A term used in building cabling infrastructure to denote the complete horizontal cabling structure from the floor distribution board to the data socket for the end-device.

Transmission capability for these links is specified in permanent link classes from A to F. Class A denotes links with low data rates (e.g. ISDN base connection), while Class F applies to multimedia applications (gigabit Ethernet with high bandwidth and outstanding NEXT and attenuation specs).

The specification covers all transmission media, connectors, sockets and patch cables. The individual components of the overall link are classified into various categories.