<s>
In	O
computer	O
networking	O
,	O
a	O
network	B-General_Concept
service	I-General_Concept
is	O
an	O
application	O
running	O
at	O
the	O
network	O
application	B-Application
layer	I-Application
and	O
above	O
,	O
that	O
provides	O
data	O
storage	O
,	O
manipulation	O
,	O
presentation	O
,	O
communication	O
or	O
other	O
capability	O
which	O
is	O
often	O
implemented	O
using	O
a	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
or	O
peer-to-peer	O
architecture	O
based	O
on	O
application	B-Application
layer	I-Application
network	O
protocols	O
.	O
</s>
<s>
Each	O
service	O
is	O
usually	O
provided	O
by	O
a	O
server	B-Application
component	I-Application
running	O
on	O
one	O
or	O
more	O
computers	O
(	O
often	O
a	O
dedicated	O
server	B-Application
computer	I-Application
offering	O
multiple	O
services	O
)	O
and	O
accessed	O
via	O
a	O
network	O
by	O
client	B-Protocol
components	I-Protocol
running	O
on	O
other	O
devices	O
.	O
</s>
<s>
Clients	O
and	O
servers	O
will	O
often	O
have	O
a	O
user	B-Application
interface	I-Application
,	O
and	O
sometimes	O
other	O
hardware	O
associated	O
with	O
it	O
.	O
</s>
<s>
Examples	O
are	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
which	O
translates	O
domain	O
names	O
to	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
addresses	O
and	O
the	O
Dynamic	B-Protocol
Host	I-Protocol
Configuration	I-Protocol
Protocol	I-Protocol
(	O
DHCP	B-Protocol
)	O
to	O
assign	O
networking	O
configuration	O
information	O
to	O
network	O
hosts	O
.	O
</s>
<s>
Authentication	B-Application
servers	I-Application
identify	O
and	O
authenticate	O
users	O
,	O
provide	O
user	O
account	O
profiles	O
,	O
and	O
may	O
log	O
usage	O
statistics	O
.	O
</s>
<s>
E-mail	O
,	O
printing	B-Application
and	O
distributed	O
(	O
network	O
)	O
file	O
system	O
services	O
are	O
common	O
services	O
on	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
.	O
</s>
<s>
Other	O
network	B-General_Concept
services	I-General_Concept
include	O
:	O
</s>
<s>
In	O
computer	B-Operating_System
network	I-Operating_System
programming	I-Operating_System
,	O
the	O
application	B-Application
layer	I-Application
is	O
an	O
abstraction	B-Architecture
layer	I-Architecture
reserved	O
for	O
communications	O
protocols	O
and	O
methods	O
designed	O
for	O
process-to-process	O
communications	O
across	O
an	O
IP	B-Protocol
network	I-Protocol
.	O
</s>
<s>
Application	B-Application
layer	I-Application
protocols	O
use	O
the	O
underlying	O
transport	B-Architecture
layer	I-Architecture
protocols	O
to	O
establish	O
host-to-host	O
connections	O
for	O
network	B-General_Concept
services	I-General_Concept
.	O
</s>
<s>
UDP	O
lacks	O
built-in	O
network	B-Protocol
congestion	I-Protocol
avoidance	O
and	O
the	O
protocols	O
that	O
use	O
it	O
must	O
be	O
extremely	O
carefully	O
designed	O
to	O
prevent	O
network	O
collapse	O
.	O
</s>
