UNIT-1st Computer Network (BCA -503)

COMPUTER NETWORK/ NETWORK: A computer network is a system that

connects two or more computing devices for transmitting and sharing information.
Examples:4G, 5G network, LAN, MAN , WAN etc.
TYPES OF NETWORKS:
Networks can be categorized in various ways depending on their size, scope, and the
technology used. Here are some common categories of networks along with
examples:
1. Personal Area Network (PAN)
 Definition: A PAN is a network organized around an individual person within
a single building. This could be a home or small office.
 Examples:
o Bluetooth-enabled devices: Connecting a smartphone to wireless
headphones.
o Home Wi-Fi network: Connecting personal devices like laptops,
tablets, and smart home devices.
2. Local Area Network (LAN)
 Definition: A LAN is a network that connects computers within a limited area
such as a residence, school, laboratory, or office building.
 Examples:
o Corporate office networks: Connecting multiple computers, printers,
and servers within a company.
o School networks: Connecting classrooms to a central server and the
internet.
3. Wireless Local Area Network (WLAN)
 Definition: A WLAN is a type of LAN that uses wireless technology (e.g.,
Wi-Fi) to connect devices.

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  Examples:
o Home Wi-Fi networks: Connecting laptops, smartphones, and smart
TVs to the internet.
o Public Wi-Fi hotspots: Available in cafes, airports, and hotels.
4. Metropolitan Area Network (MAN)
 Definition: A MAN is a network that connects users within a geographic area
or region larger than that covered by a LAN but smaller than a WAN, such as
a city.
 Examples:
o Citywide Wi-Fi networks: Provided by municipal governments.
o Cable TV networks: Often cover entire cities.
5. Wide Area Network (WAN)
 Definition: A WAN is a network that covers a broad area (e.g., any network
whose communications links cross metropolitan, regional, or national
boundaries).
 Examples:
o The Internet: The largest and most well-known example of a WAN.
o Banking networks: Connecting ATMs across a country or globally.
6. Virtual Private Network (VPN)
 Definition: A VPN extends a private network across a public network,
allowing users to send and receive data as if their devices were connected to
the private network.
 Examples:
o Corporate VPNs: Allow employees to securely connect to the
company’s network from remote locations.
o Personal VPNs: Used by individuals to secure their internet connection
and protect their online privacy.

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COMPONENTS OF DATA COMMUNICATION
Data communication refers to the exchange of data between devices through a
transmission medium. It involves several key components that ensure the successful
transmission and reception of data. Here are the main components of data
communication:
1. Message
 Definition: The message is the actual data or information that needs to be
communicated from the sender to the receiver.
 Examples: Text, images, audio, video, or any combination of these formats.
2. Sender (Transmitter)
 Definition: The sender is the device or entity that initiates the data
communication by sending the message to the receiver.
 Examples: Computers, smartphones, sensors, or any other digital device
capable of transmitting data.
3. Receiver
 Definition: The receiver is the device or entity that receives the message sent
by the sender.
 Examples: Computers, printers, smartphones, servers, or any other device
capable of receiving data.
4. Transmission Medium
 Definition: The transmission medium is the physical or logical path through
which the message travels from the sender to the receiver.
 Examples:
o Wired Media: Ethernet cables, fiber optic cables, coaxial cables.
o Wireless Media: Radio waves, microwaves, infrared, satellite signals.
5. Protocol
 Definition: A protocol is a set of rules and conventions that define how data
is transmitted, received, and interpreted between devices. It ensures proper
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 synchronization, error detection, and communication between the sender and
receiver.
 Examples:
o Internet Protocol (IP): Defines how data packets are sent across
networks.
o Transmission Control Protocol (TCP): Ensures reliable transmission
of data.
o Hypertext Transfer Protocol (HTTP): Used for transferring web
pages.
6. Encoder
 Definition: The encoder converts the message into a form that can be
transmitted over the chosen medium, typically from human-readable data into
digital signals.
 Examples: Converting text into binary code, modulating an audio signal for
transmission.
7. Decoder
 Definition: The decoder converts the received signal back into a format that
can be understood by the receiver, such as converting digital signals back into
human-readable data.
 Examples: Decoding a digital signal into text, demodulating a received
signal.
8. Modem (Modulator-Demodulator)
 Definition: A modem is a device that modulates an analog carrier signal to
encode digital information for transmission and demodulates it on the
receiving end.
 Examples: DSL modems, cable modems, dial-up modems.
9. Topology
 Definition: Network topology refers to the arrangement of different elements
(links, nodes, etc.) in a communication network.

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  Examples:
o Star Topology: All nodes are connected to a central hub.
o Ring Topology: Nodes are connected in a circular fashion.
o Bus Topology: All nodes are connected to a single communication line.
10. Error Detection and Correction
 Definition: These are techniques used to ensure data integrity during
transmission. Error detection identifies errors in the transmitted data, while
error correction attempts to fix them.
 Examples:
o Parity Check: A simple error detection method.
o Cyclic Redundancy Check (CRC): A more complex error detection
method.
o Forward Error Correction (FEC): A method that corrects errors
without retransmission.
11. Synchronization
 Definition: Synchronization refers to the coordination of timing between the
sender and receiver to ensure that data is transmitted and received in the
correct sequence and timing.
 Examples:
o Asynchronous Communication: Data is sent one byte at a time with
start and stop bits.
o Synchronous Communication: Data is sent in a continuous stream
with timing signals.
12. Network Interface Card (NIC)
 Definition: A NIC is a hardware component that connects a computer to a
network and allows it to communicate with other devices.
 Examples: Ethernet cards, Wi-Fi adapters, Bluetooth adapters.

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13. Switches and Routers
 Switches: Devices that connect multiple devices on the same network and
manage the data flow between them.
 ROUTERS: Devices that direct data packets between different networks,
often connecting a local network to the internet.
Here are the basic functions of a router in points:
I. Packet Forwarding: Directs packets between different networks based on
their destination IP addresses.
II. Routing: Determines the best path for data to travel across networks using
routing tables and protocols.
III. Traffic Management: Manages and controls network traffic to optimize
performance and reduce congestion.
IV. Path Selection: Chooses the most efficient route for data based on current
network conditions.
V. Segmentation: Divides larger networks into smaller segments to improve
performance and security.
VI. Error Reporting: Detects and reports errors or issues with network
connections and routing.
VII. Security: Implements security features such as firewalls and access control
lists (ACLs) to protect the network from unauthorized access.

 DISTRIBUTED PROCESSING ( DISTRIBUTED SYSTEM)

Distributed processing refers to a computing architecture in which multiple
processors or computers are used to process data or execute tasks simultaneously
across a distributed system. This approach leverages the computational power of
multiple devices, often located in different geographical locations, to work on a
common task or to handle various parts of a larger computation.

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Types of Distributed Processing:
1. Client-Server Model:
o Description: The client-server model is a common form of distributed
processing where clients request services or resources from a central
server.
o Examples: Web applications, email systems, online banking.
2. Peer-to-Peer (P2P) Model:
o Description: In P2P networks, all nodes are equal, and each node can
act as both a client and a server. This model distributes tasks among
peers without a central server.
o Examples: File-sharing networks like BitTorrent, blockchain
networks.
3. Cloud Computing:
o Description: Cloud computing provides distributed processing through
the internet. Resources like processing power, storage, and applications
are provided as services over the cloud.
o Examples: Amazon Web Services (AWS), Microsoft Azure, Google
Cloud Platform.
Examples of Distributed Processing Systems:
 Google’s MapReduce: A programming model for processing large data sets
with a distributed algorithm on a cluster
 LINE CONFIGURATION

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In computer networks, "line configuration" refers to how the connections between
devices are established and organized. There are several types of line configurations,
each with its own characteristics and use cases:
1. Point-to-Point Configuration:
o Description: In this setup, a direct connection exists between two
devices. This is a simple, dedicated connection between two nodes,
which can be either physical or logical.
o Examples: A direct cable between two computers or a dedicated leased
line.
2. Point-to-Multipoint Configuration:
o Description: In this arrangement, one central device (the hub)
communicates with multiple devices (the spokes). The central device
manages communication with all the connected devices.
o Examples: A wireless access point connecting to multiple devices or a
satellite link where one satellite communicates with multiple ground
stations.
3. Multipoint Configuration:
o Description: Multiple devices share a common communication
channel. Each device can potentially communicate with any other
device on the same channel.
o Examples: A bus network topology in which multiple computers are
connected to a single communication line.
4. Mesh Configuration:
o Description: Each device is connected to every other device in the
network, providing multiple paths for data to travel.
o Examples: A full mesh network where every node is interconnected,
often used in high-availability systems.
5. Hybrid Configuration:
o Description: Combines elements of different line configurations to
meet specific needs. For example, a star-bus network combines a star
topology with a bus topology.

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 o Examples: A large office network that uses a star topology for internal
connections and a bus topology for connecting multiple star networks.
 TOPOLOGY IN COMPUTER NETWORK IN BRIEF
Network topology refers to the physical or logical arrangement of
devices and connections in a network. Here’s a brief overview of
common topologies:
1. Bus Topology:
o Description: All devices are connected to a single central cable (the
bus). Data sent by any device travels along the bus and is received by
all other devices.
o Advantages: Simple and cost-effective for small networks.
o Disadvantages: A failure in the central bus can disrupt the entire
network; performance degrades with increased traffic.

2. Star Topology:
o Description: All devices are connected to a central hub or switch. Data
is sent from one device to the hub, which then distributes it to the
intended recipient.
o Advantages: Easy to manage and troubleshoot; failure of one device
does not affect the others.
o Disadvantages: Requires more cabling; failure of the central hub
affects the entire network.

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3. Ring Topology:
o Description: Devices are connected in a circular fashion, with each
device connected to two others, forming a ring. Data travels in one or
both directions around the ring.
o Advantages: Data packet collisions are minimized; predictable
performance with consistent delays.
o Disadvantages: A failure in any single connection can disrupt the entire
network; more complex to install and manage.

4. Mesh Topology:
o Description: Each device is connected to every other device in the
network. Can be fully or partially meshed.
o Advantages: High reliability and redundancy; multiple paths for data
transmission.
o Disadvantages: Expensive and complex due to the large number of
connections required.

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 o

5. Tree Topology:
o Description: A hybrid topology that combines characteristics of star
and bus topologies. Groups of star-configured networks are connected
to a central bus.
o Advantages: Scalable and hierarchical; easy to manage and expand.
o Disadvantages: Dependency on the central bus; failure in the bus can
impact the entire network.

6. Hybrid Topology:
o Description: Combines two or more different topologies to leverage
their strengths and meet specific needs.
o Advantages: Flexible and adaptable to various requirements; can
balance cost and performance.
o Disadvantages: Can be complex to design and manage; may require
careful planning and maintenance.

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  TRANSMISSION MODE
Transmission mode in computer networks refers to the method by
which data is sent over a network. It can be categorized based on the
direction of data flow and the nature of the communication. Here are
the main types:
Based on Direction of Data Flow:
1. Simplex Mode:
o Description: Data flows in only one direction from sender to receiver.
There is no feedback from the receiver to the sender.
o Examples: Keyboard to computer, or broadcast TV signals.
o Advantages: Simple and efficient for one-way communication.
2. Half-Duplex Mode:
o Description: Data can flow in both directions, but not simultaneously.
Devices take turns sending and receiving data.
o Examples: Walkie-talkies, CB radios.
o Advantages: Allows two-way communication, although not at the
same time.
o Disadvantages: Only one device can transmit at a time, which may
cause delays.
3. Full-Duplex Mode:
o Description: Data can flow in both directions simultaneously. Both
devices can send and receive data at the same time.
o Examples: Telephones, modern network connections (like Ethernet).
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 o Advantages: Efficient two-way communication without delays.
o Disadvantages: Requires more complex signaling and management.
Based on Nature of Communication:
1. Serial Transmission:
o Description: Data is transmitted one bit at a time over a single channel
or wire.
o Examples: RS-232 serial ports, USB.
o Advantages: Simple wiring, and effective for long-distance
communication.
o Disadvantages: Slower compared to parallel transmission for high data
rates.
2. Parallel Transmission:
o Description: Multiple bits are transmitted simultaneously over
multiple channels or wires.
o Examples: Computer buses, printer connections.
o Advantages: Faster data transfer rates over short distances.
o Disadvantages: More complex wiring, and less effective over long
distances due to signal degradation.
 OSI AND TCP/IP MODELS: LAYERS AND THEIR
FUNCTIONS, IN BRIEF
The OSI (Open Systems Interconnection) model and the TCP/IP
(Transmission Control Protocol/Internet Protocol) model are two
fundamental frameworks for understanding network communication.
Here’s a brief overview of their layers and functions:

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 OSI Model (7 Layers):

1. Physical Layer (Layer 1):

o Function: Transmits raw bitstreams over physical media (cables,
radio frequencies). Defines hardware components like cables, switches,
and network interfaces.
o Some are the basic functions of the Physical Layer in points:
o Data Rate Control: Manages the speed of data transmission (bit rate).
o Physical Topology: Defines the physical layout and connections in the
network.
o Modulation and Encoding: Handles signal modulation and data
encoding for transmission.
o Transmission Mode: Defines data flow direction (simplex, half-
duplex, full-duplex).
o Examples: Physical layer support the devices Ethernet cables, fiber
optics, Repeaters, Hubs, Modems.

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2. Data Link Layer (Layer 2):
o Function: Provides node-to-node data transfer and handles error
correction and detection from the Physical layer. Manages MAC
addresses and frames.
o Here are the basic functions of the Data Link Layer in points:
o Physical Addressing: Assigns and handles MAC addresses for devices
on the network.
o Flow Control: Manages data flow between sender and receiver to
prevent congestion.
o Media Access Control (MAC): Manages how data is placed on and
received from the physical medium.
o Frame Sequencing: Ensures that frames are delivered in the correct
order.
o Link Management: Establishes, maintains, and terminates
connections between devices.
o Examples: Ethernet, Wi-Fi, switches, and bridges.
3. Network Layer (Layer 3):
o Function: Determines the best path for data to travel across the network
and handles logical addressing (IP addresses). Responsible for routing
and forwarding packets.
o Here are the basic functions of the Network Layer in points:
o Routing: Determines the best path for data to travel across networks.
o Packet Forwarding: Moves packets from source to destination
through routers.
o Path Determination: Chooses the optimal route for data transmission.
o Fragmentation and Reassembly: Breaks down large packets into
smaller ones for transmission and reassembles them at the destination.
o Error Handling and Diagnostics: Provides error reporting and
diagnostic information for network issues.

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 o Traffic Control: Manages network traffic to prevent congestion and
ensure efficient data flow.
o Examples: IP (Internet Protocol), routers. Brouters (A bridge router or
brouter is a network device that works as a bridge and as a router).
o

4. Transport Layer (Layer 4):

o Function: Ensures reliable data transfer with error recovery and flow
control. Manages end-to-end communication between devices.
o Here are the basic functions of the Transport Layer in points:
o Connection Management: Establishes, maintains, and terminates
connections between devices (e.g., TCP).
o Multiplexing: Allows multiple applications to use the network
simultaneously by managing different data streams.
o End-to-End Communication: Ensures data is delivered from the
source to the destination accurately and in sequence.
o Reliable Data Transfer: Provides mechanisms (e.g.,
acknowledgments, retransmissions) to ensure data is delivered
correctly.
o Port Addressing: Uses port numbers to direct data to the correct
application or service on a device.
o Examples: TCP (Transmission Control Protocol), UDP (User
Datagram Protocol).
5. Session Layer (Layer 5):
o Function: Manages sessions or connections between applications.
Handles session establishment, maintenance, and termination.
o Here are the basic functions of the Session Layer in points:
o Session Control: Manages the dialog between devices, including who
sends and receives data (full-duplex or half-duplex).
o Dialog Separation: Separates different conversations or sessions to
prevent data mix-ups.

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 o Session Termination: Gracefully closes sessions once communication
is complete, ensuring that all data is properly transmitted.
o Examples: support devices Firewalls and Gateways. Login and logout
for Email in Google, Mobile to mobile call.
6. Presentation Layer (Layer 6):
o Function: Translates data between the application layer and the
network. Ensures data is in a readable format and handles encryption,
compression, and translation.
Here are the basic functions of the Presentation Layer in points:
o Data Translation: Converts data between the application layer format
and the network format.
o Data Encryption and Decryption: Secures data by encrypting it
before transmission and decrypting it upon reception.
o Data Compression: Reduces the size of data to optimize network
usage and speed up transmission.
o Character Encoding: Converts data into a standard character encoding
(e.g., ASCII, Unicode) for consistency.
o Data Serialization: Converts complex data structures into a byte
stream for transmission, and deserializes it back at the destination.

o Examples: SSL/TLS, data format translation (e.g., JPEG, ASCII).

7. Application Layer (Layer 7):
o Function: Provides network services directly to applications.
Interfaces with software applications to provide network services. The
application layer allows users to send each other files through a
network.
o The application layer is used by end-user software such as web
browsers and email clients. It provides protocols that allow software to
send and receive information and present meaningful data to users.
o Here are the basic functions of the Application Layer in points:

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 o User Interface: Provides an interface for users to interact with network
services and applications or Login to remote and log out to remote
computer.
o Application Services: Offers network services such as email, file
transfer, and web browsing.
o Resource Sharing: Facilitates access to and sharing of resources over
the network, such as printers and files.
o Examples: HTTP, FTP, SMTP, DNS, Gateways and Firewalls.

 THE TCP/IP MODEL

The TCP/IP model (Transmission Control Protocol/Internet Protocol)
is a conceptual framework for computer networking. It describes how
data is transmitted over networks, including the internet. The model has
four layers, each responsible for different aspects of data
communication:

1. Application Layer:
o Purpose: This layer handles high-level protocols and interacts with
software applications to implement a communicating component.
o Functions: Protocols like HTTP, FTP, SMTP, and DNS operate here. It
deals with application-specific functionalities, like web browsing,
email, and file transfer.
2. Transport Layer:

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 o Purpose: This layer ensures reliable data transfer between two devices
in a network.
o Functions: The main protocols are TCP (Transmission Control
Protocol) and UDP (User Datagram Protocol). TCP provides reliable,
ordered, and error-checked delivery of a stream of data between
applications, while UDP is faster but less reliable.
3. Internet Layer:
o Purpose: This layer is responsible for logical addressing and routing of
data packets across networks.
o Functions: The IP (Internet Protocol) is the primary protocol in this
layer, responsible for addressing and routing packets so they can travel
across networks and reach their correct destinations. ICMP (Internet
Control Message Protocol) and ARP (Address Resolution Protocol) are
also part of this layer.

4. Network Access Layer (also known as the Link Layer or Data Link Layer):
o Purpose: This layer handles the physical transmission of data on the
network.
o Functions: It manages the protocols for communication on the physical
network, including how data is formatted for transmission over the
hardware, error detection, and frame synchronization. Examples
include Ethernet and Wi-Fi.
Summary:
 Application Layer: High-level protocols (e.g., HTTP, FTP)
 Transport Layer: Data transfer (TCP, UDP)
 Internet Layer: Addressing and routing (IP)
 Network Access Layer: Physical transmission (Ethernet, Wi-Fi)
The TCP/IP model is widely used because it forms the foundation of
the internet and most modern networks.

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 MODEMS (MODULATOR-DEMODULATOR)

A modem (short for Modulator-Demodulator) is a crucial device in digital

communication, enabling the transmission of digital data over analog
communication channels like telephone lines, radio, or cable systems. The modem
serves as a bridge between digital devices (such as computers) and the analog
transmission medium.

Key Functions of a Modem:

1. Modulation:
o Purpose: Converts digital data into an analog signal for transmission
over an analog medium.
o How It Works: The modem takes the binary data (0s and 1s) from a
computer and modulates it by varying certain properties of a carrier

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 wave—such as its amplitude, frequency, or phase. This analog signal
can then be transmitted over telephone lines, radio waves, or other
analog mediums.
2. Demodulation:
o Purpose: Converts the received analog signal back into digital data that
can be understood by the receiving device.
o How It Works: Upon receiving the analog signal, the modem
demodulates it, extracting the original binary data from the modulated
signal. This data is then passed to the computer or other digital devices.
TYPES OF MODEMS:
1. Dial-up Modems:
o Function: These were widely used in the early days of the internet.
Dial-up modems connect to the internet via standard telephone lines.
o Speed: Typically provides data transfer rates up to 56 Kbps.
o Process: The modem dials a telephone number to establish a connection
with an Internet Service Provider (ISP), and the connection is
temporary.

2. DSL Modems (Digital Subscriber Line):

o Function: Uses existing telephone lines for high-speed internet access
without interfering with voice services.
o Speed: Typically offers speeds from hundreds of Kbps to several Mbps,
significantly faster than dial-up.
o Advantage: Always-on connection, so users do not need to dial in to
connect to the internet.
3. Cable Modems:
o Function: Provides high-speed internet access over the same coaxial
cables used for cable television.
o Speed: Offers speeds ranging from tens to hundreds of Mbps.
o Technology: Utilizes DOCSIS (Data Over Cable Service Interface
Specification) standards to ensure compatibility and performance.
4. Fiber Optic Modems:
o Function: Used for internet access over fiber-optic networks, which
transmit data as light signals through fiber-optic cables.
o Speed: Can offer very high speeds, often in the Gbps range.
o Advantage: Provides extremely high bandwidth and is less susceptible
to interference.
5. Wireless Modems:
o Function: Provides internet access using wireless communication, such
as cellular networks (e.g., 3G, 4G, 5G).
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 o Usage: Commonly used in mobile broadband, providing internet access
to smartphones, tablets, and laptops.

 DTE-DCE Interface
The DTE-DCE interface is a crucial concept in data communication, particularly
in the context of serial communication. DTE stands for Data Terminal
Equipment, and DCE stands for Data Circuit-terminating Equipment. This
interface defines how data is transmitted between a computer or terminal (DTE)
and a modem or another communication device (DCE).

Key Points of DTE-DCE Interface:

1. DTE (Data Terminal Equipment):
o Typically a computer, terminal, or printer.
o Initiates and controls communication.
o Sends data to the DCE and receives data from the DCE.
2. DCE (Data Circuit-terminating Equipment):
o Typically a modem, router, or network interface.
o Provides the necessary signal conversion and coding for
communication.
o Transmits data between the DTE and the communication network.
3. Connector and Cabling:
o DTE devices typically use male connectors, while DCE devices use
female connectors.
o The cabling between DTE and DCE devices can vary, with specific
wiring schemes based on the standard being used.
4. Examples:
o A computer (DTE) connected to a modem (DCE) for internet access.
o A terminal (DTE) connected to a router (DCE) for data transmission
across a network.

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DTE-DCE Communication Process:

1. Connection Setup:
o The DTE initiates a connection by sending a signal to the DCE.
o The DCE responds, indicating its readiness to establish a
communication link.
2. Data Transmission:
o Once the connection is established, data is transmitted from the DTE to
the DCE, which then relays it to the network or another device.
3. Connection Termination:
o When the communication is complete, the DTE or DCE can terminate
the connection, ending the data transmission session.

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