Physical layer

In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer.[1] This layer may be implemented by a PHY chip.

The physical layer consists of the electronic circuit transmission technologies of a network.[2] 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.[3]

The physical layer defines the means of transmitting raw bits[4] rather than logical data packets over a physical data link connecting network nodes. The bitstream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a 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 line code to use and similar low-level parameters, are specified here.

Within the semantics of the OSI model, the physical layer translates logical communications requests from the data link layer into hardware-specific operations to cause transmission or reception of electronic signals.[5][6]

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[7][8]

Relation to the Internet Protocol

The Internet protocol suite, as defined in RFC 1122 and RFC 1123, is a high-level networking description used for the Internet and similar networks. It does not define an equivalent layer that deals exclusively with hardware-level specifications and interfaces, as this model does not concern itself directly with physical interfaces. Several RFCs mention a physical layer and data link layer, but that is in the context of IEEE protocols. RFC 1122 and 1123 do not mention any physical layer functionality or physical layer standards.

List of services

The major functions and services performed by the physical layer are:

The physical layer is also concerned with:[13]


The following technologies provide physical layer services:

Network equipment

The following network equipment provides physical layer services:[14][15]

See also


  1. Banzal, Shashi (2007). Data and Computer Network Communication. Firewall Media. p. 41.
  2. Iyengar, Shisharama (2010). Fundamentals of Sensor Network Programming. Wiley. p. 136.
  3. "The Physical Layer | InterWorks". InterWorks. 2011-07-30. Retrieved 2018-08-14.
  4. Gorry Fairhurst (2001-01-01). "Physical Layer". Archived from the original on 2009-06-18.
  5. Shaw, Keith (2018-10-22). "The OSI model explained: How to understand (and remember) the 7 layer network model". Network World. Retrieved 2019-02-15.
  6. "(PDF) DATA COMMUNICATION & NETWORKING". ResearchGate. Retrieved 2019-02-15.
  7.  This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
  8. "physical signaling sublayer (PLS)". Retrieved 2011-07-29.
  9. Shekhar, Amar (2016-04-07). "Physical Layer Of OSI Model: Working Functionalities and Protocols". Fossbytes. Retrieved 2019-02-15.
  10. Bayliss, Colin R.; Bayliss, Colin; Hardy, Brian (2012-02-14). Transmission and Distribution Electrical Engineering. Elsevier. ISBN 9780080969121.
  11. "CCNA Certification/Physical Layer - Wikibooks, open books for an open world". Retrieved 2019-02-15.
  12. Bertsekas, Dimitri; Gallager, Robert (1992). Data Networks. Prentice Hall. p. 61. ISBN 0-13-200916-1.
  13. Forouzan, Behrouz A.; Fegan, Sophia Chung (2007). Data Communications and Networking. Huga Media. ISBN 9780072967753.
  14. Inc, IDG Network World (1991-02-11). Network World. IDG Network World Inc.
  15. "Hardware Elements Of Your Network". Retrieved 2019-02-15.
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