OSI Model
![OSI Model](/assets/second-brain/2020-09-08-21-22-35.png)
![OSI Model with Mnemonic](/assets/second-brain/2020-09-14-10-28-36.png)
- Open Systems Interconnection (OSI) reference model
- Describes how applications communicate over the network
- Typically described from top --> down
- Meant to make developing communication products easier
Layers
![Network layers working together](/assets/second-brain/2020-09-08-21-37-28.png)
- Lower two layers form the foundation of the Internet
- Other protocols deal with specific types of network communication
- Application, Presentation, and Session layers are often intertwined
- Can be hard to distinguish between them
- Physical layer
- Data link layer
- Network layer
- Transport layer
- Session layer
- Presentation layer
- Application layer
Protocol Data Unit (PDU)
- Technical name for bits moving from one layer to the next
![PDUs across the network](/assets/second-brain/2020-09-08-21-36-31.png)
Computer Science Networking