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In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer: the layer most closely associated with the physical connection between devices. The physical layer provides an electrical, mechanical, and procedural interface to the transmission medium.
The physical-layer specifications of the Ethernet family of computer network standards are published by the Institute of Electrical and Electronics Engineers (IEEE), which defines the electrical or optical properties and the transfer speed of the physical connection between a device and the network or between network devices.
This layer deals with the physical plugs, sockets, electrical/optical specifications and the required line codes. The physical layer includes the medium over which the digital signals are transmitted. It can be twisted pair, coaxial cable, optical fiber, wireless, or other transmission media.
The link layer corresponds to the OSI data link layer and may include similar functions as the physical layer, as well as some protocols of the OSI's network layer. These comparisons are based on the original seven-layer protocol model as defined in ISO 7498, rather than refinements in the internal organization of the network layer.
The transmission media (often referred to in the literature as the physical medium) used to link devices to form a computer network include electrical cable, optical fiber, and free space. In the OSI model, the software to handle the media is defined at layers 1 and 2 — the physical layer and the data link layer.
This article lists protocols, categorized by the nearest layer in the Open Systems Interconnection model.This list is not exclusive to only the OSI protocol family.Many of these protocols are originally based on the Internet Protocol Suite (TCP/IP) and other models and they often do not fit neatly into OSI layers.
The Ethernet PMD sublayer is part of the Ethernet physical layer (PHY). The hierarchy is as follows: Data link layer (Layer 2) Logical link control (LLC) sublayer; Medium access control (MAC) sublayer Reconciliation sublayer (RS) – This sublayer processes PHY local/remote fault messages and handles DDR conversion; PHY layer (Layer 1)
Another provision is the definition of power classes. This includes the limitation of the maximum supply voltage and supply current for intrinsically safe power supply . Further topics that are specified in the port profile specification are wiring rules, pin assignments for terminals and connectors as well as shielding and grounding rules.