In telecommunications a link is a communications channel that connects two
or more communicating devices. This link may be an actual physical link or it may
be a logical link that uses one or more actual physical links.
A telecommunications link is generally 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. When the link is a logical link the type of physical link
should always be specified Types
= Point-to-point= A point-to-point link is a dedicated
link that connects exactly two communication facilities.
= 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. 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 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 is a specific type of multipoint link which consists
of a central connection endpoint 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 – accessibility and ownership=
Links are often referred to by terms which refer to the ownership and / 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 satellite communications, an uplink is the portion of a
communications link used for the transmission of signals from an Earth
terminal to a satellite or to an airborne platform. An uplink is the
inverse of a downlink. An uplink or downlink is distinguished from reverse
link or forward link. Pertaining to GSM and cellular networks,
the radio uplink is the transmission path from the mobile station to a base
station. Traffic and signalling flows 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= In the context of satellite
communications, a downlink 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 flows within the
base station subsystem and network switching subsystem 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. This is also known as a downstream connection.
= Forward link= A forward link is the link from a fixed
location to a mobile user. If the link includes a communications relay
satellite, the forward link will consist of both an uplink and a downlink.
= Reverse link= The reverse link 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 and a downlink
which together constitute a half hop. See also
Data transmission Telecommunications network
Notes References
This article incorporates public domain material from the General Services
Administration document "Federal Standard 1037C".
This article incorporates public domain material from the United States
Department of Defense document "Dictionary of Military and Associated
Terms".