<s>
The	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
over	I-Protocol
Ethernet	I-Protocol
(	O
PPPoE	B-Protocol
)	O
is	O
a	O
network	O
protocol	O
for	O
encapsulating	B-Protocol
Point-to-Point	B-Protocol
Protocol	I-Protocol
(	O
PPP	B-Protocol
)	O
frames	O
inside	O
Ethernet	O
frames	O
.	O
</s>
<s>
It	O
appeared	O
in	O
1999	O
,	O
in	O
the	O
context	O
of	O
the	O
boom	O
of	O
DSL	O
as	O
the	O
solution	O
for	O
tunneling	B-Protocol
packets	B-Protocol
over	O
the	O
DSL	O
connection	O
to	O
the	O
ISP	O
's	O
IP	B-Protocol
network	O
,	O
and	O
from	O
there	O
to	O
the	O
rest	O
of	O
the	O
Internet	O
.	O
</s>
<s>
A	O
2005	O
networking	O
book	O
noted	O
that	O
"	O
Most	O
DSL	O
providers	O
use	O
PPPoE	B-Protocol
,	O
which	O
provides	O
authentication	O
,	O
encryption	O
,	O
and	O
compression.	O
"	O
</s>
<s>
Typical	O
use	O
of	O
PPPoE	B-Protocol
involves	O
leveraging	O
the	O
PPP	B-Protocol
facilities	O
for	O
authenticating	O
the	O
user	O
with	O
a	O
username	O
and	O
password	O
,	O
predominately	O
via	O
the	O
PAP	B-Protocol
protocol	O
and	O
less	O
often	O
via	O
CHAP	B-Protocol
.	O
</s>
<s>
Around	O
2000	O
,	O
PPPoE	B-Protocol
was	O
also	O
starting	O
to	O
become	O
a	O
replacement	O
method	O
for	O
talking	O
to	O
a	O
modem	B-Application
connected	O
to	O
a	O
computer	O
or	O
router	B-Protocol
over	O
an	O
Ethernet	O
LAN	B-General_Concept
displacing	O
the	O
older	O
method	O
,	O
which	O
had	O
been	O
USB	B-Protocol
.	O
</s>
<s>
This	O
use-case	O
,	O
connecting	O
routers	B-Protocol
to	O
modems	B-Application
over	O
Ethernet	O
is	O
still	O
extremely	O
common	O
today	O
.	O
</s>
<s>
On	O
the	O
customer-premises	O
equipment	O
,	O
PPPoE	B-Protocol
may	O
be	O
implemented	O
either	O
in	O
a	O
unified	O
residential	B-Application
gateway	I-Application
device	O
that	O
handles	O
both	O
DSL	B-Device
modem	I-Device
and	O
IP	B-Protocol
routing	I-Protocol
functions	O
or	O
in	O
the	O
case	O
of	O
a	O
simple	O
DSL	B-Device
modem	I-Device
(	O
without	O
routing	O
support	O
)	O
,	O
PPPoE	B-Protocol
may	O
be	O
handled	O
behind	O
it	O
on	O
a	O
separate	O
Ethernet-only	O
router	B-Protocol
or	O
even	O
directly	O
on	O
a	O
user	O
's	O
computer	O
.	O
</s>
<s>
(	O
Support	O
for	O
PPPoE	B-Protocol
is	O
present	O
in	O
most	O
operating	O
systems	O
,	O
ranging	O
from	O
Windows	B-Application
XP	I-Application
,	O
Linux	B-Application
to	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
.	O
)	O
</s>
<s>
More	O
recently	O
,	O
some	O
GPON-based	O
(	O
instead	O
of	O
DSL-based	O
)	O
residential	B-Application
gateways	I-Application
also	O
use	O
PPPoE	B-Protocol
,	O
although	O
the	O
status	O
of	O
PPPoE	B-Protocol
in	O
the	O
GPON	B-Architecture
standards	O
is	O
marginal	O
.	O
</s>
<s>
PPPoE	B-Protocol
was	O
developed	O
by	O
UUNET	O
,	O
Redback	O
Networks	O
(	O
now	O
Ericsson	O
)	O
and	O
RouterWare	O
(	O
now	O
Wind	O
River	O
Systems	O
)	O
and	O
is	O
available	O
as	O
an	O
informational	O
RFC	O
2516	O
.	O
</s>
<s>
In	O
the	O
world	O
of	O
DSL	O
,	O
PPPoE	B-Protocol
was	O
commonly	O
understood	O
to	O
be	O
running	O
on	O
top	O
of	O
ATM	O
(	O
or	O
DSL	O
)	O
as	O
the	O
underlying	O
transport	O
,	O
although	O
no	O
such	O
limitation	O
exists	O
in	O
the	O
PPPoE	B-Protocol
protocol	O
itself	O
.	O
</s>
<s>
For	O
example	O
,	O
PPPoEoE	O
,	O
when	O
the	O
transport	O
is	O
Ethernet	O
itself	O
,	O
as	O
in	O
the	O
case	O
of	O
Metro	B-Protocol
Ethernet	I-Protocol
networks	O
.	O
</s>
<s>
(	O
In	O
this	O
notation	O
,	O
the	O
original	O
use	O
of	O
PPPoE	B-Protocol
would	O
be	O
labeled	O
PPPoEoA	O
,	O
although	O
it	O
should	O
not	O
be	O
confused	O
with	O
PPPoA	B-Protocol
,	O
which	O
is	O
a	O
different	O
encapsulation	B-Protocol
protocol	O
.	O
)	O
</s>
<s>
PPPoE	B-Protocol
has	O
been	O
described	O
in	O
some	O
books	O
as	O
a	O
"	O
layer	O
2.5	O
"	O
protocol	O
,	O
in	O
some	O
rudimentary	O
sense	O
similar	O
to	O
MPLS	B-Protocol
because	O
it	O
can	O
be	O
used	O
to	O
distinguish	O
different	O
IP	B-Protocol
flows	O
sharing	O
an	O
Ethernet	O
infrastructure	O
,	O
although	O
the	O
lack	O
of	O
PPPoE	B-Protocol
switches	O
making	O
routing	O
decisions	O
based	O
on	O
PPPoE	B-Protocol
headers	O
limits	O
applicability	O
in	O
that	O
respect	O
.	O
</s>
<s>
Potential	O
equipment	O
vendors	O
and	O
carriers	O
alike	O
recognized	O
that	O
broadband	O
such	O
as	O
cable	B-Device
modem	I-Device
or	O
DSL	O
would	O
eventually	O
replace	O
dialup	O
service	O
,	O
but	O
the	O
hardware	O
(	O
both	O
customer	O
premises	O
and	O
LEC	O
)	O
faced	O
a	O
significant	O
low-quantity	O
cost	O
barrier	O
.	O
</s>
<s>
Initial	O
estimates	O
for	O
low-quantity	O
deployment	O
of	O
DSL	O
showed	O
costs	O
in	O
the	O
$300	O
–	O
$500	O
range	O
for	O
a	O
DSL	B-Device
modem	I-Device
and	O
$	O
300/month	O
access	O
fee	O
from	O
the	O
telco	O
,	O
which	O
was	O
well	O
beyond	O
what	O
a	O
home	O
user	O
would	O
pay	O
.	O
</s>
<s>
Thus	O
the	O
initial	O
focus	O
was	O
on	O
small	O
and	O
home	O
business	O
customers	O
for	O
whom	O
a	O
~	O
1.5	O
megabit	O
T1	B-Protocol
line	I-Protocol
(	O
at	O
the	O
time	O
$800	O
–	O
$1500	O
per	O
month	O
)	O
was	O
not	O
economical	O
,	O
but	O
who	O
needed	O
more	O
than	O
dialup	O
or	O
ISDN	B-Protocol
could	O
deliver	O
.	O
</s>
<s>
Connecting	O
an	O
entire	O
LAN	B-General_Concept
to	O
the	O
Internet	O
;	O
</s>
<s>
Providing	O
services	O
on	O
a	O
local	O
LAN	B-General_Concept
accessible	O
from	O
the	O
far	O
side	O
of	O
the	O
connection	O
;	O
</s>
<s>
These	O
requirements	O
did	O
n't	O
lend	O
themselves	O
to	O
the	O
connection	O
establishment	O
lag	O
of	O
a	O
dial-up	O
process	O
nor	O
its	O
one-computer-to-one-ISP	O
model	O
,	O
nor	O
even	O
the	O
many-to-one	O
that	O
NAT	B-Protocol
plus	O
dial-up	O
provided	O
.	O
</s>
<s>
PPPoE	B-Protocol
is	O
used	O
mainly	O
either	O
:	O
</s>
<s>
with	O
PPPoE-speaking	O
Internet	O
DSL	O
services	O
where	O
a	O
PPPoE-speaking	O
modem-router	O
(	O
residential	B-Application
gateway	I-Application
)	O
connects	O
to	O
the	O
DSL	O
service	O
.	O
</s>
<s>
Here	O
both	O
ISP	O
and	O
modem-router	O
need	O
to	O
speak	O
PPPoE	B-Protocol
.	O
</s>
<s>
(	O
Note	O
that	O
in	O
this	O
case	O
,	O
the	O
PPPoE-over-DSL	O
side	O
of	O
things	O
is	O
occasionally	O
referred	O
to	O
as	O
PPPoEoA	O
,	O
for	O
‘	O
PPPoE	B-Protocol
over	O
ATM’	O
.	O
)	O
</s>
<s>
or	O
when	O
a	O
PPPoE-speaking	O
DSL	B-Device
modem	I-Device
is	O
connected	O
to	O
a	O
PPPoE-speaking	O
Ethernet-only	O
router	B-Protocol
using	O
an	O
Ethernet	O
cable	O
.	O
</s>
<s>
The	O
equipment	O
was	O
available	O
immediately	O
,	O
as	O
was	O
the	O
service	O
,	O
and	O
a	O
whole	O
new	O
protocol	B-Protocol
stack	I-Protocol
(	O
Microsoft	O
at	O
the	O
time	O
was	O
advocating	O
fiber-based	O
atm-cells-to-the-desktop	O
,	O
and	O
L2TP	B-Application
was	O
brewing	O
as	O
well	O
,	O
but	O
was	O
not	O
near	O
completion	O
)	O
would	O
take	O
so	O
long	O
to	O
implement	O
that	O
the	O
window	O
of	O
opportunity	O
might	O
slip	O
by	O
.	O
</s>
<s>
PPPoE	B-Protocol
hoped	O
to	O
merge	O
the	O
widespread	O
Ethernet	O
infrastructure	O
with	O
the	O
ubiquitous	O
PPP	B-Protocol
,	O
allowing	O
vendors	O
to	O
reuse	O
their	O
existing	O
software	O
and	O
deliver	O
products	O
in	O
the	O
very	O
near	O
term	O
.	O
</s>
<s>
Essentially	O
all	O
operating	O
systems	O
at	O
the	O
time	O
had	O
a	O
PPP	B-Protocol
stack	O
,	O
and	O
the	O
design	O
of	O
PPPoE	B-Protocol
allowed	O
for	O
a	O
simple	O
shim	O
at	O
the	O
line-encoding	O
stage	O
to	O
convert	O
from	O
PPP	B-Protocol
to	O
PPPoE	B-Protocol
.	O
</s>
<s>
Competing	O
WAN	O
technologies	O
(	O
T1	O
,	O
ISDN	B-Protocol
)	O
required	O
a	O
router	B-Protocol
on	O
the	O
customer	O
premises	O
.	O
</s>
<s>
PPPoE	B-Protocol
used	O
a	O
different	O
Ethernet	O
frame	O
type	O
,	O
which	O
allowed	O
the	O
DSL	O
hardware	O
to	O
function	O
as	O
simply	O
a	O
bridge	B-Protocol
,	O
passing	O
some	O
frames	O
to	O
the	O
WAN	O
and	O
ignoring	O
the	O
others	O
.	O
</s>
<s>
Implementation	O
of	O
such	O
a	O
bridge	B-Protocol
is	O
multiple	O
orders	O
of	O
magnitude	O
simpler	O
than	O
a	O
router	B-Protocol
.	O
</s>
<s>
PPPoE	B-Protocol
was	O
initially	O
designed	O
to	O
provide	O
a	O
small	O
LAN	B-General_Concept
with	O
individual	O
independent	O
connections	O
to	O
the	O
Internet	O
at	O
large	O
,	O
but	O
also	O
such	O
that	O
the	O
protocol	O
itself	O
would	O
be	O
lightweight	O
enough	O
that	O
it	O
would	O
n't	O
impinge	O
on	O
the	O
hoped-for	O
home	O
usage	O
market	O
when	O
it	O
finally	O
arrived	O
.	O
</s>
<s>
While	O
success	O
on	O
the	O
second	O
matter	O
may	O
be	O
debated	O
(	O
some	O
complain	O
that	O
8	O
bytes	O
per	O
packet	B-Protocol
is	O
too	O
much	O
)	O
PPPoE	B-Protocol
clearly	O
succeeded	O
in	O
bringing	O
sufficient	O
volume	O
to	O
drive	O
the	O
price	O
for	O
service	O
down	O
to	O
what	O
a	O
home	O
user	O
would	O
pay	O
.	O
</s>
<s>
Around	O
2000	O
,	O
the	O
PPPoE	B-Protocol
protocol	O
was	O
used	O
either	O
(	O
i	O
)	O
to	O
connect	O
a	O
DSL	B-Device
modem	I-Device
to	O
a	O
computer	O
or	O
router	B-Protocol
,	O
displacing	O
the	O
earlier	O
method	O
of	O
using	O
USB	B-Protocol
,	O
or	O
(	O
ii	O
)	O
the	O
PPP+PPPoE	O
trio	O
of	O
protocol	O
headers	O
was	O
used	O
to	O
connect	O
a	O
router	B-Protocol
to	O
a	O
network	O
node	O
,	O
a	O
protocol	O
converter	O
,	O
somewhat	O
further	O
upstream	O
belonging	O
either	O
to	O
the	O
ISP	O
or	O
to	O
a	O
wholesale	O
long-distance	O
carrier	O
who	O
in	O
turn	O
connects	O
to	O
the	O
ISP	O
’s	O
IP	B-Protocol
networks	O
and	O
then	O
to	O
the	O
internet	O
.	O
</s>
<s>
The	O
first	O
use-case	O
,	O
router-to-modem	O
connection	O
,	O
involving	O
so-called	O
‘	O
PPPoEoE’	O
(	O
the	O
PPPoE	B-Protocol
protocol	O
trio	O
over	O
a	O
physical	O
Ethernet	O
LAN	B-General_Concept
)	O
,	O
is	O
still	O
very	O
much	O
in	O
use	O
today	O
for	O
connecting	O
modems	B-Application
to	O
routers	B-Protocol
if	O
PPP	B-Protocol
is	O
used	O
.	O
</s>
<s>
The	O
second	O
use-case	O
,	O
where	O
the	O
PPPoE	B-Protocol
protocol	O
trio	O
is	O
used	O
over	O
one	O
or	O
more	O
internet	O
access	O
links	O
reaching	O
upstream	O
to	O
a	O
greater	O
or	O
lesser	O
depth	O
,	O
is	O
,	O
according	O
to	O
consensus	O
,	O
only	O
still	O
used	O
for	O
historical	O
reasons	O
.	O
</s>
<s>
However	O
since	O
PPP	B-Protocol
remains	O
popular	O
with	O
some	O
ISPs	O
either	O
as	O
a	O
tunnelling	B-Protocol
protocol	I-Protocol
,	O
needed	O
where	O
an	O
ISP	O
uses	O
a	O
wholesale	O
access	O
carrier/reseller	O
or	O
because	O
the	O
features	O
of	O
PPP	B-Protocol
re	O
desired	O
,	O
or	O
both	O
.	O
</s>
<s>
As	O
mentioned	O
earlier	O
,	O
strangely	O
,	O
Ethernet	O
MAC	O
headers	O
are	O
in	O
fact	O
sometimes	O
found	O
in	O
use	O
with	O
PPPoE	B-Protocol
headers	O
even	O
when	O
the	O
Ethernet	O
protocol	O
is	O
not	O
in	O
use	O
,	O
not	O
physically	O
present	O
on	O
an	O
Ethernet	O
network	O
.	O
</s>
<s>
In	O
the	O
second	O
use	O
case	O
,	O
the	O
use	O
of	O
PPP+PPPoE+Ethernet	O
MAC	O
extends	O
to	O
a	O
variable	O
distance	O
upstream	O
.	O
</s>
<s>
It	O
may	O
be	O
confined	O
to	O
the	O
‘	O
first	O
mile’	O
:	O
a	O
copper	O
twisted	O
pair	O
in	O
ADSL	O
or	O
VDSL2/FTTC	O
involving	O
modems	B-Application
and	O
no	O
further	O
,	O
or	O
it	O
may	O
also	O
be	O
used	O
further	O
upstream	O
extending	O
to	O
a	O
BRAS	O
‘	O
Broadband	O
Remote	O
Access	O
Server’	O
or	O
‘	O
access	O
concentrator’	O
which	O
may	O
or	O
may	O
not	O
handle	O
login	O
but	O
will	O
certainly	O
be	O
a	O
protocol	O
convertor	O
of	O
some	O
sort	O
.	O
</s>
<s>
In	O
one	O
example	O
case	O
PPPoE	B-Protocol
extends	O
upstream	O
to	O
and	O
terminates	O
at	O
such	O
a	O
node	O
operated	O
by	O
a	O
wholesale	O
carrier	O
which	O
converts	O
to	O
the	O
L2TP	B-Application
tunneling	B-Protocol
protocol	I-Protocol
which	O
tunnels	O
to	O
the	O
ISP	O
’s	O
IP	B-Protocol
POPs	O
(	O
‘	O
point	O
of	O
presence’	O
)	O
.	O
</s>
<s>
The	O
PPPoE	B-Protocol
has	O
two	O
distinct	O
stages	O
:	O
</s>
<s>
Since	O
traditional	O
PPP	B-Protocol
connections	I-Protocol
are	O
established	O
between	O
two	O
end	O
points	O
over	O
a	O
serial	O
link	O
or	O
over	O
an	O
ATM	O
virtual	O
circuit	O
that	O
has	O
already	O
been	O
established	O
during	O
dial-up	O
,	O
all	O
PPP	B-Protocol
frames	O
sent	O
on	O
the	O
wire	O
are	O
sure	O
to	O
reach	O
the	O
other	O
end	O
.	O
</s>
<s>
Hence	O
before	O
exchanging	O
PPP	B-Protocol
control	O
packets	B-Protocol
to	O
establish	O
the	O
connection	O
over	O
Ethernet	O
,	O
the	O
MAC	O
addresses	O
of	O
the	O
two	O
end	O
points	O
should	O
be	O
known	O
to	O
each	O
other	O
so	O
that	O
they	O
can	O
be	O
encoded	O
in	O
these	O
control	O
packets	B-Protocol
.	O
</s>
<s>
The	O
PPPoE	B-Protocol
Discovery	O
stage	O
does	O
exactly	O
this	O
.	O
</s>
<s>
It	O
also	O
helps	O
establish	O
a	O
Session	O
ID	O
that	O
can	O
be	O
used	O
for	O
further	O
exchange	O
of	O
packets	B-Protocol
.	O
</s>
<s>
Although	O
traditional	O
PPP	B-Protocol
is	O
a	O
peer-to-peer	O
protocol	O
,	O
PPPoE	B-Protocol
is	O
inherently	O
a	O
client-server	B-Operating_System
relationship	O
since	O
multiple	O
hosts	O
can	O
connect	O
to	O
a	O
service	O
provider	O
over	O
a	O
single	O
physical	O
connection	O
.	O
</s>
<s>
PADI	O
stands	O
for	O
PPPoE	B-Protocol
Active	O
Discovery	O
Initiation	O
.	O
</s>
<s>
As	O
the	O
computer	O
does	O
not	O
know	O
the	O
MAC	O
address	O
of	O
the	O
DSL-AC	O
,	O
it	O
sends	O
out	O
a	O
PADI	O
packet	B-Protocol
via	O
an	O
Ethernet	O
broadcast	B-Operating_System
(	O
MAC	O
:	O
ff:ff:ff:ff:ff:ff	O
)	O
.	O
</s>
<s>
This	O
PADI	O
packet	B-Protocol
contains	O
the	O
MAC	O
address	O
of	O
the	O
computer	O
sending	O
it	O
.	O
</s>
<s>
Example	O
of	O
a	O
PADI-packet	O
:	O
</s>
<s>
(=	O
destination	O
)	O
is	O
the	O
Ethernet	O
broadcast	B-Operating_System
address	O
.	O
</s>
<s>
The	O
PADI	O
packet	B-Protocol
can	O
be	O
received	O
by	O
more	O
than	O
one	O
DSL-AC	O
.	O
</s>
<s>
PADO	O
stands	O
for	O
PPPoE	B-Protocol
Active	O
Discovery	O
Offer	O
.	O
</s>
<s>
Once	O
the	O
user	O
's	O
computer	O
has	O
sent	O
the	O
PADI	O
packet	B-Protocol
,	O
the	O
DSL-AC	O
replies	O
with	O
a	O
PADO	O
packet	B-Protocol
,	O
using	O
the	O
MAC	O
address	O
supplied	O
in	O
the	O
PADI	O
.	O
</s>
<s>
The	O
PADO	O
packet	B-Protocol
contains	O
the	O
MAC	O
address	O
of	O
the	O
DSL-AC	O
,	O
its	O
name	O
(	O
e.g.	O
</s>
<s>
If	O
more	O
than	O
one	O
POP	O
's	O
DSL-AC	O
replies	O
with	O
a	O
PADO	O
packet	B-Protocol
,	O
the	O
user	O
's	O
computer	O
selects	O
the	O
DSL-AC	O
for	O
a	O
particular	O
POP	O
using	O
the	O
supplied	O
name	O
or	O
service	O
.	O
</s>
<s>
Here	O
is	O
an	O
example	O
of	O
a	O
PADO	O
packet	B-Protocol
:	O
</s>
<s>
PADR	O
stands	O
for	O
PPPoE	B-Protocol
active	O
discovery	O
request	O
.	O
</s>
<s>
A	O
PADR	O
packet	B-Protocol
is	O
sent	O
by	O
the	O
user	O
's	O
computer	O
to	O
the	O
DSL-AC	O
following	O
receipt	O
of	O
an	O
acceptable	O
PADO	O
packet	B-Protocol
from	O
the	O
DSL-AC	O
.	O
</s>
<s>
It	O
confirms	O
acceptance	O
of	O
the	O
offer	O
of	O
a	O
PPPoE	B-Protocol
connection	O
made	O
by	O
the	O
DSL-AC	O
issuing	O
the	O
PADO	O
packet	B-Protocol
.	O
</s>
<s>
PADS	O
stands	O
for	O
PPPoE	B-Protocol
Active	O
Discovery	O
Session-confirmation	O
.	O
</s>
<s>
The	O
PADR	O
packet	B-Protocol
above	O
is	O
confirmed	O
by	O
the	O
DSL-AC	O
with	O
a	O
PADS	O
packet	B-Protocol
,	O
and	O
a	O
Session	O
ID	O
is	O
given	O
out	O
with	O
it	O
.	O
</s>
<s>
PADT	O
stands	O
for	O
PPPoE	B-Protocol
Active	O
Discovery	O
Termination	O
.	O
</s>
<s>
This	O
packet	B-Protocol
terminates	O
the	O
connection	O
to	O
the	O
POP	O
.	O
</s>
<s>
PPPoE	B-Protocol
is	O
used	O
to	O
connect	O
a	O
PC	O
or	O
a	O
router	B-Protocol
to	O
a	O
modem	B-Application
via	O
an	O
Ethernet	O
link	O
and	O
it	O
can	O
also	O
be	O
used	O
in	O
Internet	O
access	O
over	O
DSL	O
on	O
a	O
telephone	O
line	O
in	O
the	O
PPPoE	B-Protocol
over	O
ATM	O
(	O
PPPoEoA	O
)	O
over	O
ADSL	O
protocol	B-Protocol
stack	I-Protocol
.	O
</s>
<s>
PPPoE	B-Protocol
over	O
ATM	O
has	O
the	O
highest	O
overhead	O
of	O
the	O
popular	O
DSL	O
delivery	O
methods	O
,	O
when	O
compared	O
with	O
for	O
example	O
PPPoA	B-Protocol
(	O
RFC	O
2364	O
)	O
.	O
</s>
<s>
The	O
amount	O
of	O
overhead	O
added	O
by	O
PPPoEoA	O
on	O
a	O
DSL	O
link	O
depends	O
on	O
the	O
packet	B-Protocol
size	O
because	O
of	O
(	O
i	O
)	O
the	O
absorbing	O
effect	O
of	O
ATM	O
cell-padding	O
(	O
discussed	O
below	O
)	O
,	O
which	O
completely	O
cancels	O
out	O
additional	O
overhead	O
of	O
PPPoEoA	O
in	O
some	O
cases	O
,	O
(	O
ii	O
)	O
PPPoEoA	O
+	O
AAL5	B-Protocol
overhead	O
which	O
can	O
cause	O
an	O
entire	O
additional	O
53-byte	O
ATM	O
cell	O
to	O
be	O
required	O
,	O
and	O
(	O
iii	O
)	O
in	O
the	O
case	O
of	O
IP	B-Protocol
packets	B-Protocol
,	O
PPPoE	B-Protocol
overhead	O
added	O
to	O
packets	B-Protocol
that	O
are	O
near	O
maximum	O
length	O
(	O
‘	O
MRU’	O
)	O
may	O
cause	O
IP	B-Protocol
fragmentation	I-Protocol
,	O
which	O
also	O
involves	O
the	O
first	O
two	O
considerations	O
for	O
both	O
of	O
the	O
resulting	O
IP	B-Protocol
fragments	O
.	O
</s>
<s>
However	O
ignoring	O
ATM	O
and	O
IP	B-Protocol
fragmentation	I-Protocol
for	O
the	O
moment	O
,	O
the	O
protocol	O
header	O
overheads	O
for	O
ATM	O
payload	O
due	O
to	O
choosing	O
PPP	B-Protocol
+	O
PPPoEoA	O
can	O
be	O
as	O
high	O
as	O
44	O
bytes	O
=	O
2	O
bytes	O
(	O
for	O
PPP	B-Protocol
)	O
+	O
6	O
(	O
for	O
PPPoE	B-Protocol
)	O
+	O
18	O
(	O
Ethernet	O
MAC	O
,	O
variable	O
)	O
+	O
10	O
(	O
RFC	O
2684	O
LLC	O
,	O
variable	O
)	O
+	O
8	O
(	O
AAL5	B-Protocol
CPCS	O
)	O
.	O
</s>
<s>
Compare	O
this	O
with	O
a	O
vastly	O
more	O
header-efficient	O
protocol	O
,	O
PPP	B-Protocol
+	O
PPPoA	B-Protocol
RFC	O
2364	O
VC-MUX	O
over	O
ATM+DSL	O
,	O
which	O
has	O
a	O
mere	O
10-byte	O
overhead	O
within	O
the	O
ATM	O
payload	O
.	O
</s>
<s>
(	O
In	O
fact	O
,	O
just	O
simply	O
10	O
bytes	O
=	O
2	O
bytes	O
for	O
PPP	B-Protocol
+	O
zero	O
for	O
RFC	O
2364	O
+	O
8	O
(	O
AAL5	B-Protocol
CPCS	O
)	O
.	O
)	O
</s>
<s>
This	O
figure	O
of	O
44	O
bytes	O
AAL5	B-Protocol
payload	O
overhead	O
can	O
be	O
reduced	O
in	O
two	O
ways	O
:	O
(	O
i	O
)	O
by	O
choosing	O
the	O
RFC	O
2684	O
option	O
of	O
discarding	O
the	O
4-byte	O
Ethernet	O
MAC	O
FCS	O
,	O
which	O
reduces	O
the	O
figure	O
of	O
18	O
bytes	O
above	O
to	O
14	O
,	O
and	O
(	O
ii	O
)	O
by	O
using	O
the	O
RFC	O
2684	O
VC-MUX	O
option	O
,	O
whose	O
overhead	O
contribution	O
is	O
a	O
mere	O
2	O
bytes	O
compared	O
with	O
the	O
10	O
byte	O
overhead	O
of	O
the	O
LLC	O
alternative	O
.	O
</s>
<s>
ATM	O
AAL5	B-Protocol
requires	O
that	O
an	O
8-byte-long	O
‘	O
CPCS’	O
trailer	O
must	O
always	O
be	O
present	O
at	O
the	O
very	O
end	O
of	O
the	O
final	O
cell	O
(	O
‘	O
right	O
justified’	O
)	O
of	O
the	O
run	O
of	O
ATM	O
cells	O
that	O
make	O
up	O
the	O
AAL5	B-Protocol
payload	O
packet	B-Protocol
.	O
</s>
<s>
However	O
,	O
the	O
true	O
overhead	O
in	O
terms	O
of	O
the	O
total	O
amount	O
of	O
ATM	O
payload	O
data	O
sent	O
is	O
not	O
simply	O
a	O
fixed	O
additional	O
value	O
–	O
it	O
can	O
only	O
be	O
either	O
zero	O
or	O
48	O
bytes	O
(	O
leaving	O
aside	O
scenario	O
(	O
iii	O
)	O
mentioned	O
earlier	O
,	O
IP	B-Protocol
fragmentation	I-Protocol
)	O
.	O
</s>
<s>
This	O
is	O
because	O
ATM	O
cells	O
are	O
fixed	O
length	O
with	O
a	O
payload	O
capacity	O
of	O
48	O
bytes	O
,	O
and	O
adding	O
a	O
greater	O
extra	O
amount	O
of	O
AAL5	B-Protocol
payload	O
due	O
to	O
additional	O
headers	O
may	O
require	O
one	O
more	O
whole	O
ATM	O
cell	O
to	O
be	O
sent	O
containing	O
the	O
excess	O
.	O
</s>
<s>
An	O
example	O
:	O
In	O
the	O
case	O
of	O
a	O
1500-byte	O
IP	B-Protocol
packet	B-Protocol
sent	O
over	O
AAL5/ATM	O
with	O
PPPoEoA	O
and	O
RFC2684-LLC	O
,	O
neglecting	O
final	O
cell	O
padding	O
for	O
the	O
moment	O
,	O
one	O
starts	O
with	O
1500	O
+	O
2	O
+	O
6	O
+	O
18	O
+	O
10	O
+	O
8	O
(	O
AAL5	B-Protocol
CPCS	O
trailer	O
)	O
=	O
1544	O
bytes	O
if	O
the	O
Ethernet	O
FCS	O
is	O
present	O
,	O
or	O
else	O
+	O
2	O
+	O
6	O
+	O
14	O
+	O
10	O
+	O
8	O
=	O
40	O
bytes	O
with	O
no	O
FCS	O
.	O
</s>
<s>
Compare	O
this	O
to	O
the	O
case	O
of	O
PPP	B-Protocol
+	O
PPPoA	B-Protocol
which	O
at	O
1500	O
+	O
2	O
(	O
PPP	B-Protocol
)	O
+	O
0	O
(	O
PPPoA	B-Protocol
:	O
RFC	O
2364	O
VC-MUX	O
)	O
+	O
8	O
(	O
CPCS	O
trailer	O
)	O
=	O
1510	O
bytes	O
fits	O
in	O
32	O
cells	O
.	O
</s>
<s>
So	O
the	O
real	O
cost	O
of	O
choosing	O
PPPoEoA	O
plus	O
RFC2684-LLC	O
for	O
1500-byte	O
IP	B-Protocol
packets	B-Protocol
is	O
one	O
additional	O
ATM	O
cell	O
per	O
IP	B-Protocol
packet	B-Protocol
,	O
a	O
ratio	O
of	O
33:32	O
.	O
</s>
<s>
So	O
for	O
1500	O
byte	O
packets	B-Protocol
,	O
PPPoEoA	O
with	O
LLC	O
is	O
~	O
3.125	O
%	O
slower	O
than	O
PPPoA	B-Protocol
or	O
optimal	O
choices	O
of	O
PPPoEoA	O
header	O
options	O
.	O
</s>
<s>
For	O
some	O
packet	B-Protocol
lengths	O
the	O
true	O
additional	O
effective	O
DSL	O
overhead	O
due	O
to	O
choosing	O
PPPoEoA	O
compared	O
with	O
PPPoA	B-Protocol
will	O
be	O
zero	O
if	O
the	O
extra	O
header	O
overhead	O
is	O
not	O
enough	O
to	O
need	O
an	O
additional	O
ATM	O
cell	O
at	O
that	O
particular	O
packet	B-Protocol
length	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
1492	O
byte	O
long	O
packet	B-Protocol
sent	O
with	O
PPP	B-Protocol
+	O
PPPoEoA	O
using	O
RFC2684-LLC	O
plus	O
FCS	O
gives	O
us	O
a	O
total	O
ATM	O
payload	O
of	O
1492	O
+	O
44	O
=	O
1536	O
bytes	O
=	O
32	O
cells	O
exactly	O
,	O
and	O
the	O
overhead	O
in	O
this	O
special	O
case	O
is	O
no	O
greater	O
than	O
if	O
we	O
were	O
using	O
the	O
header-efficient	O
PPPoA	B-Protocol
protocol	O
,	O
which	O
would	O
require	O
1492	O
+	O
2	O
+	O
0	O
+	O
8	O
=	O
1502	O
bytes	O
ATM	O
payload	O
=	O
32	O
cells	O
also	O
.	O
</s>
<s>
The	O
case	O
where	O
the	O
packet	B-Protocol
length	O
is	O
1492	O
represents	O
the	O
optimum	O
efficiency	O
for	O
PPPoEoA	O
with	O
RFC2684-LLC	O
in	O
ratio	O
terms	O
,	O
unless	O
even	O
longer	O
packets	B-Protocol
are	O
allowed	O
.	O
</s>
<s>
Using	O
PPPoEoA	O
with	O
the	O
RFC2684	O
VC-MUX	O
header	O
option	O
is	O
always	O
much	O
more	O
efficient	O
than	O
the	O
LLC	O
option	O
,	O
since	O
the	O
ATM	O
overhead	O
,	O
as	O
mentioned	O
earlier	O
,	O
is	O
only	O
32	O
or	O
36	O
bytes	O
(	O
depending	O
on	O
whether	O
this	O
is	O
without	O
or	O
with	O
the	O
Ethernet	O
FCS	O
option	O
in	O
PPPoEoA	O
)	O
so	O
that	O
a	O
1500	O
byte	O
long	O
packet	B-Protocol
including	O
all	O
overheads	O
of	O
PPP	B-Protocol
+	O
PPPoEoA	O
using	O
VC-MUX	O
equates	O
to	O
a	O
total	O
1500	O
+	O
36	O
=	O
1536	O
bytes	O
ATM	O
payload	O
if	O
the	O
FCS	O
is	O
present	O
=	O
32	O
ATM	O
cells	O
exactly	O
,	O
thus	O
saving	O
an	O
entire	O
ATM	O
cell	O
.	O
</s>
<s>
With	O
short	O
packets	B-Protocol
,	O
the	O
longer	O
the	O
header	O
overheads	O
the	O
greater	O
the	O
likelihood	O
of	O
generating	O
an	O
additional	O
ATM	O
cell	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
TCP	B-Protocol
ACK	B-Protocol
packet	I-Protocol
over	O
IPv6	B-Protocol
is	O
60	O
bytes	O
long	O
,	O
and	O
with	O
overhead	O
of	O
40	O
or	O
44	O
bytes	O
for	O
PPPoEoA	O
+	O
LLC	O
this	O
requires	O
three	O
48	O
byte	O
ATM	O
cells’	O
payloads	O
.	O
</s>
<s>
As	O
a	O
comparison	O
,	O
PPPoA	B-Protocol
with	O
overheads	O
of	O
10	O
bytes	O
so	O
70	O
bytes	O
total	O
fits	O
into	O
two	O
cells	O
.	O
</s>
<s>
So	O
the	O
extra	O
cost	O
of	O
choosing	O
PPPoE/LLC	O
over	O
PPPoA	B-Protocol
is	O
50%	O
extra	O
data	O
sent	O
.	O
</s>
<s>
PPPoEoA	O
+	O
VC-MUX	O
would	O
be	O
fine	O
though	O
:	O
with	O
32	O
or	O
36	O
byte	O
overhead	O
,	O
our	O
IP	B-Protocol
packet	B-Protocol
still	O
fits	O
in	O
two	O
cells	O
.	O
</s>
<s>
In	O
all	O
cases	O
the	O
most	O
efficient	O
option	O
for	O
ATM-based	O
ADSL	O
internet	O
access	O
is	O
to	O
choose	O
PPPoA	B-Protocol
(	O
RFC2364	O
)	O
VC-MUX	O
.	O
</s>
<s>
However	O
,	O
if	O
PPPoEoA	O
is	O
required	O
,	O
then	O
the	O
best	O
choice	O
is	O
always	O
to	O
use	O
VC-MUX	O
(	O
as	O
opposed	O
to	O
LLC	O
)	O
with	O
no	O
Ethernet	O
FCS	O
,	O
giving	O
an	O
ATM	O
payload	O
overhead	O
of	O
32	O
bytes	O
=	O
2	O
bytes	O
(	O
for	O
PPP	B-Protocol
)	O
+	O
6	O
(	O
for	O
PPPoE	B-Protocol
)	O
+	O
14	O
(	O
Ethernet	O
MAC	O
,	O
no	O
FCS	O
)	O
+	O
2	O
(	O
RFC	O
2684	O
VC-MUX	O
)	O
+	O
8	O
(	O
AAL5	B-Protocol
CPCS	O
trailer	O
)	O
.	O
</s>
<s>
Unfortunately	O
some	O
DSL	O
services	O
require	O
the	O
use	O
of	O
wasteful	O
LLC	O
headers	O
with	O
PPPoE	B-Protocol
and	O
do	O
not	O
allow	O
the	O
more	O
efficient	O
VC-MUX	O
option	O
.	O
</s>
<s>
In	O
that	O
case	O
,	O
using	O
a	O
reduced	O
packet	B-Protocol
length	O
,	O
such	O
as	O
enforcing	O
a	O
maximum	O
MTU	B-Protocol
of	O
1492	O
regains	O
efficiency	O
with	O
long	O
packets	B-Protocol
even	O
with	O
LLC	O
headers	O
and	O
,	O
as	O
mentioned	O
earlier	O
,	O
in	O
that	O
case	O
no	O
extra	O
wasteful	O
ATM	O
cell	O
is	O
generated	O
.	O
</s>
<s>
On	O
an	O
Ethernet	O
LAN	B-General_Concept
,	O
the	O
overhead	O
for	O
PPP	B-Protocol
+	O
PPPoE	B-Protocol
is	O
a	O
fixed	O
2	O
+	O
6	O
=	O
8	O
bytes	O
,	O
unless	O
IP	B-Protocol
fragmentation	I-Protocol
is	O
produced	O
.	O
</s>
<s>
When	O
a	O
PPPoE-speaking	O
DSL	B-Device
modem	I-Device
sends	O
or	O
receives	O
Ethernet	O
frames	O
containing	O
PPP	B-Protocol
+	O
PPPoE	B-Protocol
payload	O
across	O
the	O
Ethernet	O
link	O
to	O
a	O
router	B-Protocol
(	O
or	O
PPPoE-speaking	O
single	O
PC	O
)	O
,	O
PPP	B-Protocol
+	O
PPPoE	B-Protocol
contributes	O
an	O
additional	O
overhead	O
of	O
8	O
bytes	O
=	O
2	O
(	O
PPP	B-Protocol
)	O
+	O
6	O
(	O
PPPoE	B-Protocol
)	O
included	O
within	O
the	O
payload	O
of	O
each	O
Ethernet	O
frame	O
.	O
</s>
<s>
This	O
added	O
overhead	O
can	O
mean	O
that	O
a	O
reduced	O
maximum	O
length	O
limit	O
(	O
so-called	O
‘	O
MTU’	O
or	O
‘	O
MRU’	O
)	O
of	O
1500	O
−	O
8	O
=	O
1492	O
bytes	O
is	O
imposed	O
on	O
(	O
for	O
example	O
)	O
IP	B-Protocol
packets	B-Protocol
sent	O
or	O
received	O
,	O
as	O
opposed	O
to	O
the	O
usual	O
1500-byte	O
Ethernet	O
frame	O
payload	O
length	O
limit	O
which	O
applies	O
to	O
standard	O
Ethernet	O
networks	O
.	O
</s>
<s>
Some	O
devices	O
support	O
RFC	O
4638	O
,	O
which	O
allows	O
negotiation	O
for	O
the	O
use	O
of	O
non-standard	O
Ethernet	O
frames	O
with	O
a	O
1508-byte	O
Ethernet	O
payload	O
,	O
sometimes	O
called	O
‘	O
baby	O
jumbo	O
frames’	O
,	O
so	O
allowing	O
a	O
full	O
1500-byte	O
PPPoE	B-Protocol
payload	O
.	O
</s>
<s>
This	O
capability	O
is	O
advantageous	O
for	O
many	O
users	O
in	O
cases	O
where	O
companies	O
receiving	O
IP	B-Protocol
packets	B-Protocol
have	O
(	O
incorrectly	O
)	O
chosen	O
to	O
block	O
all	O
ICMP	B-Protocol
responses	O
from	O
exiting	O
their	O
network	O
,	O
a	O
bad	O
practice	O
which	O
prevents	O
path	B-Protocol
MTU	I-Protocol
discovery	I-Protocol
from	O
working	O
correctly	O
and	O
which	O
can	O
cause	O
problems	O
for	O
users	O
accessing	O
such	O
networks	O
if	O
they	O
have	O
an	O
MTU	B-Protocol
of	O
less	O
than	O
1500	O
bytes	O
.	O
</s>
<s>
The	O
following	O
diagram	O
shows	O
a	O
scenario	O
where	O
an	O
Ethernet-connected	O
ADSL	B-Device
modem	I-Device
acts	O
as	O
a	O
PPPoE-to-PPPoA	O
protocol	O
converter	O
and	O
the	O
service	O
provider	O
offers	O
a	O
PPPoA	B-Protocol
service	O
and	O
does	O
not	O
understand	O
PPPoE	B-Protocol
.	O
</s>
<s>
This	O
is	O
an	O
optimally	O
protocol-efficient	O
design	O
for	O
a	O
separate	O
ADSL	B-Device
modem	I-Device
connected	O
to	O
a	O
router	B-Protocol
by	O
Ethernet	O
.	O
</s>
<s>
In	O
this	O
alternative	O
technology	O
,	O
PPPoE	B-Protocol
is	O
merely	O
a	O
means	O
of	O
connecting	O
DSL-modems	O
to	O
an	O
Ethernet-only	O
router	B-Protocol
(	O
again	O
,	O
or	O
to	O
a	O
single	O
host	O
PC	O
)	O
.	O
</s>
<s>
The	O
Draytek	O
Vigor	O
110	O
,	O
120	O
and	O
130	O
modems	B-Application
work	O
in	O
this	O
way	O
.	O
</s>
<s>
When	O
transmitting	O
packets	B-Protocol
bound	O
for	O
the	O
Internet	O
,	O
the	O
PPPoE-speaking	O
Ethernet	B-Protocol
router	I-Protocol
sends	O
Ethernet	O
frames	O
to	O
the	O
(	O
also	O
PPPoE-speaking	O
)	O
DSL	B-Device
modem	I-Device
.	O
</s>
<s>
The	O
modem	B-Application
extracts	O
PPP	B-Protocol
frames	O
from	O
within	O
the	O
received	O
PPPoE	B-Protocol
frames	O
,	O
and	O
sends	O
the	O
PPP	B-Protocol
frames	O
onwards	O
to	O
the	O
DSLAM	B-Protocol
by	O
encapsulating	B-Protocol
them	O
according	O
to	O
RFC	O
2364	O
(	O
PPPoA	B-Protocol
)	O
,	O
thus	O
converting	O
PPPoE	B-Protocol
into	O
PPPoA	B-Protocol
.	O
</s>
<s>
Since	O
the	O
point-to-point	O
connection	O
established	O
has	O
a	O
MTU	B-Protocol
lower	O
than	O
that	O
of	O
standard	O
Ethernet	O
(	O
typically	O
1492	O
vs	O
Ethernet	O
's	O
1500	O
)	O
,	O
it	O
can	O
sometimes	O
cause	O
problems	O
when	O
Path	B-Protocol
MTU	I-Protocol
Discovery	I-Protocol
is	O
defeated	O
by	O
poorly	O
configured	O
firewalls	B-Application
.	O
</s>
<s>
Although	O
higher	O
MTUs	B-Protocol
are	O
becoming	O
more	O
common	O
in	O
providers	O
 '	O
networks	O
,	O
usually	O
the	O
workaround	O
is	O
to	O
use	O
TCP	B-Protocol
MSS	O
(	O
Maximum	O
Segment	O
Size	O
)	O
"	O
clamping	O
"	O
or	O
"	O
rewrite	O
"	O
,	O
whereby	O
the	O
access	O
concentrator	O
rewrites	O
the	O
MSS	O
to	O
ensure	O
TCP	B-Protocol
peers	O
send	O
smaller	O
datagrams	O
.	O
</s>
<s>
Although	O
TCP	B-Protocol
MSS	O
clamping	O
solves	O
the	O
MTU	B-Protocol
issue	O
for	O
TCP	B-Protocol
,	O
other	O
protocols	O
such	O
as	O
ICMP	B-Protocol
and	O
UDP	B-Protocol
may	O
still	O
be	O
affected	O
.	O
</s>
<s>
RFC	O
4638	O
allows	O
PPPoE	B-Protocol
devices	O
to	O
negotiate	O
an	O
MTU	B-Protocol
of	O
greater	O
than	O
1492	O
if	O
the	O
underlying	O
Ethernet	O
layer	O
is	O
capable	O
of	O
jumbo	B-Protocol
frames	I-Protocol
.	O
</s>
<s>
Some	O
vendors	O
(	O
Cisco	O
and	O
Juniper	O
,	O
for	O
example	O
)	O
distinguish	O
PPPoE[oA]	O
from	O
PPPoEoE	O
(	O
PPPoE	B-Protocol
over	O
Ethernet	O
)	O
,	O
which	O
is	O
PPPoE	B-Protocol
running	O
directly	O
over	O
Ethernet	O
or	O
other	O
IEEE	O
802	O
networks	O
or	O
over	O
Ethernet	O
bridged	B-Protocol
over	O
ATM	O
,	O
in	O
order	O
to	O
distinguish	O
it	O
from	O
PPPoEoA	O
(	O
PPPoE	B-Protocol
over	O
ATM	O
)	O
,	O
which	O
is	O
PPPoE	B-Protocol
running	O
over	O
an	O
ATM	O
virtual	O
circuit	O
using	O
RFC	O
2684	O
and	O
SNAP	B-Protocol
encapsulation	B-Protocol
of	O
PPPoE	B-Protocol
.	O
</s>
<s>
(	O
PPPoEoA	O
is	O
not	O
the	O
same	O
as	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
over	I-Protocol
ATM	I-Protocol
(	O
PPPoA	B-Protocol
)	O
,	O
which	O
does	O
n't	O
use	O
SNAP	B-Protocol
)	O
.	O
</s>
<s>
According	O
to	O
a	O
Cisco	O
document	O
"	O
PPPoEoE	O
is	O
a	O
variant	O
of	O
PPPoE	B-Protocol
where	O
the	O
Layer	O
2	O
transport	O
protocol	O
is	O
now	O
Ethernet	O
or	O
802.1q	O
VLAN	B-General_Concept
instead	O
of	O
ATM	O
.	O
</s>
<s>
This	O
encapsulation	B-Protocol
method	O
is	O
generally	O
found	O
in	O
Metro	B-Protocol
Ethernet	I-Protocol
or	O
Ethernet	O
digital	B-Protocol
subscriber	I-Protocol
line	I-Protocol
access	I-Protocol
multiplexer	I-Protocol
(	O
DSLAM	B-Protocol
)	O
environments	O
.	O
</s>
<s>
The	O
common	O
deployment	O
model	O
is	O
that	O
this	O
encapsulation	B-Protocol
method	O
is	O
typically	O
found	O
in	O
multi-tenant	O
buildings	O
or	O
hotels	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
find	O
DSL	B-Device
modems	I-Device
,	O
such	O
as	O
the	O
Draytek	O
Vigor	O
120	O
,	O
where	O
PPPoE	B-Protocol
is	O
confined	O
to	O
the	O
Ethernet	O
link	O
between	O
a	O
DSL	B-Device
modem	I-Device
and	O
a	O
partnering	O
router	B-Protocol
,	O
and	O
the	O
ISP	O
does	O
not	O
speak	O
PPPoE	B-Protocol
at	O
all	O
(	O
but	O
rather	O
PPPoA	B-Protocol
)	O
.	O
</s>
<s>
A	O
certain	O
method	O
of	O
using	O
PPPoE	B-Protocol
in	O
conjunction	O
with	O
GPON	B-Architecture
(	O
which	O
involves	O
creating	O
a	O
VLAN	B-General_Concept
via	O
OMCI	O
)	O
has	O
been	O
patented	O
by	O
ZTE	O
.	O
</s>
<s>
PPPoE	B-Protocol
over	O
GPON	B-Architecture
is	O
reportedly	O
used	O
by	O
retail	O
service	O
providers	O
such	O
as	O
Internode	O
of	O
Australia	O
's	O
National	O
Broadband	O
Network	O
,	O
Orange	O
of	O
France	O
,	O
the	O
Philippines	O
 '	O
Globe	O
Telecom	O
and	O
Italy	O
's	O
Aruba	O
FTTH	B-Architecture
on	O
OpenFiber	O
public	O
GPON	B-Architecture
networks	O
.	O
</s>
<s>
RFC	O
6934	O
,	O
"	O
Applicability	O
of	O
Access	O
Node	O
Control	O
Mechanism	O
to	O
PON	O
based	O
Broadband	O
Networks	O
"	O
,	O
which	O
argues	O
for	O
the	O
use	O
of	O
Access	O
Node	O
Control	O
Protocol	O
in	O
PONs	O
for	O
—	O
among	O
other	O
things	O
—	O
authenticating	O
subscriber	O
access	O
and	O
managing	O
their	O
IP	B-Protocol
addresses	O
,	O
and	O
the	O
first	O
author	O
of	O
which	O
is	O
a	O
Verizon	O
employee	O
,	O
excludes	O
PPPoE	B-Protocol
as	O
an	O
acceptable	O
encapsulation	B-Protocol
for	O
GPON	B-Architecture
:	O
"	O
The	O
protocol	O
encapsulation	B-Protocol
on	O
BPON	O
is	O
based	O
on	O
multi-protocol	O
encapsulation	B-Protocol
over	O
ATM	B-Protocol
Adaptation	I-Protocol
Layer	I-Protocol
5	I-Protocol
(	O
AAL5	B-Protocol
)	O
,	O
defined	O
in	O
 [ RFC2684 ] 	O
.	O
</s>
<s>
This	O
covers	O
PPP	B-Protocol
over	O
Ethernet	O
(	O
PPPoE	B-Protocol
,	O
defined	O
in	O
 [ RFC2516 ] 	O
)	O
or	O
IP	B-Protocol
over	O
Ethernet	O
(	O
IPoE	O
)	O
.	O
</s>
<s>
The	O
protocol	O
encapsulation	B-Protocol
on	O
GPON	B-Architecture
is	O
always	O
IPoE.	O
"	O
</s>
<s>
The	O
10G-PON	B-Protocol
(	O
XG-PON	B-Protocol
)	O
standard	O
(	O
G.987	O
)	O
provides	O
for	O
802.1X	O
mutual	O
authentication	O
of	O
the	O
ONU	O
and	O
OLT	O
,	O
besides	O
the	O
OMCI	O
method	O
carried	O
forward	O
from	O
G.984	O
.	O
</s>
<s>
(	O
The	O
ONU	O
is	O
supposed	O
snoop	O
EAP-encapsulated	O
RADIUS	B-Protocol
messages	O
in	O
this	O
scenario	O
and	O
determine	O
if	O
the	O
authentication	O
was	O
successful	O
or	O
not	O
.	O
)	O
</s>
<s>
There	O
is	O
some	O
modicum	O
support	O
for	O
PPPoE	B-Protocol
specified	O
in	O
the	O
OMCI	O
standards	O
,	O
but	O
only	O
in	O
terms	O
of	O
the	O
ONU	O
being	O
able	O
to	O
filter	O
and	O
add	O
VLAN	B-General_Concept
tags	O
for	O
traffic	O
based	O
on	O
its	O
encapsulation	B-Protocol
(	O
and	O
other	O
parameters	O
)	O
,	O
which	O
includes	O
PPPoE	B-Protocol
among	O
the	O
protocols	O
that	O
ONU	O
must	O
be	O
able	O
to	O
discern	O
.	O
</s>
<s>
The	O
Broadband	O
Forum	O
's	O
TR-200	O
"	O
Using	O
EPON	O
in	O
the	O
Context	O
of	O
TR-101	O
"	O
(	O
2011	O
)	O
,	O
which	O
also	O
pertains	O
to	O
10G-EPON	B-Protocol
,	O
says	O
"	O
The	O
OLT	O
and	O
the	O
multiple-subscriber	O
ONU	O
MUST	O
be	O
able	O
to	O
perform	O
the	O
PPPoE	B-Protocol
Intermediate	O
Agent	O
function	O
,	O
as	O
specified	O
in	O
Section	O
3.9.2/TR	O
-101.	O
"	O
</s>
<s>
A	O
book	O
on	O
Ethernet	B-Protocol
in	I-Protocol
the	I-Protocol
first	I-Protocol
mile	I-Protocol
notes	O
that	O
DHCP	O
can	O
obviously	O
be	O
used	O
instead	O
of	O
PPPoE	B-Protocol
to	O
configure	O
a	O
host	O
for	O
an	O
IP	B-Protocol
session	O
,	O
although	O
it	O
points	O
out	O
that	O
DHCP	O
is	O
not	O
a	O
complete	O
replacement	O
for	O
PPPoE	B-Protocol
if	O
some	O
encapsulation	B-Protocol
is	O
also	O
desired	O
(	O
although	O
VLAN	B-General_Concept
bridges	O
can	O
fulfill	O
this	O
function	O
)	O
and	O
that	O
furthermore	O
,	O
DHCP	O
does	O
not	O
provide	O
(	O
subscriber	O
)	O
authentication	O
,	O
suggesting	O
that	O
IEEE	O
802.1X	O
is	O
also	O
needed	O
for	O
a	O
"	O
complete	O
solution	O
"	O
without	O
PPPoE	B-Protocol
.	O
</s>
<s>
(	O
This	O
book	O
assumes	O
that	O
PPPoE	B-Protocol
is	O
leveraged	O
for	O
other	O
features	O
of	O
PPP	B-Protocol
besides	O
encapsulation	B-Protocol
,	O
including	O
IPCP	B-Protocol
for	O
host	O
configuration	O
,	O
and	O
PAP	B-Protocol
or	O
CHAP	B-Protocol
for	O
authentication	O
.	O
)	O
</s>
<s>
There	O
are	O
security	O
reasons	O
to	O
use	O
PPPoE	B-Protocol
in	O
a	O
(	O
non-DSL/ATM	O
)	O
shared-medium	O
environment	O
,	O
such	O
as	O
power	B-Device
line	I-Device
communication	I-Device
networks	O
,	O
in	O
order	O
to	O
create	O
separate	O
tunnels	O
for	O
each	O
customer	O
.	O
</s>
<s>
PPPoE	B-Protocol
is	O
widely	O
used	O
on	O
WAN	O
lines	O
,	O
including	O
FTTx	B-Architecture
.	O
</s>
<s>
Many	O
FTTx	B-Architecture
residential	B-Application
gateway	I-Application
provided	O
by	O
ISP	O
has	O
integrated	O
the	O
routing	O
functions	O
.	O
</s>
