The Telecommunications entrance facility (AKA Main Distribution Frame, MDF) is the site of the building’s telecommunication service entrance and backbone connections, as well as the demarcation point that provides the interconnection to the local exchange carrier’s telecommunication closets. The TIA/EIA 568 standard suggests, but does not stipulate, that the demarcation point should be 12 inches from where the local exchange carrier’s facilities enter the building.

This location shall be designed/sized to serve the entire building based user needs. This closet is to be centrally located so as to ensure that all copper voice and data cable sheath lengths out to the outlets are less than 90 m (295 ft). This closet shall interconnect with each Telecommunications Closet (TC) or Intermediate Distribution Facility (IDF) via distinct, dedicated multimode and single-mode fiber optic backbone cables, 25 pair twisted pair CAT 5 data risers and 100 pair twisted pair voice riser cables. In smaller buildings, where only one telecommunications closet is required, the MDF will also function as the IDF.