The Physical Layer is the first and lowest layer in the seven-layer OSI model of computer networking. The Physical Layer is comprised of the basic hardware transmission technologies of a network. It is a fundamental layer underlying the logical data structures of 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 implementation of this layer is often termed PHY.
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 and properties of the electrical connectors, the frequencies to broadcast on, the modulation scheme to use and similar low-level parameters, are specified here.
Within the semantics of the OSI network architecture, the Physical Layer translates logical communications requests from the Data Link Layer into hardware-specific operations to effect transmission or reception of electronic signals.
List of Physical Layer Sevices:
The major functions and services performed by the Physical Layer are:
Bit-by-bit or symbol-by-symbol delivery Modulation Line Coding Bit synchronization in synchronous serial communication Start-stop signalling and flow control in asynchronous serial communication Circuit switching Establishment and termination of circuit switched connections Carrier sense and collision detection utilized by some level 2 multiple access protocols Equalization filtering, training sequences, pulse shaping and other signal processing of physical signals Bit rate Point-to-point, multipoint or point-to-multipoint line configuration Physical network topology, for example bus, ring, mesh or star network Serial or parallel communication Simplex, half duplex or full duplex transmission mode Autonegotiation 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 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 Um radio interface physical layer Bluetooth Physical Layer IEEE 802.11x Wi-Fi Physical Layers TransferJet Physical Layer Etherloop ARINC 818 Avionics Digital Video Bus G.hn/G.9960 Physical Layer
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