HOME

TheInfoList



OR:

In
telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...
, a main distribution frame (MDF or main frame) is a signal
distribution frame Distribution may refer to: Mathematics *Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations *Probability distribution, the probability of a particular value or value range of a varia ...
for connecting equipment ( inside plant) to cables and subscriber carrier equipment (
outside plant In telecommunication, the term outside plant has the following meanings: *In civilian telecommunications, outside plant refers to all of the physical cabling and supporting infrastructure (such as conduit, cabinets, tower or poles), and any asso ...
).


Overview

The MDF is a termination point within the local
telephone exchange telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...
where exchange equipment and terminations of
local loop In telephony, the local loop (also referred to as the local tail, subscriber line, or in the aggregate as the last mile) is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the commo ...
s are connected by jumper wires at the MDF. All cable copper pairs supplying services through
user Ancient Egyptian roles * User (ancient Egyptian official), an ancient Egyptian nomarch (governor) of the Eighth Dynasty * Useramen, an ancient Egyptian vizier also called "User" Other uses * User (computing), a person (or software) using an ...
telephone line A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. It is designed to reproduce speech of a quality that is understandable. It is the physical wire or ot ...
s are terminated at the MDF and distributed through the MDF to equipment within the local exchange e.g.
repeater In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Som ...
s and
DSLAM A digital subscriber line access multiplexer (DSLAM, often pronounced ''DEE-slam'') is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital co ...
. Cables to
intermediate distribution frame An intermediate distribution frame (IDF) is a distribution frame in a central office or customer premises, which cross connects the user cable media to individual user line circuits and may serve as a distribution point for multipair cables f ...
s (IDF) terminate at the MDF.
Trunk Trunk may refer to: Biology * Trunk (anatomy), synonym for torso * Trunk (botany), a tree's central superstructure * Trunk of corpus callosum, in neuroanatomy * Elephant trunk, the proboscis of an elephant Computing * Trunk (software), in rev ...
cables may terminate on the same MDF or on a separate trunk main distribution frame (TMDF). Like other
distribution frame Distribution may refer to: Mathematics *Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations *Probability distribution, the probability of a particular value or value range of a varia ...
s the MDF provides flexibility in assigning facilities, at lower cost and higher capacity than a
patch panel A patch panel is a device or unit featuring a number of jacks, usually of the same or similar type, for the use of connecting and routing circuits for monitoring, interconnecting, and testing circuits in a convenient, flexible manner. Patch ...
. The most common kind of large MDF is a long steel rack accessible from both sides. On one side,
termination Termination may refer to: Science *Termination (geomorphology), the period of time of relatively rapid change from cold, glacial conditions to warm interglacial condition *Termination factor, in genetics, part of the process of transcribing RNA ...
blocks are arranged horizontally at the front of rack shelves. Jumpers lie on the shelves and go through an insulated steel hoop to run vertically to other termination blocks that are arranged vertically. There is a hoop or ring at the intersection of each level and each vertical. Installing a jumper historically required two workers, one on either side of the MDF. The shelves are shallow enough to allow the rings to be within arm's reach, but the workers prefer to hang the jumper on a hook on a pole so their partner can pull it through the ring. A fanning strip at the back of each termination block prevents the wires from covering each other's terminals. With disciplined administration, the MDF can hold over a hundred thousand jumpers, with dozens changed every day, for decades without tangling. The MDF usually holds
telephone exchange telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...
protective devices including heat coils, and functions as a test point between a line and the exchange equipment.


History

Before 1960, MDF jumpers were generally
solder Solder (; NA: ) is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable ...
ed. This was reliable but slow and expensive.
Wire wrap Wire wrap is an electronic component assembly technique that was invented to wire telephone crossbar switches, and later adapted to construct electronic circuit boards. Electronic components mounted on an insulating board are interconnected by ...
was introduced in the 1960s, and punch blocks in the 1970s. In most exchanges in the UK, soldered blocks are still in use, but are being slowly phased out. Each jumper is a
twisted pair Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted b ...
. Middle 20th century jumper wires in the USA were 24 AWG single strand copper, with a soft
polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including b ...
inner jacket and a cotton wrapper, impregnated to make it slightly brittle and easy to remove neatly. Late 20th century ones had a single, thicker coating of polyethylene cross-linked to provide a suitable degree of brittleness. Some urban telephone exchange MDFs are two stories high so they do not have to be more than a city block long. A few are three stories. Access to the upper levels can be either by a traveling ladder attached to the MDF, or by mezzanine walkways at a suitable height. By British custom the cables to the outside world are terminated on the horizontal side, and the indoors equipment on the vertical side. American usage is the opposite. Smaller MDFs, and some modern large ones, are single sided so one worker can install, remove or change a jumper.
COSMOS The cosmos (, ) is another name for the Universe. Using the word ''cosmos'' implies viewing the universe as a complex and orderly system or entity. The cosmos, and understandings of the reasons for its existence and significance, are studied in ...
and other computerized
Operations Support Systems Operations support systems (OSS), operational support systems in British usage, or Operation System (OpS) in NTT, are computer systems used by telecommunications service providers to manage their networks (e.g., telephone networks). They support ...
help by assigning terminals close to one another, so most jumpers need not be long and shelves on either type of MDF do not become congested. This database keeps track of all terminals and jumpers. In the early and middle 20th century these records were kept as pencil entries in ledger books. The later database method saves much labor by permitting old jumpers to be reused for new lines. The adoption of
distributed switching Distribution may refer to: Mathematics * Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations * Probability distribution, the probability of a particular value or value range of a var ...
in the late 20th century diminished the need for large, active, central MDFs. Sometimes the MDF is combined with other kinds of
distribution frame Distribution may refer to: Mathematics *Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations *Probability distribution, the probability of a particular value or value range of a varia ...
in a CDF. The MDF in a
private branch exchange A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone syst ...
performs functions similar to those performed by the MDF in a central office.
Automated Main Distribution Frame {{Unreferenced, date=April 2018 Automated main distribution frame (AMDF), (automated switching matrix, automated distribution frame, loop management system (LMS)), a technology to provide connectivity between subscriber (local loop, outside plant) � ...
(AMDF) has been a subject of experiments.


See also

*
Distribution frame Distribution may refer to: Mathematics *Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations *Probability distribution, the probability of a particular value or value range of a varia ...
*
Intermediate distribution frame An intermediate distribution frame (IDF) is a distribution frame in a central office or customer premises, which cross connects the user cable media to individual user line circuits and may serve as a distribution point for multipair cables f ...
for more about vertical and horizontal main distribution frames.


References

* {{FS1037C MS188 Telephony equipment Telephone exchanges