chapter 9 wcdma billing system

Basic Principles of WCDMA System WCDMA Billing System

2004-08-30 Confidential Information of Huawei. No Spreading without Permission

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Chapter 9 WCDMA Billing System

In a telecomm operating network, as subscribers are offered service, service billing is accompanied. Essentially, as a measure of the network resources used by subscribers, billing is classified into Circuit Switched (CS) domain billing and Packet Service (PS) domain billing. CS domain adopts circuit switching, so call duration becomes the primary factor of billing. PS domain data works in packet transmission, so traffic is the primary factor of billing, but time is not excluded. This chapter mainly introduces the billing principles of CS domain and PS domain, including the billing architecture of Huawei core network, bill generation mechanism and processing course.

9.1 WCDMA CS Domain Billing Principles

9.1.1 WCDMA CS Domain Billing Architecture

The billing system of WCDMA system CS domain is consistent with that of GSM system, that is, the billing data are both generated by MSC/MSC Server and directly transported to billing center. Therefore, in view of the architecture, the billing system of CS domain consists of billing module of MSC/MSC Server and billing center. Between the billing module and billing center, bill data are transported with FTP/FTAM file transporting protocol.

Because no specific interface parameter is prescribed for MSC/MSC Server billing module in the protocol, the interface between MSC/MSC Server host system and billing module is an internal interface, and the implementation of the billing module is also diversified. As an example, the implementation of billing module in Huawei MSC/MSC Server is described below.



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Figure 9-1 WCDMA CS domain billing architecture

MSC/MSC Server billing system mainly consists of host modules and Bill Administration Unit (BAU). Figure 9-1 shows the CS domain billing architecture.

Host system: The bill information is generated from the host system, and firstly buffered in the bill pool of host. The original bills in the bill pool are, in the form of packet, continuously transported to BAU with TCP/IP.

Bill Administration Unit (BAU): BAU, the processing core of MSC/MSC Server billing system, is a dual-system hot backup system. Connected to the host through local area network (LAN) and to billing center through wide area network (WAN), BAU provides FTP/FTAM interface for billing center to support Server/Client in FTP and Responder in FTAM, to transport bills to billing center.

BAU functions: After saving the original bills received from the host system, it carries out sorting and format conversion for the original bills to generate the final bill. BAU saves the final bill and transports it to billing center. Specifically:

Saving original bills: After receiving the bill packets from the host, unpacking and validating the packets, BAU saves the received original bills in hard disk, then sends confirmation message to the host and makes the corresponding log record, and finally carries out sorting and format conversion for the original bills.

Sorting bills: It means classifying bills according to a domain, to process them in different flows and save them in different physical paths. All data domains in bills can be used as the criterion for sorting.

Bill format conversion: The format conversion on BAU involves choosing bill domain, changing the two-digit chronology into four-digit chronology, and converting into specified text format.

Saving final bill: After sorting and format conversion on the original bills, BAU saves the final bills in different directories according to their classification.

Billing center: Collecting and processing final CDRs, and generating final subscriber bills based on tariffs.



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9.1.2 Billing Data Generated by MSC/MSC Server

1. Bill type

MSC/MSC Server can be used as VMSC, TMSC, GMSC and SSP. Different calls may have different bill types. The major bill types are as follows:

Mobile calling bill: A bill generated when a local mobile subscriber initiates a call. Mobile called bill: A bill generated when a local mobile subscriber is called. Roaming bill: A bill generated when a subscriber of another office calls a local

subscriber. Gateway office outgoing bill: A bill generated when a local subscriber calls a

subscriber of another network. Tandem bill: A bill generated when the caller and called are not local subscribers

and this office is a TMSC. Substituting bill: When a non-prepaid subscriber calls prepaid subscriber and it is

an OVERLAY networking, SSP will replace the originating MSC to generate this bill to charge the non-prepaid calling subscriber.

Forwarding bill: A bill generated when a local subscriber is called and the call is forwarded.

Call attempt bill: A bill generated when a call is not successful. SM bill: A bill generated when an SM is originated/terminated. Special service bill: A bill generated when special service call or special service

emergency call is involved.

2. Bill format

The bill format that MSC/MSC SERVER BAU provides for billing center complies with Mobile Phone Billing Standard Pre-processing Bill Format. BAU can provide billing center with bills in binary or text format as required.

A bill mainly consists of the following information: WCDMA/GSM/PLMN resource utilization (such as MSC number and

incoming/outgoing trunk group number) Basic service utilization (in accordance with source, destination, call date, call time,

call duration, and bearer service) Supplementary services utilization (such as call forwarding) Subscriber related numbers (such as MSISDN, IMSI and MSRN)



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9.2 Billing Principles of WCDMA PS Domain

9.2.1 WCDMA PS Domain Billing System Architecture

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Figure 9-2 PS domain billing system architecture

Figure 9-2 shows the PS domain billing 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: Collecting the billing data of SGSN and GGSN. Saving for a long time and executing some pre-processing work, such as

integrating and sorting. 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.



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9.2.2 Billing Data Generated by GSN

1. Billing data

There are 5 types of CDRs generated in 3G billing: 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.

S-SMO-CDR: Generated by SGSN, used for recording billing information of SM origination.

S-SMT-CDR: Generated by SGSN, used for recording billing information of SM termination.

S-CDR: Generated by SGSN. 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: Radio resource utilization Duration GPRS resource utilization Originator and terminator External data network utilization Mobile terminal location.

2. Integration of partial CDRs

One PDP context may be corresponding to multiple partial CDRs, which are generated because of:

Data amount limitation Time limitation 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



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specific implementation of CGF. The specific implementation of CG differs with manufacturers.

CGF must offer the following functions: Collecting CDR from SGSN and GGSN Providing long-time reliable storage of CDR 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: Collecting the CDRs on CGF Figuring out charge according to bill Fully Integrating CDRs 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, as shown below.

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Figure 9-3 GTP’ Protocol

The major functions of GTP' protocol are as follows: Transporting CDRs from GSN to CGF Redirecting CDRs to another CGF Detecting the communication failure between CGF and GSN Recommending another available CGF to GSN in case of failure in one CGF Preventing duplicate CDRs.

chapter 9 wcdma billing system

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