This is seen in all networks today.
Figure 7.3 Offline 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)
C
D
F
C
G
F
Billing domain
C
T
F
Online and Offline Charging in the IMS 169
The formats of the CDRs created by the charging data function (CDF) are
defined in 3GPP TS 32.250 (for circuit-switched networks) and 3GPP TS 32.251
(for packet-switched networks). Hopefully we will not see the same drifting from the
standards as seen in previous implementations. This only increases cost to deploy new
technology and increases cost to applications.
Standardization of the CDRs also allows operators to choose among many different
vendors for back-office systems that depend on the CDRs for data. The back-office and
operational support systems (OSS/BSS) are crucial to managing a network, and they
need standard data formats to be effective.
The CDF then forwards CDRs to the charging gateway function (CGF), which in
turn interfaces to the billing system.
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