9.2.1 WCDMA PS Domain Billing System Architecture
Billing system of PS domain consists of
three parts: SGSN/GGSN billing module, CG and billing center. There is a
standard Ga interface with GTP’ protocol between SGSN/GGSN and CG. Between CG
and billing center, bill data are transported with FTP/FTAM file transporting
protocol.
The functions of each part are described as
follows:
SGSN and GGSN: Generating billing data.
CGF:
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Collecting the billing data of
SGSN and GGSN.
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Saving for a long time and
executing some pre-processing work, such as integrating and sorting.
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Transporting the collected
billing data to the billing center.
Billing System (billing
center) : Processing billing data and generating final bill.
Note: In Ga interface, the
billing data is called CDR. CDR that is Call Detail Record.
9.2.2 Billing Data Generated by GSN
1. Billing data
There are 5 types of CDRs generated in 3G billing:
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M-CDR: Generated by SGSN, used
for recording billing information of mobility management for mobile phone. It
can be configured whether to generate this bill
or not, not required normally.
or not, not required normally.
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S-SMO-CDR: Generated by SGSN,
used for recording billing information of SM origination.
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S-SMT-CDR: Generated by SGSN,
used for recording billing information of SM termination.
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S-CDR: Generated by SGSN.
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G-CDR: Generated by GGSN.
As for the same PDP course, there are 2
types of CDRs generated, S-CDR and G-CDR. Billing center usually calculates the
final charge according to G-CDR, while S-CDR is mainly used for statistics.
CDR generated in SGSN and GGSN mainly
records the following information:
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Radio resource utilization
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Duration
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GPRS resource utilization
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Originator and terminator
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External data network
utilization
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Mobile terminal location.
2. Integration of partial CDRs
One PDP context may be corresponding to
multiple partial CDRs, which are generated because of:
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Data amount limitation
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Time limitation
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Changed billing condition (such
as tariff change).
Because in the bill finally sent to
subscriber, there is only one bill in one PDP context, all partial CDRs in one
PDP context must be integrated. Integration of partial CDRs is carried out in 2
steps: The integration in the first step is carried out by CGF. This can reduce
the requirement of bandwidth between CGF and billing center and alleviate the
processing operation of billing center. For this reason or that, the
integration in this step may be incomplete. The second step is carried out by
billing center, where those CDRs that are not integrated completely in CGF will
be integrated, resulting in final CDRs.
As for each PDP context, GGSN generates one
exclusive C-ID. According to C-ID+GGSN address, it is possible to know whether two
partial CDRs belong to the same PDP context.
As for G-CDR, all partial CDRs with the
same C-ID+GGSN address must be integrated.
As for S-CDR, all partial CDRs
with the same C-ID+GGSN address and +SGSN address must be integrated.
9.2.3 CGF
CGF offers a mechanism to send the billing
information generated by GGSN and SGSN to designated billing center. CGF is an
abstract functional concept, and CG is a specific implementation of CGF. The
specific implementation of CG differs with manufacturers.
CGF must offer the following functions:
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Collecting CDR from SGSN and
GGSN
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Providing long-time reliable storage
of CDR
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Transporting CDR to billing
center.
In addition, to reduce the transmission
amount between CGF and billing center, CGF should provide some integration
function of partial CDRs to minimize the amount of CDRs transmitted to billing
center, thus lightening the bandwidth requirement for the billing center.
CGF must offer high degree
of reliability and redundancy. One GSN should be corresponding to multiple CGFs
in different levels of priority. When CGF in higher priority can not process
the communication with GSN, GSN will redirect it to CGF in lower priority.
9.2.4 Billing Center
Billing center has the following main
functions:
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Collecting the CDRs on CGF
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Figuring out charge according
to bill
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Fully Integrating CDRs
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Proofreading bills.
9.2.5 GTP' Protocol
GTP' protocol is a communication protocol
between GSN and CGF and between different CGFs. It is an application layer
protocol. The bottom protocol stack adopts UDP/TCP and IP.
The major functions of GTP' protocol are as
follows:
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Transporting CDRs from GSN to
CGF
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Redirecting CDRs to another CGF
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Detecting the communication
failure between CGF and GSN
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Recommending another available
CGF to GSN in case of failure in one CGF
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Preventing duplicate CDRs.
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