<s>
Scalable	B-Protocol
Source	I-Protocol
Routing	I-Protocol
(	O
SSR	O
)	O
is	O
a	O
routing	B-Protocol
protocol	I-Protocol
for	O
unstructured	O
networks	O
such	O
as	O
mobile	B-General_Concept
ad	I-General_Concept
hoc	I-General_Concept
networks	I-General_Concept
,	O
mesh	B-Architecture
networks	I-Architecture
,	O
or	O
sensor	B-Architecture
networks	I-Architecture
.	O
</s>
<s>
It	O
combines	O
source	B-Protocol
routing	I-Protocol
with	O
routing	O
along	O
a	O
virtual	O
ring	O
,	O
and	O
is	O
based	O
on	O
the	O
idea	O
of	O
"	O
pushing	O
Chord	B-Application
into	O
the	O
underlay	O
"	O
.	O
</s>
<s>
This	O
is	O
a	O
popular	O
concept	O
in	O
peer-to-peer	O
overlay	B-Architecture
networks	I-Architecture
like	O
Chord	B-Application
.	O
</s>
<s>
Therefore	O
,	O
flooding	B-Protocol
the	O
physical	O
network	O
can	O
be	O
avoided	O
.	O
</s>
<s>
The	O
finger	O
table	O
in	O
Chord	B-Application
,	O
which	O
provides	O
shortcuts	O
in	O
the	O
virtual	O
ring	O
,	O
is	O
replaced	O
by	O
a	O
route	O
cache	O
.	O
</s>
<s>
In	O
the	O
physical	O
network	O
SSR	O
utilizes	O
source	B-Protocol
routing	I-Protocol
.	O
</s>
<s>
This	O
facilitates	O
the	O
collection	O
of	O
routing	O
information	O
while	O
inhibiting	O
polluting	B-General_Concept
of	O
the	O
nodes	O
 '	O
route	O
caches	O
with	O
outdated	O
information	O
.	O
</s>
<s>
When	O
the	O
message	O
arrives	O
at	O
the	O
final	O
destination	O
,	O
after	O
path	O
optimization	O
(	O
using	O
Dijkstra	B-Algorithm
's	I-Algorithm
algorithm	I-Algorithm
)	O
a	O
route	O
update	O
message	O
is	O
sent	O
to	O
the	O
originator	O
node	O
,	O
thus	O
updating	O
the	O
originators	O
route	O
cache	O
.	O
</s>
<s>
While	O
SSR	O
is	O
a	O
complete	O
routing	B-Protocol
protocol	I-Protocol
(	O
cf	O
.	O
</s>
<s>
OSI	O
model	O
's	O
network	B-Application
layer	I-Application
)	O
,	O
it	O
also	O
provides	O
the	O
semantics	O
of	O
a	O
distributed	B-Operating_System
hash	I-Operating_System
table	I-Operating_System
.	O
</s>
<s>
This	O
reduces	O
the	O
overhead	O
to	O
having	O
an	O
overlay	O
protocol	O
on	O
top	O
of	O
a	O
traditional	O
routing	B-Protocol
protocol	I-Protocol
and	O
greatly	O
expedites	O
lookup	O
operations	O
in	O
MANETs	B-General_Concept
which	O
otherwise	O
would	O
rely	O
on	O
flooding	B-Protocol
,	O
provided	O
the	O
application	O
supports	O
(	O
or	O
is	O
modified	O
to	O
support	O
)	O
key-based	B-Protocol
routing	I-Protocol
.	O
</s>
<s>
SSR	O
has	O
reactive	O
as	O
well	O
as	O
proactive	O
components	O
,	O
making	O
it	O
a	O
hybrid	O
routing	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
Virtual	O
Ring	O
Routing	O
is	O
conceptually	O
similar	O
,	O
the	O
biggest	O
difference	O
being	O
the	O
usage	O
of	O
source	B-Protocol
routing	I-Protocol
in	O
SSR	O
compared	O
to	O
building	O
up	O
per-node	O
state	O
(	O
routing	O
tables	O
)	O
in	O
VRR	O
.	O
</s>
<s>
Message-Efficient	O
:	O
Only	O
local	O
broadcasts	O
,	O
no	O
global	O
flooding	B-Protocol
.	O
</s>
