2).
Since online charging takes place in real time (services are paid for prior to service
delivery), there is no need for CDRs. The account balance is charged prior to the service
being delivered, which means that the ABMF function must not only verify the
account balance but make sure that the account is decremented for the service about
to be delivered.
Figure 7.2 Online charging architecture
Circuit-switched network
element (CS-NE)
Service network element
Service network element
SIP application server (AS)
Media resource function
controller (MRFC)
Media gateway controller
function (MGCF)
Border gateway controller
function (BGCF)
Proxy ??“ CSCF (P-CSCF)
Interrogating - CSCF (I-CSCF)
Serving ??“ CSCF (S-CSCF)
Wireless LAN (WLAN)
Serving GPRS support
node (SGSN)
Gateway GPRS support
node (GGSN)
Traffic plane function (TPF)
Charging rules function
(CRF)
Application function (AF)
Online charging system (OCS)
C
T
F
O
C
F
ABMF
RF
166 Chapter 7
The CTF provides two functions within a network element. The first function is accounting
metrics collection (or usage measurements) of services used at that specific
network element, while the second function is forwarding of the usage measurements.
The accounting metrics collection can be distributed throughout the network, so if a
session is supported by multiple devices, each of those devices is capable of collecting
usage data and forwarding that data to the forwarding function.
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