Main Distribution Frame

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What Does Main Distribution Frame Mean?

A Main Distribution Frame (MDF) is a signal distribution frame or cable rack used in telephony to interconnect and manage telecommunication wiring between itself and any number of intermediate distribution frames and cabling from the telephony network it supports.

The MDF connects equipment inside a telecommunications facility to cables and subscriber carrier equipment. Every cable that supplies services to user telephones lines ends up at an MDF and is distributed through MDF to equipment within local exchanges.

Historically this would be the same as the telephone switchboards of yesteryear where telephone operators inserted connecting wires into a matrix of sockets on a patch panel to connect calls. Todays jumpers are more permanent, assigning a line to each individual subscriber account and only need to be changed as people change their numbers, to reroute networks, dedicated lines or for maintenance purposes.

Techopedia Explains Main Distribution Frame

An MDF can provide flexibility in assigning telecommunications facilities at a lower cost and higher capacity than a patch panel.


The most common kind of MDF is a long steel rack that is accessible from both sides. Termination blocks are arranged horizontally on one side at the front of the rack shelves. The jumpers lie on the shelf and move through a steel hoop in order to run through vertically arranged termination blocks.

A typical MDF can hold hundreds of thousands of jumpers and dozens of them can be changed every day for decades without tangling when administered by experienced professionals. Jumpers are twisted pairs of cable, each one corresponding to an individual telephone line.

MDFs are single-sided so that the workers can install, remove or change jumpers. However,
old manual jumpering systems are now mostly automated using automated main distribution frames. Computer systems that control MDF operations assign terminals close to one another so that jumpers need not be long and shelves are not congested with wires as the jumpers are shorter.

MDFs in private branch exchanges perform functions that are similar to those performed by those in central offices but on a smaller scale.


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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.