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.
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 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.
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.
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.
Links are often referred to by terms that refer to the ownership or accessibility of the 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).
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.