<s>
FTZ	O
1	O
TR	O
6	O
(	O
or	O
1	O
TR	O
6	O
)	O
is	O
the	O
standard	O
for	O
the	O
obsolete	O
German	O
national	O
digital	B-General_Concept
signalling	O
protocol	O
(	O
D	B-Protocol
channel	I-Protocol
protocol	O
)	O
used	O
for	O
the	O
ISDN	B-Protocol
.	O
</s>
<s>
It	O
has	O
been	O
superseded	O
by	O
DSS1	B-Protocol
but	O
is	O
still	O
in	O
use	O
on	O
some	O
lines	O
and	O
private	B-Device
exchanges	I-Device
.	O
</s>
<s>
ISDN	B-Protocol
subscribers	O
would	O
get	O
a	O
sequence	O
of	O
10	O
subsequent	O
subscriber	O
numbers	O
,	O
the	O
last	O
digit	O
of	O
which	O
being	O
the	O
EAZ	O
.	O
</s>
<s>
1TR6	O
also	O
offered	O
semipermanent	O
connections	O
,	O
which	O
were	O
(	O
comparatively	O
cheap	O
)	O
leased	B-Architecture
lines	I-Architecture
that	O
could	O
be	O
temporarily	O
disabled	O
to	O
use	O
the	O
B	B-Protocol
channel	I-Protocol
for	O
other	O
purposes	O
.	O
</s>
