GSM – RATING OVERVIEW

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Contents

• Recap of GSM Overview

• Rating Fundamentals

• CDR Structure

• Charging – Call Scenarios

• Upcoming Sessions

• Telecom Roaming

GSM

BSC

GSM

BSC

GSM

BSC

GSM

BSC

GSM MSC

HLR , VLR, EIR, AuC

BTS

CELL

The GSM network can be divided into three broad parts

- 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)

- 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.

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.

Mobile station

GSM Over view – Few Points to Remember

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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 androaming 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 currentlocation area

The directory number dialed to reach a mobile subscriber is called the Mobile Subscriber ISDN (MSISDN), this number includes acountry code and a National Destination Code that identifies the subscriber's operator. The last few digits of the remainingsubscriber 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 allOutgoing, Outgoing International etc..Call hold - Puts an active call on hold, Call Waiting, Advice of Charge, AoC - Provides the userwith 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 andcertain 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.

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Rating - Overview

GSM MSC

Billing

Server Database

Rating

Engine

GSM

MSC

Mediation

Device

Mobile Switching Center

Mobile Station

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.

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.

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.

Mobile station

ASN.1 file Text CDR file

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.

After calculating the charges

of the calls, it generates the

summary information

required by the BILLING

module that generates the

bills for the customer.

CIF (Common Internal

Format) is different for

different switches and the

information available in

those are also not uniform.

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CDR Structure20204162444839042024080312 024080312 0011 31624000070 2041601187885 20080829123123009920000000 31624702386

20

204162444839042

024080312

024080312

00

11

31624000070

2041601187885

20080829123123

009920

000000

31624702386

No. Description Mandatory Length (bytes)

1 Record type Y 2

2 S.P. IMSI Y 15

3 Dialed digits Y 24

4 Printed dialed digits Y 24

5 Service type Y 2

6 Service code Y 4

7 MSC address Y 15

8 Network Code + LAC + Cell ID Y 13

9 Filler N 1

10 Start timestamp Y 14

11 Call duration Y 6

12 Data volume Y 6

13 Call reference Y 15

14 Seq no N 2

15 Filler N 41

16 S.P. MSISDN N 20

17 Filler N 8

18 Premium charge N 10

19 Premium number class event type N 1

20 Premium number class N 10

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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.

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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.

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Rating - Basic Modules

LOADING

CLUBBING

MATCHING

RATINGBilling

Database

Input CDR file from MD

Take the file from the specific directory, read records, do some validation and store into the database transaction table

Take long duration records from the long duration table, club them and put the clubbed record in the transaction table

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” .

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.

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Charging of CDRsCDR 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 This CDR is generated for each invocation of the supplementary services used by the mobile subscriber.

This CDR is used for charging the mobile subscriber for the invocation of the supplementary services. Some of the supplementary services are CLIP, CLIR, CH, CW etc.

A0 Transit This CDR is generated when a call goes out of a mobile network or comes into a mobile network from any other network.

This CDR is not used for any Rating purpose.

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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

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