Within the OSI reference model, which layer is Layer 1 and deals with the physical means of transmitting raw bits over a medium?

Difficulty: Easy

Correct Answer: physical layer

Explanation:


Introduction / Context:
The OSI model splits networking into seven layers. The lowest layer defines the mechanical, electrical, optical, and procedural characteristics for moving bits across a link. Identifying this layer is foundational for troubleshooting cabling, signaling, and connectors.



Given Data / Assumptions:

  • We are mapping the layer number (1) to its name and responsibility.
  • Focus is on raw bit transmission over the physical medium.


Concept / Approach:
Layer 1 is the Physical layer. It specifies voltage levels, timing, pinouts, modulation, line coding, wavelengths, and connectors. It does not include framing or addressing (Layer 2) nor routing (Layer 3).



Step-by-Step Solution:
Recall OSI stack from bottom up: Physical, Data Link, Network, Transport, Session, Presentation, Application.Match Layer 1 to “Physical.”Confirm scope: signaling and media only.


Verification / Alternative check:
Ethernet physicals (e.g., 1000BASE-T, 10GBASE-SR) and fiber standards are classic Layer-1 examples; MAC addressing belongs to Layer 2.



Why Other Options Are Wrong:
link layer: This is Layer 2 (Data Link).


transport / network: Layer 4 and 3 respectively; not physical signaling.


None of the above: Physical layer fits exactly.



Common Pitfalls:
Attributing error detection or media access to Layer 1; those are Layer-2 responsibilities.



Final Answer:
physical layer

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