<s>
Geographic	B-Protocol
routing	I-Protocol
(	O
also	O
called	O
georouting	B-Protocol
or	O
position-based	B-Protocol
routing	I-Protocol
)	O
is	O
a	O
routing	B-Protocol
principle	O
that	O
relies	O
on	O
geographic	O
position	O
information	O
.	O
</s>
<s>
It	O
is	O
mainly	O
proposed	O
for	O
wireless	B-General_Concept
networks	I-General_Concept
and	O
based	O
on	O
the	O
idea	O
that	O
the	O
source	O
sends	O
a	O
message	O
to	O
the	O
geographic	O
location	O
of	O
the	O
destination	O
instead	O
of	O
using	O
the	O
network	B-Protocol
address	I-Protocol
.	O
</s>
<s>
In	O
the	O
area	O
of	O
packet	B-Application
radio	I-Application
networks	O
,	O
the	O
idea	O
of	O
using	O
position	O
information	O
for	O
routing	B-Protocol
was	O
first	O
proposed	O
in	O
the	O
1980s	O
for	O
interconnection	O
networks	O
.	O
</s>
<s>
Geographic	B-Protocol
routing	I-Protocol
requires	O
that	O
each	O
node	B-Protocol
can	O
determine	O
its	O
own	O
location	O
and	O
that	O
the	O
source	O
is	O
aware	O
of	O
the	O
location	O
of	O
the	O
destination	O
.	O
</s>
<s>
With	O
this	O
information	O
,	O
a	O
message	O
can	O
be	O
routed	B-Protocol
to	O
the	O
destination	O
without	O
knowledge	O
of	O
the	O
network	B-Architecture
topology	I-Architecture
or	O
a	O
prior	O
route	O
discovery	O
.	O
</s>
<s>
There	O
are	O
various	O
approaches	O
,	O
such	O
as	O
single-path	O
,	O
multi-path	O
and	O
flooding-based	O
strategies	O
(	O
see	O
for	O
a	O
survey	O
)	O
.	O
</s>
<s>
Most	O
single-path	O
strategies	O
rely	O
on	O
two	O
techniques	O
:	O
greedy	B-Protocol
forwarding	I-Protocol
and	O
face	B-Protocol
routing	I-Protocol
.	O
</s>
<s>
Greedy	B-Protocol
forwarding	I-Protocol
tries	O
to	O
bring	O
the	O
message	O
closer	O
to	O
the	O
destination	O
in	O
each	O
step	O
using	O
only	O
local	O
information	O
.	O
</s>
<s>
Thus	O
,	O
each	O
node	B-Protocol
forwards	O
the	O
message	O
to	O
the	O
neighbor	O
that	O
is	O
most	O
suitable	O
from	O
a	O
local	O
point	O
of	O
view	O
.	O
</s>
<s>
Alternatively	O
,	O
one	O
can	O
consider	O
another	O
notion	O
of	O
progress	O
,	O
namely	O
the	O
projected	O
distance	O
on	O
the	O
source-destination-line	O
(	O
MFR	O
,	O
NFP	O
)	O
,	O
or	O
the	O
minimum	O
angle	O
between	O
neighbor	O
and	O
destination	O
(	O
Compass	O
Routing	B-Protocol
)	O
.	O
</s>
<s>
It	O
is	O
known	O
that	O
the	O
basic	O
greedy	O
strategy	O
and	O
MFR	O
are	O
loop	O
free	O
,	O
while	O
NFP	O
and	O
Compass	O
Routing	B-Protocol
are	O
not	O
.	O
</s>
<s>
Greedy	B-Protocol
forwarding	I-Protocol
can	O
lead	O
into	O
a	O
dead	O
end	O
,	O
where	O
there	O
is	O
no	O
neighbor	O
closer	O
to	O
the	O
destination	O
.	O
</s>
<s>
Then	O
,	O
face	B-Protocol
routing	I-Protocol
helps	O
to	O
recover	O
from	O
that	O
situation	O
and	O
find	O
a	O
path	O
to	O
another	O
node	B-Protocol
,	O
where	O
greedy	B-Protocol
forwarding	I-Protocol
can	O
be	O
resumed	O
.	O
</s>
<s>
A	O
recovery	O
strategy	O
such	O
as	O
face	B-Protocol
routing	I-Protocol
is	O
necessary	O
to	O
assure	O
that	O
a	O
message	O
can	O
be	O
delivered	O
to	O
the	O
destination	O
.	O
</s>
<s>
The	O
combination	O
of	O
greedy	B-Protocol
forwarding	I-Protocol
and	O
face	B-Protocol
routing	I-Protocol
was	O
first	O
proposed	O
in	O
1999	O
under	O
the	O
name	O
GFG	O
(	O
Greedy-Face-Greedy	O
)	O
.	O
</s>
<s>
Face	B-Protocol
routing	I-Protocol
depends	O
on	O
a	O
planar	O
subgraph	O
in	O
general	O
;	O
however	O
distributed	O
planarization	O
is	O
difficult	O
for	O
real	O
wireless	O
sensor	O
networks	O
and	O
does	O
not	O
scale	O
well	O
to	O
3D	O
environments	O
.	O
</s>
<s>
Although	O
originally	O
developed	O
as	O
a	O
routing	B-Protocol
scheme	O
that	O
uses	O
the	O
physical	O
positions	O
of	O
each	O
node	B-Protocol
,	O
geographic	B-Protocol
routing	I-Protocol
algorithms	O
have	O
also	O
been	O
applied	O
to	O
networks	O
in	O
which	O
each	O
node	B-Protocol
is	O
associated	O
with	O
a	O
point	O
in	O
a	O
virtual	O
space	O
,	O
unrelated	O
to	O
its	O
physical	O
position	O
.	O
</s>
<s>
The	O
process	O
of	O
finding	O
a	O
set	O
of	O
virtual	O
positions	O
for	O
the	O
nodes	O
of	O
a	O
network	O
such	O
that	O
geographic	B-Protocol
routing	I-Protocol
using	O
these	O
positions	O
is	O
guaranteed	O
to	O
succeed	O
is	O
called	O
greedy	B-Protocol
embedding	I-Protocol
.	O
</s>
