<s>
A	O
digital	B-Protocol
subscriber	I-Protocol
line	I-Protocol
access	I-Protocol
multiplexer	I-Protocol
(	O
DSLAM	B-Protocol
,	O
often	O
pronounced	O
DEE-slam	O
)	O
is	O
a	O
network	O
device	O
,	O
often	O
located	O
in	O
telephone	O
exchanges	O
,	O
that	O
connects	O
multiple	O
customer	O
digital	O
subscriber	B-Architecture
line	I-Architecture
(	O
DSL	O
)	O
interfaces	O
to	O
a	O
high-speed	O
digital	O
communications	O
channel	O
using	O
multiplexing	B-Architecture
techniques	O
.	O
</s>
<s>
Its	O
cable	B-Device
internet	I-Device
(	O
DOCSIS	B-Protocol
)	O
counterpart	O
is	O
the	O
Cable	B-Device
modem	I-Device
termination	I-Device
system	I-Device
.	O
</s>
<s>
Customer	O
premises	O
:	O
DSL	B-Device
modem	I-Device
terminating	O
the	O
ADSL	O
,	O
SHDSL	O
or	O
VDSL	O
circuit	O
and	O
providing	O
a	O
LAN	B-General_Concept
or	O
interface	O
to	O
a	O
single	O
computer	O
or	O
LAN	B-General_Concept
segment	O
.	O
</s>
<s>
Local	B-Architecture
loop	I-Architecture
:	O
the	O
telephone	O
company	O
wires	O
from	O
a	O
customer	O
to	O
the	O
telephone	O
exchange	O
or	O
to	O
a	O
serving	O
area	O
interface	O
,	O
often	O
called	O
the	O
"	O
last	B-Protocol
mile	I-Protocol
"	O
(	O
LM	O
)	O
.	O
</s>
<s>
Main	B-Device
distribution	I-Device
frame	I-Device
(	O
MDF	O
)	O
:	O
a	O
wiring	O
rack	O
that	O
connects	O
outside	O
subscriber	B-Architecture
lines	I-Architecture
with	O
internal	O
lines	O
.	O
</s>
<s>
xDSL	B-Algorithm
filters	I-Algorithm
:	O
DSL	B-Algorithm
filters	I-Algorithm
are	O
used	O
in	O
the	O
telephone	O
exchange	O
to	O
split	O
voice	O
from	O
data	O
signals	O
.	O
</s>
<s>
The	O
voice	O
signal	O
can	O
be	O
routed	O
to	O
a	O
plain	O
old	O
telephone	O
service	O
(	O
POTS	O
)	O
provider	O
,	O
digital	O
telephone	O
exchange	O
or	O
left	O
unused	O
whilst	O
the	O
data	O
signal	O
is	O
routed	O
to	O
the	O
ISP	O
DSLAM	B-Protocol
via	O
the	O
HDF	O
(	O
see	O
next	O
entry	O
)	O
.	O
</s>
<s>
DSLAM	B-Protocol
:	O
a	O
device	O
for	O
DSL	O
service	O
.	O
</s>
<s>
The	O
DSLAM	B-Protocol
port	O
where	O
the	O
subscriber	O
local	B-Architecture
loop	I-Architecture
is	O
connected	O
converts	O
analog	O
electrical	O
signals	O
to	O
data	O
traffic	O
(	O
upstream	O
traffic	O
for	O
data	O
upload	O
)	O
and	O
data	O
traffic	O
to	O
analog	O
electrical	O
signals	O
(	O
downstream	O
for	O
data	O
download	O
)	O
.	O
</s>
<s>
The	O
DSLAM	B-Protocol
equipment	O
collects	O
the	O
data	O
from	O
its	O
many	O
modem	B-Application
ports	B-Protocol
and	O
aggregates	O
their	O
voice	O
and	O
data	O
traffic	O
into	O
one	O
complex	O
composite	O
"	O
signal	O
"	O
via	O
multiplexing	B-Architecture
.	O
</s>
<s>
Depending	O
on	O
its	O
device	O
architecture	O
and	O
setup	O
,	O
a	O
DSLAM	B-Protocol
aggregates	O
the	O
DSL	O
lines	O
over	O
its	O
Asynchronous	O
Transfer	O
Mode	O
(	O
ATM	O
)	O
,	O
Frame	B-Protocol
Relay	I-Protocol
,	O
and/or	O
Internet	B-Protocol
Protocol	I-Protocol
network	O
,	O
i.e.	O
,	O
an	O
IP-DSLAM	O
using	O
Packet	O
Transfer	O
Mode	O
-	O
Transmission	O
Convergence	O
(	O
PTM-TC	O
)	O
protocol(s )	O
stack	O
.	O
</s>
<s>
The	O
aggregated	O
traffic	O
is	O
then	O
directed	O
to	O
a	O
telco	O
's	O
backbone	B-General_Concept
switch	O
,	O
via	O
an	O
access	O
network	O
(	O
AN	O
)	O
,	O
also	O
called	O
a	O
Network	O
Service	O
Provider	O
(	O
NSP	O
)	O
,	O
at	O
up	O
to	O
10	O
Gbit/s	O
data	O
rates	O
.	O
</s>
<s>
The	O
DSLAM	B-Protocol
acts	O
like	O
a	O
network	B-Protocol
switch	I-Protocol
since	O
its	O
functionality	O
is	O
at	O
Layer	B-Protocol
2	I-Protocol
of	O
the	O
OSI	O
model	O
.	O
</s>
<s>
Therefore	O
,	O
it	O
cannot	O
re-route	O
traffic	O
between	O
multiple	O
IP	B-Protocol
networks	O
,	O
only	O
between	O
ISP	O
devices	O
and	O
end-user	O
connection	O
points	O
.	O
</s>
<s>
The	O
DSLAM	B-Protocol
traffic	O
is	O
switched	O
to	O
a	O
Broadband	O
Remote	O
Access	O
Server	O
where	O
the	O
end-user	O
traffic	O
is	O
then	O
routed	O
across	O
the	O
ISP	O
network	O
to	O
the	O
Internet	O
.	O
</s>
<s>
Customer-premises	O
equipment	O
that	O
interfaces	O
well	O
with	O
the	O
DSLAM	B-Protocol
to	O
which	O
it	O
is	O
connected	O
may	O
take	O
advantage	O
of	O
enhanced	O
telephone	O
voice	O
and	O
data	O
line	O
signaling	O
features	O
and	O
the	O
bandwidth	O
monitoring	O
and	O
compensation	O
capabilities	O
it	O
supports	O
.	O
</s>
<s>
A	O
DSLAM	B-Protocol
may	O
or	O
may	O
not	O
be	O
located	O
in	O
the	O
telephone	O
exchange	O
,	O
and	O
may	O
also	O
serve	O
multiple	O
data	O
and	O
voice	O
customers	O
within	O
a	O
neighborhood	O
serving	O
area	O
interface	O
,	O
sometimes	O
in	O
conjunction	O
with	O
a	O
digital	B-Application
loop	I-Application
carrier	I-Application
.	O
</s>
<s>
DSLAMs	B-Protocol
are	O
also	O
used	O
by	O
hotels	O
,	O
lodges	O
,	O
residential	O
neighborhoods	O
,	O
and	O
other	O
businesses	O
operating	O
their	O
own	O
private	O
telephone	O
exchange	O
.	O
</s>
<s>
In	O
addition	O
to	O
being	O
a	O
data	O
switch	O
and	O
multiplexer	O
,	O
a	O
DSLAM	B-Protocol
is	O
also	O
a	O
large	O
collection	O
of	O
modems	B-Application
.	O
</s>
<s>
Each	O
modem	B-Application
on	O
the	O
aggregation	O
card	O
communicates	O
with	O
a	O
single	O
subscriber	O
's	O
DSL	B-Device
modem	I-Device
.	O
</s>
<s>
This	O
modem	B-Application
functionality	O
is	O
integrated	O
into	O
the	O
DSLAM	B-Protocol
itself	O
instead	O
of	O
being	O
done	O
via	O
an	O
external	O
device	O
like	O
a	O
20th-century	O
voiceband	O
modem	B-Application
.	O
</s>
<s>
Like	O
traditional	O
voice-band	O
modems	B-Application
,	O
a	O
DSLAM	B-Protocol
's	O
integrated	O
DSL	B-Device
modems	I-Device
are	O
usually	O
able	O
to	O
probe	O
the	O
line	O
and	O
to	O
adjust	O
themselves	O
to	O
electronically	O
or	O
digitally	O
compensate	O
for	O
forward	O
echoes	O
and	O
other	O
bandwidth-limiting	O
factors	O
in	O
order	O
to	O
move	O
data	O
at	O
the	O
maximum	O
possible	O
connection	O
rate	O
.	O
</s>
<s>
This	O
compensation	O
capability	O
also	O
takes	O
advantage	O
of	O
the	O
better	O
performance	O
of	O
"	O
balanced	O
line	O
"	O
DSL	O
connections	O
,	O
providing	O
capabilities	O
for	O
LAN	B-General_Concept
segments	O
longer	O
than	O
physically	O
similar	O
unshielded	O
twisted	O
pair	O
(	O
UTP	O
)	O
Ethernet	O
connections	O
,	O
since	O
the	O
balanced	O
line	O
type	O
is	O
generally	O
required	O
for	O
its	O
hardware	O
to	O
function	O
correctly	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
longer	O
the	O
wire	O
between	O
DSLAM	B-Protocol
and	O
subscriber	O
,	O
the	O
slower	O
the	O
maximum	O
possible	O
data	O
rate	O
due	O
to	O
the	O
lower	O
frequencies	O
being	O
used	O
to	O
limit	O
the	O
total	O
attenuation	O
(	O
or	O
due	O
to	O
the	O
higher	O
number	O
of	O
errors	O
at	O
higher	O
frequencies	O
,	O
effectively	O
lowering	O
the	O
overall	O
frequency/data	O
rate	O
)	O
.	O
</s>
<s>
Local	O
conditions	O
may	O
vary	O
,	O
especially	O
beyond	O
2km	O
,	O
often	O
necessitating	O
a	O
closer	O
DSLAM	B-Protocol
to	O
bring	O
acceptable	O
bandwidths	O
:	O
</s>
<s>
Customers	O
connect	O
to	O
the	O
DSLAM	B-Protocol
through	O
ADSL	B-Device
modems	I-Device
or	O
DSL	B-Device
routers	I-Device
,	O
which	O
are	O
connected	O
to	O
the	O
PSTN	O
network	O
via	O
typical	O
unshielded	O
twisted	O
pair	O
telephone	O
lines	O
.	O
</s>
<s>
Each	O
DSLAM	B-Protocol
has	O
multiple	O
aggregation	O
cards	O
,	O
and	O
each	O
such	O
card	O
can	O
have	O
multiple	O
ports	B-Protocol
to	O
which	O
the	O
customers	O
 '	O
lines	O
are	O
connected	O
.	O
</s>
<s>
Typically	O
a	O
single	O
DSLAM	B-Protocol
aggregation	O
card	O
has	O
24	O
ports	B-Protocol
,	O
but	O
this	O
number	O
can	O
vary	O
with	O
each	O
manufacturer	O
.	O
</s>
<s>
The	O
most	O
common	O
DSLAMs	B-Protocol
are	O
housed	O
in	O
a	O
telco-grade	O
chassis	O
,	O
which	O
are	O
supplied	O
with	O
(	O
nominal	O
)	O
48	O
volts	O
DC	O
.	O
</s>
<s>
Hence	O
a	O
typical	O
DSLAM	B-Protocol
setup	O
may	O
contain	O
power	O
converters	O
,	O
DSLAM	B-Protocol
chassis	O
,	O
aggregation	O
cards	O
,	O
cabling	O
,	O
and	O
upstream	O
links	O
.	O
</s>
<s>
On	O
the	O
upstream	O
trunk	O
(	O
ISP	O
)	O
side	O
many	O
early	O
DSLAMs	B-Protocol
used	O
ATM	O
—	O
and	O
this	O
approach	O
was	O
standardized	O
by	O
the	O
DSL	O
Forum	O
—	O
with	O
Gigabit	O
Ethernet	O
support	O
appearing	O
sometime	O
later	O
.	O
</s>
<s>
Today	O
,	O
the	O
most	O
common	O
upstream	O
links	O
in	O
these	O
DSLAMs	B-Protocol
use	O
Gigabit	O
Ethernet	O
or	O
multi-gigabit	O
fiber	B-Architecture
optic	I-Architecture
links	O
.	O
</s>
<s>
IP-DSLAM	O
stands	O
for	O
Internet	B-Protocol
Protocol	I-Protocol
Digital	B-Protocol
Subscriber	I-Protocol
Line	I-Protocol
Access	I-Protocol
Multiplexer	I-Protocol
.	O
</s>
<s>
User	O
traffic	O
is	O
mostly	O
IP	B-Protocol
based	O
.	O
</s>
<s>
Traditional	O
20th	O
century	O
DSLAMs	B-Protocol
used	O
Asynchronous	O
Transfer	O
Mode	O
(	O
ATM	O
)	O
technology	O
to	O
connect	O
to	O
upstream	O
ATM	O
routers/switches	O
.	O
</s>
<s>
The	O
DSLAM	B-Protocol
simply	O
extracted	O
the	O
ATM	O
signals	O
from	O
the	O
DSL	O
signal	O
,	O
and	O
passed	O
the	O
ATM	O
signal	O
to	O
ATM	O
routers	B-Protocol
,	O
which	O
then	O
extract	O
the	O
IP	B-Protocol
traffic	O
and	O
pass	O
it	O
on	O
to	O
an	O
IP	B-Protocol
router	I-Protocol
in	O
an	O
IP	B-Protocol
network	O
.	O
</s>
<s>
This	O
division	O
of	O
work	O
was	O
thought	O
to	O
be	O
sensible	O
because	O
DSL	O
itself	O
is	O
based	O
on	O
ATM	O
,	O
and	O
could	O
theoretically	O
carry	O
data	O
other	O
than	O
IP	B-Protocol
in	O
that	O
ATM	O
stream	O
.	O
</s>
<s>
In	O
contrast	O
,	O
an	O
IP-DSLAM	O
extracts	O
the	O
IP	B-Protocol
traffic	O
in	O
the	O
DSLAM	B-Protocol
itself	O
and	O
passes	O
it	O
on	O
to	O
an	O
IP	B-Protocol
router	I-Protocol
.	O
</s>
<s>
The	O
advantages	O
of	O
IP-DSLAM	O
over	O
a	O
traditional	O
ATM	O
DSLAM	B-Protocol
are	O
that	O
the	O
merged	O
equipment	O
is	O
less	O
expensive	O
to	O
make	O
and	O
operate	O
and	O
can	O
offer	O
a	O
richer	O
set	O
of	O
features	O
.	O
</s>
