OSI Model

The Open Systems Interconnection (OSI) model is the structure that explains a networking system. The model has 7 layers and was first conceived in the 1970s when networking was initially conceived. In a nut shell the OSI model is the list of operations that happen within a networking system. It is also a universal language of networking. The 7 layers are as follows: Application, Presentation, Session, Transport, Network, Data Link, and Physical.

Layer 7: Application

This layer is what the user interacts with directly. Applications such as web browsers and email clients utilize this layer to communicate. However software applications are not actually part of the layer itself, instead the layer is what is responsible for transmitting the data that the software needs to the user. An example of an application protocol is HTTP.

Layer 6: Presentation

The presentation layer is responsible for preparing the data before it reaches the application layer. Its preparation includes the translation and encryption of data. An example of how layer 6 functions is if two devices with different encoding methods need to communicate with each other. Layer 6 would first add encryption for the data coming from the first device then translate it into a syntax the other device understands and decode it so that the information can be properly displayed on the second device. Another important job for layer 6 is the compression that it provides when delivering data.

Layer 5: Session

Layer 5 is used to create and close sessions when two devices are communicating. For example when one device wants to communicate with another a session is opened and once the communication stops the session is closed. Since layer 5 is responsible for sessions it’s also responsible for synchronizing data between devices.

Layer 4: Transport

This layer is responsible for getting the data from one device to the other. This means that the data which is broken up into chunks before layer is reassembled by layer 4. Another two important responsibilities are flow and error control. These two factors determine how fast data is sent and whether the data sent is complete.

Layer 3: Network

The network layer is what transfers data between networks. This layer breaks up information into packets and sends to another device. If there isn’t communication between two networks this layer isn’t used. The network layer also tries to find the best route to transfer data from one network to another.

Layer 2: Data Link

Layer 2 is very similar to layer 3 because it facilitates the transfer of packets within a local area network. This means that information is still converted into packets but there isn’t communication between two networks instead information is only transported within one network. Layer 2 is also responsible for flow and error control.

Layer 1: Physical

This layer as the name suggests involves the physical components of networking. Physical equipment such as routers and cables are used to move information from network to network.

-Allen Shen



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