TryHackMe Room: Networking Concepts
The OSI Model
The OSI (Open Systems Interconnection) model is a conceptual model developed by the International Organization for Standardization (ISO) that describes how communications should occur in a computer network. In other words, the OSI model defines a framework for computer network communications. Although this model is theoretical, it is vital to learn and understand as it helps grasp networking concepts on a deeper level. The OSI model is composed of seven layers:
- Physical Layer
- Data Link Layer
- Network Layer
- Transport Layer
- Session Layer
- Presentation Layer
- Application Layer
The numbering starts with the physical layer being layer 1, while the top layer, the application layer, is layer 7. To help you remember the layers from bottom to top, you can use a mnemonic such as “Please Do Not Throw Spinach Pizza Away.” You can check the Internet for other easy-to-remember acronyms if this helps you memorise them. Remembering the OSI model layers with their layer numbers is important; otherwise, you will struggle to understand terms such as “layer 3 switch” or “layer 7 firewall.”
Layer 1: Physical Layer
The physical layer, also referred to as layer 1, deals with the physical connection between devices; this includes the medium, such as a wire, and the definition of the binary digits 0 and 1. Data transmission can be via an electrical, optical, or wireless signal. Consequently, we need data cables or antennas, depending on our physical medium.
In addition to Ethernet cable, shown in the illustration below, and optical fibre cable, examples of the physical layer medium include the WiFi radio bands, the 2.4 GHz band, the 5 GHz band, and the 6 GHz band.
