<s>
mod_qos	O
is	O
a	O
quality	O
of	O
service	O
(	O
QoS	O
)	O
module	O
for	O
the	O
Apache	B-Application
HTTP	I-Application
server	I-Application
implementing	O
control	O
mechanisms	O
that	O
can	O
provide	O
different	O
priority	O
to	O
different	O
requests	O
.	O
</s>
<s>
A	O
web	B-Application
server	I-Application
can	O
only	O
serve	O
a	O
limited	O
number	O
of	O
concurrent	O
requests	O
.	O
</s>
<s>
It	O
is	O
used	O
to	O
define	O
different	O
priorities	O
to	O
different	O
pages	O
or	O
applications	O
within	O
a	O
web	B-Application
server	I-Application
.	O
</s>
<s>
Connection	O
level	O
control	O
:	O
mod_qos	O
controls	O
the	O
number	O
of	O
TCP	O
connections	O
to	O
the	O
web	B-Application
server	I-Application
.	O
</s>
<s>
Bandwidth	O
level	O
control	O
:	O
throttles	O
requests/responses	O
to	O
certain	O
URL	O
on	O
the	O
web	B-Application
server	I-Application
.	O
</s>
<s>
The	O
module	O
can	O
be	O
useful	O
when	O
used	O
in	O
a	O
reverse	B-General_Concept
proxy	I-General_Concept
in	O
order	O
to	O
divide	O
up	O
resources	O
to	O
different	O
webserver	B-Application
.	O
</s>
<s>
The	O
first	O
use	O
case	O
shows	O
how	O
mod_qos	O
can	O
avoid	O
service	O
outage	O
of	O
a	O
web	B-Application
server	I-Application
due	O
to	O
slow	O
responses	O
of	O
a	O
single	O
application	O
.	O
</s>
<s>
Due	O
to	O
many	O
waiting	O
requests	O
,	O
the	O
web	B-Application
server	I-Application
runs	O
out	O
of	O
free	O
TCP	O
connections	O
and	O
is	O
not	O
able	O
to	O
process	O
other	O
requests	O
to	O
application	O
/aaa	O
or	O
/bbb	O
.	O
</s>
<s>
This	O
accelerates	O
access	O
to	O
the	O
web	B-Application
server	I-Application
due	O
to	O
less	O
and	O
optimised	O
network	O
traffic	O
.	O
</s>
<s>
A	O
single	O
client	O
may	O
open	O
many	O
simultaneous	O
TCP	O
connections	O
in	O
order	O
to	O
download	O
different	O
content	O
from	O
the	O
web	B-Application
server	I-Application
.	O
</s>
<s>
mod_qos	O
may	O
help	O
to	O
protect	O
an	O
Apache	B-Application
web	I-Application
server	I-Application
against	O
low-bandwidth	O
DoS	O
attacks	O
by	O
enforcing	O
a	O
minimum	O
upload/download	O
throughput	O
a	O
client	O
must	O
generate	O
.	O
</s>
<s>
The	O
initial	O
release	O
of	O
mod_qos	O
was	O
created	O
in	O
May	O
2007	O
and	O
published	O
on	O
SourceForge.net	B-Application
as	O
an	O
open	O
source	O
software	O
project	O
.	O
</s>
<s>
It	O
was	O
able	O
to	O
limit	O
the	O
number	O
of	O
concurrent	O
HTTP	O
requests	O
for	O
specified	O
resources	O
(	O
path	O
portion	O
of	O
request	O
URLs	O
)	O
on	O
the	O
web	B-Application
server	I-Application
.	O
</s>
<s>
More	O
features	O
were	O
added	O
and	O
some	O
of	O
them	O
were	O
useful	O
to	O
protect	O
Apache	B-Application
servers	I-Application
against	O
DoS	O
attacks	O
.	O
</s>
<s>
In	O
2012	O
,	O
mod_qos	O
was	O
included	O
to	O
the	O
Ubuntu	B-Operating_System
Linux	I-Operating_System
distribution	I-Operating_System
.	O
</s>
