<s>
In	O
other	O
words	O
,	O
if	O
the	O
router	B-Protocol
tries	O
to	O
send	O
out	O
data	O
and	O
the	O
connection	O
is	O
off	O
,	O
then	O
the	O
router	B-Protocol
will	O
automatically	O
establish	O
a	O
connection	O
,	O
send	O
the	O
information	O
,	O
and	O
close	O
the	O
connection	O
when	O
no	O
more	O
data	O
needs	O
to	O
be	O
sent	O
.	O
</s>
<s>
The	O
physical	O
connection	O
consists	O
of	O
the	O
actual	O
cable	O
that	O
connects	O
computers	O
on	O
the	O
network	O
and	O
the	O
network	B-Protocol
interface	I-Protocol
card	I-Protocol
that	O
allows	O
for	O
communication	O
over	O
these	O
cables	O
.	O
</s>
<s>
DDR	O
uses	O
a	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
(	O
PPP	O
)	O
link	O
,	O
which	O
handles	O
all	O
networking	O
functions	O
such	O
as	O
sending	O
,	O
receiving	O
and	O
compressing	O
the	O
signals	O
between	O
two	O
computers	O
on	O
the	O
internet	O
.	O
</s>
<s>
DDR	O
connections	O
are	O
inherently	O
slow	O
and	O
service	O
fees	O
are	O
charged	O
like	O
phone	O
calls	O
depending	O
on	O
the	O
uptime	B-Device
.	O
</s>
<s>
DDR	O
can	O
be	O
used	O
with	O
modems	B-Application
or	O
Integrated	B-Protocol
Services	I-Protocol
Digital	I-Protocol
Network	I-Protocol
(	O
ISDN	B-Protocol
)	O
connections	O
,	O
which	O
allow	O
it	O
to	O
achieve	O
a	O
maximum	O
connection	O
speed	O
of	O
only	O
1.544	O
Mbit/s	O
in	O
the	O
US	O
and	O
2.048	O
Mbit/s	O
in	O
Europe	O
and	O
Australia	O
.	O
</s>
<s>
Despite	O
its	O
drawbacks	O
,	O
there	O
are	O
two	O
important	O
reasons	O
why	O
Dial-on-Demand	B-Protocol
routing	I-Protocol
is	O
used	O
today	O
:	O
reliability	O
and	O
cost	O
.	O
</s>
<s>
Interesting	O
traffic	O
can	O
also	O
be	O
defined	O
such	O
that	O
only	O
SSH	B-Protocol
packets	O
are	O
allowed	O
to	O
establish	O
the	O
link	O
.	O
</s>
<s>
For	O
example	O
,	O
RIP	B-Protocol
v1	O
,	O
which	O
updates	O
every	O
30	O
seconds	O
,	O
would	O
cause	O
the	O
connection	O
to	O
be	O
initialized	O
on	O
every	O
update	O
.	O
</s>
<s>
Other	O
routing	O
protocols	O
such	O
as	O
Open	B-Protocol
Shortest	I-Protocol
Path	I-Protocol
First	I-Protocol
(	O
OSPF	B-Protocol
)	O
and	O
Enhanced	B-Protocol
Interior	I-Protocol
Gateway	I-Protocol
Routing	I-Protocol
Protocol	I-Protocol
(	O
EIGRP	B-Protocol
)	O
only	O
send	O
updates	O
when	O
a	O
connection	O
changes	O
.	O
</s>
<s>
These	O
routing	O
protocols	O
are	O
ideal	O
for	O
DDR	O
and	O
must	O
be	O
configured	O
with	O
"	O
default-information	O
originate	O
"	O
on	O
a	O
Cisco	O
router	B-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
if	O
two	O
dialer	O
map	O
commands	O
on	O
the	O
Serial	B-Protocol
Interface	I-Protocol
0/0/0	O
(	O
Serial	B-Protocol
port	I-Protocol
0	O
of	O
module	O
0	O
of	O
interface	O
0	O
)	O
have	O
the	O
same	O
next	O
hop	O
address	O
,	O
or	O
the	O
IP	O
address	O
of	O
the	O
connection	O
at	O
the	O
destination	O
end	O
,	O
but	O
with	O
different	O
phone	O
numbers	O
,	O
then	O
the	O
first	O
number	O
is	O
dialed	O
and	O
only	O
once	O
the	O
wait-for-carrier	O
timer	O
expires	O
will	O
the	O
next	O
number	O
be	O
dialed	O
.	O
</s>
