Editing Physical layer (section)

== Services ==
The major functions and services performed by the physical layer are:
The physical layer performs bit-by-bit or [[Symbol rate|symbol-by-symbol]] data delivery over a physical [[transmission medium]].<ref>{{Cite web|url=https://fossbytes.com/physical-layer/|title=Physical Layer Of OSI Model: Working Functionalities and Protocols|last=Shekhar|first=Amar|date=2016-04-07|website=Fossbytes|language=en-US|access-date=2019-02-15}}</ref> It provides a standardized interface to the transmission medium, including<ref>{{Cite book|url=https://books.google.com/books?id=cLwO-Hh6_VEC&q=The+physical+layer+Providing+a+standardized+interface+to+a+physical+transmission+medium,+including++Mechanical+specification+of+electrical+connectors+and+cables,+for+example+maximum+cable+length+Electrical+specification+of+transmission+line+signal+level+and+impedance+Radio+interface,+including+electromagnetic+spectrum+frequency+allocation+and+specification+of+signal+strength,+analog+bandwidth,+etc.+Specifications+for+IR+over+optical+fiber+or+a+wireless+IR+communication+link|title=Transmission and Distribution Electrical Engineering|last1=Bayliss|first1=Colin R.|last2=Bayliss|first2=Colin|last3=Hardy|first3=Brian|date=2012-02-14|publisher=Elsevier|isbn=9780080969121|language=en}}</ref><ref>{{Cite web|url=https://en.wikibooks.org/wiki/CCNA_Certification/Physical_Layer|title=CCNA Certification/Physical Layer - Wikibooks, open books for an open world|website=en.wikibooks.org|access-date=2019-02-15}}</ref> a mechanical specification of [[electrical connector]]s and [[Electrical cable|cables]], for example maximum cable length, an electrical specification of [[transmission line]] [[signal level]] and [[electrical impedance|impedance]]. The physical layer is responsible for [[electromagnetic compatibility]] including [[electromagnetic spectrum]] [[frequency allocation]] and specification of [[signal strength]], analog [[Bandwidth (signal processing)|bandwidth]], etc. The transmission medium may be electrical or optical  over [[optical fiber]] or a wireless communication link such as [[free-space optical communication]] or [[radio]].

[[Line coding]] is used to convert data into a pattern of electrical fluctuations which may be [[modulated]] onto a [[carrier wave]] or [[infrared light]]. The flow of data is managed with [[bit synchronization]] in synchronous [[serial communication]] or [[start-stop signalling]] and [[flow control (data)|flow control]] in [[asynchronous serial communication]]. Sharing of the transmission medium among multiple network participants can be handled by simple [[circuit switching]] or [[multiplexing]]. More complex [[medium access control]] protocols for sharing the transmission medium may use [[carrier sense]] and [[collision detection]] such as in Ethernet's [[Carrier-sense multiple access with collision detection]] (CSMA/CD).

To optimize reliability and efficiency, signal processing techniques such as [[Equalization (communications)|equalization]], [[training sequence]]s and [[pulse shaping]] may be used. [[Error correction code]]s and techniques including [[forward error correction]]<ref>{{cite book|last1= Bertsekas|first1= Dimitri |last2=Gallager |first2= Robert |title= Data Networks |url= https://archive.org/details/isbn_9780132009164|url-access= limited|publisher= Prentice Hall |year= 1992|isbn= 0-13-200916-1|page=[https://archive.org/details/isbn_9780132009164/page/61 61]}}</ref> may be applied to further improve reliability.

Other topics associated with the physical layer include: [[bit rate]]; [[point-to-point (telecommunications)|point-to-point]], multipoint or [[point-to-multipoint]] line configuration; physical [[network topology]], for example [[bus network|bus]], [[ring network|ring]], [[mesh network|mesh]] or [[star network]]; [[serial communication|serial]] or [[parallel communication|parallel]] communication; [[simplex communication|simplex]], [[half duplex]] or [[full duplex]] transmission mode; and [[autonegotiation]]<ref>{{Cite book|url=https://books.google.com/books?id=bwUNZvJbEeQC&q=The+physical+layer+is+also+concerned+with:++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|title=Data Communications and Networking|last1=Forouzan|first1=Behrouz A.|last2=Fegan|first2=Sophia Chung|date=2007|publisher=Huga Media|isbn=9780072967753|language=en}}</ref><!--[[User:Kvng/RTH]]-->