<s>
The	O
purpose	O
of	O
the	O
diameter	B-Protocol
credit	O
control	O
application	O
is	O
to	O
provide	O
a	O
framework	O
for	O
real-time	O
charging	O
,	O
primarily	O
meant	O
for	O
the	O
communication	O
between	O
gateways/control	O
-points	O
and	O
the	O
back-end	O
account/balance	O
systems	O
(	O
typically	O
an	O
Online	O
Charging	O
System	O
)	O
.	O
</s>
<s>
The	O
diameter	B-Protocol
credit	O
control	O
application	O
does	O
not	O
specify	O
which	O
type	O
units	O
are	O
bought/used	O
and	O
which	O
items	O
are	O
charged	O
.	O
</s>
<s>
Diameter	B-Protocol
credit	O
control	O
also	O
specifies	O
how	O
to	O
handle	O
the	O
fairly	O
complex	O
issue	O
of	O
multiple	O
unit	O
types	O
used/charged	O
against	O
a	O
single	O
user	O
balance	O
.	O
</s>
<s>
In	O
order	O
to	O
support	O
Credit	O
Control	O
via	O
Diameter	B-Protocol
,	O
there	O
are	O
two	O
Diameter	B-Protocol
messages	O
,	O
the	O
CCR	O
(	O
Credit	O
Control	O
Request	O
)	O
and	O
the	O
CCA	O
(	O
Credit	O
Control	O
Answer	O
)	O
.	O
</s>
<s>
The	O
message	O
may	O
also	O
be	O
generated	O
by	O
other	O
diameter	B-Protocol
applications	O
,	O
such	O
as	O
NASREQ	O
(	O
RFC4005	O
)	O
for	O
sessions	O
that	O
are	O
time/usage	O
-limited	O
.	O
</s>
<s>
The	O
Used-Units	O
AVP	B-Application
contains	O
the	O
actual	O
usage	O
)	O
.	O
</s>
<s>
If	O
the	O
subscriber	O
did	O
not	O
terminate	O
the	O
session	O
himself	O
but	O
instead	O
depleted	O
his	O
balance	O
then	O
the	O
server	O
would	O
have	O
responded	O
earlier	O
with	O
reject	O
to	O
an	O
update	O
message	O
,	O
possibly	O
telling	O
the	O
client/control	O
-point	O
to	O
redirect	O
traffic	O
(	O
this	O
normally	O
only	O
makes	O
sense	O
for	O
HTTP/WAP	O
traffic	O
)	O
.	O
</s>
<s>
0	O
–	O
1	O
Zero	O
or	O
one	O
instance	O
of	O
the	O
AVP	B-Application
MAY	O
be	O
present	O
in	O
the	O
message	O
.	O
</s>
<s>
-	O
Diameter	B-Protocol
Network	O
Access	O
Server	O
Application	O
.	O
</s>
<s>
-	O
Diameter	B-Protocol
Credit-Control	I-Protocol
Application	I-Protocol
.	O
</s>
<s>
-	O
3GPP	O
Telecommunication	O
management	O
-	O
Charging	O
management	O
-	O
Diameter	B-Protocol
charging	O
applications	O
.	O
</s>
