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Physical layer

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"PHY" redirects here. For other uses, seePHY (disambiguation).
OSI model
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1.Physical layer

In the seven-layerOSI modelofcomputer networking,thephysical layerorlayer 1is 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 shapes and properties of theelectrical connectors,the frequencies to transmit on, theline codeto use and similar low-level parameters, are specified by the physical layer.

At the electrical layer, the physical layer is commonly implemented by dedicatedPHYchip or, inelectronic design automation(EDA), by adesign block.Inmobile computing,theMIPI Alliance*-PHYfamily of interconnect protocols are widely used.

Historically, the OSI model is closely associated with internetworking, such as theInternet protocol suiteandEthernet,which were developed in the same era, along similar lines, though with somewhat different abstractions. Beyond internetworking, the OSI abstraction can be brought to bear on all forms of device interconnection in data communications and computational electronics.

Role[edit]

The physical layer defines the means of transmitting a stream of rawbits[2]over a physicaldata linkconnecting networknodes.Thebitstreammay be grouped into code words or symbols and converted to a physicalsignalthat is transmitted over atransmission medium.

The physical layer consists of theelectronic circuittransmission technologies of a network.[3]It is a fundamental layer underlying the higher level functions in a network, and can be implemented through a great number of different hardware technologies with widely varying characteristics.[4]

Within the semantics of the OSI model, the physical layer translates logical communications requests from thedata link layerinto hardware-specific operations to cause transmission or reception of electronic (or other) signals.[5][6]The physical layer supports higher layers responsible for generation of logicaldata packets.

Physical signaling sublayer[edit]

In a network usingOpen Systems Interconnection(OSI) architecture, thephysical signaling sublayeris the portion of the physical layer that[7][8]

Relation to the Internet protocol suite[edit]

TheInternet protocol suite,as defined inRFC 1122andRFC 1123,is a high-level networking description used for the Internet and similar networks. It does not define a layer that deals exclusively with hardware-level specifications and interfaces, as this model does not concern itself directly with physical interfaces.[9][10]

Services[edit]

The major functions and services performed by the physical layer are: The physical layer performs bit-by-bit orsymbol-by-symboldata delivery over a physicaltransmission medium.[11]It provides a standardized interface to the transmission medium, including[12][13]a mechanical specification ofelectrical connectorsandcables,for example maximum cable length, an electrical specification oftransmission linesignal levelandimpedance.The physical layer is responsible forelectromagnetic compatibilityincludingelectromagnetic spectrumfrequency allocationand specification ofsignal strength,analogbandwidth,etc. The transmission medium may be electrical or optical overoptical fiberor a wireless communication link such asfree-space optical communicationorradio.

Line codingis used to convert data into a pattern of electrical fluctuations which may bemodulatedonto acarrier waveorinfrared light.The flow of data is managed withbit synchronizationin synchronousserial communicationorstart-stop signallingandflow controlinasynchronous serial communication.Sharing of the transmission medium among multiple network participants can be handled by simplecircuit switchingormultiplexing.More complexmedium access controlprotocols for sharing the transmission medium may usecarrier senseandcollision detectionsuch as in Ethernet'sCarrier-sense multiple access with collision detection(CSMA/CD).

To optimize reliability and efficiency, signal processing techniques such asequalization,training sequencesandpulse shapingmay be used.Error correction codesand techniques includingforward error correction[14]may be applied to further improve reliability.

Other topics associated with the physical layer include:bit rate;point-to-point,multipoint orpoint-to-multipointline configuration; physicalnetwork topology,for examplebus,ring,meshorstar network;serialorparallelcommunication;simplex,half duplexorfull duplextransmission mode; andautonegotiation[15]

PHY[edit]

RTL8201 Ethernet PHY chip
Texas Instruments DP83825 – 3 × 3 mm 3.3 V PHY chip
"PHY" redirects here. For other uses, seePHY (disambiguation).

APHY,an abbreviation forphysical layer,is anelectronic circuit,usually implemented as anintegrated circuit,required to implement physical layer functions of theOSI modelin anetwork interface controller.

A PHY connects alink layerdevice (often called MAC as an acronym formedium access control) to a physical medium such as anoptical fiberorcopper cable.A PHY device typically includes bothphysical coding sublayer(PCS) andphysical medium dependent(PMD) layer functionality.[16]

-PHYmay also be used as a suffix to form a short name referencing a specific physical layer protocol, for exampleM-PHY.

Modular transceivers forfiber-optic communication(like theSFPfamily) complement a PHY chip and form thePMDsublayer.

Ethernet physical transceiver[edit]

MicrelKS8721CL – 3.3 V single power supply 10/100BASE-TX/FX MII physical layer transceiver

TheEthernet PHYis a component that operates at the physical layer of theOSI network model.It implements the physical layer portion of the Ethernet. Its purpose is to provide analog signal physical access to the link. It is usually interfaced with amedia-independent interface(MII) to a MAC chip in amicrocontrolleror another system that takes care of the higher layer functions.

More specifically, the Ethernet PHY is a chip that implements the hardware send and receive function of Ethernetframes;it interfaces between the analog domain ofEthernet's line modulationand the digital domain of link-layerpacket signaling.[17]The PHY usually does not handle MAC addressing, as that is thelink layer's job. Similarly,Wake-on-LANandBoot ROMfunctionality is implemented in thenetwork interface card(NIC), which may have PHY, MAC, and other functionality integrated into one chip or as separate chips.

Common Ethernet interfaces include fiber or two to four copper pairs for data communication. However, there now exists a new interface, called Single Pair Ethernet (SPE), which is able to utilize a single pair of copper wires while still communicating at the intended speeds.Texas InstrumentsDP83TD510E[18]is an example of a PHY which uses SPE.

Examples include theMicrosemiSimpliPHY and SynchroPHY VSC82xx/84xx/85xx/86xx family,MarvellAlaska 88E1310/88E1310S/88E1318/88E1318S Gigabit Ethernet transceivers, Texas Instruments DP838xx family[19]and offerings from Intel[20]and ICS.[21]

Other applications[edit]

Technologies[edit]

The following technologies provide physical layer services:[22]

See also[edit]

References[edit]

  1. ^"X.225: Information technology – Open Systems Interconnection – Connection-oriented Session protocol: Protocol specification".Archivedfrom the original on 1 February 2021.Retrieved10 March2023.
  2. ^Gorry Fairhurst (2001-01-01)."Physical Layer".Archived fromthe originalon 2009-06-18.
  3. ^Iyengar, Shisharama (2010).Fundamentals of Sensor Network Programming.Wiley. p. 136.ISBN978-1423902454.
  4. ^"The Physical Layer | InterWorks".InterWorks.2011-07-30.Retrieved2018-08-14.
  5. ^Shaw, Keith (2018-10-22)."The OSI model explained: How to understand (and remember) the 7 layer network model".Network World.Archived fromthe originalon December 4, 2017.Retrieved2019-02-15.
  6. ^"DATA COMMUNICATION & NETWORKING".ResearchGate.Retrieved2019-02-15.
  7. ^Public DomainThis article incorporatespublic domain materialfromFederal Standard 1037C.General Services Administration.Archived fromthe originalon 2022-01-22.
  8. ^"physical signaling sublayer (PLS)".Archived fromthe originalon 2010-12-27.Retrieved2011-07-29.
  9. ^"rfc1122".datatracker.ietf.org.Retrieved2021-07-28.
  10. ^"rfc1123".datatracker.ietf.org.Retrieved2021-07-28.
  11. ^Shekhar, Amar (2016-04-07)."Physical Layer Of OSI Model: Working Functionalities and Protocols".Fossbytes.Retrieved2019-02-15.
  12. ^Bayliss, Colin R.; Bayliss, Colin; Hardy, Brian (2012-02-14).Transmission and Distribution Electrical Engineering.Elsevier.ISBN9780080969121.
  13. ^"CCNA Certification/Physical Layer - Wikibooks, open books for an open world".en.wikibooks.org.Retrieved2019-02-15.
  14. ^Bertsekas, Dimitri; Gallager, Robert (1992).Data Networks.Prentice Hall. p.61.ISBN0-13-200916-1.
  15. ^Forouzan, Behrouz A.; Fegan, Sophia Chung (2007).Data Communications and Networking.Huga Media.ISBN9780072967753.
  16. ^Mauricio Arregoces; Maurizio Portolani (2003).Data Center Fundamentals.ISBN9781587050237.Retrieved2015-11-18.
  17. ^"microcontroller - what is the difference between PHY and MAC chip - Electrical Engineering Stack Exchange".Electronics.stackexchange.com. 2013-07-11.Retrieved2015-11-18.
  18. ^"DP83TD510E Ultra Low Power 802.3cg 10Base-T1L 10M Single Pair Ethernet PHY"(PDF).Texas Instruments.Retrieved12 October2020.
  19. ^"Ethernet PHYs".Texas Instruments.Retrieved12 October2020.
  20. ^Intel PHY controllers brochure
  21. ^osuosl.org - ICS1890 10Base-T/100Base-TX Integrated PHYceiver datasheet
  22. ^"Physical Layer | Layer 1".The OSI-Model.Retrieved2021-07-28.

External links[edit]

Retrieved from "https://en.wikipedia.org/w/index.php?title=Physical_layer&oldid=1221993965#PHY"