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Sources: 
  - https://www.geeksforgeeks.org/computer-networks/physical-layer-in-osi-model/
  - https://www.techtarget.com/searchnetworking/definition/physical-layer

====== The Physical Layer ======

The physical layer is the bottom-most layer of [[osi_model|OSI]]. 

Its function is to transport data using electrical, mechanical or procedural interfaces. It is the closest layer to the physical connection between devices.

==== Functions ====

  - Sending raw data as bits over a physical medium.
  - Converting data into signals (encoding) and turning them back into data (decoding).
  - Ensuring signals are transmitted correctly.
  - Modulation.
  - Deciding how data flows through transmission modes, controlling the speed and timing of data transmission.
  - Synchronization.

==== Topologies ====

{{ :most-common-types-of-network-topology.jpg?400|}}

  * mesh topology;
  * star topology;
  * bus topology;
  * ring topology;
  * tree topology;
  * hybrid topology.

==== Transmission modes ====

  * Simplex mode: only 1 node can transmit data and the other node receives data.
  * Half-duplex mode: 2 nodes can send and receive data but not at the same time.
  * Full-duplex mode: data can be sent and received from both nodes at the same time.

==== Devices ====

  * [[network-hub|Hubs]]
  * [[network-repeater|Repeaters]]