3/10/2025

Outline
• Layered architecture
• Significance of layered architecture
Layered Architecture of Computer
• Reference Models
Networks • OSI reference model
• TCP/IP
Swagat Ranjan Sahoo
Assistant Professor

Department of Computer Science and Engineering

GL Bajaj Institute of Technology and Management, Greater Noida-201306,
India

Person3/10/2025
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Layered Architecture Layered Architecture

Computer Network Models Layered Architecture
• A communication subsystem is a complex piece of Hardware and • The main aim of the layered architecture is to divide the design into
software small pieces.
• Early attempts for implementing the software for such subsystems • Each lower layer adds its services to the higher layer to provide a full
were based on a single, complex, unstructured program with many set of services to manage communications and run the applications.
interacting components • It provides modularity and clear interfaces, i.e., provides interaction
• The resultant software was very difficult to test and modify between subsystems.
• To solve this ISO has developed a layered approach • It ensures the independence between layers by providing the
• In a layered approach, the networking concept is divided into several services from lower to higher layer without defining how the services
layers, and each layer is assigned a particular task are implemented.
• Any modification in a layer will not affect the other layers.
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Layered Architecture Layered Architecture

Layered Architecture Layered Architecture
The basic elements of layered architecture are services, protocols, and
interfaces
• Service: It is a set of actions that a layer provides to the higher layer
• Protocol: It defines a set of rules that a layer uses to exchange information
with peer entity. These rules mainly concern about both the contents and
order of the messages used
• Interface: It is a way through which the message is transferred from one
layer to another layer
• In a layer n architecture, layer n on one machine will have a communication
with the layer n on another machine and the rules used in a conversation Note: Every layer clubs together all procedures, protocols, and methods which it requires to execute its
are known as a layer n protocol piece of task.
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Layered Architecture Layered Architecture

Significance of Layered Architecture Significance of Layered Architecture
Modularity: Troubleshooting and Debugging
• The community stack may be divided into layers so that every layer • Layered architecture makes it possible to isolate issues into
can be one after the other planned, carried out, and maintained. particular layers
• This modularity allows network setting up and simplifying
improvements and updates.
• Makes finding and fixing community issues simpler.
Interoperability: Scalability
• The uniform compatibility of various suppliers' software programs • As networks develop in size and complexity, extra layers or
and hardware components is made possible via standardised protocols may be delivered to accommodate new
interfaces between layers. requirements without disrupting existing functionalities.
• In circumstances with heterogeneous networks, interoperability is
critical.
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Layered Architecture Layered Architecture

Significance of Layered Architecture Layered Tasks
An example from the everyday life
Security
The layered technique allows security features to be applied at
a couple of degrees, protecting the community from various
threats.
Efficiency
Each layer specializes in a selected factor to improve the
performance.
Hierarchy?
Services

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Layered Architecture Reference Model

Why layered communication? There are two reference models used to demonstrate the layered approach
• To reduce complexity of communication task by splitting it into several • OSI reference model
layered small tasks • TCP/IP Protocol suite
• Functionality of the layers can be changed as long as the service provided
to the layer above stays unchanged
• makes easier maintenance & updating

• Each layer has its own task

• Each layer has its own protocol

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Reference Model Reference Model

OSI Reference Model
• OSI stands for Open Systems Interconnection.
• It has been developed by ISO – ‘International Organization for
Standardization‘, in the year 1984.
• It is a 7 layer architecture with each layer having specific functionality to
perform.
1. OSI reference model • All these 7 layers work collaboratively to transmit the data from one person
to another across the globe.
• The term “open” denotes the ability to connect any two systems which
conform to the reference model and associated standards.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model

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Reference Model Reference Model

OSI Reference Model OSI Reference Model

 The lower 4 layers (transport, network, data link and physical —Layers 4, 3, 2, and 1) are concerned
with the flow of data from end to end through the network.

 The upper four layers of the OSI model (application, presentation and session—Layers 7, 6 and 5)
are orientated more toward services to the applications.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
As the message travels from device A to device B, it may pass through
many intermediate nodes. These intermediate nodes usually involve only
the first three layers of the OSI model.

 The Data Link layer determines the next node where the message is supposed
to be forwarded and the network layer determines the final recipient.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Physical Layer Physical Layer
• It is the lowest layer of the OSI model. • The physical layer
• The physical layer is responsible for movements of individual bits from one • receives bits from the
data-link layer
node to another node.
• sends through the
• Transmission media is another hidden layer under the physical layer. transmission media
• It establishes, maintains and deactivates the physical connection.
• Two devices are connected by a transmission medium (cable or air).
• The transmission medium does not carry bits; it carries electrical or optical
signals.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Functions of a Physical layer Data-Link Layer
• Line Configuration: It defines the way how two or more devices can be • This layer is responsible for the error-free transfer of data frames.
connected physically. • The data link layer transforms the physical layer, a raw transmission
• Data Transmission: It defines the transmission mode whether it is facility, to a reliable link and is responsible for node-to-node delivery.
simplex, half-duplex or full-duplex mode between the two devices on • It makes the physical layer appear error-free to the upper layer
the network. (network layer).
• Topology: It defines the way how network devices are arranged. • The data link layer packages data from the physical layer into groups
• Signals: It determines the type of signal used for transmitting the called frames
information.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Data-Link Layer Functions of the Data-link layer
If frames are to be distributed • Framing
to different systems on the • Translates the physical's raw bit stream into packets known as Frames.
network, the data link layer • Adds the header and trailer to the frame
adds a header to the frame to • Header which is added to the frame contains the hardware destination
define the physical address of and source address
the sender (source address) • Physical Addressing
and/or receiver (destination • Adds a header to the frame that contains a destination address.
address) of the frame. • Frame is transmitted to the destination address mentioned in the
header

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Functions of the Data-link layer Functions of the Data-link layer
• Flow Control • Error Control
• Flow control is the main functionality of the Data-link layer • Achieved by adding a calculated value CRC (Cyclic Redundancy Check)
• Technique through which the constant data rate is maintained on both that is placed to the Data link layer's trailer which is added to the
the sides so that no data get corrupted message frame before it is sent to the physical layer.
• Ensures that the transmitting station such as a server with higher • If any error seems to occur, then the receiver sends the
processing speed does not exceed the receiving station, with lower acknowledgment for the retransmission of the corrupted frames.
processing speed

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Functions of the Data-link layer Network Layer
• Access Control: When two or more devices are connected to
the same communication channel, then the data link layer
protocols are used to determine which device has control over
the link at a given time.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Network Layer Network Layer
• It is in layer 3 that manages device addressing, tracks the location of • The network layer also has some auxiliary protocols that help IP in its delivery and
devices on the network. routing tasks
• Provides details that enable data to be routed between devices in an • The Internet Control Message Protocol (ICMP)helps IP to report some problems when
routing a packet
environment using
• The Internet Group Management Protocol (IGMP) is another protocol that helps IP in
• multiple networks
multitasking
• sub-networks
• The Dynamic Host Configuration Protocol (DHCP) helps IP to get the network layer
• both
address for a host
• The network layer is responsible for creating a connection between the
source computer and the destination computer The communication at
the network layer is host to host
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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Network Layer Functions of Network Layer:
• Responsible for addressing messages and data so they are sent to the correct • Internetworking
destination, and for translating logical addresses and names into physical addresses. • An internetworking is the main responsibility of the network layer
• Since there can be several routers from the source to the destination, the routers in • It provides a logical connection between different devices
the path are responsible for choosing the best route for each packet
• Addressing
• Networking components that operate at the network layer include routers and their
• A Network layer adds the source and destination address to the header of the
software.
frame
• Network layer in the Internet includes the main protocol, Internet Protocol (IP), that • Addressing is used to identify the device on the internet.
defines the format of the packet, called a datagram at the network layer.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Functions of Network Layer: Transport Layer
• Routing • The Transport layer is in Layer 4 ensures that messages are transmitted in
• Routing is the major component of the network layer the order in which they are sent and there is no duplication of data
• It determines the best optimal path out of the multiple paths from source to the • The transport layer controls and ensures the end-to-end integrity of the
destination data message propagated through the network between two devices
• Packetizing • Provides reliable and transparent transfer of data between two
• A Network Layer receives the packets from the upper layer and converts them endpoints
into packets. This process is known as Packetizing.
• It is achieved by Internet Protocol (IP). • The main responsibility of the transport layer is to transfer the data
completely

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Transport Layer (Steps followed) Transport Layer
1. The transport layer at the source host gets the message from the
application layer
2. Encapsulates the data in the transport layer (called a segment or a user
datagram in different protocols)
3. Sends it through the logical connection, to the network layer

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Transport Layer Transport Layer
The two protocols used in this layer are • Transmission Control Protocol
• Transmission Control Protocol (TCP) • It is a standard protocol that allows the systems to communicate over the
internet.
• User Datagram Protocol (UDP) • It establishes and maintains a connection between hosts.
• When data is sent over the TCP connection, then the TCP protocol divides the
data into smaller units known as segments.
• Each segment travels over the internet using multiple routes, and they arrive in
different orders at the destination.
• The transmission control protocol reorders the packets in the correct order at the
receiving end.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Transport Layer Functions of Transport Layer
• User Datagram Protocol • Service-point addressing
• User Datagram Protocol is a transport layer protocol. • Computers run several programs simultaneously due to this reason, the
• It is an unreliable transport protocol as in this case receiver does not send any transmission of data from source to the destination not only from one computer
acknowledgment when the packet is received to another computer but also from one process to another process.
• Sender does not wait for any acknowledgement • The transport layer adds the header that contains the address known as a
• This makes a protocol unreliable. service-point address or port address.
• The responsibility of the network layer is to transmit the data from one computer
to another computer and the responsibility of the transport layer is to transmit
the message to the correct process.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Functions of Transport Layer Functions of Transport Layer
• Segmentation and reassembly • Connection control
• When the transport layer receives the message from the upper layer, it divides • Transport layer provides two services Connection-oriented service and
the message into multiple segments, and each segment is assigned with a connectionless service.
sequence number that uniquely identifies each segment. • A connectionless service treats each segment as an individual packet, and they all
• When the message has arrived at the destination, then the transport layer travel in different routes to reach the destination.
reassembles the message based on their sequence numbers. • A connection-oriented service makes a connection with the transport layer at the
destination machine before delivering the packets.
• In connection-oriented service, all packets travel in the single route.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Functions of Transport Layer Session Layer
• Flow control • It defines how to start, control and end conversations (called sessions)
• The transport layer is also responsible for flow control but it is performed end-to- between applications.
end rather than across a single link.
• The Session layer is used to establish, maintain and synchronizes the
• Error control interaction between communicating devices.
• The transport layer is also responsible for Error control. • Session responsibilities include network log-on and log-off procedures
• Error control is performed end-to-end rather than across a single link. and user authentication.
• The sender transport layer ensures that the message reaches the destination
without any error. • Session layer characteristics include virtual connections between
applications or entities

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OSI Reference Model OSI Reference Model
Session Layer Functions of Session layer
• Dialog control: it allows the communication between two processes
which can be either half-duplex or full-duplex.
• Synchronization: Session layer adds some checkpoints when transmitting
the data in a sequence.
• If some error occurs in the middle of the transmission of data, then the
transmission will take place again from the checkpoint.
• This process is known as Synchronization and recovery.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Presentation Layer Presentation Layer
• Responsible for translation, compression, and encryption. • At the receiving side, the presentation layer receives data from the
• The presentation layer at sending side receives the data from the session layer decompresses and decrypts the data as required and
application layer adds header which contains information related to translates it back as per the encoding scheme used at the receiver.
encryption and compression and sends it to the session layer. • Presentation functions include
• data file formatting
• encoding
• encryption and decryption of data messages
• dialogue procedures
• data compression algorithms
• synchronization
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• interruption, and termination. Computer Networks
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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Presentation Layer Functions of Presentation layer:
• Translation
• The processes in two systems exchange the information in the form of character
strings, numbers and so on.
• Different computers use different encoding methods, the presentation layer
handles the interoperability between the different encoding methods.
• It converts the data from sender-dependent format into a common format and
changes the common format into receiver-dependent format at the receiving
end.

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OSI Reference Model OSI Reference Model
Functions of Presentation layer: Application Layer
• Encryption • Responsible for providing services to the user.
• Encryption is needed to maintain privacy. • An application layer serves as a window for users and application
• Encryption is a process of converting the sender-transmitted information into processes to access network service.
another form and sends the resulting message over the network.
• It handles issues such as network transparency, resource allocation, etc.
• Compression
• Data compression is a process of compressing the data, i.e., it reduces the • An application layer is not an application, but it performs the application
number of bits to be transmitted. layer functions.
• Data compression is very important in multimedia such as text, audio, video. • This layer provides the network services to the end-users.

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Reference Model Reference Model

OSI Reference Model OSI Reference Model
Application Layer Application Layer
• Communication at the application layer is between two processes  X. 400 (Electronic Mail Protocol)
• To communicate, a process sends a request to the other process and  X. 500 (Directory Server Protocol)
receives a response
• Process to process communication is the duty of the application layer

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Reference Model Reference Model

OSI Reference Model
Functions of Application layer:
• File transfer, access, and management (FTAM): An application layer
allows a user to access the files in a remote computer, to retrieve the
files from a computer and to manage the files in a remote computer.
• Mail services: An application layer provides the facility for email
forwarding and storage. 2. TCP/IP Protocol Suite
• Directory services: An application provides the distributed database
sources and is used to provide that global information about various
objects.

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TCP/IP Protocol Suite TCP/IP Protocol Suite
• The U.S. Department of Defense (DoD) created the TCP/IP reference
model because it wanted a network that could survive any conditions,
even a nuclear war.
• Transmission Control Protocol/Internet Protocol (TCP/IP) model is a set of
communication protocols that allow communication across multiple
diverse networks.
• TCP/IP is a hierarchical protocol comprised of either three or four layers.
• The three-layer version of TCP/IP contains the network, transport and
application layers.
• Four layer versions specify the host to network layer.
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Reference Model Reference Model

TCP/IP Protocol Suite TCP/IP Protocol Suite
• The designers of TCP/IP felt that the higher-level protocols should include • One of its protocols, the transmission control protocol (TCP), provides
the session and presentation layer details. excellent and flexible ways to create reliable, well-flowing, low-error
• They simply created an application layer that handles high-level network communications.
protocols, issues of representation, encoding, and dialog control. • TCP is a connection-oriented protocol.
• The TCP/IP combines all application-related issues into one layer, and • The other protocol is User Datagram Protocol (UDP) which is a
assures this data is properly packaged for the next layer. connection less protocol.
• The TCP/IP transport layer deals with the quality-of-service issues of
reliability, flow control, and error correction.

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Reference Model Reference Model

TCP/IP Protocol Suite TCP/IP Protocol Suite
• The purpose of the Internet layer is to send source packets from any
network on the internetwork and have them arrive at the destination
independent of the path and networks they took to get there.
• The specific protocol that governs this layer is called the Internet
protocol (IP).
• Best path determination and packet switching occur at this layer.
• The network access layer also called the host-to-network layer is
concerned with all of the issues of physically delivering data packets
using frames or cells.

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TCP/IP Protocol Suite TCP/IP Protocol Suite
Differences between OSI and TCP/IP
• TCP/IP combines the presentation and session layer issues into its
application layer
• TCP/IP combines the OSI data link and physical layers into one layer
• TCP/IP appears simpler because it has fewer layers
• TCP/IP protocols are the standards around which the Internet developed,
so the TCP/IP model gains credibility just because of its protocols. In
contrast, typically networks aren't built on the OSI protocol, even though
the OSI model is used as a guide.
Addressing in TCP/IP Protocol Suite

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Thank you!

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