What is OSI Model?

Summary

The OSI model is a seven-layer framework that explains how applications communicate over networks. Starting from the Application layer, it includes Presentation, Session, Transport, Network, Data Link, and Physical layers. Each layer has a specific role, from user interaction and data formatting to actual data transmission and hardware interaction. The model aids in understanding network operations and ensures compatibility among networking devices and software.

Takeaways

• 🌐 OSI stands for Open Systems Interconnection and serves as a framework for how applications communicate over a network.
• 📚 The model consists of seven layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical.
• 🔍 Each layer has a specific role, from providing network services to users at the Application layer to handling the physical transmission of data at the Physical layer.
• 🌐 The Application layer (Layer 7) is where most users interact, offering services like HTTP for web browsers and applications like Office, Outlook, and Skype.
• 🔐 The Presentation layer (Layer 6) is responsible for syntax processing, such as encrypting and decrypting data for secure transmission.
• 🔗 The Session layer (Layer 5) manages the establishment, direction, and termination of connections, including authentication and reconnection in case of network interruptions.
• 🚚 The Transport layer (Layer 4) oversees the transmission of data, determining how much data to send, the speed, and the destination, with protocols like TCP and UDP.
• 🗺️ The Network layer (Layer 3) handles routing, ensuring data reaches its intended destination, and is where IP addresses and routing protocols like ARP are managed.
• 🔌 The Data Link layer (Layer 2) is complex and often divided into MAC and LLC sublayers, dealing with physical addressing and error checking in data transmission.
• 🔩 The Physical layer (Layer 1) is the electrical/physical aspect of the model, involving network cables, wireless frequencies, and the actual transmission of data bits.
• 🛠️ The OSI model guides developers and vendors in creating compatible communication products and software, facilitating smooth and standardized network operations.

Q & A

What does OSI stand for and what is its purpose?

OSI stands for Open Systems Interconnection. It is a conceptual framework that defines standards for how applications communicate over a network.

How many layers are there in the OSI model?

There are seven layers in the OSI model.

What are the seven layers of the OSI model?

The seven layers of the OSI model are Application, Presentation, Session, Transport, Network, Data Link, and Physical.

Which layer of the OSI model do most users interact with?

Most users interact with the Application layer, which is layer 7.

What is the primary function of the Application layer?

The Application layer provides network services to the end user, such as protocols that work with the data the client is using.

Can you give examples of protocols used in the Application layer?

Examples of protocols used in the Application layer include HTTP for web browsers and applications like Office, Outlook, and Skype.

What is the role of the Presentation layer in the OSI model?

The Presentation layer, or layer 6, is responsible for syntax processing and converting data from one format to another, such as decrypting and processing encrypted data.

What happens at the Session layer?

The Session layer, or layer 5, manages the construction, direction, and conclusion of connections between devices, including authentication and reconnection in case of network interruptions.

What is the main responsibility of the Transport layer?

The Transport layer, or layer 4, is responsible for the transmission of data across network connections, including coordinating how much data to send, how fast, and where it goes.

How does the Network layer contribute to data transmission?

The Network layer, or layer 3, handles the routing of data, determining the correct destination for each frame of data, and managing the mapping between logical and physical addresses using protocols like IP and ARP.

What are the sublayers of the Data Link layer?

The Data Link layer, or layer 2, is divided into sublayers called Media Access Control (MAC) and Logical Link Control (LLC), which set up links across the physical network and manage physical addressing methods.

What is the significance of the Physical layer in the OSI model?

The Physical layer, or layer 1, is responsible for the actual transmission of digital data bits over network communications media, such as electrical cables, wireless radio frequencies, and optical signals.

Why is the OSI model important for developers and vendors?

The OSI model serves as a guide for developers and vendors to ensure that communication products and software programs are compatible and work in cooperation with a commonly established model.

Outlines

00:00

🌐 Understanding the OSI Model

The OSI model, or Open Systems Interconnection, is a conceptual framework that outlines how applications communicate over a network. It consists of seven layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical. Each layer has a specific role, from providing network services to the end user at the Application layer to handling the transmission of data bits at the Physical layer. The model aids in understanding what occurs within a networking system and is crucial for the development of compatible communication products and software programs.

05:03

🔍 Deep Dive into OSI Model Layers

This paragraph delves into the specifics of each OSI model layer. The Application layer (layer 7) interacts with users and applications like web browsers and Office software. The Presentation layer (layer 6) is responsible for syntax processing and data conversion. The Session layer (layer 5) manages connections, authentication, and reconnection. The Transport layer (layer 4) oversees data transmission, with protocols like TCP and UDP. The Network layer (layer 3), notably using IP, handles routing and address mapping with ARP. The Data Link layer (layer 2), which includes MAC and LLC sublayers, sets up links and checks for transmission errors. Finally, the Physical layer (layer 1) deals with the actual transmission of data bits through various media. The OSI model serves as a guide for developers to ensure compatibility among different networking components.

Keywords

💡OSI Model

The OSI Model, or Open Systems Interconnection Model, is a conceptual framework that standardizes the functions of a networking system into seven distinct layers. It serves as a guide for developers and vendors to ensure compatibility and interoperability among different networking technologies. In the video, the OSI Model is the central theme, with each layer being described to help viewers understand how data is transmitted and processed across a network.

💡Application Layer

The Application Layer is the topmost layer of the OSI Model, which provides network services to end-users. It is the layer where most users interact, as it includes protocols and applications like web browsers (HTTP), Office, Outlook, and Skype. The video script mentions this layer as the starting point for data transmission, highlighting its role in facilitating user interactions with network services.

💡Presentation Layer

The Presentation Layer, or layer 6, is responsible for syntax processing, which involves converting data from one format to another. This layer ensures that data is presented in a format that can be understood by the receiving application. An example given in the script is the decryption and processing of encrypted data from an online store, showcasing how this layer translates data for secure transmission.

💡Session Layer

The Session Layer, or layer 5, manages the establishment, direction, and termination of connections between network devices. It supports various types of connections and handles authentication and reconnection in case of network interruptions. The video emphasizes this layer's role in maintaining and managing the sessions that enable communication between devices.

💡Transport Layer

The Transport Layer, or layer 4, is crucial for the transmission of data across network connections. It coordinates the amount of data sent, the speed of transmission, and the destination. The video mentions protocols like TCP and UDP, which provide services such as error recovery and data flow management, illustrating the importance of this layer in ensuring reliable data transfer.

💡Network Layer

The Network Layer, or layer 3, is responsible for the routing of data packets. It examines each frame to determine if the data has reached its final destination and manages the forwarding of data to the correct destination. The video script explains the role of IP within TCP/IP as a key component of this layer, which also handles the mapping of logical to physical addresses using ARP.

💡Data Link Layer

The Data Link Layer, or layer 2, is considered the most complex layer as it is often divided into sublayers like MAC and LLC. This layer sets up links across the physical network, checks for transmission errors, and packages bits into data frames. The video provides examples such as 802.11 wireless specifications and Ethernet, which are part of the MAC layer, to illustrate how this layer manages physical addressing and error checking.

💡Physical Layer

The Physical Layer, or layer 1, is the lowest layer of the OSI Model and represents the electrical and physical aspects of a network. It includes network cables, power plugs, wireless radio frequencies, and other hardware components. The video script describes this layer as the starting point for troubleshooting network issues, emphasizing its role in transmitting digital data bits over various communication media.

💡Protocols

Protocols are set rules that govern the format and transmission of data. They are essential for the proper functioning of the OSI Model layers. The video mentions several protocols, such as HTTP for web browsing, TCP and UDP for data transmission, and ARP for address resolution. These protocols ensure that data is transmitted and received correctly across the network.

💡Ethernet

Ethernet is a widely used family of networking technologies for local area networks (LANs). It is mentioned in the video as one of the methods facilitated by the Data Link and Physical layers for the transmission of signals. Ethernet standards, such as 802.3, define the physical and data link layer specifications for wired Ethernet, which is crucial for understanding the practical application of these layers.

💡Wireless Protocols

Wireless protocols, such as Wi-Fi, are methods for transmitting data over wireless networks. The video script includes Wi-Fi as an example of how the OSI Model layers facilitate the transmission of signals. These protocols operate over radio frequencies and are essential for understanding the role of the Physical Layer in wireless communication.

Highlights

OSI stands for Open Systems Interconnection, a framework for how applications communicate over a network.

The OSI model consists of seven layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical.

The layers facilitate the transmission of signals over various networking protocols like Ethernet, Fiber Optic, Wi-Fi, etc.

The Application layer (layer 7) provides network services to end users and includes protocols like HTTP, used by web browsers.

Office, Outlook, and Skype are examples of applications that utilize the Application layer.

The Presentation layer (layer 6) is responsible for syntax processing and data format conversion.

Data encryption and decryption are handled by the Presentation layer for secure transactions.

The Session layer (layer 5) manages the construction, direction, and conclusion of connections between devices.

The Transport layer (layer 4) coordinates data transmission, including how much data to send and how fast.

TCP and UDP are widely known protocols that provide services at the Transport layer.

The Network layer (layer 3) handles data routing and uses IP, the Internet's commonly known network layer.

ARP (Address Resolution Protocol) is used by the Network layer to map logical to physical addresses.

The Data Link layer (layer 2) is complex and often divided into MAC and LLC sublayers.

The Data Link layer checks for transmission errors and packages bits into data frames.

802.11 wireless specifications and Ethernet are examples of the MAC layer within the Data Link layer.

The Physical layer (layer 1) encompasses network cables, power plugs, wireless radio frequencies, and other physical components.

The Physical layer transmits digital data bits from the source to the destination devices over network media.

The OSI model serves as a guide for developers and vendors to ensure compatibility in communication products and software.

Transcripts

OSI stands for Open Systems Interconnection

and is a conceptual framework

for how applications communicate over a network.

There are seven layers within the model

and the layers depiction is used to help users identify

what is happening within a networking system.

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The OSI model layers are typically described from the top layer down.

The layers are described as Application,

Presentation, Session, Transport, Network, Data Link, and Physical.

These layers are provided by a mixture of network card drivers,

operating systems, applications, and networking hardware

that facilitate the transmission of signals over Ethernet,

Fiber Optic, Wi-Fi, or other wireless protocols.

We’ll describe the layers from the top down

as the top layer is the Application layer or layer 7.

This is the layer that most users interact with and will recognize.

The Application layer provides network services to the end user.

These services are protocols

that work with the data the client is using.

One of these protocols may be HTTP

that is used with web browsers such as Google Chrome,

Firefox, and Internet Explorer.

Other examples of applications that use this layer

are Office, Outlook, and Skype.

All of those interactive applications provide a set of services

that allow the application layer to supply data to

and receive data from the Presentation layer.

The Presentation layer, or layer 6,

performs the uncomplicated task of syntax processing

or converting data from one format to another.

For example, consider you are ordering something from an online store.

These transactions are typically handled in a secure transmission

which means that the data passing between the “store”

or the Website Application

will transmit encrypted data to the Presentation layer

that will need to be decrypted and processed.

This layer handles translating the data from the top layer,

which is presented in application format,

to network format and vice versa.

After the Presentation layer processes the data from one format to another,

the information is then passed to the Session layer

or the Application layer depending on whether the data

is transmitting or receiving.

At the Session layer, or layer 5, the construction,

direction, and conclusion of connections between devices occur.

This layer supports multiple types of connections

as well as being responsible for authentication and reconnection

if a network interruption should occur.

After the session is established

the data then passes to or from the Transport layer.

The Transport layer, or layer 4,

is responsible for the transmission of data across network connections.

This layer coordinates how much data to send, how fast,

where it goes, and these sorts of things.

Of the most widely known protocols for internet applications,

these services may be provided by Transmission Control Protocol

or TCP and User Datagram Protocol or UDP.

Other protocols may provide additional capabilities

including error recovery, data flow, and retransmission.

Once the Transport layer has completed its function,

the data is then passed to or from the Network layer.

The Network layer, or layer 3, handles the routing of the data.

After the data arrives at this layer,

each frame of data is examined to conclude

if the data has reached its ultimate target.

The layer sends data to the correct destination

on outgoing transmissions and receives incoming transmissions as well.

The IP portion of TCP/IP

is the commonly known network layer for the Internet.

This layer also manages the mapping between logical addresses

and physical addresses,for IP addresses,

this is accomplished through Address Resolution Protocol or ARP.

The data is then passed to the next required layer

which is the Data Link layer.

The Data Link layer, or layer 2,

is considered the most complex of the layers.

This layer is often divided into sublayers

called Media Access Control or MAC and Logical Link Control or LLC.

The layer sets up links across the physical network.

When this layer receives data from the Physical layer,

it checks for transmission errors

and then packages the bits into data frames.

From there, this layer manages the physical addressing methods

for the MAC or LLC layers.

An example of the MAC layer includes 802.11

wireless specifications as well as Ethernet.

At the Data Link layer, the data passes to or from the final layer

in the OSI model which is the Physical layer.

The Physical layer, or layer 1, is the electrical/physical layer of the model.

This layer encompasses the network cables, power plugs,

cable pinouts, wireless radio frequencies, connectors,

transceivers, receivers, repeaters, pulses of light, electric voltages, etc.

When troubleshooting problems,

this is typically the first place to start.

Is the device plugged in?

Is the wireless card working?

At this layer, the model transmits the digital data bits from the source

or sending devices Physical layer,

over network communications media,

which can be electrical, mechanical,

or radio, to the receiving or destination devices Physical layer.

The OSI model is a guide for developers and vendors

to smooth the progress of developing communication products and software programs

that will work in cooperation with a commonly established model.

Once you understand the model,

you can then understand which protocols and devices

will be compatible with one another.

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