<s>
The	O
plumber	B-Application
,	O
in	O
the	O
Plan	B-Operating_System
9	I-Operating_System
from	I-Operating_System
Bell	I-Operating_System
Labs	I-Operating_System
and	O
Inferno	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
is	O
a	O
mechanism	O
for	O
reliable	O
uni	B-Protocol
-	O
or	O
multicast	O
inter-process	B-Operating_System
communication	I-Operating_System
of	O
formatted	O
textual	O
messages	O
.	O
</s>
<s>
It	O
uses	O
the	O
Plan	B-Operating_System
9	I-Operating_System
network	O
file	O
protocol	O
,	O
9P	B-Operating_System
,	O
rather	O
than	O
a	O
special-purpose	O
IPC	O
mechanism	O
.	O
</s>
<s>
The	O
plumber	B-Application
is	O
the	O
9P	B-Operating_System
file	O
server	O
that	O
provides	O
this	O
service	O
.	O
</s>
<s>
Since	O
the	O
messages	O
are	O
9P	B-Operating_System
,	O
they	O
are	O
network	O
transparent	O
.	O
</s>
