<s>
In	O
telephony	O
,	O
a	O
main	B-Device
distribution	I-Device
frame	I-Device
(	O
MDF	O
or	O
main	O
frame	O
)	O
is	O
a	O
signal	O
distribution	O
frame	O
for	O
connecting	O
equipment	O
(	O
inside	O
plant	O
)	O
to	O
cables	O
and	O
subscriber	B-Protocol
carrier	I-Protocol
equipment	O
(	O
outside	O
plant	O
)	O
.	O
</s>
<s>
The	O
MDF	O
is	O
a	O
termination	O
point	O
within	O
the	O
local	O
telephone	O
exchange	O
where	O
exchange	O
equipment	O
and	O
terminations	O
of	O
local	B-Architecture
loops	I-Architecture
are	O
connected	O
by	O
jumper	O
wires	O
at	O
the	O
MDF	O
.	O
</s>
<s>
repeaters	O
and	O
DSLAM	B-Protocol
.	O
</s>
<s>
Trunk	O
cables	O
may	O
terminate	O
on	O
the	O
same	O
MDF	O
or	O
on	O
a	O
separate	O
trunk	O
main	B-Device
distribution	I-Device
frame	I-Device
(	O
TMDF	O
)	O
.	O
</s>
<s>
Like	O
other	O
distribution	O
frames	O
the	O
MDF	O
provides	O
flexibility	O
in	O
assigning	O
facilities	O
,	O
at	O
lower	O
cost	O
and	O
higher	O
capacity	O
than	O
a	O
patch	B-Protocol
panel	I-Protocol
.	O
</s>
<s>
Wire	O
wrap	O
was	O
introduced	O
in	O
the	O
1960s	O
,	O
and	O
punch	B-Protocol
blocks	I-Protocol
in	O
the	O
1970s	O
.	O
</s>
<s>
The	O
adoption	O
of	O
distributed	B-Device
switching	I-Device
in	O
the	O
late	O
20th	O
century	O
diminished	O
the	O
need	O
for	O
large	O
,	O
active	O
,	O
central	O
MDFs	O
.	O
</s>
<s>
The	O
MDF	O
in	O
a	O
private	B-Device
branch	I-Device
exchange	I-Device
performs	O
functions	O
similar	O
to	O
those	O
performed	O
by	O
the	O
MDF	O
in	O
a	O
central	O
office	O
.	O
</s>
<s>
Automated	O
Main	B-Device
Distribution	I-Device
Frame	I-Device
(	O
AMDF	O
)	O
has	O
been	O
a	O
subject	O
of	O
experiments	O
.	O
</s>
