<s>
Automatic	B-Device
Link	I-Device
Establishment	I-Device
,	O
commonly	O
known	O
as	O
ALE	O
,	O
is	O
the	O
worldwide	O
de	O
facto	O
standard	O
for	O
digitally	O
initiating	O
and	O
sustaining	O
HF	B-Algorithm
radio	I-Algorithm
communications	O
.	O
</s>
<s>
ALE	O
is	O
a	O
feature	O
in	O
an	O
HF	B-Algorithm
communications	O
radio	O
transceiver	O
system	O
that	O
enables	O
the	O
radio	O
station	O
to	O
make	O
contact	O
,	O
or	O
initiate	O
a	O
circuit	O
,	O
between	O
itself	O
and	O
another	O
HF	B-Algorithm
radio	I-Algorithm
station	O
or	O
network	O
of	O
stations	O
.	O
</s>
<s>
The	O
purpose	O
is	O
to	O
provide	O
a	O
reliable	O
rapid	O
method	O
of	O
calling	O
and	O
connecting	O
during	O
constantly	O
changing	O
HF	B-Algorithm
ionospheric	O
propagation	O
,	O
reception	O
interference	O
,	O
and	O
shared	O
spectrum	O
use	O
of	O
busy	O
or	O
congested	O
HF	B-Algorithm
channels	O
.	O
</s>
<s>
A	O
standalone	O
ALE	O
radio	O
combines	O
an	O
HF	B-Algorithm
SSB	B-Device
radio	I-Device
transceiver	O
with	O
an	O
internal	O
microprocessor	B-General_Concept
and	O
MFSK	B-Device
modem	B-Application
.	O
</s>
<s>
It	O
is	O
programmed	O
with	O
a	O
unique	O
ALE	B-General_Concept
address	I-General_Concept
,	O
similar	O
to	O
a	O
phone	O
number	O
(	O
or	O
on	O
newer	O
generations	O
,	O
a	O
username	O
)	O
.	O
</s>
<s>
When	O
not	O
actively	O
in	O
contact	O
with	O
another	O
station	O
,	O
the	O
HF	B-Algorithm
SSB	B-Device
transceiver	O
constantly	O
scans	O
through	O
a	O
list	O
of	O
HF	B-Algorithm
frequencies	O
called	O
channels	O
,	O
listening	O
for	O
any	O
ALE	O
signals	O
transmitted	O
by	O
other	O
radio	O
stations	O
.	O
</s>
<s>
It	O
decodes	O
calls	O
and	O
soundings	O
sent	O
by	O
other	O
stations	O
and	O
uses	O
the	O
bit	O
error	O
rate	O
to	O
store	O
a	O
quality	O
score	O
for	O
that	O
frequency	O
and	O
sender-address	O
.	O
</s>
<s>
To	O
reach	O
a	O
specific	O
station	O
,	O
the	O
caller	O
enters	O
the	O
ALE	B-General_Concept
Address	I-General_Concept
.	O
</s>
<s>
The	O
ALE	O
controller	O
selects	O
the	O
best	O
available	O
idle	O
channel	O
for	O
that	O
destination	O
address	B-General_Concept
.	O
</s>
<s>
The	O
two	O
stations	O
 '	O
ALE	O
controllers	O
automatically	O
handshake	B-Protocol
to	O
confirm	O
that	O
a	O
link	O
of	O
sufficient	O
quality	O
has	O
been	O
established	O
,	O
then	O
notify	O
the	O
operators	O
that	O
the	O
link	O
is	O
up	O
.	O
</s>
<s>
If	O
the	O
callee	O
fails	O
to	O
respond	O
or	O
the	O
handshaking	B-Protocol
fails	O
,	O
the	O
originating	O
ALE	O
node	O
usually	O
selects	O
another	O
frequency	O
either	O
at	O
random	O
or	O
by	O
making	O
a	O
guess	O
of	O
varying	O
sophistication	O
.	O
</s>
<s>
Alternatively	O
,	O
digital	O
data	O
can	O
be	O
exchanged	O
via	O
a	O
built-in	O
or	O
external	B-Application
modem	I-Application
(	O
such	O
as	O
a	O
STANAG	O
5066	O
or	O
MIL-STD-188-110B	O
serial	O
tone	O
modem	B-Application
)	O
depending	O
on	O
needs	O
and	O
availability	O
.	O
</s>
<s>
Due	O
to	O
the	O
vagaries	O
of	O
ionospheric	O
communications	O
,	O
HF	B-Algorithm
radio	I-Algorithm
as	O
used	O
by	O
large	O
governmental	O
organizations	O
in	O
the	O
mid-20th	O
century	O
was	O
traditionally	O
the	O
domain	O
of	O
highly	O
skilled	O
and	O
trained	O
radio	O
operators	O
.	O
</s>
<s>
One	O
of	O
the	O
new	O
characteristics	O
that	O
embedded	O
microprocessors	O
and	O
computers	O
brought	O
to	O
HF	B-Algorithm
radio	I-Algorithm
via	O
ALE	O
,	O
was	O
alleviation	O
of	O
the	O
need	O
for	O
the	O
radio	O
operator	O
to	O
constantly	O
monitor	O
and	O
change	O
the	O
radio	O
frequency	O
manually	O
to	O
compensate	O
for	O
ionospheric	O
conditions	O
or	O
interference	O
.	O
</s>
<s>
For	O
the	O
average	O
user	O
of	O
ALE	O
,	O
after	O
learning	O
how	O
to	O
work	O
the	O
basic	O
functions	O
of	O
the	O
HF	B-Algorithm
transceiver	O
,	O
it	O
became	O
similar	O
to	O
operating	O
a	O
cellular	O
mobile	O
phone	O
.	O
</s>
<s>
With	O
a	O
radio	O
operator	O
initiating	O
a	O
call	O
,	O
the	O
process	O
normally	O
takes	O
a	O
few	O
minutes	O
for	O
the	O
ALE	O
to	O
pick	O
an	O
HF	B-Algorithm
frequency	O
that	O
is	O
optimum	O
for	O
both	O
sides	O
of	O
the	O
communication	O
link	O
.	O
</s>
<s>
In	O
this	O
respect	O
,	O
the	O
longstanding	O
need	O
in	O
HF	B-Algorithm
radio	I-Algorithm
for	O
repetitive	O
calling	O
on	O
pre-determined	O
time	O
schedules	O
or	O
tedious	O
monitoring	O
static	O
is	O
eliminated	O
.	O
</s>
<s>
In	O
modern	O
HF	B-Algorithm
communications	O
,	O
ALE	O
has	O
largely	O
replaced	O
HF	B-Algorithm
prediction	O
charts	O
,	O
propagation	O
beacons	O
,	O
chirp	O
sounders	O
,	O
propagation	O
prediction	O
software	O
,	O
and	O
traditional	O
radio	O
operator	O
educated	O
guesswork	O
.	O
</s>
<s>
ALE	O
is	O
most	O
commonly	O
used	O
for	O
hooking	O
up	O
operators	O
for	O
voice	O
contacts	O
on	O
SSB	B-Device
(	O
single-sideband	B-Device
modulation	I-Device
)	O
,	O
HF	B-Algorithm
internet	O
connectivity	O
for	O
email	O
,	O
SMS	B-Device
phone	O
texting	O
or	O
text	O
messaging	O
,	O
real-time	O
chat	O
via	O
HF	B-Algorithm
text	O
,	O
Geo	O
Position	O
Reporting	O
,	O
and	O
file	O
transfer	O
.	O
</s>
<s>
High	B-Algorithm
Frequency	I-Algorithm
Internet	O
Protocol	O
or	O
HFIP	O
may	O
be	O
used	O
with	O
ALE	O
for	O
internet	O
access	O
via	O
HF	B-Algorithm
.	O
</s>
<s>
The	O
essence	O
of	O
ALE	O
techniques	O
is	O
the	O
use	O
of	O
automatic	O
channel	O
selection	O
,	O
scanning	O
receivers	O
,	O
selective	O
calling	O
,	O
handshaking	B-Protocol
,	O
and	O
robust	O
burst	O
modems	B-Application
.	O
</s>
<s>
It	O
uses	O
the	O
fact	O
that	O
all	O
ALE	O
messages	O
use	O
forward	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
(	O
FEC	O
)	O
redundancy	B-General_Concept
.	O
</s>
<s>
This	O
information	O
is	O
coupled	O
with	O
the	O
ALE	B-General_Concept
address	I-General_Concept
of	O
the	O
sending	O
node	O
and	O
the	O
channel	O
the	O
message	O
was	O
received	O
on	O
,	O
and	O
stored	O
in	O
the	O
node	O
's	O
Link	O
Quality	O
Analysis	O
(	O
LQA	O
)	O
memory	O
.	O
</s>
<s>
When	O
a	O
call	O
is	O
initiated	O
,	O
the	O
LQA	O
lookup	B-Data_Structure
table	I-Data_Structure
is	O
searched	O
for	O
matches	O
involving	O
the	O
target	O
ALE	B-General_Concept
address	I-General_Concept
and	O
the	O
best	O
historic	O
channel	O
is	O
used	O
to	O
call	O
the	O
target	O
station	O
.	O
</s>
<s>
If	O
further	O
digital	O
communication	O
is	O
desired	O
,	O
it	O
may	O
take	O
place	O
via	O
external	O
data	O
modems	B-Application
or	O
via	O
optional	O
modems	B-Application
built	O
into	O
the	O
ALE	O
terminal	O
.	O
</s>
<s>
This	O
unusual	O
usage	O
of	O
FEC	O
redundancy	B-General_Concept
is	O
the	O
primary	O
innovation	O
that	O
differentiates	O
ALE	O
from	O
previous	O
selective	O
calling	O
systems	O
which	O
either	O
decoded	O
a	O
call	O
or	O
failed	O
to	O
decode	O
due	O
to	O
noise	O
or	O
interference	O
.	O
</s>
<s>
The	O
redundancy-based	O
scoring	O
inherent	O
in	O
ALE	O
thus	O
allows	O
for	O
selecting	O
the	O
"	O
best	O
"	O
available	O
channel	O
and	O
(	O
in	O
more	O
advanced	O
ALE	O
nodes	O
)	O
using	O
all	O
decoded	O
traffic	O
over	O
some	O
time	O
window	O
to	O
sort	O
channels	O
into	O
a	O
list	O
of	O
decreasing	O
probability-to-contact	O
,	O
significantly	O
reducing	O
co-channel	O
interference	O
to	O
other	O
users	O
as	O
well	O
as	O
dramatically	O
decreasing	O
the	O
time	O
needed	O
to	O
successfully	O
link	O
with	O
the	O
target	O
node	O
.	O
</s>
<s>
Techniques	O
used	O
in	O
the	O
ALE	O
standard	O
include	O
automatic	O
signaling	O
,	O
automatic	O
station	O
identification	O
(	O
sounding	O
)	O
,	O
polling	B-General_Concept
,	O
message	O
store-and-forward	B-Protocol
,	O
linking	O
protection	O
and	O
anti-spoofing	O
to	O
prevent	O
hostile	O
denial	O
of	O
service	O
by	O
ending	O
the	O
channel	O
scanning	O
process	O
.	O
</s>
<s>
Optional	O
ALE	O
functions	O
include	O
polling	B-General_Concept
and	O
the	O
exchange	O
of	O
orderwire	O
commands	O
and	O
messages	O
.	O
</s>
<s>
ALE	O
evolved	O
from	O
older	O
HF	B-Algorithm
radio	I-Algorithm
selective	O
calling	O
technology	O
.	O
</s>
<s>
Over	O
time	O
,	O
demand	O
for	O
ALE	O
capabilities	O
spread	O
and	O
by	O
the	O
late	O
1990s	O
,	O
most	O
new	O
government	O
HF	B-Algorithm
radios	I-Algorithm
purchased	O
were	O
designed	O
to	O
meet	O
at	O
least	O
the	O
minimum	O
ALE	O
interoperability	O
standard	O
,	O
making	O
them	O
eligible	O
for	O
use	O
with	O
standard	O
ALE	O
node	O
gear	O
.	O
</s>
<s>
As	O
the	O
standards	O
were	O
adopted	O
by	O
other	O
governments	O
worldwide	O
,	O
more	O
manufacturers	O
produced	O
competitively	O
priced	O
HF	B-Algorithm
radios	I-Algorithm
to	O
meet	O
this	O
demand	O
.	O
</s>
<s>
By	O
the	O
year	O
2000	O
,	O
there	O
were	O
enough	O
civilian	O
and	O
government	O
organizations	O
worldwide	O
using	O
ALE	O
that	O
it	O
became	O
a	O
de	O
facto	O
HF	B-Algorithm
interoperability	O
standard	O
for	O
situations	O
where	O
a	O
priori	O
channel	O
and	O
address	B-General_Concept
coordination	O
is	O
possible	O
.	O
</s>
<s>
By	O
enabling	O
a	O
station	O
to	O
participate	O
nearly	O
simultaneously	O
in	O
many	O
different	O
HF	B-Algorithm
networks	O
,	O
ALE	O
allows	O
for	O
convenient	O
cross-organization	O
message	O
passing	O
and	O
monitoring	O
without	O
requiring	O
dedicated	O
separate	O
equipment	O
and	O
operators	O
for	O
each	O
partner	O
organization	O
.	O
</s>
<s>
The	O
more	O
common	O
2G	O
ALE	O
signal	O
waveform	O
is	O
designed	O
to	O
be	O
compatible	O
with	O
standard	O
3kHz	O
SSB	B-Device
narrowband	O
voice	O
channel	O
transceivers	O
.	O
</s>
<s>
The	O
modulation	O
method	O
is	O
8ary	O
Frequency	O
Shift	O
Keying	O
or	O
8FSK	O
,	O
also	O
sometimes	O
called	O
Multi	O
Frequency	O
Shift	O
Keying	O
MFSK	B-Device
,	O
with	O
eight	O
orthogonal	O
tones	O
between	O
750	O
and	O
2500Hz	O
.	O
</s>
<s>
The	O
received	O
signal	O
is	O
usually	O
decoded	O
using	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
techniques	O
that	O
are	O
capable	O
of	O
recovering	O
the	O
8FSK	O
signal	O
at	O
a	O
negative	O
decibel	O
signal-to-noise	O
ratio	O
(	O
i.e.	O
,	O
the	O
signal	O
may	O
be	O
recovered	O
even	O
when	O
it	O
is	O
below	O
the	O
noise	O
level	O
)	O
.	O
</s>
<s>
The	O
over-the-air	O
layers	O
of	O
the	O
protocol	O
involve	O
the	O
use	O
of	O
forward	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
,	O
redundancy	B-General_Concept
,	O
and	O
handshaking	B-Protocol
transponding	O
similar	O
to	O
those	O
used	O
in	O
ARQ	B-Error_Name
techniques	O
.	O
</s>
<s>
The	O
3G	O
ALE	O
modem	B-Application
signal	O
also	O
provides	O
better	O
robustness	B-Application
and	O
can	O
work	O
in	O
channel	O
conditions	O
that	O
are	O
less	O
favorable	O
than	O
2G	O
ALE	O
.	O
</s>
<s>
Although	O
3G	O
ALE	O
is	O
more	O
reliable	O
and	O
has	O
significantly	O
enhanced	O
channel-time	O
efficiency	O
,	O
the	O
existence	O
of	O
a	O
large	O
installed	B-Operating_System
base	I-Operating_System
of	O
2G	O
ALE	O
radio	O
systems	O
and	O
the	O
wide	O
availability	O
of	O
moderately	O
priced	O
(	O
often	O
military	O
surplus	O
)	O
equipment	O
,	O
has	O
made	O
2G	O
the	O
baseline	O
standard	O
for	O
global	O
interoperability	O
.	O
</s>
<s>
Largely	O
due	O
to	O
the	O
ubiquity	O
of	O
2G	O
ALE	O
,	O
it	O
became	O
the	O
primary	O
method	O
for	O
providing	O
interoperability	O
on	O
HF	B-Algorithm
between	O
governmental	O
and	O
non-governmental	O
disaster	O
relief	O
and	O
emergency	O
communications	O
entities	O
,	O
and	O
amateur	O
radio	O
volunteers	O
.	O
</s>
<s>
Nearly	O
every	O
major	O
HF	B-Algorithm
radio	I-Algorithm
manufacturer	O
in	O
the	O
world	O
builds	O
ALE	O
radios	O
to	O
the	O
2G	O
standard	O
to	O
meet	O
the	O
high	O
demand	O
that	O
new	O
installations	O
of	O
HF	B-Algorithm
radio	I-Algorithm
systems	O
conform	O
to	O
this	O
standard	O
protocol	O
.	O
</s>
<s>
Disparate	O
entities	O
that	O
historically	O
used	O
incompatible	O
radio	O
methods	O
were	O
then	O
able	O
to	O
call	O
and	O
converse	O
with	O
each	O
other	O
using	O
the	O
common	O
2G	O
ALE	O
platform	B-Device
.	O
</s>
<s>
ALE	O
radio	O
communication	O
systems	O
for	O
both	O
HF	B-Algorithm
regional	O
area	O
networks	O
and	O
HF	B-Algorithm
interoperability	O
communications	O
are	O
in	O
service	O
among	O
emergency	O
and	O
disaster	O
relief	O
agencies	O
as	O
well	O
as	O
military	O
and	O
guard	O
forces	O
.	O
</s>
<s>
The	O
increasing	O
need	O
for	O
instant	O
connectivity	O
for	O
logistical	O
and	O
tactical	O
disaster	O
relief	O
response	O
communications	O
,	O
such	O
as	O
the	O
2004	O
Indian	O
Ocean	O
earthquake	O
tsunami	B-Application
led	O
to	O
ITU	O
actions	O
of	O
encouragement	O
to	O
countries	O
around	O
the	O
world	O
toward	O
loosening	O
restrictions	O
on	O
such	O
communications	O
and	O
equipment	O
border	O
transit	O
during	O
catastrophic	O
disasters	O
.	O
</s>
<s>
The	O
need	O
for	O
interoperability	O
on	O
HF	B-Algorithm
led	O
to	O
the	O
adoption	O
of	O
open	O
networks	O
by	O
hams	O
.	O
</s>
<s>
Each	O
amateur	O
radio	O
ALE	O
station	O
uses	O
the	O
operator	O
's	O
call	O
sign	O
as	O
the	O
address	B-General_Concept
,	O
also	O
known	O
as	O
the	O
ALE	B-General_Concept
Address	I-General_Concept
,	O
in	O
the	O
ALE	O
radio	O
controller	O
.	O
</s>
<s>
The	O
lowest	O
common	O
denominator	O
technique	O
enables	O
any	O
manufacturer	O
's	O
ALE	O
radios	O
or	O
software	O
to	O
be	O
used	O
for	O
HF	B-Algorithm
interoperability	O
communications	O
and	O
networking	O
.	O
</s>
<s>
In	O
this	O
technique	O
,	O
active	O
ALE	O
frequencies	O
include	O
pseudorandom	B-Error_Name
periodic	O
polite	O
station	O
identification	O
,	O
while	O
passive	O
ALE	O
frequencies	O
are	O
silently	O
scanned	O
for	O
selective	O
calling	O
.	O
</s>
<s>
Hot	B-General_Concept
standby	I-General_Concept
ALE	O
nets	O
are	O
in	O
constant	O
operation	O
24/7/365	O
for	O
International	O
Emergency	O
and	O
Disaster	O
Relief	O
communications	O
.	O
</s>
<s>
International	O
amateur	O
radio	O
ALE	O
High	B-Algorithm
Frequency	I-Algorithm
channels	O
are	O
frequency	O
coordinated	O
with	O
all	O
Regions	O
of	O
the	O
(	O
IARU	O
entity	O
of	O
ITU	O
)	O
,	O
for	O
international	O
,	O
regional	O
,	O
national	O
,	O
and	O
local	O
use	O
in	O
the	O
Amateur	O
Radio	O
Service	O
.	O
</s>
<s>
See	O
HFLINK	O
for	O
more	O
information	O
about	O
Amateur	O
Radio	O
Service	O
ALE	O
Automatic	B-Device
Link	I-Device
Establishment	I-Device
.	O
</s>
<s>
Automatic	B-Device
Link	I-Device
Establishment	I-Device
ALE	O
channel	O
frequencies	O
in	O
the	O
Amateur	O
Radio	O
Service	O
are	O
internationally	O
coordinated	O
with	O
selective	O
calling	O
Selcall	O
channels	O
for	O
interoperability	O
purposes	O
.	O
</s>
<s>
Net	O
is	O
the	O
ALE	O
net	O
address	B-General_Concept
or	O
Selcall	O
net	O
name	O
.	O
</s>
