What is the name of the Protocol Data Unit (PDU) at Layer 1?

The Protocol Data Unit (PDU) at Layer 1 of the OSI model is referred to as "bits." Layer 1, also known as the Physical Layer, is responsible for the actual transmission of raw data over a physical medium. At this layer, data is not structured into frames, packets, or segments as seen in higher layers. Instead, it focuses on the transmission of binary information, represented in the form of electrical signals, light pulses, or radio waves.

This Layer 1 PDU reflects the most basic form of data: individual bits that are sent across the network medium. Understanding the significance of bits in the context of Layer 1 is crucial for grasping how data physically moves through various types of network infrastructures, such as Ethernet cables or wireless connections. The layering model emphasizes the role of each layer in the networking process, with bits being the foundational unit at the Physical Layer, defining how data exists and travels in its most elemental form.