An In-Depth Examination of the OSI Model and Its Layers

This report provides a detailed overview of the OSI model, a conceptual framework for standardizing communication functions in computer systems. It dissects the model into its seven layers: physical, data link, network, transport, session, presentation, and application. Each layer's function is explained, including the devices used (e.g., hubs, routers, firewalls), applications, protocols (e.g., TCP, IP), and services offered (e.g., error control, addressing, encryption). The report emphasizes the importance of the OSI model in understanding network architecture and how software and hardware interact to facilitate data transmission. The discussion covers how each layer contributes to the overall process of communication, from the transmission of raw data to the user applications, and how they interact with each other to ensure reliable and efficient data transfer. The conclusion highlights the OSI model's significance in understanding network technologies and its role in the interoperability of diverse communication systems.

Running head: OSI MODEL
OSI Model
Name of the Student
Name of the University
Author Note

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Table of Contents
Introduction:....................................................................................................................................2
Layer 1: Physical Layer...................................................................................................................2
Layer 2: Data Link Layer................................................................................................................3
Layer 3: Network Layer...................................................................................................................4
Layer 4: Transport Layer.................................................................................................................5
Layer 5: Session Layer....................................................................................................................6
Layer 6: Presentation Layer.............................................................................................................6
Layer 7: Application Layer..............................................................................................................7
Conclusion:......................................................................................................................................8
References:......................................................................................................................................9

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Introduction:
The open system interconnection model or the OSI model is considered as a conceptual
model that is used for standardizing and characterizing communication functionalities of a
computer system without regard to the underlying technology and internal structure [1]. The
main purpose of the OSI model is interoperability of diverse type of communication system by
utilization of standard protocol of communication. Through the OSI model, the communication
system is partitioned into some abstraction layers. The original version of the OSI model consists
of a total of seven layers [2]. In these abstraction layers, a specific layer serves the above layer of
it while that specific layer is served by the below layer. The OSI model is actually an Open
System Interconnection project at the ISO or the International Organization for Standardization.
It is previously mentioned that the original OSI does have seven layers. These seven
layers are the physical layer, data link layer, network layer, transport layer, session layer,
presentation layer and application layer. In the following section of this report, all of these seven
layers will be discussed briefly. Here, applications, devices, services and protocols in each of
these seven layers will be evaluated briefly.
Layer 1: Physical Layer
The physical layer of the OSI model takes the responsibility of reception and
transmission of the unstructured raw data among a physical transmission medium and a device.
Currently, in the physical layer, there are several devices which are operational. The main
devices that are used in the physical layer are the hubs, repeaters, network interface cards,
connectors and cables [3]. The repeaters are used for regeneration of the electrical signals that
have weakened due to the distance issue. Hub is another important device in the physical layer,

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which is used as a common point of connection for the optical fibres or twisted pair cables that
connects devices within a local area network.
There are various applications that are executed by the physical layer of the OSI model.
Here, one of the main responsibility of the physical layer is sending bits one computer system to
another computer. The physical layer is capable of converting the digital bits into other types of
signal which includes optical, radio and electrical signals [4]. Also, the physical layer defines the
transmission rate, and it is the number of bits per second.
Some specific type of protocol is also used in the physical layer. The important protocols
of the physical layer are the DSL, CSMA/CD and RS-232. The DSL is the digital subscriber line.
RS-232 is mainly used in the serial ports of the computer systems.
The services performed by the physical layer are upon the request of the data link layer.
The main services performed by the physical are terminating and establishing of connections to a
communication medium, performing efficient sharing within multiple devices and conversion of
the digital type of data, understandable by digital computers and analogue signals.
Layer 2: Data Link Layer
In data link layer also different types of devices are used. The important devices that are
used in the data link layer are the modems, bridges, 2-layer switches and the network cards. Each
of the devices plays an important role in the data link layer.
The data link layer is the second layer in the OSI model. The data link layer is used in the
OSI model for performing three important applications. The first important application of the
data link layer is dealing with the transmission error [5]. Secondly, the data link layer is

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important for regulating the data flow. Lastly, another application of the data link layer is
providing an appropriate interface to the network layer.
Considering the protocols, there is a total of six protocols that are operated in the data
link layer. The first protocol is the SDLC protocol or the synchronous data link protocol. The
other protocols of the data link layer are the high-level data link protocol, point-to-point protocol,
serial line interface protocol, network control protocol and link control protocol.
There is a total of six services which are executed by the data link layer. Framing and link
access is one important service provided by the data link layer. Reliable delivery is another
important service that is provided by the data link layer [6]. The remaining services offered by
the data link layer are the error detection, flow control, error correction and half-duplex and full-
duplex.
Layer 3: Network Layer
The main devices which are used in the network layer are the brouters, routers and 3-
layer switches. All of these devices play an important role in the network layer.
The main application of the network layer is controlling the subnet operation. Here, the
network layer utilized for delivering the packets from the source point to the destination point
across multiple links [7]. The network layer can be omitted if the two computer systems are
connected in the same link.
Some important protocols which are currently active in the network layer are the
connectionless networking protocol, internet protocol, routing information protocol, address
resolution protocol, hot standby routing protocol and IPsec.

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There are mainly four services which are performed by the network layer. The first
service is the internetworking. Through internetworking, a logical connection is established
among different devices. The next service is addressing service. The addressing service is used
for identification of the devices on the internet. Routing is another service in the network layer
which determines the best optimal path from the source point to the destination point.
Packetizing is the last service provided by network layer which is used for receiving packets
from the upper layer and converting into the packets.
Layer 4: Transport Layer
The transport layer mainly includes two important devices. Gateways and the firewalls
are the main devices that are used in the transport layer.
The main application of the transport layer is ensuring that all the units of data that has
been delivered do not have any type of error, and it also ensured that all the data follows an
appropriate sequence. Reliability of the link is also maintained by the transport layer by proper
error and flow control.
There are mainly two important protocol that is used in the transport layer is the user
datagram protocol and transmission control protocol (TCP). The user datagram protocol is
actually an unreliable type of protocol [8]. The transmission control protocol allows the system
so that the system can communicate over the internet.
Total five services are executed in the transport layer. These five services are the error
control service, flow control, connection control, segmentation and reassembly and the service
point addressing. All of these five services are important for the transport layer for performing
important operations.

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Layer 5: Session Layer
The transport layer and the session layer uses a similar kind of devices. The session layer
includes firewalls, gateways and PCs as devices which are operational at the session layer.
The main application of the session layer is establishing, maintaining and synchronizing
the interactions among the communicating devices [9]. In this way, it actually manages the end-
user applications.
In the session layer, there are some important protocols are used. These important
protocols of the session layer include the point-to-point tunnelling protocol, remote procedure
call protocol, session description protocol and the session control protocol.
There are two important services which are executed by the session layer. These two
services are synchronization and dialogue control. There are some specific checkpoints are
included by the session layer during transmission of the data. In this case, if any type of error
occurs during the data transmission, then the transmission will be starting again from the nearest
checkpoint [10]. This service is synchronization. Dialogue control is important for creating
dialogue among two processes which is useful, allowing communication among two processes.
Layer 6: Presentation Layer
In the aspect of devices used, the presentation layer is exactly the same as the session
layer. Means, the presentation layer includes the devices PCs, firewalls and gateways.
There are some important applications which are performed by the presentation layer.
The main application of the presentation layer is concerned with semantic and the syntax of the
information exchanged among two systems. Another application of the presentation layer is that
it acts as a data translator for the network.

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The main protocols that are used in the presentation layer are the secure socket layer
protocol and the transport layer security protocol. Other two protocols of the presentation layer
are the XDR protocol and the MIME protocol.
There is a total of three important services which are provided by the presentation layer.
These three services are compression, encryption and translation. In compression, the transmitted
data is compressed for reducing the number of bits that needs to be transferred [11]. Encryption
service is important in the presentation layer so that data privacy can be maintained for the data
which will be transmitted. The translation is the service through which two system exchanges
information among each other in the form of character strings.
Layer 7: Application Layer
In the aspect of devices, for the application layer again, the firewall and the gateways are
common. Other than that all the end devices are included in the application layer, which includes
the servers, PCs, phones and the other end-user devices.
The application layers include some of the important applications that need to be
executed properly. The main application of the application layer is providing a window for the
users so that network service can be accessed. Also, the application layer is important for dealing
with some specific issues, which includes handling the issues regarding the transparency of the
network and allocation of the resources. Also, the application layer is important for providing
network services to the end-users.
The important protocols that are functional within the application layer are the simple
object access protocol, simple service discovery protocol, domain name system protocol, DHCP,
file transfer protocol, SMTP, SSH and Telnet.

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There are a total of three important services which are provided by the application layer.
These services are the directory services, mail services and file transfer, access and management
services. The directory service is used for providing global information regarding various objects
[12]. The mail service is important for email storage and forwarding. The transfer, access and
management service is useful for allowing the users to access the files in a remote environment
where the files can be accessed from a computer system.
Conclusion:
From the above discussion, it can be concluded that the OSI model is very much
important as it helps to understand the big picture that is associated with a network. The OSI
model can help to understand how software and the hardware is capable of working together.
Also, the OSI model can help to understand the new technologies. From the discussion, it has
been identified that the OSI model is having a total of seven layers. These seven layers are the
physical layer, data link layer, network layer, transport layer, session layer, presentation layer
and the application layer. In this report, all of these seven layers have been discussed briefly. For
each of the layers, the important devices have been explained. After the explanation of the
devices, applications performed by each of the layers has been discussed. In the following
section of the report, respective protocols for each of these layers has been discussed, and
services provided by these layers have been demonstrated.

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References:
[1] J. Zhao et al., "The Discussion about Mechanism of Data Transmission in the OSI
Model", Proceedings of the 2018 International Conference on Transportation & Logistics,
Information & Communication, Smart City (TLICSC 2018), 2018. Available: 10.2991/tlicsc-
18.2018.1
[2] M. Moreira Santos and P. Alcívar Marcillo, "Security in the data link layer of the OSI model
on LANs wired Cisco", Journal of Science and Research: Revista Ciencia e Investigación, vol.
3, no. 2017, pp. 106-112, 2018. Available: 10.26910/issn.2528-8083vol3isscitt2017.2018pp106-
112
[3] S. Pechetti, A. Jindal and R. Bose, "Exploiting Mapping Diversity for Enhancing Security at
Physical Layer in the Internet of Things", IEEE Internet of Things Journal, vol. 6, no. 1, pp. 532-
544, 2019. Available: 10.1109/jiot.2018.2842056
[4] H. El-Sallabi, Y. Basahl and A. Aldosari, "Physical Layer Security based on Time Reversal
Technique for Urban Radio Channels", 2018 IEEE International Symposium on Antennas and
Propagation & USNC/URSI National Radio Science Meeting, 2018. Available:
10.1109/apusncursinrsm.2018.8609033
[5] L. Lopacinski, M. Eissa, G. Panic, A. Hasani and R. Kraemer, "Modular Data Link Layer
Processing for THz communication", 2019 IEEE 22nd International Symposium on Design and
Diagnostics of Electronic Circuits & Systems (DDECS), 2019. Available:
10.1109/ddecs.2019.8724657

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[6] L. Lopacinski, M. Eissa, G. Panic, M. Brzozowski, A. Hasani and R. Kraemer,
"Implementation of a Multi-Core Data Link Layer Processor for THz Communication", 2018
IEEE 87th Vehicular Technology Conference (VTC Spring), 2018. Available:
10.1109/vtcspring.2018.8417522
[7] H. Peng, L. Liang, X. Shen and G. Li, "Vehicular Communications: A Network Layer
Perspective", IEEE Transactions on Vehicular Technology, vol. 68, no. 2, pp. 1064-1078, 2019.
Available: 10.1109/tvt.2018.2833427
[8] E. Bonfoh, S. Medjiah, C. Chassot and J. Aguilar, "Towards the Virtualization of Transport-
level Functions and Protocols", 2018 International Conference on Smart Communications in
Network Technologies (SaCoNeT), 2018. Available: 10.1109/saconet.2018.8585578
[9] U. Kalim, M. Gardner, E. Brown and W. Feng, "SLIM: Enabling Transparent Extensibility
and Dynamic Configuration via Session-Layer Abstractions", 2017 ACM/IEEE Symposium on
Architectures for Networking and Communications Systems (ANCS), 2017. Available:
10.1109/ancs.2017.30
[10] G. Howser, "The OSI Seven Layer Model", Computer Networks and the Internet, pp. 7-32,
2019. Available: 10.1007/978-3-030-34496-2_2
[11] S. Madhu, M. BalRaju and P. Reddy, "Enhancing transport of media using MAC layer
based approach", 2017 International Conference on Computer Communication and Informatics
(ICCCI), 2017. Available: 10.1109/iccci.2017.8117725
[12] S. Mijovic, E. Shehu and C. Buratti, "Comparing application layer protocols for the Internet
of Things via experimentation", 2016 IEEE 2nd International Forum on Research and

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Technologies for Society and Industry Leveraging a better tomorrow (RTSI), 2016. Available:
10.1109/rtsi.2016.7740559