The Physical Layer is the first level in the seven-layer OSI model of computer networking. It translates communications requests from the data link layer into hardware-specific operations to affect transmission or reception of electronic signals.
The Physical Layer is a fundamental layer upon which all higher level functions in a network are based. However, 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 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 hardware 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, which modulation scheme to use and similar low-level parameters are specified here.
Physical signaling sublayer
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:
Source: from Federal Standard 1037C
List of Physical Layer services
The major functions and services performed by the Physical Layer are:
The Physical Layer is also concerned with
Physical Layer examples
- V.92 telephone network modems
- IRDA Physical Layer
- USB Physical Layer
- Firewire
- EIA RS-232, EIA-422, EIA-423, RS-449, RS-485
- ITU Recommendations: see ITU-T
- DSL
- ISDN
- T1 and other T-carrier links, and E1 and other E-carrier links
- 10BASE-T, 10BASE2, 10BASE5, 100BASE-TX, 100BASE-FX, 100BASE-T, 1000BASE-T, 1000BASE-SX and other varieties of the Ethernet physical layer
- Varieties of 802.11
- SONET/SDH
- GSM radio interface
- Bluetooth Physical Layer
- IEEE 802.11x Wi-Fi Physical Layers
- Etherloop
Hardware equipment (network node) examples
Relation to TCP/IP model
The TCP/IP model has no equivalent layer that deals exclusively with hardware-level specifications, as this model does not concern itself directly with physical interfaces. It assumes a functioning host operating system with a facility to transmit raw data blocks onto the local network. TCP/IP simply places all hardware specific components of the operating system, as well as interface firmware, etc., into the Link Layer. The TCP/IP model is not a top/down comprehensive design reference for general networks and networking hardware. It was formulated for the purpose of illustrating the design of the suite of internetworking methods used in the Internet Protocol suite into logical group functions.
See also
References
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