The physical layer is level one in the seven-level
OSI model of
computer networking as well as in the five-layer
TCP/IP reference model. It performs services requested by the
data link layer. The physical layer is the most basic network layer, providing only the means of transmitting raw bits rather than packets over a physical
data link connecting
network nodes. No packet headers nor trailers are consequently added to the data by the physical layer. The
bit stream may be grouped into code words or symbols, and converted to a physical
signal, which is transmitted over a physical
transmission medium. The physical layer provides an electrical, mechanical, and procedural interface to the transmission medium. The shapes of the
electrical connectors, which frequencies to broadcast on, what
modulation scheme to use and similar low-level parameters are specified here. An analogy of this layer in a physical mail network would be the roads along which the vans carrying the mail drive.
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