<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
the	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
over	I-Protocol
ATM	I-Protocol
(	O
PPPoA	B-Protocol
)	O
is	O
a	O
layer	O
2	O
data-link	O
protocol	O
typically	O
used	O
to	O
connect	O
domestic	O
broadband	O
modems	O
to	O
ISPs	O
via	O
phone	O
lines	O
.	O
</s>
<s>
It	O
is	O
used	O
mainly	O
with	O
DOCSIS	B-Protocol
and	O
DSL	O
carriers	O
,	O
by	O
encapsulating	B-Protocol
PPP	B-Protocol
frames	O
in	O
ATM	O
AAL5	B-Protocol
.	O
</s>
<s>
Point-to-Point	B-Protocol
Protocol	I-Protocol
over	O
Asynchronous	O
Transfer	O
Mode	O
(	O
PPPoA	B-Protocol
)	O
is	O
specified	O
by	O
The	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
in	O
RFC	O
2364	O
.	O
</s>
<s>
It	O
offers	O
standard	O
PPP	B-Protocol
features	O
such	O
as	O
authentication	O
,	O
encryption	O
,	O
and	O
compression	B-General_Concept
.	O
</s>
<s>
It	O
also	O
supports	O
the	O
encapsulation	B-Protocol
types	O
:	O
VC-MUX	O
and	O
LLC	O
-	O
see	O
.	O
</s>
<s>
If	O
it	O
is	O
used	O
as	O
the	O
connection	O
encapsulation	B-Protocol
method	O
on	O
an	O
ATM	O
based	O
network	O
it	O
can	O
reduce	O
overhead	O
significantly	O
compared	O
with	O
PPPoEoA	B-Protocol
–	O
by	O
between	O
0	O
and	O
~	O
3.125	O
%	O
for	O
long	O
packets	O
,	O
depending	O
on	O
the	O
packet	O
length	O
and	O
also	O
on	O
the	O
choices	O
of	O
header	O
options	O
in	O
PPPoEoA	B-Protocol
–	O
see	O
PPPoEoA	B-Protocol
protocol	O
overheads	O
.	O
</s>
<s>
This	O
is	O
because	O
it	O
uses	O
headers	O
that	O
are	O
short	O
so	O
imposes	O
minimal	O
overheads	O
,	O
2	O
bytes	O
for	O
PPP	B-Protocol
and	O
8	O
bytes	O
for	O
PPPoA	B-Protocol
(	O
with	O
the	O
RFC2364	O
VC-MUX	O
option	O
)	O
=	O
10	O
bytes	O
.	O
</s>
<s>
It	O
also	O
avoids	O
the	O
issues	O
that	O
PPPoE	B-Protocol
suffers	O
from	O
,	O
related	O
to	O
sometimes	O
needing	O
to	O
use	O
an	O
IP	O
MTU	B-Protocol
of	O
1492	O
bytes	O
or	O
less	O
,	O
lower	O
than	O
the	O
standard	O
1500	O
bytes	O
.	O
</s>
<s>
The	O
use	O
of	O
PPPoA	B-Protocol
over	O
PPPoE	B-Protocol
is	O
not	O
geographically	O
significant	O
;	O
rather	O
,	O
it	O
varies	O
by	O
the	O
provider	O
's	O
preference	O
.	O
</s>
<s>
Configuration	O
of	O
a	O
PPPoA	B-Protocol
requires	O
PPP	B-Protocol
configuration	O
and	O
ATM	O
configuration	O
.	O
</s>
<s>
These	O
data	O
are	O
generally	O
stored	O
in	O
a	O
cable	B-Device
modem	I-Device
or	O
DSL	B-Device
modem	I-Device
,	O
and	O
may	O
or	O
may	O
not	O
be	O
visible	O
to	O
—	O
or	O
configurable	O
by	O
—	O
an	O
end-user	O
.	O
</s>
<s>
PPP	B-Protocol
configuration	O
generally	O
includes	O
:	O
user	O
credentials	O
,	O
user	O
name	O
and	O
password	O
,	O
and	O
is	O
unique	O
to	O
each	O
user	O
.	O
</s>
<s>
ATM	O
configuration	O
can	O
either	O
be	O
performed	O
manually	O
,	O
or	O
it	O
may	O
be	O
hard-coded	O
(	O
or	O
pre-set	O
)	O
into	O
the	O
firmware	B-Application
of	O
a	O
DSL	B-Device
modem	I-Device
provided	O
by	O
the	O
user	O
's	O
ISP	O
;	O
it	O
cannot	O
be	O
automatically	O
negotiated	O
.	O
</s>
