Physical Layer

The physical layer is the lowest layer of the OSI model. This layer controls the way unstructured, raw, bit -stream data is sent and received over a physical medium. This layer is composed of the electrical, optical, and physical components of the network. The physical layer carries the signals for all of the higher layers.

To better accommodate the characteristics of the physical medium and to assist in bit and frame synchronization, data encoding modifies the simple, digital signal pattern (1s and 0s) used by the computer.

Data encoding determines:

  • Which signal pattern represents a binary 0 and a binary 1.

  • How the receiving station recognizes when an encoded bit starts.

  • How the receiving station delimits a frame.

The physical components (such as wiring, connectors, and pin-outs) determine:

  • Whether an external transceiver is used to connect to the medium.

  • How many pins the connectors have and what role each pin performs.

The transmission technique determines whether the encoded bits are transmitted by means of baseband (digital) signaling or broadband (analog) signaling.

The physical means of transmission,such as a network adapter or fiber optic adapter, determines whether it is appropriate to transmit bits as electrical or optical signals.