<s>
In	O
computing	O
,	O
Advanced	O
Program	O
to	O
Program	O
Communication	O
or	O
APPC	O
is	O
a	O
protocol	O
which	O
computer	B-Application
programs	I-Application
can	O
use	O
to	O
communicate	O
over	O
a	O
network	B-Architecture
.	O
</s>
<s>
APPC	O
is	O
at	O
the	O
application	B-Application
layer	I-Application
in	O
the	O
OSI	O
model	O
,	O
it	O
enables	O
communications	O
between	O
programs	O
on	O
different	O
computers	O
,	O
from	O
portables	O
and	O
workstations	O
to	O
midrange	O
and	O
host	O
computers	O
.	O
</s>
<s>
APPC	O
was	O
developed	O
in	O
1982	O
as	O
a	O
component	O
of	O
IBM	O
's	O
Systems	B-Architecture
Network	I-Architecture
Architecture	I-Architecture
(	O
SNA	B-Architecture
)	O
.	O
</s>
<s>
Several	O
APIs	B-General_Concept
were	O
developed	O
for	O
programming	O
languages	O
such	O
as	O
COBOL	B-Application
,	O
PL/I	B-Language
,	O
C	B-Language
or	O
REXX	B-Language
.	O
</s>
<s>
APPC	O
serves	O
as	O
a	O
translator	O
between	O
application	O
programs	O
and	O
the	O
network	B-Architecture
.	O
</s>
<s>
When	O
an	O
application	O
on	O
your	O
computer	O
passes	O
information	O
to	O
the	O
APPC	O
software	O
,	O
APPC	O
translates	O
the	O
information	O
and	O
passes	O
it	O
to	O
a	O
network	B-Architecture
interface	O
,	O
such	O
as	O
a	O
LAN	O
adapter	O
card	O
.	O
</s>
<s>
The	O
information	O
travels	O
across	O
the	O
network	B-Architecture
to	O
another	O
computer	O
,	O
where	O
the	O
APPC	O
software	O
receives	O
the	O
information	O
from	O
the	O
network	B-Architecture
interface	O
.	O
</s>
<s>
APPC	O
is	O
mainly	O
used	O
by	O
IBM	O
installations	O
running	O
operating	O
systems	O
such	O
z/OS	B-Application
(	O
formerly	O
MVS	O
then	O
OS/390	O
)	O
,	O
z/VM	B-Application
(	O
formerly	O
VM/CMS	O
)	O
,	O
z/TPF	B-Operating_System
,	O
IBM	B-Application
i	I-Application
(	O
formerly	O
OS/400	B-Application
)	O
,	O
OS/2	B-Application
,	O
AIX	B-Application
and	O
z/VSE	B-Application
(	O
formerly	O
DOS/VSE	B-Application
)	O
.	O
</s>
<s>
Microsoft	O
also	O
includes	O
SNA	B-Architecture
support	O
in	O
Microsoft	O
's	O
Host	B-Application
Integration	I-Application
Server	I-Application
.	O
</s>
<s>
Major	O
IBM	O
software	O
products	O
also	O
include	O
support	O
for	O
APPC	O
,	O
including	O
CICS	B-Application
,	O
Db2	B-Application
,	O
CIM	O
and	O
WebSphere	B-Application
MQ	I-Application
.	O
</s>
<s>
Unlike	O
TCP/IP	B-Protocol
,	O
in	O
which	O
both	O
communication	O
partners	O
always	O
possess	O
a	O
clear	O
role	O
(	O
one	O
is	O
always	O
server	B-Operating_System
,	O
and	O
others	O
always	O
the	O
client	O
)	O
,	O
APPC	O
is	O
a	O
peer-to-peer	O
protocol	O
.	O
</s>
<s>
The	O
communication	O
partners	O
in	O
APPC	O
are	O
equal	O
,	O
every	O
application	O
can	O
be	O
both	O
server	B-Operating_System
and	O
client	O
equally	O
.	O
</s>
<s>
Transmission	O
of	O
the	O
data	O
is	O
made	O
then	O
by	O
'	O
data	O
sessions	O
 '	O
,	O
their	O
log	O
modes	O
can	O
be	O
determined	O
in	O
detail	O
from	O
the	O
VTAM	B-Application
administrator	O
(	O
e.g.	O
</s>
<s>
For	O
each	O
such	O
use	O
,	O
an	O
APPC	O
session	O
is	O
created	O
and	O
used	O
in	O
a	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
fashion	O
by	O
the	O
Conversational	O
Communications	O
Manager	O
of	O
Distributed	B-Operating_System
Data	I-Operating_System
Management	I-Operating_System
Architecture	I-Operating_System
(	O
DDM	O
)	O
.	O
</s>
<s>
Message	O
formats	O
and	O
protocols	O
were	O
defined	O
for	O
accessing	O
and	O
managing	O
record-oriented	O
files	O
,	O
stream-oriented	O
files	O
,	O
relational	O
databases	O
(	O
as	O
the	O
base	O
architecture	O
of	O
Distributed	B-Language
Relational	I-Language
Database	I-Language
Architecture	I-Language
(	O
DRDA	B-Language
)	O
)	O
,	O
and	O
other	O
services	O
.	O
</s>
<s>
A	O
variety	O
of	O
DDM	O
and	O
DRDA	B-Language
products	O
were	O
implemented	O
by	O
IBM	O
and	O
other	O
vendors	O
.	O
</s>
<s>
With	O
the	O
increasing	O
prevalence	O
of	O
TCP/IP	B-Protocol
,	O
APPC	O
has	O
declined	O
,	O
although	O
many	O
IBM	O
systems	O
have	O
translators	O
,	O
such	O
as	O
Enterprise	O
Extender	O
(	O
RFC	O
2353	O
)	O
,	O
to	O
allow	O
sending	O
APPC-formatted	O
traffic	O
over	O
IP	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
APPC	O
should	O
not	O
be	O
confused	O
with	O
the	O
similarly	O
named	O
APPN	B-Architecture
(	O
Advanced	B-Architecture
Peer-to-Peer	I-Architecture
Networking	I-Architecture
)	O
.	O
</s>
<s>
By	O
contrast	O
,	O
APPN	B-Architecture
manages	O
communication	O
between	O
machines	O
,	O
including	O
routing	O
,	O
and	O
operates	O
at	O
the	O
transport	O
and	O
network	B-Architecture
layers	O
.	O
</s>
