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| '''Physical Medium Dependent''' sublayers or '''PMDs''' further help to define the [[physical layer]] of [[computer network]] protocols.
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| They define the details of transmission and reception of individual bits on a physical medium. These responsibilities encompass bit timing, signal encoding, interacting with the physical medium, and the properties of the cable, optical fiber, or wire itself. Common examples are specifications for [[Fast Ethernet]], [[Gigabit Ethernet]] and [[10 Gigabit Ethernet]] defined by the [[Institute of Electrical and Electronics Engineers]] (IEEE).
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| For [[cable modems]] Physical Medium Dependent sublayers define the physical sub-layer which also includes the [[MPEG]] sub-layer.{{Citation needed|date=January 2008}} | |
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| ==Description==
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| The Ethernet PMD sublayer is part of the [[Ethernet physical layer]] (PHY). The hierarchy is as follows:
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| * Data Link Layer (Layer 2)
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| ** LLC ([[Logical Link Control]] Sublayer)
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| ** MAC ([[Media Access Control]] Sublayer)
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| *** RS (Reconciliation Sublayer) - This sublayer processes PHY Local/Remote Fault messages and handles DDR conversion
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| * PHY Layer (Layer 1)
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| ** PCS ([[Physical Coding Sublayer]]) - This sublayer performs auto-negotiation and coding such as 8b/10b
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| ** PMA (Physical Medium Attachment Sublayer) - This sublayer performs PMA framing, octet synchronization/detection, and <math>x^7+x^6+1</math> scrambling/descrambling
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| ** PMD (Physical Medium Dependent Sublayer) - This sublayer consists of a transceiver for the physical medium
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| ==Physical Medium Dependent Sublayer specifications==
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| ===10 Gigabit Ethernet===
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| {{Merge to |10 Gigabit Ethernet |date=June 2011}}
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| ;10GBASE-E: has been defined for [[single mode fiber]] operations only. It operates in the 1550 [[nanometer|nm]] band allowing for distances of up to 40 km to be reached.
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| ;10GBASE-L: was also defined for single mode fiber operations, uses the 1300 nm band allowing it to reach up to 10 km.
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| ;10GBASE-S: was defined for use in [[multimode fiber]] and ultimately costs less than the other 10GbE standards. It uses 850 nm lasers and only reaches distances ranging between 26 to 82 metres on older fiber technology. In newer optimized multimode fibers (a.k.a. OM3) it can reach up to 300 m.
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| ;10GBASE-LX4: uses four lasers that each transmit at 3.125 Gbit/s. The receiver is arranged in a [[wavelength]]-division [[multiplexor|multiplexing]] manner. On legacy FDDI multimode fiber it can reach up to 300 m while on [[single mode fiber]] it can reach up to 10 km.
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| After these specifications have been laid out, they are then completed with [[local area network]] and [[wide area network]] specifications using different [[Physical Coding Sublayer]] standards.
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| ==References==
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| *{{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|accessdate=2007-12-31}}
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| *[http://www.xilinx.com/systemio/1gbsx_phy/basics.htm Ethernet 1000BASE-X PCS/PMA Technology Basics]{{dead link|date=May 2013}}
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| *[http://standards.ieee.org/getieee802/802.3.html IEEE 802.3-2005 Specification]
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| [[Category:Ethernet]]
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