OSI Model(Open Systems Interconnection)

what is OSI model?

The OSI stands for open systems interconnection and it is a comceptual a 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.

# 7 Application layer

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 browers 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 and receive data from the Presentation layer.

# 6 Presentation layer

The presentation layer performs uncomplicated task of syntax processing or converting data from one format to another.
For instance, considering you are ordering something from an online store.
These transactions are typically handle 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 Application layer depending on the application data is transmitting or receiving.

# 5 Session layer

At the Sesion layer, 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 Sessin layer is established, the data then passes to or from the Transport Layer.

# 4 Tansport layer

The transport layer is reponsible 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 know protocols for internet applications, these services may be provided by Transmission Control Protocol (TCP) and User Datagram Protocol(UDP).

Other protocols may provide additional capabilities including error recovery, data flow, and retransmission.

Once the Transport layer has completed its functions, the data is then passed to or from the Network layer.

# 3 Network layer

The network layer 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 traget.
The layer sends data to the correct destination on outgoing transmissions and receives incoming transmission as well.
The IP protion of TCP/IP is the commonly know 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 (ARP).
The data is then passed to the next required layer, which is the
Data Link Layer.

# 2 Network layer

The Data LInk Layer is considered the most complex of the layers. This layer is often divided into sublayers, called Media Access Control(MAC) and Logical Link Control(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 whireless specifications as well as Ethrnet.
At the Data Link Layer, the data passes to or from the final layer, which is the Physical layer.

# 1 Physical layer

The Physical layer 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.