<s>
Android	B-Application
Cloud	I-Application
to	I-Application
Device	I-Application
Messaging	I-Application
(	O
commonly	O
referred	O
to	O
as	O
Cloud	O
to	O
Device	O
Messaging	O
)	O
,	O
or	O
C2DM	B-Application
,	O
is	O
a	O
defunct	O
mobile	O
notification	B-General_Concept
service	I-General_Concept
that	O
was	O
developed	O
by	O
Google	B-Application
and	O
replaced	O
by	O
the	B-Application
Google	I-Application
Cloud	O
Messaging	O
service	O
.	O
</s>
<s>
It	O
enabled	O
developers	O
to	O
send	O
data	O
from	O
servers	O
to	O
Android	B-Application
applications	I-Application
and	O
Chrome	B-Application
extensions	O
.	O
</s>
<s>
C2DM	B-Application
originally	O
launched	O
in	O
2010	O
and	O
was	O
available	O
beginning	O
with	O
version	O
2.2	O
of	O
Android	B-Application
.	O
</s>
<s>
On	O
June	O
27	O
,	O
2012	O
,	O
Google	B-Application
unveiled	O
the	B-Application
Google	I-Application
Cloud	O
Messaging	O
service	O
aimed	O
at	O
replacing	O
C2DM	B-Application
,	O
citing	O
improvements	O
to	O
authentication	O
and	O
delivery	O
,	O
new	O
API	O
endpoints	O
and	O
messaging	O
parameters	O
,	O
and	O
the	O
removal	O
of	O
API	O
rate	O
limits	O
and	O
maximum	O
message	O
sizes	O
.	O
</s>
<s>
Google	B-Application
announced	O
official	O
deprecation	O
of	O
the	O
C2DM	B-Application
service	O
in	O
August	O
2012	O
,	O
and	O
released	O
documentation	O
to	O
assist	O
developers	O
with	O
migrating	O
to	O
the	O
new	O
service	O
.	O
</s>
<s>
The	O
C2DM	B-Application
service	O
was	O
discontinued	O
for	O
existing	O
applications	O
and	O
completely	O
shut	O
down	O
on	O
October	O
20	O
,	O
2015	O
.	O
</s>
<s>
The	O
C2DM	B-Application
service	O
consisted	O
of	O
sub-services	O
and	O
interfaces	O
necessary	O
with	O
maintaining	O
security	O
and	O
reliability	O
.	O
</s>
<s>
When	O
an	O
application	O
registered	O
for	O
C2DM	B-Application
messages	O
and	O
data	O
,	O
it	O
received	O
a	O
C2DM	B-Application
Registration	O
ID	O
from	O
the	O
service	O
.	O
</s>
<s>
Upon	O
sending	O
a	O
data	O
or	O
push	O
request	O
,	O
the	O
server	O
sent	O
an	O
authentication	O
request	O
and	O
the	O
C2DM	B-Application
Registration	O
ID	O
of	O
the	O
device	O
to	O
the	O
C2DM	B-Application
authentication	O
service	O
,	O
which	O
responded	O
with	O
an	O
authentication	O
token	O
upon	O
success	O
.	O
</s>
<s>
When	O
the	O
device	O
received	O
the	O
information	O
from	O
the	O
C2DM	B-Application
,	O
the	O
request	O
was	O
removed	O
from	O
the	O
C2DM	B-Application
queue	O
.	O
</s>
<s>
Shortly	O
after	O
announcing	O
the	B-Application
Google	I-Application
Cloud	O
Messaging	O
service	O
,	O
Google	B-Application
published	O
documentation	O
to	O
guide	O
application	O
developers	O
with	O
migrating	O
from	O
the	O
C2DM	B-Application
and	O
onto	O
the	O
new	O
service	O
.	O
</s>
<s>
Migrating	O
to	O
the	O
service	O
required	O
SDK	O
and	O
code	O
changes	O
,	O
as	O
well	O
as	O
a	O
release	O
of	O
an	O
application	O
update	O
to	O
the	O
publish	O
repository	O
(	O
such	O
as	O
Google	B-Application
Play	I-Application
)	O
for	O
downloading	O
and	O
updating	O
.	O
</s>
<s>
The	O
C2DM	B-Application
and	O
the	B-Application
Google	I-Application
Cloud	O
Messaging	O
service	O
were	O
not	O
interoperable	O
between	O
each	O
other	O
;	O
you	O
could	O
not	O
send	O
data	O
requests	O
using	O
one	O
service	O
to	O
be	O
received	O
and	O
processed	O
on	O
the	O
client	O
app	O
using	O
the	O
other	O
.	O
</s>
