In a

telecommunications network A telecommunications network is a group of nodes interconnected by telecommunications links that are used to exchange messages between the nodes. The links may use a variety of technologies based on the methodologies of circuit switching, message ...

, a link is a

communication channel A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for informa ...

that connects two or more devices for the purpose of

data transmission Data transmission and data reception or, more broadly, data communication or digital communications is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal transmitted over a point-to-point o ...

. 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 established within the network between two endpoints. The network, rather than having a fixed data rate reservation ...

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 A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. C ...

s, terrestrial

radio communications Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...

infrastructure and

computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...

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 In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theory), vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two ...

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

point-to-point link In telecommunications, a point-to-point connection refers to a communications connection between two communication endpoints or nodes. An example is a telephone call, in which one telephone is connected with one other, and what is said by one c ...

is a dedicated link that connects exactly two communication facilities (e.g., two

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 Classic Ethernet is a family of 10 Mbit/s Ethernet standards, which is the first generation of Ethernet standards. In 10BASE-X, the 10 represents its maximum throughput of 10 Mbit/s, BASE indicates its use of baseband transmission, and ...

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 Frame Relay is a standardized wide area network (WAN) technology that specifies the physical and data link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated Se ...

links, as well as

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

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

point-to-multipoint link In telecommunications, point-to-multipoint communication (P2MP, PTMP or PMP) is communication which is accomplished via a distinct type of one-to-many connection, providing multiple paths from a single location to multiple locations. Point-to ...

(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. Any transmission of data that originates from the central CE is received by all of the peripheral CEs 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 specific 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 Radio communication service or radiocommunication service is according to Article 1.19 of the International Telecommunication Union's Radio Regulations (ITU RR),ITU Radio Regulations, Section III – Radio services, Article 1.19, definition: Ra ...

, an uplink (UL or U/L) is the portion of a

feeder link A feeder link is – according to ''Article 1.115'' of the International Telecommunication Union´s (ITU) ITU Radio Regulations (RR)ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.115, definition: ''feeder link'' – ...

used for the transmission of signals from an

earth station A ground station, Earth station, or Earth terminal is a terrestrial radio station designed for extraplanetary telecommunication with spacecraft (constituting part of the ground segment of the spacecraft system), or reception of radio waves fro ...

to a

space radio station Space radio station (short: space station) is a radio station located on an object travelling beyond the major portion of the Earth's atmosphere.ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.64, definition: ''space ra ...

space radio system Space radio system (also: ''space system'') is – according to ''article 1.110'' of the International Telecommunication Union's (ITU) ITU Radio Regulations (RR)ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.110, d ...

high altitude platform station Atmospheric satellite (United States usage, abbreviated atmosat) or pseudo-satellite (British usage) is a marketing term for an aircraft that operates in the atmosphere at high altitudes for extended periods of time, in order to provide servic ...

. *Pertaining to

GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...

and cellular networks, the radio uplink is the transmission path from the

mobile station A mobile station (MS) comprises all user equipment and computer software, software needed for communication with a Cellular network, mobile network. The term refers to the global system connected to the mobile network, i.e. a mobile phone or mob ...

(cell phone) to a

base station Base station (or base radio station) is – according to the International Telecommunication Union's (ITU) Radio Regulations (RR) – a "land station in the land mobile service." The term is used in the context of mobile telephony, wireless com ...

(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 A data circuit-terminating equipment (DCE) is a device that sits between the data terminal equipment (DTE) and a data transmission circuit. It is also called data communication(s) equipment and data carrier equipment. Usually, the DTE device is ...

toward the

network core A backbone or core network is a part of a computer network which interconnects networks, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building ...

. This is also known as an

upstream Upstream may refer to: * Upstream (bioprocess) * ''Upstream'' (film), a 1927 film by John Ford * Upstream (networking) * ''Upstream'' (newspaper), a newspaper covering the oil and gas industry * Upstream (petroleum industry) * Upstream (software ...

connection.

Downlink

*Pertaining to

, a downlink (DL or D/L) is the portion of a

used for the transmission of signals from a

to an

. *In the context of satellite communications, a downlink (DL) is the link from a satellite to a ground station. *Pertaining to cellular networks, the radio downlink is the transmission path from a cell site to the cell phone. Traffic and signalling flowing within the

base station subsystem The base station subsystem (BSS) is the section of a traditional cellular telephone network which is responsible for handling traffic and signaling between a mobile phone and the network switching subsystem. The BSS carries out transcoding of s ...

(BSS) and

network switching subsystem Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call out and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mobi ...

(NSS) may also be identified as uplink and downlink. *Pertaining to computer networks, a downlink is a connection from data communications equipment towards

data terminal equipment Data terminal equipment (DTE) is an end instrument that converts user information into signals or reconverts received signals. These can also be called tail circuits. A DTE device communicates with the data circuit-terminating equipment (DCE) ...

. This is also known as a

downstream Downstream may refer to: * Downstream (bioprocess) * Downstream (manufacturing) * Downstream (networking) * Downstream (software development) * Downstream (petroleum industry) * Upstream and downstream (DNA), determining relative positions on DNA ...

connection.

Forward link

A forward link is the link from a fixed location (e.g., a

) to a mobile user. If the link includes a communications relay satellite, the forward link will consist of both an

uplink 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 physical link or a virtual circuit that uses one or more physical links or shar ...

(base station to satellite) and a downlink (satellite to mobile user).Basics of C & Ku Band
Scatmag.com

Reverse link

The reverse link (sometimes called a ''

return channel In communications systems, the return channel (also reverse channel or return link) is the transmission link from a user terminal to the central hub. Return links are often, but not always, slower than the corresponding forward links. Examples where ...

'') 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

(mobile station to satellite) and a

downlink 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 physical link or a virtual circuit that uses one or more physical links or shar ...

(satellite to base station) which together constitute a half

hop A hop is a type of jump. Hop or hops may also refer to: Arts and entertainment * ''Hop'' (film), a 2011 film * Hop! Channel, an Israeli TV channel * ''House of Payne'', or ''HOP'', an American sitcom * Lindy Hop, a swing dance of the 1920s and ...

References

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