<s>
Hierarchical	B-Protocol
state	I-Protocol
routing	I-Protocol
(	O
HSR	O
)	O
,	O
proposed	O
in	O
Scalable	O
Routing	O
Strategies	O
for	O
Ad	O
Hoc	O
Wireless	O
Networks	O
by	O
Iwata	O
et	O
al	O
.	O
</s>
<s>
(	O
1999	O
)	O
,	O
is	O
a	O
typical	O
example	O
of	O
a	O
hierarchical	B-Protocol
routing	I-Protocol
protocol	O
.	O
</s>
<s>
HSR	O
maintains	O
a	O
hierarchical	B-Protocol
topology	B-Architecture
,	O
where	O
elected	O
clusterheads	O
at	O
the	O
lowest	O
level	O
become	O
members	O
of	O
the	O
next	O
higher	O
level	O
.	O
</s>
<s>
Nodes	O
which	O
want	O
to	O
communicate	O
to	O
a	O
node	B-Protocol
outside	O
of	O
their	O
cluster	B-Architecture
ask	O
their	O
clusterhead	O
to	O
forward	O
their	O
packet	O
to	O
the	O
next	O
level	O
,	O
until	O
a	O
clusterhead	O
of	O
the	O
other	O
node	B-Protocol
is	O
in	O
the	O
same	O
cluster	B-Architecture
.	O
</s>
<s>
The	O
packet	O
then	O
travels	O
down	O
to	O
the	O
destination	O
node	B-Protocol
.	O
</s>
<s>
Furthermore	O
,	O
HSR	O
proposes	O
to	O
cluster	B-Architecture
nodes	O
in	O
a	O
logical	O
way	O
instead	O
of	O
in	O
a	O
geological	O
way	O
:	O
members	O
of	O
the	O
same	O
company	O
or	O
in	O
the	O
same	O
battlegroup	O
are	O
clustered	O
together	O
,	O
assuming	O
they	O
will	O
communicate	O
much	O
within	O
the	O
logical	O
cluster	B-Architecture
.	O
</s>
<s>
HSR	O
does	O
not	O
specify	O
how	O
a	O
cluster	B-Architecture
is	O
to	O
be	O
formed	O
.	O
</s>
