<s>
In	O
telecommunications	O
,	O
a	O
digital	B-Protocol
multiplex	I-Protocol
hierarchy	I-Protocol
is	O
a	O
hierarchy	O
consisting	O
of	O
an	O
ordered	O
repetition	O
of	O
tandem	B-Application
digital	B-General_Concept
multiplexers	O
that	O
produce	O
signals	O
of	O
successively	O
higher	O
data	O
rates	O
at	O
each	O
level	O
of	O
the	O
hierarchy	O
.	O
</s>
<s>
Digital	B-General_Concept
multiplexing	B-Architecture
hierarchies	O
may	O
be	O
implemented	O
in	O
many	O
different	O
configurations	O
depending	O
on	O
;	O
(	O
a	O
)	O
the	O
number	O
of	O
channels	O
desired	O
,	O
(	O
b	O
)	O
the	O
signaling	O
system	O
to	O
be	O
used	O
,	O
and	O
(	O
c	O
)	O
the	O
bit	O
rate	O
allowed	O
by	O
the	O
communications	O
media	O
.	O
</s>
<s>
Some	O
currently	O
available	O
digital	B-General_Concept
multiplexers	O
have	O
been	O
designated	O
as	O
Dl-	B-Protocol
,	I-Protocol
DS-	I-Protocol
,	I-Protocol
or	I-Protocol
M-series	I-Protocol
,	O
all	O
of	O
which	O
operate	O
at	O
T-carrier	O
rates	O
.	O
</s>
<s>
In	O
the	O
design	O
of	O
digital	B-Protocol
multiplex	I-Protocol
hierarchies	I-Protocol
,	O
care	O
must	O
be	O
exercised	O
to	O
ensure	O
interoperability	O
of	O
the	O
multiplexers	O
used	O
in	O
the	O
hierarchy	O
.	O
</s>
<s>
Digroup	B-Protocol
is	O
an	O
abbreviation	O
for	O
digital	B-General_Concept
group	O
.	O
</s>
<s>
In	O
telephony	O
,	O
a	O
basic	O
group	O
in	O
the	O
digital	B-Protocol
multiplex	I-Protocol
hierarchy	I-Protocol
.	O
</s>
<s>
In	O
the	O
North	O
American	O
and	O
Japanese	O
T-carrier	O
digital	B-General_Concept
hierarchies	O
,	O
each	O
digroup	B-Protocol
supports	O
12	O
PCM	O
voice	O
channels	O
or	O
their	O
equivalent	O
in	O
other	O
services	O
.	O
</s>
<s>
The	O
DS1	O
line	O
rate	O
(	O
2	O
digroups	B-Protocol
plus	O
overhead	O
bits	O
)	O
is	O
1.544	O
Mbit/s	O
,	O
supporting	O
24	O
voice	O
channels	O
or	O
their	O
equivalent	O
in	O
other	O
services	O
.	O
</s>
<s>
In	O
the	O
E-carrier	O
European	O
hierarchy	O
,	O
each	O
digroup	B-Protocol
supports	O
15	O
PCM	O
channels	O
or	O
their	O
equivalent	O
in	O
other	O
services	O
.	O
</s>
<s>
The	O
DS1	O
line	O
rate	O
(	O
2	O
digroups	B-Protocol
plus	O
overhead	O
bits	O
)	O
is	O
2.048	O
Mbit/s	O
,	O
supporting	O
30	O
voice	O
channels	O
or	O
their	O
equivalent	O
in	O
other	O
services	O
.	O
</s>
