Theoretical stack of 7 levels that explain how networks operate

Enables multi-vendor networks

Not actually used, instead it is TCP. However, used when troubleshooting and describing network operations.

The layers are structured in the following way (bottom-up)

Layer 1 - Physical - lowest layer carries the data across physical hardware (i.e. ethernet cables)

Layer 2 - Data Link - physical addresses are added to the data (source and destination MAC addresses)

Layer 3 - Network - IP addressing and routing routers operate source and destination IP addresses

Layer 4 - Transport - adds transport protocols such as TCP used for error handling and sequencing, the layer also adds and destination port numbers

Layer 5 - Session - layer responsible for establishing and terminating connections between devices

Layer 6 - Presentation - formats the data in a way the receiving application can understand it, this layer can also encrypt data if needed

Layer 7 - Application - where the application and user communicate

A way of remembering the layers is through an acronym APSTNDP - All People Seem To Need Data Processing

The way it is processed is in 7-1 order from sending device to receiving device in 1-7.

TCP/IP Model

Same description as the OSI Model, except it is used in the real-world

Decapsulation is the process of a receiving device removing the headers and trailers that were added to a data packet during encapsulation. Think of it as unwrapping a series of nested packages.

Encapsulation (below screenshot) is the process of adding headers and sometimes trailers to a data packet as it moves down the layers of the network stack, from the application layer to the physical layer, at a source device.