Editing Network switch (section)

== Overview ==
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A switch is a device in a [[computer network]] that connects other devices together. Multiple data cables are plugged into a switch to enable communication between different networked devices. Switches manage the flow of data across a network by transmitting a received [[network packet]] only to the one or more devices for which the packet is intended. Each networked device connected to a switch can be identified by its [[network address]], allowing the switch to direct the flow of traffic maximizing the security and efficiency of the network.

A switch is more intelligent than an [[Ethernet hub]], which simply retransmits packets out of every port of the hub except the port on which the packet was received, unable to distinguish different recipients, and achieving an overall lower network efficiency.

An Ethernet switch operates at the [[data link layer]] (layer&nbsp;2) of the [[OSI model]] to create a separate [[collision domain]] for each switch port. Each device connected to a switch port can transfer data to any of the other ports at any time and the transmissions will not interfere.{{efn|In [[half duplex]] mode, each switch port can only ''either'' receive from ''or'' transmit to its connected device at a certain time. In [[full duplex]] mode, each switch port can simultaneously transmit ''and'' receive, assuming the connected device also supports full-duplex mode.<ref>{{cite web
 | url = http://www.ciscopress.com/articles/article.asp?p=2181836&seqNum=5
 | title = Cisco Networking Academy's Introduction to Basic Switching Concepts and Configuration
 | date = 2014-03-31 | access-date = 2015-08-17
 | publisher = [[Cisco Systems]]
}}</ref>}} Because [[Broadcasting (networking)|broadcasts]] are still being forwarded to all connected devices by the switch, the newly formed [[network segment]] continues to be a [[broadcast domain]]. Switches may also operate at higher layers of the OSI model, including the network layer and above. A switch that also operates at these higher layers is known as a [[multilayer switch]].

Segmentation involves the use of a switch to split a larger collision domain into smaller ones in order to reduce collision probability and to improve overall network throughput. In the extreme case (i.e. micro-segmentation), each device is directly connected to a switch port dedicated to the device. In contrast to an Ethernet hub, there is a separate collision domain on each switch port. This allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full-duplex mode. Full-duplex mode has only one transmitter and one receiver per collision domain, making collisions impossible.

The network switch plays an integral role in most modern Ethernet [[local area network]]s (LANs). Mid-to-large-sized LANs contain a number of linked managed switches. [[Small office/home office]] (SOHO) applications typically use a single switch, or an all-purpose device such as a [[residential gateway]] to access small office/home [[broadband]] services such as [[DSL]] or [[cable Internet]]. In most of these cases, the end-user device contains a [[Router (computing)|router]] and components that interface to the particular physical broadband technology.

Many switches have pluggable modules, such as [[Small Form-factor Pluggable]] (SFP) modules. These modules often contain a transceiver that connects the switch to a physical medium, such as a fiber optic cable.<ref>{{cite web | url=https://www.lightwaveonline.com/optical-tech/transmission/article/16647873/evolutionary-trends-in-pluggable-optical-modules | title=Evolutionary trends in pluggable optical modules | date=January 2004 }}</ref><ref>{{cite web |url=https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6800/hardware/installation/guide/b_c6800_modules/b_c6800_modules_appendix_0111.pdf |title=Pluggable Transceivers, Module Connectors |publisher=[[Cisco]] |access-date=2024-08-19}}</ref> Alternatively, DAC (Direct Attach Copper) cables may be used in place of modules.<ref>https://www.servethehome.com/what-is-a-direct-attach-copper-dac-cable/</ref> These modules were preceded by [[Medium Attachment Unit]]s connected via [[Attachment Unit Interface]]s to switches<ref>{{cite book | url=https://books.google.com/books?id=ZO9RWurSS0IC&dq=Medium+Attachment+Unit&pg=PA502 | title=Telecommunications Technology Handbook | isbn=978-1-58053-708-7 | last1=Minoli | first1=Daniel | date=2003 | publisher=Artech House }}</ref><ref>{{cite web | url=https://books.google.com/books?id=sg0EAAAAMBAJ&dq=aui+switch&pg=PA81 | title=Network World | date=25 December 1995 – 1 January 1996 }}</ref> and have evolved over time: the first modules were [[Gigabit interface converter]]s, followed by [[XENPAK]] modules, SFP modules, [[XFP transceiver]]s,  
SFP+ modules, QSFP,<ref>{{cite web | url=https://books.google.com/books?id=35a5omClefUC&dq=qsfp+module&pg=PA10 | title=Fiber optics weekly update }}</ref> QSFP-DD,<ref>{{cite web | url=https://www.edn.com/qsfp-dd-pluggable-modules-boost-data-density/ | title=QSFP-DD pluggable modules boost data density | date=9 November 2017 }}</ref> and OSFP<ref>{{cite web | url=https://www.lightwaveonline.com/optical-tech/transmission/article/14204706/osfp-msa-unveils-osfp-40-specification-for-additional-800g-module-applications-eyes-16t | title=OSFP MSA unveils OSFP 4.0 Specification for additional 800G module applications, eyes 1.6T | date=7 June 2021 }}</ref> modules. Pluggable modules are also used for transmitting video in broadcast applications.<ref>{{cite web | url=https://www.tvtechnology.com/news/the-evolution-of-the-pluggable-module | title=The evolution of the pluggable module | date=August 2012 }}</ref><ref>{{cite web | url=https://www.thebroadcastbridge.com/content/entry/6365/understanding-ip-broadcast-production-networks-routers-and-switches | title=Understanding IP Broadcast Production Networks: Part 2 - Routers & Switches - the Broadcast Bridge - Connecting IT to Broadcast | date=30 May 2023 }}</ref> With the advent of increased speeds together with Co-packaged optics (CPO), which bring the transceivers close to the switching chip of the switch, reducing power consumption, pluggable modules become replaceable laser light sources, and fiber optics are connected directly to the front of the switch instead of through pluggable modules. CPO is also considerably easier to adapt to water cooling.<ref>https://www.nextplatform.com/2025/03/18/nvidia-weaves-silicon-photonics-into-infiniband-and-ethernet/</ref><ref>https://eps.ieee.org/images/files/Photonics_TC_Co-Packaged_Optics_Final.pdf</ref><ref>https://www.eetimes.com/silicon-photonics-and-co-packaged-optics-shine-a-light-at-ofc-2025/</ref><ref>https://spectrum.ieee.org/co-packaged-optics</ref>