The physical layer consists of the electronic circuit transmission technologies of a network. It is a fundamental layer underlying the higher level functions in a network. Due to the plethora of available hardware technologies with widely varying characteristics, this is perhaps the most complex layer in the OSI architecture.
The physical layer defines the means of transmitting raw bits rather than logical data packets over a physical data link connecting network nodes. The bit stream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a transmission medium. The physical layer provides an electrical, mechanical, and procedural interface to the transmission medium. The shapes and properties of the electrical connectors, the frequencies to broadcast on, the line code to use and similar low-level parameters, are specified here.
Within the semantics of the OSI model, the physical layer translates logical communications requests from the data link layer into hardware-specific operations to cause transmission or reception of electronic signals.
In a local area network (LAN) or a metropolitan area network (MAN) using open systems interconnection (OSI) architecture, the physical signaling sublayer is the portion of the physical layer that:
The Internet protocol suite, defined in RFC 1122 and RFC 1123, is a high-level networking description used for the Internet and similar networks. It does not define an equivalent layer that deals exclusively with hardware-level specifications and interfaces, as this model does not concern itself directly with physical interfaces. Several RFCs mention a physical layer and data link layer, but that is in the context of IEEE protocols. RFC 1122 and 1123 do not mention any physical layer functionality or physical layer standards.
This section is in a list format that may be better presented using prose. (October 2017)
The major functions and services performed by the physical layer are:
The physical layer is also concerned with:
The following technologies provide physical layer services:
The following network equipment provides physical layer services: