<s>
Triangular	B-Protocol
routing	I-Protocol
is	O
a	O
method	O
for	O
transmitting	O
packets	O
of	O
data	O
in	O
communications	O
networks	O
.	O
</s>
<s>
It	O
uses	O
a	O
form	O
of	O
routing	B-Protocol
that	O
sends	O
a	O
packet	O
to	O
a	O
proxy	O
system	O
before	O
transmission	O
to	O
the	O
intended	O
destination	O
.	O
</s>
<s>
Triangular	B-Protocol
routing	I-Protocol
is	O
a	O
problem	O
in	O
mobile	B-Protocol
IP	I-Protocol
;	O
however	O
,	O
it	O
finds	O
applications	O
in	O
other	O
networking	O
situations	O
,	O
for	O
instance	O
to	O
avoid	O
problems	O
associated	O
with	O
network	B-Protocol
address	I-Protocol
translation	I-Protocol
(	O
NAT	O
)	O
,	O
implemented	O
for	O
example	O
by	O
Skype	B-Application
.	O
</s>
<s>
Therefore	O
different	O
routing	B-Protocol
must	O
be	O
used	O
for	O
the	O
different	O
directions	O
.	O
</s>
<s>
In	O
mobile	B-Protocol
IP	I-Protocol
,	O
packets	O
that	O
are	O
sent	O
to	O
a	O
mobile	O
host	O
by	O
the	O
correspondent	O
host	O
are	O
first	O
routed	B-Protocol
to	O
the	O
mobile	O
host	O
's	O
home	O
agent	O
and	O
then	O
forwarded	O
to	O
the	O
mobile	O
host	O
at	O
its	O
current	O
location	O
by	O
its	O
home	O
agent	O
.	O
</s>
<s>
For	O
mobile	B-Protocol
IP	I-Protocol
,	O
routing	B-Protocol
optimization	O
is	O
necessary	O
because	O
all	O
packets	O
sent	O
to	O
the	O
mobile	O
host	O
(	O
MH	O
)	O
shall	O
pass	O
through	O
the	O
home	O
agent	O
(	O
HA	O
)	O
but	O
the	O
route	O
may	O
not	O
be	O
the	O
best	O
.	O
</s>
<s>
The	O
mobile	B-Protocol
IP	I-Protocol
with	O
route	O
optimization	O
sets	O
high	O
requirements	O
on	O
the	O
CH	O
.	O
</s>
<s>
To	O
avoid	O
this	O
,	O
many	O
mobile	B-Protocol
IP	I-Protocol
implementations	O
offer	O
the	O
option	O
of	O
tunneling	O
packets	O
from	O
the	O
mobile	O
host	O
through	O
the	O
home	O
agent	O
,	O
too	O
.	O
</s>
<s>
Unlike	O
in	O
mobile	B-Protocol
IPv4	I-Protocol
,	O
mobile	B-Protocol
IPv6	I-Protocol
avoids	O
triangular	B-Protocol
routing	I-Protocol
and	O
is	O
therefore	O
as	O
efficient	O
as	O
native	O
IPv6	B-Protocol
.	O
</s>
