The OSI reference model (Open Systems Interconnection model) defines seven layers, which divide the communication between two end points in a telecommunication network: Layer 7: Application Layer, Layer 6: Presentation Layer, Layer 5: Session Layer, Layer 4: Transport Layer, Layer 3: Network Layer, Layer 2: Data Link Layer and Layer 1: Physical Layer. When thinking about security of an environment, all layers should be considered. Thus, physical security measures on layer 1 against threats such as equipment overheating may be as important as threats on other layers.
