A distribution frame is a rack in a telecommunications central office to which wiring for one set of wires is patched to another set of wires. The primary distribution frame from which all outside plant local loops are connected is referred to as the Main Distribution Frame (MDF). This tutorial will focus on the function of the MDF.

The MDF connects the ouside plant wiring to the inside facilities, specifically, the digital cross-connecting switches (DCCS). Telecommunications companies make a practice of pre-provisioning the capacity on their DCCS to the MDF where all outside connections are also patched down. Each external connection shares a copper connector that connects one punch location on the front of the MDF to a single punch location on the back of the MDF. I refer to these patching points as 'punches' because a tool is used to make the copper connection and it punches the wire into the MDF's connector.

A given DCCS can handle a specific number of voice lines. When a digital cross-connecting switch is installed, twisted copper wiring is punched down to the back of the DCCS. The other end of the copper wiring is patched to the back of the MDF, even though no voice line is intended to be connected to it yet. This allows a telephone lineman to enter later and punch in your new telephone line.

When a home's telephone service is 'turned on', frequently the connection is punched down at the MDF. When phone service is lost, the connection at the MDF is frequently the cause (a lineman accidentally removed the wrong pair of wires).


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