OSI Network Model

Open Systems Interconnection (OSI) model - a conceptual framework that describes the functions of a networking or telecommunication system.

The OSI model has 7 layers. 


Layer 7 - Application Layer

This is what the user communicates with. It is the applications that we used - Google Chrome & Skype are examples. 


Layer 6 - Presentation 

This is where data is converted from the application framework into something that the network understand. The data would be encrypted here for example. 


Layer 5 - Session

Computer need to create a session between the two devices so they can speak to each other. This is done here. The computer communicate telling each other how much time they should wait for a response from each other and what they should do when the task has been completed (end session) etc. 


Layer 4 - Transport 

The Transport Layer deals with the coordination of the data transfer between end systems and hosts. This is where the protocol is decided on. TCP/IP is commonly used here. This is only where a port number will be decided. 


Layer 3 - Network

This layer is responsible for packet forwarding, including routing through different routers. This is where IP addresses are assigned. 


Layer 2 - Data Link

The Data Link Layer provides node-to-node data transfer. This is where MAC addresses are assigned. 


Layer 1 - Physical

This is just the physical hardware that makes all of the above work. Such as NICs, networking cables and the router itself. 

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