Layer 1 – Physical
The Physical, and lowest layer of the model, covers how unstructured data, like bits, is transmitted. Some concrete examples of this are the ways wires are configured, the way signals are transferred over those wires, and the radio frequencies computers use. Technology such as WiFi, Bluetooth, and cable standards such as CAT5 and CAT6 all operate at this layer. This layer also includes the hardware part of modems, adapters, and repeaters.
Over these wires and signals, the raw data bits are received as a stream of
1s. Fixing errors that occur just at this layer means considering physical damage or interference.
Layer 2 – Data Link
The Data Link layer covers how data is sent from device to device when they are connected on the same local network.
The data link layer includes many functionalities:
- It structures incoming or outgoing data bits into data frames.
- It involves physical addresses of devices, called Media Access Control (MAC) address. All devices have a unique 48-bit MAC address where the first 24 bits relate to the manufacturer, and the last 24 bits make it unique to each device.
- It routes data frames to the correct physical addresses. A switch (could be your computer or router) keeps track of local devices and their MAC addresses and makes sure data frames get to the correct physical location.
- It ensures the flow of data is synchronized between devices, so data doesn’t jam up the memory of a slow receiving physical device.
- It detects errors within data frames. This involves a system of error control!