In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of

data transmission Data communication, including data transmission and data reception, is the transfer of data, signal transmission, transmitted and received over a Point-to-point (telecommunications), point-to-point or point-to-multipoint communication chann ...

. The link may be a dedicated physical link or a

virtual circuit A virtual circuit (VC) is a means of transporting data over a data network, based on packet switching and in which a connection is first established across the network between two endpoints. The network, rather than having a fixed data rate reser ...

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 satellites, terrestrial radio communications infrastructure and

computer network A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or b ...

s to connect two or more points. The term ''link'' is widely used in computer networking to refer to the communications facilities that connect nodes of a network. 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

A point-to-point link is a dedicated link that connects exactly two communication facilities (e.g., two 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 ATM and Frame Relay links, as well as

X.25 X.25 is an ITU-T standard protocol suite for Packet switched network, packet-switched data communication in wide area network, wide area networks (WAN). It was originally defined by the CCITT, International Telegraph and Telephone Consultative Co ...

networks when used as links for a network-layer protocol like 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

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 station (cell site). Traffic and signalling flowing within the BSS and 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 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 A cellular network or mobile network is a telecommunications network where the link to and from end nodes is wireless network, wireless and the network is distributed over land areas called ''cells'', each served by at least one fixed-locatio ...

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

s, a downlink is a connection from data communications equipment toward data terminal equipment. This is also known as a 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 relay satellite, the forward link will consist of both an uplink (base station to satellite) and a downlink (satellite to mobile user).Basics of C & Ku Band
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Reverse link

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 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.

References

* * {{Telecommunications Telecommunications Telecommunications engineering Communication circuits Broadcast engineering Telecommunications infrastructure