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					      Basic Principles of WCDMA System                                           WCDMA Billing System




                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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                                             Host system        Bill service console
                 MSC/MSC Server
                 MSC/



                                                                    Internal interface

                                                                                             LAN


                                                                                         FTP/FTAM transmission
                                                                                               protocol

                                           Heartbeat
                                         network cable
                 Highly-reliable
                 system design Active server             Standby ROUTER
                                          Disk array      server
                                                                                         IP network

                                BAU

                                                          Large-capacity
                                                         storage capability                                Billing center
                                                                                                                  3

                                           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


                                                   Data Network
                                                    (Internet)


                                                                  Inter-PLMN
                                                                  Network

                                                    Gi                  Gp



                                                                       PS Domain

                                                         GGSN
                                                                        G-CDR
                                                                                        CDR


                                                                       Ga               CDR    Billing
                                                           Gn
                                                                                CGF            System
                            SCF
                                                                       Ga               CDR


                                       CAP
                                                                            M-CDR
                                                         SGSN               S-CDR
                                                                            S-SMO-CDR
                                                                            S-SMT-CDR



                                         Gb                          IuPS


                          BSS                                                  RNS

                             BSC                                RNC

                           BTS   BTS
                                                         Node B         Node B



                                    Um             Uu

                                              MS




                                       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.

                                             GTP'                    GTP'
                                             UDP                    UDP
                                              IP                      IP
                                              L2                     L2
                                              L1                     L1
                                                          Ga
                                            GSN/CGF                 CGF

                                               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.




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