GSM Rating Overview
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The document provides an overview of GSM rating and call charging. It discusses the structure of call detail records (CDRs) generated in the GSM network, which contain call information used for rating calls and calculating charges. Different types of CDRs are generated for various call scenarios, such as mobile originating calls, roaming calls, call forwarding, SMS, and supplementary services. The rating module processes the CDRs by matching call records, calculating appropriate charges, and storing results in billing tables to generate customer invoices.
GSM Rating Overview
- 1. GSM – RATING OVERVIEW 1
- 2. Contents • Recap of GSM Overview • Rating Fundamentals • CDR Structure • Charging – Call Scenarios • Upcoming Sessions • Telecom Roaming
- 3. GSM Over view – Few Points to Remember The GSM network can be divided into three broad parts GSM Mobile station BSC GSM MSC HLR , VLR, EIR, AuC GSM - Mobile Station (carried by the subscriber) - Base Station Subsystem controls the radio link with the Mobile Station - Mobile services Switching Center (MSC), performs the switching of calls between the mobile users, and between mobile and fixed network users. The mobile station (MS) consists of : - Mobile equipment (the terminal) , identified by the International Mobile Equipment Identity (IMEI) GSM - A smart card called the Subscriber Identity Module (SIM). The SIM card contains the International Mobile Subscriber Identity (IMSI) used to identify the subscriber to the system, a secret key for authentication and some other information. BSC BSC BTS CELL GSM BSC The IMEI and the IMSI are independent, thereby allowing personal mobility. The SIM card may be protected against unauthorized use by a password or personal identity number. The Base Station Subsystem is composed of two parts : - Base Transceiver Station (BTS) : Houses the radio transceivers that define a cell and handles the radio-link protocols with the Mobile Station - Base Station Controller (BSC) : Manages the radio resources for one or more BTSs. It handles radio-channel setup, frequency hopping, and handovers, The BSC is the connection between the mobile station and the Mobile service Switching Center (MSC). Mobile services Switching Center (MSC) : Acts like a normal switching node of the PSTN or ISDN, and additionally provides all the functionality needed to handle a mobile subscriber, such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber.
- 4. GSM Over view – Few Points to remember The Home Location Register (HLR) and Visitor Location Register (VLR), together with the MSC, provide the call routing and roaming capabilities of GSM The Equipment Identity Register (EIR) is a database that contains a list of all valid mobile equipment on the network. The Authentication Center (AuC) is a protected database that stores a copy of the secret key stored in each subscriber's SIM card, which is used for authentication and encryption over the radio channel Updating Locations are required when moving between location areas, and mobile stations are paged in the cells of their current location area The directory number dialed to reach a mobile subscriber is called the Mobile Subscriber ISDN (MSISDN), this number includes a country code and a National Destination Code that identifies the subscriber's operator. The last few digits of the remaining subscriber number identify the subscriber's HLR within the home PLMN. GSM Services are categorized into Teleservices ( Basic Telephony, Facsimile group, Emergency calls, Telex, Short Message Services, Fax mail and Voice mail ) and Supplementary Services ( Call Forwarding - when the called mobile is busy (CFB), unreachable (CFNRc) or if there is no reply (CFNRy). Call forwarding can also be applied unconditionally (CFU). Call Barring – Barring all Outgoing, Outgoing International etc..Call hold - Puts an active call on hold, Call Waiting, Advice of Charge, AoC - Provides the user with an online charge information, Multiparty service. Possibility of establishing a multiparty conversation. Closed User Group, CUG. - Corresponds to a group of users with limited possibilities of calling (only the people of the group and certain numbers). Calling Line Identification Presentation, CLIP. It supplies the called user with the ISDN of the calling user. Calling Line Identification Restriction, CLIR. It enables the calling user to restrict the presentation.
- 5. Rating - Overview GSM MSC Polls the CDR file from the GSM MSC, converts the file from ASN.1 format to common Text format and sends to the Billing Server. Mobile Switching Center Billing Mobile station Server Database Mediation ASN.1 file GSM MSC The RATING module is responsible for the calculation of charges for the different type of Call Detail Records (CDR) generated in the GSM (Global System of Mobile) switch. The records can be for an voice call, SMS, Data services etc. Receives the call from a mobile or a landline and transfers the call to a mobile or to a different switch. It generates the CDR having the information of the call made or received by a mobile subscriber. Mobile Station Device CIF (Common Internal Format) is different for different switches and the information available in those are also not uniform. Text CDR file Rating Receives the file from the mediation device, Process it for calculating the charges of the calls and stores the charging information in the Billing server database. The billing process that generates he bills against the customers picks this data. Engine After calculating the charges of the calls, it generates the summary information required by the BILLING module that generates the bills for the customer.
- 6. CDR Structure 20204162444839042024080312 024080312 0011 31624000070 2041601187885 20080829123123009920000000 31624702386 20 204162444839042 000000 31624702386 S.P. IMSI Y 15 Dialed digits Y 24 4 Printed dialed digits Y 24 Service type Y 2 6 Service code Y 4 MSC address Y 15 8 Network Code + LAC + Cell ID Y 13 Filler N 1 10 Start timestamp Y 14 Call duration Y 6 12 Data volume Y 6 Call reference Y 15 14 Seq no N 2 15 009920 2 13 20080829123123 2 11 2041601187885 Y 9 31624000070 Record type 7 11 Length (bytes) 5 00 Mandatory 3 024080312 Description 1 024080312 No. Filler N 41 16 S.P. MSISDN N 20 17 Filler N 8 18 Premium charge N 10 19 Premium number class event type Premium number class N 1 N 10 20
- 7. CDRs – How it looks Record Number: This is a sequence number generated in the switch for each record. Calling IMSI: This is the International Mobile Subscriber Identity code that is unique in the world and which is embedded in the SIM (Subscriber Identity Module) card. If the calling party is a landline, then this number is NULL. Calling Number: This is the mobile number or a landline number that has originated the call. Calling IMEI: This is the International Mobile Equipment Identity that is an unique number for the handset. Called IMSI: This is the International Mobile Subscriber Identity code of the called party. If the called party is a landline number, then this field is NULL. Called Number: This is the called number. Called IMEI: This is the International Mobile Equipment Identity of the called party. Called Number TON: This is the called number Type Of Number .The values indicates whether the called number is a STD, ISD or a local number Partial Output Record Number: This states whether the call is a complete call or it is a partial call. In case of complete call in ERICSSON switch, the value is 0, else it is a running number starting from 1. Last Partial Output Number: This states whether the call is the last call for the long duration call set or not. For calls that are partial, the value is 0 and for the last record, the value is 1. No of supplementary service record: This says the supplementary service record number if one supplementary call contains more than one record. SS Code: This is a two-digit code for the type of supplementary service used. These codes are GSM defined.
- 8. CDRs – How it looks Dialed Digits: This is the digit dialed by the calling party. This number can be same as the called number or different depending on the switch. Some switch like ERICSSON doesn’t give the value of this field. LAC: This is the Location Area Code. In GSM, the area are divided into hexagonal LAC and Cells. The LAC and CELL are grouped into ZONES Cell ID: This is a sub division of the LAC. One LAC may contain one or multiple Cells. MSC ID: This is an id generated for the GSM MSC. Out Circuit Group: This is id of the physical link between switches meant for outgoing calls. Out Circuit ID: This is a subdivision of the Circuit Group. One circuit group may contain one or multiple circuit Ids. Some switches like ERICSSON does not provide this field. In Circuit Group: This is id of the physical link between switches meant for incoming calls. In Circuit ID: Same as out circuit id. * Basic Service Type: This is the GSM defined basic service like Telephony, Data etc. The value for this field for telephony is “00”. Basic Service Code: This is the sub division of the Basic Service. Speech service comes under Telephony and the value is “11”. Start Time: This is the call start time with time stamp. Duration: This is the duration of the call. MSRN: This is the Mobile Subscriber Roaming Number that is generated for each Mobile Terminating Call. This field identifies whether the called person was roaming at the time of the call. This field contains a value only in the RCF (Roaming Call Forwarding) CDR.
- 9. Rating - Basic Modules Take long duration records from the long duration table, club them and put the clubbed record in the transaction table CLUBBING Take a block of READY TO PROCESS records, calculate the charges of the calls, group them by customer contract and update in the history table as well as billing table for bill processing. Take the next block. Continue. Input CDR file from MD LOADING Billing RATING Database Take the file from the specific directory, read records, do some validation and store into the database transaction table MATCHING Find out the MTC corresponding to an MOC and vice versa, update the MOC record with the LAC, CELL of the MTC and vice versa and update the status of the record to “ready to process” .
- 10. Charging of CDRs CDR TYPE PRODUCT WHEN GENERATED USE A1 MOC This type of CDR is generated when a Mobile Station (MS) originates a call from his mobile. The call may be terminated to another mobile or a landline phone. This is a very important CDR for the mobile operator because a lot of revenue comes from these CDR. The call is charged for Airtime and DOT depending on where the call has terminated. Same type of CDR comes whether the call is a local, STD or ISD call. A2 RCF This is a ticket generated in the GSM MSC for all incoming calls meant for its own subscriber. The CDR is generated irrespective of whether the called party is roaming or not. This is a very important CDR for identifying a roaming call and charging the call. When the called person is roaming, the Local Airtime part of the call is charged by this CDR and the Roaming part comes in the TAP (Transfer Account Protocol) file. A3 CF This is the ticket generated in the GSM MSC when the called party forwards the incoming calls to some other number. The forwarded number may be another mobile number, a landline number or a voice mail number. This CDR is used for charging the forwarding party for the forwarded leg of the call. The charging for this call is usage based, meaning the charges are directly dependent on the time for which the call was forwarded. A4 MTC This is generated when a mobile subscriber receives a call. The call may be originated by another mobile or a landline. This is also a very important CDR for the Billing system. In the networks where the incoming is given free, the charging of this call will not be that important, but the main importance lies in finding the termination zone of the call which is used for charging the corresponding Mobile Originating Call. A5 SMSO This is generated when a mobile subscriber originates a SMS from his mobile. This CDR is used for charging the mobile for the SMS that he sends from his mobile. Generally a fixed charge is taken for one SMSO. A7 SMSI This is generated when a mobile subscriber receives an SMS from any other mobile subscriber. This CDR is used for charging the mobile for the SMS that he receives in his mobile. Generally a fixed charge is taken for one SMSI. A9 SS A0 Transit This CDR is generated for each invocation of This CDR is used for charging the mobile subscriber for the invocation of the the supplementary services used by the mobile supplementary services. Some of the supplementary services are CLIP, CLIR, subscriber. CH, CW etc. This CDR is generated when a call goes out of a This CDR is not used for any Rating purpose. mobile network or comes into a mobile network from any other network.
- 11. Call Scenarios ( Sample Cases ) Normal Outgoing Calls • Mobile to Mobile ( Same Service provider ) • Mobile to Mobile ( Different Service provider ) • Mobile to PSTN Roaming Outgoing Calls • Mobile to Visiting Location’s Mobile number • Mobile to Home Location Number • Mobile to PSTN Roaming Incoming Calls • From Visiting Location’s Mobile number • From Home Location Number • From PSTN