer
• Application Services: It provides network services to applications, such as email, file transfer,
and web browsing. Applications communicate with each other over the network through this
layer.
• Data Representation: The Application Layer often handles data formatting and presentation. It
ensures that the data sent by an application is presented in a format that can be understood by the
receiving application.
• Protocol Specification: This layer defines the protocols that applications use to communicate
over the network. Common protocols include HTTP (Hypertext Transfer Protocol) for web
services, SMTP (Simple Mail Transfer Protocol) for email, and FTP (File Transfer Protocol) for
file transfers.
• Session Management: While session management is more often associated with the Session
Layer in the OSI model, some aspects are handled at the Application Layer. It manages the
initiation, maintenance, and termination of communication sessions between applications.
• Error Handling and Recovery: It can implement mechanisms for error handling and recovery,
ensuring reliable communication between applications.
• User Interface: For many network applications, the Application Layer interacts directly with the
end-user, providing interfaces and experiences through which users can access network services.
 Presentation layer
• Key Uses of the Presentation Layer
• Data Translation: The Presentation Layer converts data between different formats. For example, it
translates data from a format used by the application into a format suitable for the network, and vice
versa. This ensures that data can be interpreted correctly by different systems.
• Data Encryption/Decryption: This layer is responsible for data encryption and decryption, providing
confidentiality and security for data transmitted over the network. It ensures that sensitive information
is protected during transit.
• Data Compression/Decompression: The Presentation Layer handles data compression, reducing the
size of data to optimize network bandwidth. It also decompresses data at the receiving end, ensuring
that the original data is restored.
• Data Serialization/Deserialization: It converts complex data structures (such as objects) into a format
that can be easily transmitted over the network (serialization). At the receiving end, it reconstructs the
data into its original structure (deserialization).
• Character Encoding: This layer manages character encoding conversions, such as translating text from
one character set (e.g., ASCII, Unicode) to another, ensuring that text is represented correctly across
different systems.
• Syntax Negotiation: The Presentation Layer can negotiate and agree on the syntax (format) to be used
for communication between two devices. This is particularly important when different systems are
involved, each using different data representations.
• Data Formatting: It standardizes data formats to ensure compatibility between different systems and
applications. For example, it may convert image file formats (e.g., JPEG to PNG) to ensure that the
receiving application can process the image correctly.
 Key Uses of the Session Layer
• Session Establishment, Management, and Termination:
– Establishment: The Session Layer sets up and establishes communication sessions between two devices or
applications. This involves negotiating and coordinating the session parameters, such as session ID,
synchronization points, and more.
– Management: Once established, the Session Layer manages the session, ensuring that data flows smoothly and in
the correct sequence. It monitors the session, handling any issues that arise during communication.
– Termination: After the communication is complete, the Session Layer properly terminates the session, ensuring
that all resources are released and the connection is closed gracefully.
• Synchronization:
– The Session Layer provides synchronization by inserting checkpoints or synchronization points into a data stream
during transmission. If a session is interrupted or fails, it can be resumed from the last checkpoint, rather than
starting over from the beginning. This is particularly important for long data transfers.
• Dialog Control:
– The Session Layer manages the dialog between two devices or applications. It controls the flow of information
and can operate in full-duplex (simultaneous two-way communication) or half-duplex (one direction at a time)
modes. This ensures that both parties can communicate efficiently without conflicts.
• Session Recovery:
– In case of a failure or interruption, the Session Layer can recover the session using the synchronization points. It
ensures that the communication can resume without losing data, improving the reliability of network
communication.
• Session Security:
– The Session Layer can implement security measures, such as authentication and authorization, to ensure that only
authorized users or applications can establish a session. This adds an additional layer of security to network
communication.
• Session Multiplexing:
– It allows multiple sessions to be managed simultaneously over the same network connection. The Session Layer
ensures that data streams from different sessions do not interfere with each other, maintaining the integrity of each
session.
• Reliable Data Transfer: Key Uses of the Transport Layer
– The Transport Layer ensures that data is delivered accurately and in the correct order. It handles error detection
and correction, retransmitting data if errors are detected or if data is lost during transmission.
• Segmentation and Reassembly:
– Large data messages are often too big to be transmitted as a single unit. The Transport Layer breaks down these
messages into smaller segments for transmission. At the receiving end, it reassembles the segments back into the
original message.
• Flow Control:
– The Transport Layer manages the flow of data between devices to prevent overwhelming the receiver. It uses
techniques like windowing to control the rate at which data is sent, ensuring that the sender doesn't send data
faster than the receiver can process it.
• Connection Establishment and Termination:
– For connection-oriented communication (such as TCP), the Transport Layer is responsible for establishing a
connection between the sender and receiver before data transfer begins. Once the communication is complete, it
terminates the connection gracefully.
• Multiplexing:
– The Transport Layer enables multiple applications or processes to use the network simultaneously by using port
numbers. It directs the data to the correct application on the receiving device, even when multiple applications are
communicating over the network.
• Error Detection and Correction:
– The Transport Layer provides mechanisms for detecting errors in the transmitted data (using checksums) and
correcting them. If an error is detected, it can request retransmission of the affected data.
• End-to-End Communication:
– The Transport Layer provides end-to-end communication between the source and destination devices, ensuring
that data is reliably transferred across the network, regardless of the underlying network technologies.
• Quality of Service (QoS):
– The Transport Layer can manage and prioritize data traffic based on the type of service required. For example, it
can ensure that real-time data like voice and video are delivered with minimal delay, while other types of data may
be given lower priority.
 Key Uses of the Network Layer
• Routing:
– The Network Layer determines the optimal path for data to travel from the source to the destination across different
networks. Routing algorithms consider various factors like network topology, traffic load, and link cost to select the
most efficient route for data transmission.
• Logical Addressing:
– This layer assigns logical addresses (such as IP addresses) to devices on the network. These addresses are used to
identify the source and destination of data packets, ensuring that data is delivered to the correct recipient.
• Packet Forwarding:
– Once the best route is determined, the Network Layer forwards data packets along this path. Routers, operating at the
Network Layer, receive packets and forward them to the next hop on the route until they reach the final destination.
• Fragmentation and Reassembly:
– The Network Layer can fragment large data packets into smaller pieces to accommodate the maximum transmission
unit (MTU) of different networks. At the destination, the Network Layer reassembles these fragments into the original
packet.
• Inter-networking:
– The Network Layer allows different networks to connect and communicate with each other. It handles the differences
between various network technologies, enabling data to travel across diverse network types (e.g., Ethernet, Wi-Fi).
• Error Handling and Diagnostics:
– The Network Layer provides mechanisms for error handling, such as detecting and reporting network problems. It may
include diagnostic tools like ICMP (Internet Control Message Protocol) to help troubleshoot network issues and ensure
reliable communication.
• Traffic Control and Congestion Management:
– The Network Layer can implement policies for controlling traffic and managing congestion in the network. It may use
techniques like packet prioritization, load balancing, and congestion avoidance to optimize network performance and
prevent bottlenecks.
• Quality of Service (QoS):
– The Network Layer can provide QoS features that prioritize certain types of traffic, ensuring that critical data (such as
 Key Uses of the Data Link Layer
• Framing:
– The Data Link Layer packages raw bits from the Physical Layer into structured units called frames. Each frame contains not only
the raw data but also metadata like addresses and error-checking codes, ensuring the data can be correctly interpreted by the
receiving device.
• Addressing:
– This layer uses physical or MAC (Media Access Control) addresses to identify devices on the same local network segment. MAC
addresses ensure that data frames are delivered to the correct hardware device on a network.
• Error Detection and Correction:
– The Data Link Layer includes mechanisms for detecting errors that occur during the transmission of data frames. Techniques like
checksums or cyclic redundancy checks (CRC) are used to identify corrupted frames. In some cases, the Data Link Layer can also
request retransmission of corrupted frames (error correction).
• Flow Control:
– The Data Link Layer manages the rate at which data is sent to ensure that the sender does not overwhelm the receiver,
especially if the receiver has limited processing capacity or buffer space. This helps prevent data loss and ensures smooth
communication between devices.
• Media Access Control (MAC):
– This layer controls how devices on a shared network medium (like Ethernet) gain access to the physical transmission medium. It
manages collisions and ensures that data frames are transmitted efficiently, using methods like Carrier Sense Multiple Access
with Collision Detection (CSMA/CD) in Ethernet networks.
• Link Establishment and Termination:
– The Data Link Layer establishes and terminates logical connections between two directly connected nodes. It manages the
initiation and conclusion of data exchanges, ensuring that resources are allocated and released appropriately.
• Data Synchronization:
– This layer ensures that the sender and receiver are synchronized for the correct interpretation of the bitstream. It handles
timing issues that could otherwise cause errors in data interpretation.
• Logical Link Control (LLC):
– The LLC sublayer of the Data Link Layer provides a means for identifying the network layer protocol to be used (e.g., IP). It also
provides flow control and error management above the Media Access Control (MAC) sublayer.
 Introduction to Physical Layer
• - Role of the Physical Layer
• - Transmission Media Overview
 Key Uses of the Physical Layer
• Bit Transmission:
– The Physical Layer is responsible for transmitting raw bits (0s and 1s) from one device to another over a physical medium. This
transmission can occur through various means, such as electrical signals over copper wires, light pulses in fiber optics, or radio
waves in wireless communication.
• Physical Connections:
– This layer manages the physical connections between devices, including the type of cables (e.g., twisted pair, coaxial, fiber optic),
connectors, and network interfaces. It ensures that the devices are physically connected so that data can be transmitted.
• Signal Encoding and Modulation:
– The Physical Layer encodes data into signals that can be transmitted over the chosen medium. This may involve converting digital
data into analog signals (modulation) or using other encoding schemes to represent bits. It also handles the modulation and
demodulation processes in analog communication.
• Data Rate Control:
– The Physical Layer determines the data transmission rate, which is the speed at which bits are transmitted over the network
(measured in bits per second, or bps). It ensures that the transmitter and receiver are synchronized in terms of the data rate to
avoid errors.
• Synchronization:
– It ensures that both the sender and receiver are synchronized in time, so the receiver knows when to sample the signal to
accurately interpret the bits. This prevents timing errors and ensures accurate data interpretation.
• Line Configuration:
– The Physical Layer handles the physical layout of the network, including the configuration of point-to-point, multipoint, or bus, ring,
and star topologies. It determines how devices are arranged and connected on the network.
• Transmission Mode:
– It manages the transmission mode, which can be simplex (one-way communication), half-duplex (two-way communication, but one
direction at a time), or full-duplex (two-way communication simultaneously). This helps in efficient utilization of the transmission
medium.
• Physical Topology:
– The Physical Layer defines the physical topology of the network, which is the arrangement of devices and how they are connected.
Examples include bus, ring, star, mesh, and hybrid topologies.
• Medium Access Control (MAC):
– While typically associated with the Data Link Layer, in some technologies, the Physical Layer is involved in managing how devices
 Transmission Media
• - Guided Media
• - Twisted-Pair Cable
• - Coaxial Cable
• - Fiber Optic Cable
• - Unguided Media (Wireless)
• - Radio Waves
• - Microwaves
• - Infrared
 Guided media
• refers to physical pathways that guide the
transmission of data signals from one device to
another. These pathways are physical cables or
lines that confine the signal to a specific path,
ensuring that it travels in a controlled direction
from the sender to the receiver. Guided media are
typically used in wired communication networks
and can be contrasted with unguided media (such
as wireless communication), where signals are
transmitted through the air or space
 Types of Guided Media

• Twisted Pair Cable:

– Description: Consists of pairs of insulated copper wires twisted
together. The twisting helps reduce electromagnetic interference
(EMI) from external sources and crosstalk between adjacent pairs
within the cable.
– Types:
• Unshielded Twisted Pair (UTP): Commonly used in Ethernet networks.
UTP cables lack additional shielding, making them less expensive but
more susceptible to interference.
• Shielded Twisted Pair (STP): Includes an additional shielding layer around
the twisted pairs, providing better protection against interference, often
used in environments with high EMI.
– Uses: Telephone networks, Ethernet LANs, DSL lines(Digital
Subscriber Line).
 Coaxial Cable

• Description: Consists of a central conductor

(usually copper) surrounded by an insulating
layer, a metallic shield, and an outer insulating
layer. The shielding helps prevent signal loss
and interference.
• Uses: Cable television networks, broadband
internet connections, and older Ethernet
networks (e.g., 10BASE2, 10BASE5).
 Fiber Optic Cable:

• Description: Uses light pulses to transmit data through strands of

glass or plastic fibers. Each fiber is as thin as a human hair and
can carry large amounts of data over long distances with minimal
signal loss.
• Types:
– Single-Mode Fiber (SMF): Has a small core (about 8-10 micrometers)
and transmits infrared laser light. It supports higher bandwidth and
longer distances, typically used for long-distance communication.
– Multi-Mode Fiber (MMF): Has a larger core (about 50-62.5
micrometers) and transmits infrared light from LEDs. It is typically used
for shorter distances due to higher modal dispersion.
• Uses: High-speed data transmission for internet, cable television,
telephone networks, and data centers.
• Advantages of Guided Media
• Security: Guided media are more secure because the data transmission is confined to the
physical medium, making it less susceptible to interception or eavesdropping compared to
wireless media.
• Reliability: These media are less affected by external environmental factors like weather,
making them more reliable for consistent data transmission.
• Speed and Bandwidth: Guided media, especially fiber optics, offer higher data transfer
speeds and greater bandwidth, supporting large-scale and high-speed communication
networks.
• Disadvantages of Guided Media
• Cost: The installation of guided media, particularly fiber optic cables, can be expensive
due to the cost of materials and labor.
• Physical Limitations: Guided media require physical connections between devices, which
can limit mobility and require significant infrastructure for installation over long distances.
• Maintenance: Damage to the physical medium (e.g., cuts in the cable) can disrupt
communication and require repairs, which may be costly and time-consuming.
 Applications of Guided Media

• Local Area Networks (LANs): Twisted pair cables

are commonly used to connect computers and
other devices within a local network.
• Telecommunications: Coaxial cables and fiber
optic cables are used in telephone networks and
for broadband internet connections.
• Data Centers: Fiber optic cables are widely used
in data centers for high-speed data transfer
between servers and storage devices.
 Unguided media
• Unguided media, also known as wireless media,
refers to the methods of transmitting data without
the use of physical cables or wires. Instead of being
confined to a specific path like guided media,
unguided media use electromagnetic waves (such
as radio, microwave, or infrared signals) to
transmit data through the air, space, or even water.
These signals can travel through a variety of
environments and do not require a physical
medium to guide them.
 Types of Unguided Media

• Radio Waves:
– Description: Radio waves are electromagnetic waves with frequencies ranging from 3
kHz to 300 GHz. They can travel long distances and penetrate through buildings,
making them ideal for broadcasting and communication.
– Uses: AM/FM radio, television broadcasts, mobile phones, Wi-Fi, Bluetooth, and
satellite communication.
– Characteristics: They can cover large areas, but the quality and strength of the signal
can be affected by obstacles, distance, and interference from other signals.
• Microwaves:
– Description: Microwaves are electromagnetic waves with frequencies ranging from 1
GHz to 300 GHz. They are typically used for point-to-point communication because
they can be focused into narrow beams.
– Uses: Satellite communication, cellular networks, wireless LANs, and radar systems.
– Characteristics: Microwaves require a clear line of sight between the transmitter and
receiver, as they cannot easily penetrate obstacles like buildings. They can cover
medium to long distances but are more susceptible to interference from physical
obstacles and weather conditions.
• Infrared Waves:
• Description: Infrared waves have frequencies just below
visible light, ranging from 300 GHz to 430 THz. They are
typically used for short-range communication.
• Uses: Remote controls, short-range communication between
devices (e.g., wireless keyboards and mice), and certain
wireless LANs.
• Characteristics: Infrared communication requires a direct line
of sight between the transmitter and receiver, as infrared
waves cannot penetrate walls or other solid objects. They are
generally used for indoor, short-range communication.
• Light Waves (Visible Light Communication):
• Description: Light waves use visible light or ultraviolet light for
communication. This form of communication can be extremely
fast and is typically used in specific applications.
• Uses: Fiber-optic communications (internally within the fiber),
Li-Fi (Light Fidelity) Li-Fi (Light Fidelity) is a wireless
technology that uses light to transmit data and determine the
position of devices., and certain secure communication
systems.
• Characteristics: Light waves require a clear line of sight and
are typically used in environments where interference from
other sources is minimal
 Advantages of Unguided Media

• Mobility: Unguided media allow for the mobility of

devices, as there are no physical connections restricting
movement. This is crucial for mobile communications,
such as smartphones and wireless internet.
• Ease of Installation: Setting up a wireless network is often
easier and faster compared to installing physical cables,
especially in difficult terrains or over long distances.
• Broad Coverage: Wireless signals can cover large areas,
making them suitable for broadcasting, satellite
communication, and large-scale wireless networks like
cellular networks.
 Disadvantages of Unguided Media

• Interference: Wireless signals are susceptible to interference

from other wireless devices, weather conditions, and
physical obstacles, which can degrade signal quality and
reliability.
• Security: Unguided media are more vulnerable to
eavesdropping and unauthorized access because the signals
can be intercepted by anyone within range, making
encryption and security protocols essential.
• Limited Bandwidth: Some types of wireless communication,
particularly radio and infrared, may offer limited bandwidth
compared to wired options like fiber optics, affecting data
transmission speed and capacity.
 Applications of Unguided Media

• Wi-Fi Networks: Used for wireless local area networks (WLANs) to

provide internet access to devices without the need for physical cables.
• Mobile Communications: Cellular networks use radio waves and
microwaves to provide voice and data services to mobile phones and
other devices.
• Satellite Communication: Satellites use microwaves to relay signals
over long distances, providing services like television broadcasting, GPS,
and internet access in remote areas.
• Remote Controls: Infrared waves are commonly used in remote
controls for TVs, air conditioners, and other electronic devices.
• Bluetooth: A short-range wireless technology that uses radio waves to
connect devices like headphones, speakers, and keyboards to
computers and smartphones.
 Switching
• - What is Switching?
• - Types of Switching
• - Circuit Switching
• - Packet Switching
 How Circuit Switching Works

• Connection Establishment:
– Before data can be transmitted, a connection or circuit must be established
between the sender and the receiver. This involves identifying a path through
the network that links the two parties.
– The circuit is composed of a series of physical or logical links between network
nodes, such as switches and routers.
• Data Transmission:
– Once the circuit is established, data is transmitted continuously over the same
path for the duration of the communication session.
– The data follows the same route, and since the circuit is dedicated, there is
minimal delay or variation in transmission.
• Connection Termination:
– After the communication session ends, the circuit is terminated. The network
resources (e.g., bandwidth, switches) that were reserved for the circuit are
released and made available for other users or sessions.
 Key Characteristics of Circuit Switching

• Dedicated Path: The communication path is exclusively

reserved for the entire duration of the communication session,
ensuring consistent and reliable data transmission.
• Fixed Bandwidth: The bandwidth allocated for the circuit
remains constant throughout the session, regardless of
whether data is actively being transmitted.
• Connection-Oriented: Communication requires a connection
to be established before data can be sent, making circuit
switching inherently connection-oriented.
• Minimal Delay: Since the circuit is dedicated, there is minimal
delay in data transmission, making it suitable for real-time
communication.
 Types of Circuit Switching

• Space-Division Circuit Switching:

– In this method, different physical paths are used to
establish circuits between devices. Separate wires or
frequency channels are dedicated to each connection.
• Time-Division Circuit Switching:
– In this method, multiple circuits share the same
physical path, but each circuit is given a dedicated
time slot for data transmission. This technique is
commonly used in digital communication systems like
TDM (Time Division Multiplexing).
 Packet Switching
• - Introduction to Packet Switching
• - Types of Packet Switching
• - Datagram Packet Switching
• - Virtual Circuit Packet Switching
 Packet switching
• is a method of data transmission where data is
broken down into smaller units called packets
before being sent over a network. Unlike circuit
switching, which establishes a dedicated path for
the entire duration of a communication session,
packet switching allows packets to travel
independently through the network, potentially
taking different routes to reach the destination.
Once all the packets arrive at the destination, they
are reassembled into the original data.
 How Packet Switching Works

• Data Segmentation:
– Before transmission, the original data (such as a file, message, or stream of data) is divided
into smaller, manageable packets. Each packet typically contains a portion of the data along
with headers that include important information such as source and destination addresses,
sequence numbers, and error-checking data.
• Routing:
– Each packet is sent independently through the network. Since there is no dedicated path,
packets may take different routes based on the current network conditions, such as traffic
load or available bandwidth.
– Routers and switches in the network determine the best path for each packet based on
factors like destination address, network congestion, and routing protocols.
• Reassembly:
– Once the packets reach their destination, they are reassembled into the original data based
on the sequence numbers included in each packet's header. If any packets are missing or
corrupted, the system can request retransmission of those specific packets.
• Error Checking and Correction:
– Packets often include error-checking data in their headers. The receiving device checks for
errors and can request retransmission of any corrupted packets, ensuring data integrity.
 Key Characteristics of Packet Switching

• Efficient Resource Utilization:

– Network resources (e.g., bandwidth, router processing) are shared among
multiple users. This leads to efficient use of the network, as packets from
different communications can share the same network links.
• Dynamic Routing:
– Packets can take different routes to reach the destination, allowing the
network to adapt to changing conditions like congestion or network failures.
• Scalability:
– Packet switching supports a large number of users and diverse types of
communication, including data, voice, and video, making it suitable for the
Internet and large-scale networks.
• Robustness:
– If a particular route is congested or fails, packets can be rerouted through
alternate paths, improving network reliability and fault tolerance.
 Advantages of Packet Switching

• Advantages of Packet Switching

• Flexibility: Packet switching allows for dynamic routing and efficient use of network
resources. It can handle varying traffic loads and adapt to network changes.
• Scalability: It supports a large number of users and diverse types of data traffic, making it
suitable for the growth and complexity of modern networks.
• Efficiency: By sharing network resources among multiple users and allowing packets to
take different routes, packet switching maximizes resource utilization and reduces idle
time.
• Disadvantages of Packet Switching
• Latency: Packets may experience variable delays and jitter due to the different routes they
take and network congestion. This can impact real-time applications like voice and video
calls.
• Overhead: The inclusion of metadata in each packet and the need for reassembly at the
destination add overhead to the data transmission process.
• Packet Loss: While packet switching includes error-checking mechanisms, packets can still
be lost or delayed, requiring retransmission and potentially affecting the overall
communication efficiency.
 Virtual circuit packet switching
• Virtual circuit packet switching is a network
communication method that combines
elements of both circuit-switched and packet-
switched networks.
 How Virtual Circuit Packet Switching Works

• Establishing a Virtual Circuit:

– Setup Phase: Before data transmission, a virtual circuit is established. This involves creating
a logical path through the network from the sender to the receiver. Network switches and
routers along this path reserve resources and store routing information about the circuit.
– Signaling: The setup process often uses signaling protocols to manage the creation of the
virtual circuit and ensure that resources are allocated along the route.
• Data Transmission:
– Packet Transfer: Once the virtual circuit is established, data is sent in packets. Each packet
carries a virtual circuit identifier (VCI) in its header, which tells each switch or router how to
handle the packet. All packets for a particular virtual circuit follow the same path.
– Consistency: Since the path is pre-determined and consistent for all packets in the virtual
circuit, packets arrive in the same order they were sent. This simplifies the management of
data flow and ensures that packets are delivered in sequence.
• Tearing Down the Circuit:
– Teardown Phase: After the data transfer is complete, the virtual circuit is dismantled. This
involves clearing the resources and routing information from the network switches and
routers. This phase ensures that the resources can be used for other connections.
 Advantages

• Guaranteed Path: The fixed path ensures a predictable route and quality of
service, which can be crucial for applications requiring stable performance.
• Ordering and Reliability: Packets are sent along the same route, which
simplifies the task of reordering and managing data integrity.
• Resource Allocation: Resources can be reserved for the duration of the
connection, which helps in managing network load and performance.
• Disadvantages
• Setup and Teardown Overhead: The process of establishing and dismantling
a virtual circuit introduces additional overhead and complexity.
• Less Flexibility: The fixed path means that if there’s a network issue on the
path, the connection can be affected. This contrasts with datagram packet
switching, where packets can take alternative routes if needed.
• Scalability Issues: Managing a large number of virtual circuits and their
states can become complex and resource-intensive in very large networks.
 Applications

• Virtual circuit packet switching is used in

various technologies, including:
• Frame Relay: Used for connecting local area
networks (LANs) over a wide area network
(WAN).
• Asynchronous Transfer Mode (ATM): Used for
high-speed networking with guaranteed QoS.