<s>
The	O
Hazy-Sighted	B-Protocol
Link	I-Protocol
State	I-Protocol
Routing	I-Protocol
Protocol	I-Protocol
(	O
HSLS	O
)	O
is	O
a	O
wireless	O
mesh	B-Architecture
network	I-Architecture
routing	B-Protocol
protocol	I-Protocol
being	O
developed	O
by	O
the	O
CUWiN	O
Foundation	O
.	O
</s>
<s>
This	O
is	O
an	O
algorithm	O
allowing	O
computers	O
communicating	O
via	O
digital	O
radio	O
in	O
a	O
mesh	B-Architecture
network	I-Architecture
to	O
forward	O
messages	O
to	O
computers	O
that	O
are	O
out	O
of	O
reach	O
of	O
direct	O
radio	O
contact	O
.	O
</s>
<s>
Its	O
network	O
overhead	O
is	O
theoretically	O
optimal	O
,	O
utilizing	O
both	O
proactive	O
and	O
reactive	O
link-state	B-Protocol
routing	I-Protocol
to	O
limit	O
network	O
updates	O
in	O
space	O
and	O
time	O
.	O
</s>
<s>
This	O
is	O
accomplished	O
by	O
using	O
a	O
carefully	O
designed	O
balance	O
of	O
update	O
frequency	O
,	O
and	O
update	O
extent	O
in	O
order	O
to	O
propagate	O
link	B-Protocol
state	I-Protocol
information	O
optimally	O
.	O
</s>
<s>
Unlike	O
traditional	O
methods	O
,	O
HSLS	O
does	O
not	O
flood	O
the	O
network	O
with	O
link-state	B-Protocol
information	O
to	O
attempt	O
to	O
cope	O
with	O
moving	O
nodes	O
that	O
change	O
connections	O
with	O
the	O
rest	O
of	O
the	O
network	O
.	O
</s>
<s>
Link-state	B-Protocol
algorithms	I-Protocol
are	O
theoretically	O
attractive	O
because	O
they	O
find	O
optimal	O
routes	O
,	O
reducing	O
waste	O
of	O
transmission	O
capacity	O
.	O
</s>
<s>
The	O
inventors	O
of	O
HSLS	O
claim	O
that	O
routing	B-Protocol
protocols	I-Protocol
fall	O
into	O
three	O
basically	O
different	O
schemes	O
:	O
proactive	O
(	O
such	O
as	O
OLSR	B-Protocol
)	O
,	O
reactive	O
(	O
such	O
as	O
AODV	B-Device
)	O
,	O
and	O
algorithms	O
that	O
accept	O
sub-optimal	O
routings	O
.	O
</s>
<s>
The	O
routing	O
information	O
is	O
called	O
a	O
"	O
link	B-Protocol
state	I-Protocol
update.	O
"	O
</s>
<s>
The	O
distance	O
that	O
a	O
link-state	B-Protocol
is	O
copied	O
is	O
the	O
"	O
time	B-Protocol
to	I-Protocol
live	I-Protocol
"	O
and	O
is	O
a	O
count	O
of	O
the	O
number	O
of	O
times	O
it	O
may	O
be	O
copied	O
from	O
one	O
node	O
to	O
the	O
next	O
.	O
</s>
<s>
These	O
strategies	O
are	O
blended	O
by	O
limiting	O
link	B-Protocol
state	I-Protocol
updates	O
in	O
time	O
and	O
space	O
.	O
</s>
<s>
By	O
limiting	O
the	O
time	B-Protocol
to	I-Protocol
live	I-Protocol
the	O
amount	O
of	O
transmission	O
capacity	O
is	O
reduced	O
.	O
</s>
<s>
By	O
definition	O
,	O
a	O
link-state	B-Protocol
algorithm	O
uses	O
the	O
available	O
information	O
to	O
produce	O
the	O
best	O
route	O
,	O
so	O
routing	O
is	O
as	O
optimal	O
as	O
possible	O
,	O
given	O
the	O
available	O
information	O
.	O
</s>
<s>
The	O
scheme	O
is	O
adapted	O
from	O
two	O
limited	O
link-state	B-Protocol
routing	I-Protocol
algorithms	O
.	O
</s>
<s>
One	O
,	O
"	O
Near-Sighted	O
Link-State	B-Protocol
Routing	I-Protocol
"	O
is	O
limited	O
in	O
space	O
,	O
in	O
the	O
number	O
of	O
node-hops	O
that	O
routing	O
information	O
may	O
be	O
transmitted	O
.	O
</s>
<s>
The	O
other	O
routing	O
algorithm	O
,	O
"	O
Discretized	O
Link-State	B-Protocol
Routing	I-Protocol
"	O
limits	O
the	O
times	O
that	O
the	O
routing	O
information	O
may	O
be	O
transmitted	O
.	O
</s>
<s>
They	O
then	O
made	O
some	O
reasonable	O
assumptions	O
and	O
used	O
a	O
mathematical	O
optimization	O
to	O
find	O
the	O
times	O
to	O
transmit	O
link	B-Protocol
state	I-Protocol
updates	O
,	O
and	O
also	O
the	O
breadth	O
of	O
nodes	O
that	O
the	O
link	B-Protocol
state	I-Protocol
updates	O
should	O
cover	O
.	O
</s>
<s>
The	O
algorithm	O
has	O
a	O
few	O
special	O
features	O
to	O
cope	O
with	O
cases	O
that	O
are	O
common	O
in	O
radio	O
networks	O
,	O
such	O
as	O
unidirectional	O
links	O
,	O
and	O
looped-transmission	O
caused	O
by	O
out-of-date	O
routing	B-Protocol
tables	I-Protocol
.	O
</s>
<s>
Many	O
of	O
the	O
simpler	O
mesh	O
routing	B-Protocol
protocols	I-Protocol
just	O
flood	O
the	O
whole	O
network	O
with	O
routing	O
information	O
whenever	O
a	O
link	O
changes	O
.	O
</s>
<s>
The	O
system	O
requires	O
capable	O
nodes	O
with	O
large	O
amounts	O
of	O
memory	O
to	O
maintain	O
routing	B-Protocol
tables	I-Protocol
.	O
</s>
<s>
The	O
asymptotic	O
scalability	O
of	O
its	O
total	O
overhead	O
is	O
compared	O
to	O
standard	O
link	B-Protocol
state	I-Protocol
which	O
scales	O
as	O
,	O
where	O
N	O
is	O
the	O
number	O
of	O
nodes	O
in	O
the	O
network	O
.	O
</s>
<s>
This	O
issue	O
is	O
present	O
to	O
some	O
extent	O
in	O
all	O
link	B-Protocol
state	I-Protocol
protocols	I-Protocol
,	O
because	O
the	O
link	B-Protocol
state	I-Protocol
database	O
may	O
still	O
contain	O
an	O
announcement	O
from	O
a	O
failed	O
node	O
.	O
</s>
<s>
However	O
,	O
protocols	O
like	O
OSPF	B-Protocol
will	O
propagate	O
a	O
link	B-Protocol
state	I-Protocol
update	O
from	O
the	O
failed	O
nodes	O
neighbors	O
,	O
and	O
thus	O
all	O
nodes	O
will	O
learn	O
quickly	O
of	O
the	O
failed	O
node	O
's	O
demise	O
(	O
or	O
disconnection	O
)	O
.	O
</s>
<s>
While	O
the	O
papers	O
describing	O
HSLS	O
do	O
not	O
focus	O
on	O
security	O
,	O
techniques	O
such	O
as	O
digital	O
signatures	O
on	O
routing	O
updates	O
can	O
be	O
used	O
with	O
HSLS	O
(	O
similar	O
to	O
OSPF	B-Protocol
with	O
Digital	O
Signatures	O
)	O
,	O
and	O
BBN	O
has	O
implemented	O
HSLS	O
with	O
digital	O
signatures	O
on	O
neighbor	O
discovery	O
messages	O
and	O
link	B-Protocol
state	I-Protocol
updates	O
.	O
</s>
<s>
Such	O
schemes	O
are	O
challenging	O
in	O
practice	O
because	O
in	O
the	O
ad	B-Protocol
hoc	I-Protocol
environment	O
reachability	O
of	O
public	B-Architecture
key	I-Architecture
infrastructure	I-Architecture
servers	O
cannot	O
be	O
assured	O
.	O
</s>
<s>
Like	O
almost	O
all	O
routing	B-Protocol
protocols	I-Protocol
,	O
HSLS	O
does	O
not	O
include	O
mechanisms	O
to	O
protect	O
data	O
traffic	O
.	O
</s>
<s>
(	O
See	O
IPsec	B-Protocol
and	O
TLS	B-Protocol
.	O
)	O
</s>
