Physical Layer positioning and interaction with data link layer

  • In the overall context of computer communication, the physical and data link layer together are responsible for carrying information/data between adjacent nodes (next hop). 
  • At the source node, data that is to be carried to an adjacent next hop node, is split into smaller units called frames (sequence of bits). The physical layer treats the frames as a sequence of bits and transmits these bits to the peer physical layer of a next hop node. Transmission at the physical layer is done by converting the bits into electromagnetic voltages/optical signals and sent via. a telecommunication wired/wireless link.
  • Therefore, in all the layering models, the physical layer is the bottom most layer.
  • The physical layer implementation in a node/device interacts with the data link layer of the same node and it also interacts with the physical layer of a peer node.

This is illustrated in the diagram given below:

Positioning of Physical Layer

Positioning of Physical Layer

As given in the diagram above,

  • At the source node, frames from the data link layer are treated as a sequence of bits and sent as electromagnetic/optical signals by the physical layer through a telecommunication link.
  • At the receiver, the peer physical layer converts the received signals via. the telecommunication links into sequence of bits and hands it over to the data link layer. The data link layer assembles these bits into frames and processes the data further.

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