<s>
Nortel	O
's	O
Switch56	B-Device
was	O
a	O
networking	O
protocol	O
built	O
on	O
top	O
of	O
the	O
telephone	O
cabling	O
hardware	O
of	O
their	O
Digital	B-Protocol
Multiplex	I-Protocol
System	I-Protocol
and	O
other	O
telephone	O
switches	O
.	O
</s>
<s>
The	O
name	O
comes	O
from	O
the	O
fact	O
that	O
Switch56	B-Device
carried	O
56	O
kbit/s	O
of	O
data	O
on	O
its	O
64	O
kbit/s	O
lines	O
,	O
as	O
opposed	O
to	O
most	O
systems	O
,	O
including	O
ISDN	B-Protocol
,	O
where	O
the	O
entire	O
64	O
kbit/s	O
bandwidth	O
was	O
available	O
for	O
data	O
.	O
</s>
<s>
Switch56	B-Device
"	O
folded	O
"	O
the	O
two	O
sources	O
of	O
data	O
into	O
one	O
,	O
placing	O
a	O
single	O
bit	O
from	O
the	O
command	O
channel	O
onto	O
the	O
end	O
of	O
every	O
7	O
bits	O
of	O
data	O
,	O
similar	O
to	O
the	O
original	O
T-carrier	O
supervision	O
scheme	O
.	O
</s>
<s>
Switch56	B-Device
was	O
built	O
on	O
top	O
of	O
the	O
basic	O
Nortel	O
hardware	O
to	O
allow	O
computers	O
to	O
put	O
data	O
into	O
the	O
existing	O
telephony	O
network	O
.	O
</s>
<s>
Although	O
slow	O
compared	O
to	O
even	O
contemporary	O
systems	O
,	O
Switch56	B-Device
allowed	O
network	O
traffic	O
to	O
flow	O
not	O
only	O
within	O
an	O
office	O
like	O
other	O
LAN	B-General_Concept
systems	O
,	O
but	O
between	O
any	O
branch	O
offices	O
that	O
were	O
connected	O
using	O
a	O
Nortel	O
PBX	B-Device
like	O
the	O
Meridian	B-Device
Norstar	I-Device
.	O
</s>
<s>
This	O
was	O
a	O
much	O
easier	O
option	O
to	O
install	O
than	O
ISDN	B-Protocol
for	O
most	O
offices	O
,	O
requiring	O
nothing	O
more	O
than	O
a	O
Switch56	B-Device
bridge	O
to	O
their	O
existing	O
network	O
.	O
</s>
<s>
For	O
the	O
LAN	B-General_Concept
role	O
new	O
telephone	O
terminals	O
were	O
produced	O
with	O
a	O
RS-232C	O
port	O
on	O
the	O
back	O
,	O
which	O
were	O
then	O
plugged	O
into	O
the	O
user	O
's	O
computer	O
and	O
used	O
with	O
custom	O
software	O
.	O
</s>
<s>
Although	O
interesting	O
in	O
theory	O
,	O
it	O
appears	O
Switch56	B-Device
saw	O
little	O
use	O
in	O
this	O
role	O
.	O
</s>
