Editing Telecommunications link

{{Short description|Communication channel between two or more devices}}
{{Use British English|date=April 2020}}
In a [[telecommunications network]], a '''link''' is a [[communication channel]] that connects two or more devices for the purpose of [[data transmission]]. The link may be a dedicated [[Data link|physical link]] or a [[virtual circuit]] that uses one or more physical links or shares a physical link with other telecommunications links.

A telecommunications link is generally based on one of several types of information transmission paths such as those provided by [[communication satellite]]s, terrestrial [[radio communications]] infrastructure and [[computer network]]s to connect two or more points.

The term ''link'' is widely used in computer networking to refer to the communications facilities that connect [[Node (networking)|nodes]] of a network.<ref name="atis">{{cite web|url=http://www.atis.org/glossary/definition.aspx?id=4188|title=network topology|author=ATIS committee PRQC|publisher=[[Alliance for Telecommunications Industry Solutions]]|work=ATIS Telecom Glossary 2007|access-date=2008-10-10|archive-date=2018-08-03|archive-url=https://web.archive.org/web/20180803014106/http://www.atis.org/glossary/definition.aspx?id=4188|url-status=dead}}</ref>

Sometimes the communications facilities that provide the communication channel that constitutes a link are also included in the definition of ''link''. 

==Types==

===Point-to-point===<!-- This section is linked from [[Packet]] -->
A [[point-to-point link]] is a dedicated link that connects exactly two communication facilities (e.g., two [[Node (networking)|nodes]] of a network, an intercom station at an entryway with a single internal intercom station, a radio path between two points, etc.).

===Broadcast===
Broadcast links connect two or more nodes and support ''broadcast transmission'', where one node can transmit so that all other nodes can receive the same transmission. [[Classic Ethernet]] is an example.

===Multipoint===
Also known as a ''multidrop'' link, a multipoint link is a link that connects ''two or more'' nodes.  Also known as general topology networks, these include [[Asynchronous Transfer Mode|ATM]] and [[Frame Relay]] links, as well as [[X.25]] networks when used as links for a [[network-layer protocol]] like [[Internet Protocol|IP]].

Unlike broadcast links, there is no mechanism to efficiently send a single message to all other nodes without copying and retransmitting the message.

===Point-to-multipoint===
A [[point-to-multipoint link]] (or simply a ''multipoint'') is a specific type of multipoint link which consists of a central connection endpoint (CE) that is connected to multiple peripheral CEs. All of the peripheral CEs receive any transmission of data that originates from the central CE while any transmission of data that originates from any of the peripheral CEs is only received by the central CE.

=== Private and public ===
Links are often referred to by terms that refer to the ownership or accessibility of the link.
* A ''private link'' is a link that is either owned by a specific entity or a link that is only accessible by a particular entity.
* A ''public link'' is a link that uses the public switched telephone network or other public utility or entity to provide the link and which may also be accessible by anyone.
*

== Direction ==
[[File:Uplink y Downlink.jpg|thumb|250px|{{center| ''Feeder links'', here: ''uplink / downlink''}}]]

=== Uplink ===
{{redirect|Uplink}}
*Pertaining to [[radiocommunication service]], an '''uplink''' (UL or U/L) is the portion of a [[feeder link]] used for the transmission of signals from an [[earth station]] to a [[space radio station]], [[space radio system]] or [[high altitude platform station]].
*Pertaining to [[GSM]] and cellular networks, the radio uplink is the transmission path from the [[mobile station]] (cell phone) to a [[base transceiver station|base station]] (cell site). Traffic and signalling flowing within the [[Base Station Subsystem|BSS]] and [[Network and Switching Subsystem|NSS]] may also be identified as uplink and downlink.
*Pertaining to computer networks, an uplink is a connection from [[data communications equipment]] toward the [[network core]]. This is also known as an [[upstream (networking)|upstream]] connection.

=== Downlink ===
*Pertaining to [[radiocommunication service]], a '''downlink''' (DL or D/L) is the portion of a [[feeder link]] used for the transmission of signals from a [[space radio station]], [[space radio system]] or [[high altitude platform station]] to an [[earth station]].
*In the context of [[satellite communications]], a '''downlink''' (DL) is the link from a satellite to a [[ground station]].
*Pertaining to [[cellular network]]s, the radio downlink is the transmission path from a [[cell site]] to the [[cell phone]]. Traffic and signalling flowing within the [[base station subsystem]] (BSS) and [[network switching subsystem]] (NSS) may also be identified as uplink and downlink.
*Pertaining to [[computer network]]s, a downlink is a connection from data communications equipment toward [[data terminal equipment]]. This is also known as a [[downstream (networking)|downstream]] connection.

=== Forward link ===
A '''forward link''' is the link from a fixed location (e.g., a [[base station]]) to a mobile user. If the link includes a [[communications satellite|communications relay satellite]], the forward link will consist of both an [[uplink]] (base station to satellite) and a downlink (satellite to mobile user).<ref>[http://www.scatmag.com/technical/techarticle-mar05.pdf Basics of C & Ku Band] {{Webarchive|url=https://web.archive.org/web/20150724005815/http://www.scatmag.com/technical/techarticle-mar05.pdf |date=2015-07-24 }} Scatmag.com</ref>

=== Reverse link ===
{{See also|Backhaul (telecommunications)|Return channel}}

The '''reverse link''' (sometimes called a ''[[return channel]]'') is the link from a mobile user to a fixed base station.

If the link includes a [[communication satellite|communications relay satellite]], the reverse link will consist of both an [[uplink]] (mobile station to satellite) and a [[downlink]] (satellite to base station) which together constitute a half [[Hop (telecommunications)|hop]].

==References==
{{reflist}}
{{refbegin}}
* {{FS1037C MS188}}
* {{DODDIC}}
{{refend}}

{{Telecommunications}}
[[Category:Telecommunications]]
[[Category:Telecommunications engineering]]
[[Category:Communication circuits]]
[[Category:Broadcast engineering]]
[[Category:Telecommunications infrastructure]]