Communication channel between two or more devices
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 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 networks
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.
[1]
Sometimes the communications facilities that provide the communication channel that constitutes a link are also included in the definition of
link
.
Types
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Point-to-point
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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
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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
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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
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
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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. 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
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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
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Uplink
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Downlink
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Forward link
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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).
[2]
Reverse link
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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
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