The **Open Systems Interconnection model** (**OSI model**) describes _seven layers_ that computer systems use to communicate over a network. Each layer in the OSI model has well-defined functions, and the methods of each layer communicate and interact with those of the layers immediately above and below as appropriate.^[[OSI model - Wikipedia](https://en.wikipedia.org/wiki/OSI_model)] | Number | Name | Description | Example | | --- | --- | --- | --- | | 7 | Application Layer | Human-computer interaction layer, where applications can access the network services. | HTTP(S), FTP, SMTP, DNS, etc. | | 6 | Presentation Layer | Ensures that data is in a useable format and is where data encryption occurs | x | | 5 | Session Layer | Maintains connections and is reponsible for controlling ports and sessions | x | | 4 | Transport Layer | Transmits data using transmission protocols including TCP and UDP | TCP, UDP, ... | | 3 | Network Layer | Decides which physical path the data will take | x | | 2 | Data Link Layer | Defines the format of data on the network | x | | 1 | Physical Layer | Transmits raw bit stream over the physical medium | Cable or Wireless connection |