Editing Network topology (section)

==Links==
{{further|data transmission}}
The transmission media (often referred to in the literature as the ''physical media'') used to link devices to form a computer network include [[electrical cables]] ([[Ethernet]], [[HomePNA]], [[power line communication]], [[G.hn]]), [[optical fiber]] ([[fiber-optic communication]]), and [[radio waves]] ([[wireless networking]]). In the [[OSI model]], these are defined at layers 1 and 2 — the physical layer and the data link layer.

A widely adopted ''family'' of transmission media used in local area network ([[LAN]]) technology is collectively known as [[Ethernet]]. The media and protocol standards that enable communication between networked devices over Ethernet are defined by [[IEEE 802.3]]. Ethernet transmits data over both copper and fiber cables.  Wireless LAN standards (e.g. those defined by [[IEEE 802.11]]) use radio waves, or others use [[IrDA|infrared]] signals as a transmission medium. [[Power line communication]] uses a building's power cabling to transmit data.

===Wired technologies===
[[File:Fibreoptic.jpg|thumb|upright=0.7|alt=Bundle of glass threads with light emitting from the ends|[[Fiber-optic cable]]s are used to transmit light from one computer/network node to another.]]
The orders of the following wired technologies are, roughly, from slowest to fastest transmission speed.

*''[[Coaxial cable]]'' is widely used for cable television systems, office buildings, and other work-sites for local area networks. The cables consist of copper or aluminum wire surrounded by an insulating layer (typically a flexible material with a high dielectric constant), which itself is surrounded by a conductive layer. The insulation between the conductors helps maintain the characteristic impedance of the cable which can help improve its performance. Transmission speed ranges from 200 million bits per second to more than 500 million bits per second.
*''[[ITU-T]] [[G.hn]]'' technology uses existing [[home wiring]] ([[Ethernet over coax|coaxial cable]], phone lines and [[Power line communication|power lines]]) to create a high-speed (up to 1 Gigabit/s) local area network.
* ''[[Signal trace]]s'' on [[printed circuit board]]s are common for board-level serial communication, particularly between certain types integrated circuits, a common example being [[Serial Peripheral Interface Bus|SPI]].
*''[[Ribbon cable]]'' (untwisted and possibly unshielded) has been a cost-effective media for serial protocols, especially within metallic enclosures or rolled within copper braid or foil, over short distances, or at lower data rates.  Several serial network protocols can be deployed without shielded or twisted pair cabling, that is, with flat or ribbon cable, or a hybrid flat and twisted ribbon cable, should [[Electromagnetic compatibility|EMC]], length, and [[Bandwidth (computing)|bandwidth]] constraints permit: [[RS-232]],<ref>[https://www.jameco.com/z/GCAR11-R-Cable-Serial-Male-To-Female-25L-4-DB25-M-DB25-28-AWG-300V-Gray_12408.html Cable Serial Male To Female 25L 4' DB25 M-DB25 28 AWG 300V Gray], Part no.: 12408, Jameco Electronics.</ref> [[RS-422]], [[RS-485]],<ref>AN-1057 [http://www.ti.com/lit/an/snla049b/snla049b.pdf Ten ways to bulletproof RS-485 Interfaces], [[Texas Instruments]], p. 5. </ref> [[CAN Bus|CAN]],<ref>[[CANopen]],[https://www.phoenixcontact.com/assets/downloads_ed/global/web_dwl_technical_info/CANopen.pdf CANopen DR-303 V1.0 Cabling and Connector Pin Assignment], [[CAN in Automation]], p. 10.</ref> [[GPIB]], [[SCSI]],<ref>Advantech Co., Ltd., Cable 50-Pin SCSI Ribbon type # PCL-10152-3E ([[Mouser Electronics]] #923-PCL-10152-3E)</ref> etc.
*''[[Twisted pair]] wire'' is the most widely used medium for all telecommunication.{{cn|date=May 2021}} Twisted-pair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer network cabling (wired [[Ethernet]] as defined by [[IEEE 802.3]]) consists of 4 pairs of copper cabling that can be utilized for both voice and data transmission. The use of two wires twisted together helps to reduce [[crosstalk]] and [[electromagnetic induction]]. The transmission speed ranges from 2 million bits per second to 10 billion bits per second. Twisted pair cabling comes in two forms: unshielded twisted pair (UTP) and shielded twisted pair (STP). Each form comes in several category ratings, designed for use in various scenarios.

[[File:World map of submarine cables.png|thumb|alt=World map with red and blue lines|2007 map showing submarine optical fiber telecommunication cables around the world]]
*An ''[[optical fiber]]'' is a glass fiber. It carries pulses of light that represent data. Some advantages of optical fibers over metal wires are very low transmission loss and immunity from electrical interference. Optical fibers can simultaneously carry multiple wavelengths of light, which greatly increases the rate that data can be sent, and helps enable data rates of up to trillions of bits per second. Optic fibers can be used for long runs of cable carrying very high data rates, and are used for [[undersea communications cables]] to interconnect continents.

Price is a main factor distinguishing wired- and wireless technology options in a business. Wireless options command a price premium that can make purchasing wired computers, printers and other devices a financial benefit. Before making the decision to purchase hard-wired technology products, a review of the restrictions and limitations of the selections is necessary. Business and employee needs may override any cost considerations.<ref>[http://smallbusiness.chron.com/disadvantages-wired-technology-17833.html], The Disadvantages of Wired Technology, Laura Acevedo, Demand Media.</ref>

===Wireless technologies===
[[File:Wireless network.jpg|thumb|right|alt=Black laptop with router in the background |Personal computers are very often connected to networks using wireless links.]]
{{Main|Wireless network}}
*''Terrestrial [[microwave]]''&nbsp;– Terrestrial microwave communication uses Earth-based transmitters and receivers resembling satellite dishes. Terrestrial microwaves are in the low gigahertz range, which limits all communications to line-of-sight. Relay stations are spaced approximately {{convert|50|km|mi|abbr=on|sigfig=1}} apart.
*''[[Communications satellite]]s''&nbsp;– Satellites communicate via microwave radio waves, which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically in [[geostationary orbit]] {{convert|35786|km|mi|abbr=on}} above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.
*''[[Cellular network|Cellular]] and PCS systems'' use several radio communications technologies. The systems divide the region covered into multiple geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.
*''Radio and [[spread spectrum]] technologies''&nbsp;– Wireless local area networks use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. [[IEEE 802.11]] defines a common flavor of open-standards wireless radio-wave technology known as [[Wi-Fi]].
*''[[Free-space optical communication]]'' uses visible or invisible light for communications. In most cases, [[line-of-sight propagation]] is used, which limits the physical positioning of communicating devices.

===Exotic technologies===
There have been various attempts at transporting data over exotic media:

* [[IP over Avian Carriers]] was a humorous April fool's [[Request for Comments]], issued as '''RFC 1149'''. It was implemented in real life in 2001.<ref>{{cite web|url=http://www.blug.linux.no/rfc1149 |title=Bergen Linux User Group's CPIP Implementation |publisher=Blug.linux.no |access-date=2014-03-01}}</ref>
* Extending the Internet to interplanetary dimensions via radio waves, the [[Interplanetary Internet]].<ref>{{citation |url=http://www.ipnsig.org/reports/ISART9-2000.pdf |archive-url=https://web.archive.org/web/20120113053223/http://www.ipnsig.org/reports/ISART9-2000.pdf |archive-date=2012-01-13 |title=Interplanetary Internet |publisher=Third Annual International Symposium on Advanced Radio Technologies |author=A. Hooke |date=September 2000 |access-date=2011-11-12}}</ref>

Both cases have a large [[round-trip delay time]], which gives slow two-way communication, but does not prevent sending large amounts of information.