The OSI Model.
The OSI Model (Open Systems Interconnection Model) is a conceptual framework used to describe the functions of a networking system. The OSI model characterizes computing functions into a universal set of rules and requirements in order to support interoperability between different products and software.
THE OSI MODEL
The OSI partitions a communication system into seven layers. The layers are:
- Application layer,
- Presentation layer,
- Session layer,
- Transport layer,
- Network layer,
- Data Link layer,
- Physical layer.
You might, be wondering what is the relation between a sausage pizza and the OSI model.
You can remember the layer names with one simple phrase:
Please do not throw sausage pizza away.
Physical, Data link, Network, Transport, Session, Presentation, Application.
The layers
Let’s start understanding the OSI model from the top layer to the bottom layer, starting from the application layer.
7. Application layer :
This is the topmost layer in the seven OSI Layers. This is the layer that the end-user is actually interacting with. Application layer allows access to network resources.
6. Presentation Layer :
The presentation layer can also be called as the “translation layer”. It “translates” data going to and from the application layer. Basically User interacts with Application layer, which sends the data down to Presentation layer.
5. Session Layer :
The session layer is responsible for coordinating sessions between machines. To provide authentication and security, a session must be created for two devices on the network to connect with each other. This layer creates, manages, and ends these sessions.
4. Transport Layer :
The transport layer is the “traffic control” of networks. This layer has a very important job. It decides how much information should be sent at a time. So, when you are communicating with a website, this layer will decide how much data you can transfer and receive at a given point of time.
3. Network Layer :
The network layer is the “post office” of networks. The main job of this layer is to move packets from source to destination and provide inter-networking. This is the layer that the routers operate on. Since routers operate at the network level, hence we can say that the IP address is at the network level.
2. Data Link Layer :
The data link layer is responsible for the node to node delivery of the message. The main function of this layer is to make sure data transfer is error-free from one node to another, over the physical layer. When a packet arrives in a network, it is the responsibility of DLL to transmit it to the Host using its MAC address.
1. Physical Layer :
This is the layer on which the real transmission of data bits takes place through a medium. This layer is, as the name suggests, all the physical stuff that connects the computers together.
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