<s>
A	O
terminal	B-Protocol
node	I-Protocol
controller	I-Protocol
(	O
TNC	O
)	O
is	O
a	O
device	O
used	O
by	O
amateur	O
radio	O
operators	O
to	O
participate	O
in	O
AX.25	B-Protocol
packet	B-Application
radio	I-Application
networks	O
.	O
</s>
<s>
It	O
is	O
similar	O
in	O
function	O
to	O
the	O
Packet	B-Protocol
Assembler/Disassemblers	I-Protocol
used	O
on	O
X.25	B-Protocol
networks	O
,	O
with	O
the	O
addition	O
of	O
a	O
modem	B-Application
to	O
convert	O
baseband	O
digital	O
signals	O
to	O
audio	O
tones	O
.	O
</s>
<s>
In	O
1983	O
,	O
the	O
Tucson	O
Amateur	O
Packet	B-Application
Radio	I-Application
(	O
TAPR	O
)	O
association	O
produced	O
complete	O
kits	O
for	O
their	O
TNC-1	O
design	O
.	O
</s>
<s>
TNC+	O
also	O
included	O
an	O
assembler	O
and	O
a	O
version	O
of	O
Forth	O
(	O
STOIC	B-Language
)	O
,	O
which	O
runs	O
on	O
the	O
TNC+	O
itself	O
,	O
to	O
support	O
developing	O
new	O
programs	O
and	O
protocols	O
.	O
</s>
<s>
A	O
typical	O
model	O
consists	O
of	O
a	O
microprocessor	B-Architecture
,	O
a	O
modem	B-Application
,	O
and	O
software	O
(	O
in	O
EPROM	B-General_Concept
)	O
that	O
implements	O
the	O
AX.25	B-Protocol
protocol	O
and	O
provides	O
a	O
command	B-Application
line	I-Application
interface	I-Application
to	O
the	O
user	O
.	O
</s>
<s>
(	O
Commonly	O
,	O
this	O
software	O
provides	O
other	O
functionality	O
as	O
well	O
,	O
such	O
as	O
a	O
basic	O
bulletin	B-Application
board	I-Application
system	I-Application
to	O
receive	O
messages	O
while	O
the	O
operator	O
is	O
away	O
.	O
)	O
</s>
<s>
Because	O
the	O
TNC	O
contains	O
all	O
the	O
intelligence	O
needed	O
to	O
communicate	O
over	O
an	O
AX.25	B-Protocol
network	B-Architecture
,	O
no	O
external	O
computer	O
is	O
required	O
.	O
</s>
<s>
All	O
of	O
the	O
network	B-Architecture
's	O
resources	O
can	O
be	O
accessed	O
using	O
a	O
dumb	B-General_Concept
terminal	I-General_Concept
.	O
</s>
<s>
Data	O
from	O
the	O
terminal	O
is	O
formatted	O
into	O
AX.25	B-Protocol
packets	O
and	O
modulated	B-Application
into	O
audio	O
signals	O
(	O
in	O
traditional	O
applications	O
)	O
for	O
transmission	O
by	O
the	O
radio	O
.	O
</s>
<s>
In	O
addition	O
to	O
these	O
functions	O
,	O
the	O
TNC	O
manages	O
the	O
radio	O
channel	O
according	O
to	O
guidelines	O
in	O
the	O
AX.25	B-Protocol
specification	O
.	O
</s>
<s>
Since	O
the	O
late	O
1990s	O
,	O
most	O
AX.25	B-Protocol
usage	O
has	O
shifted	O
to	O
a	O
different	O
one-to-many	O
communication	O
paradigm	O
with	O
the	O
Automatic	B-Application
Packet	I-Application
Reporting	I-Application
System	I-Application
(	O
APRS	O
)	O
.	O
</s>
<s>
The	O
TNCs	O
of	O
the	O
1980s	O
and	O
1990s	O
were	O
complete	O
solutions	O
that	O
only	O
needed	O
a	O
radio	O
and	O
an	O
optional	O
dumb	B-General_Concept
terminal	I-General_Concept
.	O
</s>
<s>
As	O
home	O
computers	O
made	O
their	O
way	O
into	O
ham	O
"	O
shacks	O
,	O
"	O
there	O
was	O
a	O
movement	O
toward	O
simpler	O
,	O
cheaper	O
"	B-Protocol
KISS	I-Protocol
"	I-Protocol
(	O
Keep	O
It	O
Simple	O
,	O
Stupid	O
)	O
devices	O
.	O
</s>
<s>
These	O
have	O
a	O
modem	B-Application
and	O
minimal	O
processing	O
of	O
the	O
AX.25	B-Protocol
protocol	O
.	O
</s>
<s>
A	O
"	O
soundcard	B-Device
"	O
is	O
used	O
for	O
audio	O
to	O
and	O
from	O
the	O
radio	O
.	O
</s>
<s>
Modern	O
software	O
TNCs	O
,	O
using	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
(	O
DSP	O
)	O
techniques	O
,	O
can	O
successfully	O
decode	O
poor	O
quality	O
signals	O
that	O
the	O
older	O
equipment	O
ca	O
n't	O
.	O
</s>
<s>
The	O
connectors	O
used	O
for	O
this	O
purpose	O
vary	O
widely	O
across	O
TNC	O
manufacturers	O
,	O
but	O
modern	O
radios	O
that	O
offer	O
data	O
ports	O
have	O
widely	O
adopted	O
the	O
Mini-DIN	B-Protocol
6-pin	O
connector	O
.	O
</s>
<s>
TNCs	O
were	O
originally	O
designed	O
to	O
accept	O
messages	O
from	O
a	O
human	O
typing	O
on	O
a	O
dumb	B-General_Concept
terminal	I-General_Concept
.	O
</s>
<s>
This	O
could	O
also	O
be	O
used	O
with	O
the	O
serial	B-Protocol
port	I-Protocol
of	O
a	O
personal	O
computer	O
.	O
</s>
<s>
Serial	B-Protocol
ports	I-Protocol
are	O
now	O
pretty	O
much	O
extinct	O
,	O
but	O
USB-to-serial	O
converter	O
cables	O
are	O
available	O
.	O
</s>
<s>
Modern	O
Software	O
TNCs	O
provide	O
TCP/IP	B-Protocol
interfaces	O
that	O
can	O
be	O
accessed	O
across	O
computer	B-Architecture
networks	I-Architecture
.	O
</s>
<s>
For	O
example	O
,	O
it	O
is	O
possible	O
to	O
run	O
a	O
software	O
TNC	O
on	O
a	O
Raspberry	B-Operating_System
Pi	I-Operating_System
near	O
the	O
radio	O
and	O
access	O
it	O
from	O
a	O
laptop	O
computer	O
in	O
another	O
location	O
.	O
</s>
<s>
Software	O
TNCs	O
also	O
provide	O
"	O
pseudo	B-Protocol
terminals	I-Protocol
"	O
so	O
they	O
can	O
be	O
used	O
with	O
old	O
applications	O
that	O
only	O
know	O
how	O
to	O
use	O
serial	B-Protocol
ports	I-Protocol
.	O
</s>
