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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.
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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
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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
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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
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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
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the outside world are terminated on the horizontal side, and the indoors equipment on the vertical side. American usage is the opposite.
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Smaller MDFs, and some modern large ones, are single sided so one worker can install, remove or change a jumper.
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in the 1970s. In most exchanges in the UK, soldered blocks are still in use, but are being slowly phased out.
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are terminated at the MDF and distributed through the MDF to equipment within the local exchange e.g.
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The most common kind of large MDF is a long steel rack accessible from both sides. On one side,
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the MDF provides flexibility in assigning facilities, at lower cost and higher capacity than a
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later database method saves much labor by permitting old jumpers to be reused for new lines.
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are connected by jumper wires at the MDF. All cable copper pairs supplying services through
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cables may terminate on the same MDF or on a separate trunk main distribution frame (TMDF).
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MDF newly installed in a large urban exchange, early 20th century, no jumpers yet
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performs functions similar to those performed by the MDF in a central office.
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in the late 20th century diminished the need for large, active, central MDFs.
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for more about vertical and horizontal main distribution frames.
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234:. Middle 20th century jumper wires in the USA were 24
280:Sometimes the MDF is combined with other kinds of
82:Small, single-sided MDF for a military base, 1940s
257:Obsolete MDF in a cold-war era telephone exchange
134:The MDF is a termination point within the local
219:. This was reliable but slow and expensive.
246:to provide a suitable degree of brittleness.
138:where exchange equipment and terminations of
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199:between a line and the exchange equipment.
301:(AMDF) has been a subject of experiments.
66:Learn how and when to remove this message
215:Before 1960, MDF jumpers were generally
29:This article includes a list of general
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238:single strand copper, with a soft
35:it lacks sufficient corresponding
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299:Automated Main Distribution Frame
223:was introduced in the 1960s, and
354: This article incorporates
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159:intermediate distribution frames
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367:General Services Administration
316:Intermediate distribution frame
90:Modern main distribution frame
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191:protective devices including
161:(IDF) terminate at the MDF.
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267:Operations Support Systems
114:for connecting equipment (
244:polyethylene cross-linked
293:private branch exchange
265:and other computerized
100:main distribution frame
50:more precise citations.
362:Federal Standard 1037C
356:public domain material
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187:The MDF usually holds
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375: (in support of
275:distributed switching
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195:, and functions as a
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399:Telephone exchanges
394:Telephony equipment
170:distribution frames
311:Distribution frame
282:distribution frame
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189:telephone exchange
136:telephone exchange
120:subscriber carrier
112:distribution frame
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230:Each jumper is a
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369:. Archived from
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273:The adoption of
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337:"MDF Jumpering"
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42:Please help to
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291:The MDF in a
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157:. Cables to
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124:outside plant
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371:the original
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240:polyethylene
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116:inside plant
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377:MIL-STD-188
181:termination
174:patch panel
168:Like other
140:local loops
122:equipment (
48:introducing
388:Categories
323:References
197:test point
193:heat coils
108:main frame
31:references
221:Wire wrap
151:repeaters
96:telephony
56:June 2015
305:See also
217:soldered
130:Overview
203:History
44:improve
263:COSMOS
33:, but
358:from
284:in a
163:Trunk
155:DSLAM
153:and
144:user
98:, a
286:CDF
236:AWG
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106:or
104:MDF
94:In
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Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
