Suggest an editImprove this articleRefine the answer for “What data is transmitted at the physical layer?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**At the physical layer**, bits (0 and 1) are transmitted as electrical, optical, or radio signals. **Key point:** the physical layer does not know what these bits mean - text, video, or an IP packet - and does not transmit frames, packets, or addresses.Shown above the full answer for quick recall.Answer (EN)ImageAt the **physical layer**, what gets transmitted is **not data in the usual sense**, but **raw bits, 0s and 1s**, converted into a **physical signal**. --- ## Short answer for the interview > **The physical layer transmits bits (0 and 1) in the form of electrical, optical, or radio signals.** --- ## In detail, in plain language ### What exactly is transmitted The physical layer works with: - **bits**: `1010100110` - **signals** that represent these bits: - voltage - light pulses - radio waves It **does not know** what these bits mean: text, video, or an IP packet. --- ## What this data looks like at the physical layer Depending on the medium: ### Copper cable (Ethernet) - 1 is a high voltage level - 0 is a low voltage level ### Fiber optic - 1 means there is a light pulse - 0 means there is no light pulse ### Wi-Fi - 1 and 0 are different radio signal parameters (frequency, phase, amplitude) --- ## What is **not** in physical layer data A very important point. At the physical layer, the following are **NOT transmitted**: - frames - packets - IP addresses - MAC addresses - ports - protocol headers All of this appears **at higher layers**. --- ## A visual analogy Imagine Morse code: - The physical layer is: - short and long signals - sound, light, or a radio wave - The meaning of the message is already **not the physical layer's concern**. --- ## Summary **The physical layer transmits:** - a stream of bits (0 and 1) - in the form of physical signals - without understanding the structure or meaning of the dataFor the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.