Physical layer

Source: Wikipedia, the free encyclopedia.
"PHY" redirects here. For other uses, see PHY (disambiguation).
OSI model
by layer
7.  Application layer
6.  Presentation layer
5.  Session layer
4.  Transport layer
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2.  Data link layer
1.  Physical layer

In the seven-layer OSI model of computer networking, the physical layer or layer 1 is 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 the electrical connectors, the frequencies to transmit on, the line code to use and similar low-level parameters, are specified by the physical layer.

At the electrical layer, the physical layer is commonly implemented by dedicated

PHY chip or, in electronic design automation (EDA), by a design block. In mobile computing, the MIPI Alliance *-PHY
family of interconnect protocols are widely used.

Historically, the OSI model is closely associated with internetworking, such as the Internet protocol suite and Ethernet, 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

The physical layer defines the means of transmitting a stream of raw bits[2] 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 consists of the electronic circuit transmission 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 the data link layer into 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 logical data packets.

Physical signaling sublayer

In a network 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 suite

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 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

The major functions and services performed by the physical layer are: The physical layer performs bit-by-bit or

signal strength, analog 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
.

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

forward error correction[14]
may be applied to further improve reliability.

Other topics associated with the physical layer include:

full duplex transmission mode; and autonegotiation[15]

PHY

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

A PHY, an abbreviation for physical layer, is an electronic circuit, usually implemented as an integrated circuit, required to implement physical layer functions of the OSI model in a network interface controller.

A PHY connects a

copper cable. A PHY device typically includes both physical coding sublayer (PCS) and physical medium dependent (PMD) layer functionality.[16]

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

Modular transceivers for

SFP family) complement a PHY chip and form the PMD
sublayer.

Ethernet physical transceiver

Micrel KS8721CL – 3.3 V single power supply 10/100BASE-TX/FX MII physical layer transceiver

The Ethernet PHY is a component that operates at the physical layer of the OSI 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 a media-independent interface (MII) to a MAC chip in a microcontroller or 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 Ethernet

network 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 Instruments DP83TD510E[18] is an example of a PHY which uses SPE.

Examples include the

Marvell Alaska 88E1310/88E1310S/88E1318/88E1318S Gigabit Ethernet transceivers, Texas Instruments DP838xx family[19] and offerings from Intel[20] and ICS.[21]

Other applications

Technologies

The following technologies provide physical layer services:[22]

See also

References

  1. ^ "X.225 : Information technology – Open Systems Interconnection – Connection-oriented Session protocol: Protocol specification". Archived from the original on 1 February 2021. Retrieved 10 March 2023.
  2. ^ Gorry Fairhurst (2001-01-01). "Physical Layer". Archived from the original on 2009-06-18.
  3. ISBN 978-1423902454
    .
  4. ^ "The Physical Layer | InterWorks". InterWorks. 2011-07-30. Retrieved 2018-08-14.
  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. ^ "DATA COMMUNICATION & NETWORKING". ResearchGate. Retrieved 2019-02-15.
  7. ^ Public Domain This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22.
  8. ^ "physical signaling sublayer (PLS)". Archived from the original on 2010-12-27. Retrieved 2011-07-29.
  9. ^ "rfc1122". datatracker.ietf.org. Retrieved 2021-07-28.
  10. ^ "rfc1123". datatracker.ietf.org. Retrieved 2021-07-28.
  11. ^ Shekhar, Amar (2016-04-07). "Physical Layer Of OSI Model: Working Functionalities and Protocols". Fossbytes. Retrieved 2019-02-15.
  12. ISBN 9780080969121
    .
  13. ^ "CCNA Certification/Physical Layer - Wikibooks, open books for an open world". en.wikibooks.org. Retrieved 2019-02-15.
  14. ISBN 0-13-200916-1
    .
  15. ISBN 9780072967753
    .
  16. ISBN 9781587050237
    . Retrieved 2015-11-18.
  17. ^ "microcontroller - what is the difference between PHY and MAC chip - Electrical Engineering Stack Exchange". Electronics.stackexchange.com. 2013-07-11. Retrieved 2015-11-18.
  18. ^ "DP83TD510E Ultra Low Power 802.3cg 10Base-T1L 10M Single Pair Ethernet PHY" (PDF). Texas Instruments. Retrieved 12 October 2020.
  19. ^ "Ethernet PHYs". Texas Instruments. Retrieved 12 October 2020.
  20. ^ Intel PHY controllers brochure
  21. ^ osuosl.org - ICS1890 10Base-T/100Base-TX Integrated PHYceiver datasheet
  22. ^ "Physical Layer | Layer 1". The OSI-Model. Retrieved 2021-07-28.

External links

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