imported>GoldRomean: Adding local short description: "Networking protocol sublayer", overriding Wikidata description "part of a communications system physical device (PHY)"

2025-04-07T18:02:03Z

Adding local short description: "Networking protocol sublayer", overriding Wikidata description "part of a communications system physical device (PHY)"

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{{Short description|Networking protocol sublayer}}
The '''physical coding sublayer''' ('''PCS''') is a networking protocol sublayer in the [[Fast Ethernet]], [[Gigabit Ethernet]], and [[10 Gigabit Ethernet]] standards. It resides at the top of the [[physical layer]] (PHY), and provides an interface between the '''physical medium attachment''' ('''PMA''') sublayer and the [[media-independent interface]] (MII). It is responsible for data encoding and decoding, [[Scrambler|scrambling and descrambling]], alignment marker insertion and removal, block and symbol redistribution, and lane block synchronization and deskew.<ref name="Ethernet: The Definitive Guide">{{cite book | last = Spurgeon | first = Charles | title = Ethernet: The Definitive Guide | publisher = O'Reilly | year = 2014 | pages = 198 | isbn = 978-1449361846 }}</ref>

== Description ==
The Ethernet PCS sublayer is at the top of the Ethernet [[physical layer]] (PHY). The hierarchy is as follows:

* [[Data link layer]] (Layer 2)
** [[Logical link control]] (LLC) sublayer
** [[Medium access control]] (MAC) sublayer
*** Reconciliation sublayer (RS){{dash}}This sublayer processes PHY local/remote fault messages and handles DDR conversion
* [[physical layer|PHY Layer]] (Layer 1)
** Physical coding sublayer (PCS){{dash}}This sublayer determines when a functional link has been established, provides rate difference compensation, and performs coding such as [[64b/66b encoding]] and <math>x^{58}+x^{39}+1</math> [[Scrambler|scrambling/descrambling]]
** Physical medium attachment (PMA) sublayer{{dash}}This sublayer performs PMA framing, octet synchronization/detection, and <math>x^{7}+x^{6}+1</math> scrambling/descrambling
** [[Physical medium dependent]] (PMD) sublayer{{dash}}This sublayer consists of a transceiver for the physical medium

== Specifications ==

===10 Mbit/s Ethernet===
* Classic Ethernet uses [[Manchester code]] in the [[physical layer#Physical signaling sublayer|Physical signaling sublayer]] (PLS), encoding each bit as a high-low (logical zero) or low-high transition (logical one).<ref>IEEE 802.3 ''1.4 Definitions''</ref>

===Fast Ethernet ===
* 100BASE-X for fiber (100BASE-FX) and twisted pair copper (100BASE-TX) encodes data [[nibble]]s to five-bit code groups ([[4B5B]]).<ref>IEEE 802.3 Clause 24.1.4.1</ref>

=== Gigabit Ethernet ===
*1000BASE-X for fiber and 150 Ω balanced copper (twinaxial) uses [[8b/10b encoding]] with a [[symbol rate]] of 1.25 GBd.<ref>IEEE 802.3-2012 Clause 36</ref>
*1000BASE-T for twisted pair copper splits the data into four lanes and uses four-dimensional, five-level (quinary) [[trellis modulation]] with [[PAM-5]] and a symbol rate of 125 MBd.<ref>IEEE 802.3-2012 Clause 40</ref>

===2.5 and 5 Gigabit Ethernet===
* 2.5GBASE-T and 5GBASE-T use the same encoding as 10GBASE-T slowed by a factor of four or two, respectively.

=== 10 Gigabit Ethernet ===
*10GBASE-R (LAN) is the serial encoded PCS using [[64b/66b encoding]] that allows for Ethernet framing at a rate of 10.3125 Gbit/s. This rate does not match the rate 9.953 Gbit/s used in [[SONET]] and SDH and is not supported over a WAN based on SONET or SDH.
*10GBASE-X (LAN/WAN) uses 8b/10b encoding over four lanes at 3.125 GBd each and is used for 10GBASE-LX4 (single-mode and multi-mode fiber), 10GBASE-CX4 (twinax), and 10GBASE-KX4 (backplane).<ref>IEEE 802.3 ''48. Physical Coding Sublayer (PCS) and Physical Medium Attachment (PMA) sublayer, type 10GBASE-X''</ref>
*10GBASE-W (WAN) defines WAN encoding for 10GbE. It uses 64/66b encoding and lowers the MAC rate to 9.95 Gbit/s, so that is compatible with SONET STS-192c data rates and SDH VC-4-64 transmission standards when wrapped into a SONET frame.
*10GBASE-T for twisted pair copper splits the data into four lanes and uses 64B/65B encoding, scrambling, and 128 double-square (DSQ128) checkerboard encoding with PAM-16 generated at 800 MBd.<ref>IEEE 802.3 Clause 55.3.2</ref>

=== 25 Gigabit Ethernet ===
* 25GBASE-R uses the same 64b/66b encoding as 10GBASE-R with a speed-up to 25.78125 GBd.<ref>{{Cite web|url=http://www.ieee802.org/3/by/public/Jan15/baden_3by_01b_0115.pdf |title=IEEE 802.3by 25G Ethernet TF, A BASELINE PROPOSAL FOR RS, PCS, AND FEC |date=2015-01-12 |access-date=2016-08-06}}</ref>

=== 40/100 Gigabit Ethernet ===
* 40GBASE-R and 100GBASE-R use 64b/66b encoding over multiple lanes of 10.3125 GBd or 25.78125 GBd each. These lanes – four for 40 Gbit/s, four or ten for 100 Gbit/s per direction – are either transmitted separately over short distance or together with coarse [[wavelength division multiplexing]] on long distance fiber (-LR).<ref>IEEE 802.3 Clauses 82-89</ref>

==See also==
* [[PHY-Level Collision Avoidance]]

== References ==
{{reflist}}
*{{cite journal|last=Barbieri |first=Alessandro |title=10 GbE and Its X Factors |journal=Packet: Cisco Systems Users Magazine |volume=17 |issue=3 |pages=25–28 |url=http://www.cisco.com/asiapac/campaigns/metroethernet/files/10ge_po_pack_mag_arti.pdf |access-date=2007-12-31 |url-status=dead |archive-url=https://web.archive.org/web/20110608032208/http://www.cisco.com/asiapac/campaigns/metroethernet/files/10ge_po_pack_mag_arti.pdf |archive-date=2011-06-08 }}

== External links ==
* [https://grouper.ieee.org/groups/802/3/ae/public/mar00/figueira_1_0300.pdf IEEE 802.3 Meeting]
* [https://web.archive.org/web/20110716191855/http://www.xilinx.com/systemio/1gbsx_phy/basics.htm Ethernet 1000BASE-X PCS/PMA Technology Basics]

{{Ethernet}}

[[Category:Ethernet]]

Physical coding sublayer - Revision history

imported>GoldRomean: Adding local short description: "Networking protocol sublayer", overriding Wikidata description "part of a communications system physical device (PHY)"