Telecommunications link

In atelecommunications network,alinkis acommunication channelthat connects two or more devices for the purpose ofdata transmission.The link may be a dedicatedphysical linkor avirtual circuitthat 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 bycommunication satellites,terrestrialradio communicationsinfrastructure andcomputer networksto connect two or more points.

The termlinkis widely used in computer networking to refer to the communications facilities that connectnodesof a network.

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

Types

Point-to-point

Apoint-to-point linkis a dedicated link that connects exactly two communication facilities (e.g., twonodesof 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 supportbroadcast transmission,where one node can transmit so that all other nodes can receive the same transmission.Classic Ethernetis an example.

Multipoint

Also known as amultidroplink, a multipoint link is a link that connectstwo or morenodes. Also known as general topology networks, these includeATMandFrame Relaylinks, as well asX.25networks when used as links for anetwork-layer protocollikeIP.

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

Apoint-to-multipoint link(or simply amultipoint) 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.

• Aprivate linkis a link that is either owned by a specific entity or a link that is only accessible by a particular entity.
• Apublic linkis 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

Feeder links,here:uplink / downlink

Uplink

"Uplink" redirects here. For other uses, seeUplink (disambiguation).

• Pertaining toradiocommunication service,anuplink(UL or U/L) is the portion of afeeder linkused for the transmission of signals from anearth stationto aspace radio station,space radio systemorhigh altitude platform station.
• Pertaining toGSMand cellular networks, the radio uplink is the transmission path from themobile station(cell phone) to abase station(cell site). Traffic and signalling flowing within theBSSandNSSmay also be identified as uplink and downlink.
• Pertaining to computer networks, an uplink is a connection fromdata communications equipmenttoward thenetwork core.This is also known as anupstreamconnection.

Downlink

• Pertaining toradiocommunication service,adownlink(DL or D/L) is the portion of afeeder linkused for the transmission of signals from aspace radio station,space radio systemorhigh altitude platform stationto anearth station.
• In the context ofsatellite communications,adownlink(DL) is the link from a satellite to aground station.
• Pertaining tocellular networks,the radio downlink is the transmission path from acell siteto thecell phone.Traffic and signalling flowing within thebase station subsystem(BSS) andnetwork switching subsystem(NSS) may also be identified as uplink and downlink.
• Pertaining tocomputer networks,a downlink is a connection from data communications equipment towarddata terminal equipment.This is also known as adownstreamconnection.

Forward link

Aforward linkis the link from a fixed location (e.g., abase station) to a mobile user. If the link includes acommunications relay satellite,the forward link will consist of both anuplink(base station to satellite) and a downlink (satellite to mobile user).

Reverse link

See also:Backhaul (telecommunications)andReturn channel

Thereverse link(sometimes called areturn channel) is the link from a mobile user to a fixed base station.

If the link includes acommunications relay satellite,the reverse link will consist of both anuplink(mobile station to satellite) and adownlink(satellite to base station) which together constitute a halfhop.

References

• This article incorporatespublic domain materialfromFederal Standard 1037C.General Services Administration.Archived fromthe originalon 2022-01-22.(in support ofMIL-STD-188).
• This article incorporatespublic domain materialfromDictionary of Military and Associated Terms.United States Department of Defense.