OSI Model

'Open Systems Interconnection' model.

A conceptual model that categorizes and standardizes the different functions in a network.

Created by the 'Internation Organization for Standardization' (ISO).

Functions are divided into 7 'layers'.

These layers work together to make the network work.

Layers

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

Mnemonic

All

People

Seem

To

Need

Data

Processing

Adjacent-layer Interactions

Refers to the interaction between different layers of the OSI Model.

Encapsulation

The data begins in the topmost layer (Layer 7) and goes through all layers before being sent, in each layer, a new piece of information is added.

De-encapsulation

Is the inverse process.

Same-layer interaction

Refers to the interaction between the same layer on different hosts. This concept allows you to 'ignore' the other layers involved and focus on the interactions between a single layer on different devices.

The Upper Layers

Network engineers don't usually work with the top 3 layers.

Application developers work with the top layers of the OSI model to connect their applications over networks.