<s>
A	O
Directory	B-Application
System	I-Application
Agent	I-Application
(	O
DSA	O
)	O
is	O
the	O
element	O
of	O
an	O
X.500	B-Protocol
directory	I-Protocol
service	O
that	O
provides	O
User	B-Protocol
Agents	I-Protocol
with	O
access	O
to	O
a	O
portion	O
of	O
the	O
directory	O
(	O
usually	O
the	O
portion	O
associated	O
with	O
a	O
single	O
Organizational	B-Protocol
Unit	I-Protocol
)	O
.	O
</s>
<s>
X.500	B-Protocol
is	O
an	O
international	O
standard	O
developed	O
by	O
the	O
International	O
Organization	O
for	O
Standardization	O
(	O
ISO	O
)	O
and	O
the	O
International	O
Telecommunication	O
Union	O
(	O
ITU-T	O
)	O
.	O
</s>
<s>
The	O
model	O
and	O
function	O
of	O
a	O
directory	B-Application
system	I-Application
agent	I-Application
are	O
specified	O
in	O
.	O
</s>
<s>
In	O
Microsoft	O
's	O
Active	B-Protocol
Directory	I-Protocol
the	O
DSA	O
is	O
a	O
collection	O
of	O
servers	O
and	O
daemon	B-Operating_System
processes	O
that	O
run	O
on	O
Windows	B-Device
Server	I-Device
systems	O
that	O
provide	O
various	O
means	O
for	O
clients	O
to	O
access	O
the	O
Active	B-Protocol
Directory	I-Protocol
data	O
store	O
.	O
</s>
<s>
Clients	O
connect	O
to	O
an	O
Active	B-Protocol
Directory	I-Protocol
DSA	O
using	O
various	O
communications	O
protocols	O
:	O
</s>
