<s>
V5	O
is	O
a	O
family	O
of	O
telephone	O
network	O
protocols	O
defined	O
by	O
ETSI	O
which	O
allow	O
communications	O
between	O
the	O
telephone	O
exchange	O
,	O
also	O
known	O
in	O
the	O
specifications	O
as	O
the	O
local	O
exchange	O
(	O
LE	O
)	O
,	O
and	O
the	O
local	B-Architecture
loop	I-Architecture
.	O
</s>
<s>
The	O
final	O
link	O
to	O
the	O
local	B-Architecture
loop	I-Architecture
remained	O
the	O
same	O
with	O
digital	O
signalling	O
(	O
ISDN	B-Protocol
)	O
and	O
analogue	O
signalling	O
for	O
basic	O
telephony	O
(	O
also	O
known	O
as	O
POTS	O
in	O
the	O
industry	O
)	O
.	O
</s>
<s>
The	O
protocols	O
are	O
based	O
on	O
the	O
principle	O
of	O
common-channel	O
signaling	O
where	O
message-based	B-Architecture
signalling	O
for	O
all	O
subscribers	O
uses	O
the	O
same	O
signalling	O
channel(s )	O
rather	O
than	O
separate	O
channels	O
existing	O
for	O
different	O
subscribers	O
.	O
</s>
<s>
V5.1	O
(	O
ETS	O
300	O
324-1	O
)	O
in	O
which	O
there	O
is	O
a	O
1	O
to	O
1	O
correspondence	O
between	O
subscriber	B-Architecture
lines	I-Architecture
and	O
bearer	O
channels	O
in	O
the	O
aggregate	O
link	O
to	O
the	O
exchange	O
.	O
</s>
<s>
V5.2	O
(	O
ETS	O
300	O
347-1	O
)	O
which	O
provides	O
for	O
concentration	B-Architecture
where	O
there	O
are	O
not	O
enough	O
bearer	O
channels	O
in	O
the	O
aggregate	O
link(s )	O
to	O
accommodate	O
all	O
subscribers	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
V5.1	O
only	O
supports	O
the	O
Control	O
,	O
PSTN	O
and	O
ISDN	B-Protocol
protocols	O
.	O
</s>
<s>
V5	O
layer	O
3	O
protocols	O
are	O
transported	O
on	O
a	O
layer	O
2	O
protocol	O
called	O
LAPV5	O
,	O
a	O
variation	O
of	O
the	O
LAP-D	O
or	O
Link	O
Access	O
Procedures	O
,	O
D	O
channel	O
ISDN	B-Protocol
transport	O
layer	O
.	O
</s>
<s>
In	O
particular	O
the	O
PSTN	O
protocol	O
was	O
re-used	O
and	O
combined	O
with	O
ISDN	B-Protocol
to	O
provide	O
a	O
service	O
to	O
the	O
subscriber	O
.	O
</s>
<s>
The	O
AN	O
reference	O
point	O
was	O
replaced	O
by	O
an	O
ISDN-like	O
NTE	O
.	O
</s>
<s>
This	O
NTE	O
managed	O
an	O
analogue	O
service	O
and	O
a	O
basic	O
rate	O
ISDN	B-Protocol
service	O
to	O
the	O
subscribers	O
home	O
.	O
</s>
