1. All the cabling and equipment installed in a telecommunications facility, including the main distribution frame (MDF) and all the equipment extending inward therefrom, such as PABX or central office equipment, MDF protectors, and grounding systems.
2. In radio and radar systems, all communications-electronics (C-E) equipment that is installed in buildings.
Source: from Federal Standard 1037C and from MIL-STD-188