<s>
D	B-Protocol
channel	I-Protocol
(	O
delta	O
channel	O
)	O
is	O
a	O
telecommunications	O
term	O
which	O
refers	O
to	O
the	O
ISDN	B-Protocol
channel	O
in	O
which	O
the	O
control	O
and	O
signalling	O
information	O
is	O
carried	O
.	O
</s>
<s>
The	O
bit	O
rate	O
of	O
the	O
D	B-Protocol
channel	I-Protocol
of	O
a	O
basic	B-Protocol
rate	I-Protocol
interface	I-Protocol
is	O
16	O
kbit/s	O
,	O
whereas	O
it	O
amounts	O
to	O
64	O
kbit/s	O
on	O
a	O
primary	B-Protocol
rate	I-Protocol
interface	I-Protocol
.	O
</s>
<s>
For	O
DSS1	B-Protocol
signalling	O
,	O
the	O
D	B-Protocol
channel	I-Protocol
layer	O
2	O
protocol	O
is	O
Q.921	O
also	O
called	O
LAPD	O
and	O
it	O
carries	O
Layer	O
3	O
messages	O
according	O
to	O
Q.931	O
protocol	O
.	O
</s>
