The portion of premises telecommunications cabling that provides connections between telecommunications closets, equipment rooms, and entrance facilities. The backbone cabling consists of the transmission media (optical fiber cable), main and intermediate cross-connects, and terminations for the horizontal cross-connect, equipment rooms, and entrance facilities. The backbone cabling can further be classified as interbuilding backbone (cabling between buildings), or intrabuilding backbone (cabling within a building).

The portion of the cabling that provides connections between communication closets, equipment rooms and entrance facilities.

The cabling that distributes voice and data services between the equipment room, telecommunications closets, and between buildings. See ' Horizontal Cabling.'