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In telecommunications a link is the 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. When the link is a logical link the type of physical link should always be specified (e.g., data link, uplink, downlink, fiber optic link, point-to-point link, etc.) This term is widely used in computer networking (see Data link) to refer to the communications facilities that connect nodes of a network.^[1]

Note: Sometimes the communications facilities that provide the communications channel that constitutes a link are also included in the definition of link.

Contents 1 Types of links 1.1 Point-to-point 1.2 Broadcast 1.3 Multipoint 1.3.1 Point-to-multipoint 1.4 Private and Public - Accessibility and Ownership 1.4.1 Private links 1.4.2 Public links 2 References

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. 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 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.

This term is also often used as a synonym for multipoint, as defined above.

Quite often, links are 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.

1. ^ ATIS Committee T1A1 Performance and Signal Processing (2005). ANS T1.523-2001, Telecom Glossary 2000. ATIS Committee T1A1. 

• Federal Standard 1037C
• MIL-STD-188
• Department of Defense Dictionary of Military and Associated Terms