The OSI Layer 1, also known as the Physical Layer, is responsible for the transmission and reception of raw binary data over a physical medium. The most fundamental unit at this layer is the bit.
Bit = Binary Digit (0 or 1)
It is transmitted over physical media (cables, radio signals, etc.)
Frames (A) exist at Layer 2 (Data Link Layer), not Layer 1.
Bytes (C) are groups of 8 bits, but bits are still the smallest indivisible transmission unit.
Headers (D) are metadata used at Layers 2–7; not relevant to Layer 1.
MTCNA Official Training Manual – OSI Model Chapter:
“Layer 1 transmits raw bits over a transmission medium. These bits form the foundation for higher-layer data structures.”
René Meneses MTCNA Guide – OSI Model Breakdown:
“Physical Layer (Layer 1) carries bits, not frames or bytes. It's concerned with voltages, cables, connectors, and signal encoding.”
Terry Combs Notes – OSI Layers:
“Layer 1 = Bits. Nothing more. Frames come into play in Layer 2.”
Answer: B
