5 Charging Principles

32.0153G call and event data for the Packet Switched (PS) domain3GPPCharging managementRelease 1999Telecommunications managementTS

5.1 Requirements

Based on the requirements in 3GPP TS 22.115 here are the specific details relating to the packet domain.

1) Every PDP context shall be assigned a unique identity number for billing purposes. (i.e. the charging id).

2) Data volumes on both the uplink and downlink direction shall be counted separately. The data volumes shall reflect the data as delivered to and from the user.

3) The charging mechanisms shall provide the duration of the PDP context with date and time information.

4) The GPRS operator may define a subset of the charging information specified by GPRS charging standards. This means that it shall be possible to configure the SGSN and GGSN for the CDR information generated.

  1. The GSNs shall be capable of handling specific charging characteristics provided through either HLR subscription data or default values. This is to improve charging record generation efficiency determined by the operator, based on the configuration of CDR trigger parameters at the GSNs.
  2. SGSN shall support charging of CAMEL services.

5.2 Charging Information

Charging information in the GPRS network is collected for each MS by the SGSNs and GGSNs, which are serving that MS. The information that the operator uses to generate an invoice to the subscriber is operator-specific. Billing aspects, e.g. a regular fee for a fixed period, are outside the scope of the present document.

The SGSN collects charging information for each MS related with the radio network usage, while the GGSN collects charging information for each MS related with the external data network usage. Both GSNs also collect charging information on usage of the GPRS network resources.

The GSNs shall collect the following charging information:

  1. usage of the radio interface: the charging information shall describe the amount of data transmitted in MO and MT directions categorised with QoS and user protocols;
  2. usage duration: Duration of PDP context is counted as the time interval from PDP Context activation to PDP Context Deactivation.
  3. usage of the general GPRS resources: the charging information shall describe the usage of other GPRS-related resources and the MSs GPRS network activity (e.g. mobility management).
  4. destination and source: the charging information shall provide the actual source addresses used by the subscriber for the PDP context.. The charging information shall describe the destination addresses with a level of accuracy as determined by the Access Point Name (APN).
  5. usage of the external data networks: the charging information shall describe the amount of data sent and received to and from the external data network.

    External networks can be identified by the Access Point Name (APN).

  6. location of MS: HPLMN, VPLMN, plus optional higher-accuracy location information.

    The highest accuracy location information available in GGSN is SGSN address.

5.3 Charging Data Collection Principles

Call data record generation and contents should be flexible and unnecessary redundancy in data should be avoided.

  1. Each PDP context generates its own record types (the S-CDR for the SGSN and the G-CDR for the GGSN related to PDP contexts).
  2. The SGSN can optionally provide a record for mobility management of the attached MS in the M-CDR.
  3. The SGSN shall provide two SMS related records, in case of GPRS delivered MO short message S-SMO-CDR and MT short message S-SMT-CDR.
  4. MS Location information shall be included in the SGSN PDP context records.
  5. Records shall only include relevant information, i.e. traffic activity since last record.

    The criteria for record generation is based on real-time needs, information safety (backup) and some specific events, such as expiry of the partial record timer(s), transferred data volume limit(s), inter SGSN routing area update, inter/intra system handover.

  6. Change of tariff period (if used) should not cause new CDRs to be sent to avoid peaks in data transfer. Instead such events should close the existing volume counters and open new ones when appropriate traffic is detected. This can be done by having a new record in the same message. It is up to the operator how often the CDRs are transferred from a GSN.
  7. Both SGSN and GGSN nodes shall collect information from same chargeable sessions (PDP contexts). A unique reference (Charging ID in combination with GGSN address) is needed to enable correlation between information from several records produced from same PDP context.
  8. The RNC shall collect the amount of not transferred downlink data, i.e., data that the RNC has either discarded or forwarded to a 2G‑SGSN, for an MS’s RABs when instructed by the 3G‑SGSN.

5.3a Volume counting in RNC

The 3G-SGSN counts all downlink data sent to the RNC over Iu interface. Any discarded data between MS and RNC causes inaccurate charging, as the 3G-SGSN cannot account for this and subsequently causing overcharging. Additionally any buffered data in the RNC at RAB release or forwarded to another SGSN during handover is possible counted again i.e. twice, which causes overcharging.

To avoid inaccurate charging at the 3G-SGSN, the 3G-SGSN will always instruct the RNC at RAB set-up to count the unsent downlink data towards the MS.

The reporting of unsent data by the RNC to the 3G-SGSN will only occur at RAB release. Examples when this occurs are at termination of the PDP context, handover or PDP Context Preservation (see 3GPP TS 23.060 [8]).

The reporting of unsent data by the RNC to the 3G-SGSN will only occur at RAB release. This occurs at either the termination of the PDP context or handover.

The 3G-SGSN shall not use the optional ‘Data Volume Request’ message to RNC in any situation, as this shall cause a significant performance impact to both the RNC and 3G-SGSN.

When 3G-SGSN receives a report of unsent data volume from the RNC at RAB release. The 3G-SGSN shall report this value to the ‘RNC Unsent Downlink Volume’ field in the S-CDR.

5.4 Generation of Charging ID

The concept of serving connections is different in the GSM switching network to that for the GPRS network. Therefore different mechanisms are needed to supply the Billing System (BS) centres with charging information.

Circuit switched calls can be charged in one MSC (the anchor MSC) where all relevant data is available. That is guaranteed by routing all signalling information though the anchor MSC even if the traffic channel of a call is routed through another MSC due to handover.

In a GPRS network the complete PDP context handling can be switched over from an old SGSN to a new SGSN due to routing area updates with the consequence that charging records will be generated in more than one SGSN. Furthermore different data has to be collected in the SGSNs and GGSNs. So for one PDP context, charging records are needed from both the SGSN and GGSN.

The Billing System (BS) shall be provided with all relevant information from the network to charge for that one activated PDP context.

During the active PDP context all records, which belong to this context could normally be identified by the TID. However:

– an MS can activate and deactivate PDP contexts in a very short time interval, and these PDP contexts can have the same TID (only parallel established PDP contexts have different TIDs);

– different SGSNs can be involved in the same PDP context as described above;

– the timing clocks of the GSN elements may not be fully synchronised.

Therefore it is nearly impossible for a billing post-processing system to gather the records of one PDP context only by using the IMSI, NSAPI (TID) and time.

This is solved by assigning a unique Charging ID number (C-ID) to all records generated for that one PDP context.

The unique C-ID is generated in the GGSN when the PDP context is activated. A C-ID is generated for each activated context, so that each has a unique C-ID. The C-ID shall be transferred from the GGSN to the new SGSN in the routing area update response message. All CDRs for each activated PDP context generated by each SGSNs and GGSNs shall therefore contain the same unique combination of the C-ID and GGSN address, to permit subsequent Charging Gateway / Billing System (BS) correlation of the generated CDRs.

This combination of GGSN address together with the C-ID should be a unique identification over a long period of time in all GPRS networks.

5.5 Charging for SMS in GPRS

SMS transmission (MO or MT) can be provided over GPRS via the SGSN. The SGSN shall provide an S-SMO-CDR when short message is mobile originated and an S-SMT-CDR when it is mobile terminated. In addition, also SMS-IWMSC (MO-SMS) and SMS-GMSC (MT-SMS) may provide SMS related CDRs as described in 3GPP TS 32.005 [23].

No active PDP context is required when sending or receiving short messages. If the subscriber has an active PDP context, volume counters of S-CDR are not updated due to short message delivery.

The contents of S-SMO and S-SMT CDRs are presented in Table 8 and Table 9.

5.6 Charging Triggers – CDR Generation

The S-CDR, M-CDR G-CDR, S-SMO-CDR and S-SMT-CDR are generated by the SGSN and GGSN to collect charging information such that they may be subsequently transferred to the Charging Gateway Function.

Charging Characteristics may be specified for a PDP context. It is determined as described in subclause 5.7.1.2 and 5.7.3. If set, it will determine the S-CDRs and G-CDRs generation and trigger values. If no Charging Characteristics are set for a PDP context, a default set of trigger values shall be applied.

In the GSNs it shall be possible to activate and deactivate CDR generation for each Charging Characteristics. If CDR generation is activated, it shall be possible to define separate trigger conditions values per Charging Characteristics for the following triggers:

  • data volume limit;
  • time (duration limit);
  • maximum number of charging conditions changes (QoS change, Tariff Time change).

The following subclauses describe the trigger conditions for collection of charging information and CDR generation by the SGSN/GGSN.

5.6.1 Triggers for S-CDR Charging Information Collection

An S-CDR is used to collect charging information related to the PDP context data information for a GPRS mobile in the SGSN.

If according to the Charging Characteristics of a PDP context, CDR generation is activated an S-CDR shall be opened at PDP context activation, and record includes details such as Record Type, Served IMSI, Sequence Number etc. Not all of the charging information to be collected is static, and other charging information is directly dependent on dynamic GPRS usage.

The subsequent subclauses identify the conditions for adding information to, and closing of the S-CDR for generation towards the CGF.

5.6.1.1 Triggers for S-CDR Charging Information Addition

The "List of Traffic Volumes" attribute of the S-CDR consists of a set of containers, which are added when specific trigger conditions are met, and identify the volume count separated for uplink and downlink traffic on encountering that trigger condition.

Table 1: Triggers for S-CDR charging information addition

Trigger Conditions

Description/Behaviour

QoS Change

A change in the QoS shall result in a "List of Traffic Data Volumes" container being added to the CDR.

Tariff Time Change

On reaching the Tariff Time Change a "List of Traffic Data Volumes " container shall be added to the CDR.

CDR Closure

A list of "List of Traffic Data Volumes" container shall be added to the S-CDR.

5.6.1.2 Triggers for S-CDR Closure

The S-CDR shall be closed on encountering some trigger conditions. Table 2 identifies which conditions are supported to permit closure of the S-CDR.

Table 2: Triggers for S-CDR closure

Closure Conditions

Description/Behaviour

End of PDP Context within the SGSN

Deactivation of the PDP context in the SGSN shall result in the CDR being closed. The trigger condition covers:-

– termination of PDP context,

– SGSN change (inter-SGSN routing area update including system handover),

– any abnormal release.

Partial Record Reason

O&M reasons permit the closure of the CDR for internal reasons. The trigger condition covers:-

– data volume limit,

– time (duration) limit,

– maximum number of charging condition changes,

– management intervention.

The Partial Record generation trigger thresholds are those associated to the Charging Characteristics of the related PDP context. The Charging Characteristics of the PDP context are determined as follows:

  • If a "PDP context Charging Characteristics" is present in the subscriber’s data for this PDP context, than it shall be used;
  • If there is no "PDP context Charging Characteristics" but a "Subscribed Charging Characteristics" is present in the subscriber’s data, the "Subscribed Charging Characteristics" shall be used;
  • If neither a "PDP context Charging Characteristics" nor a "Subscribed Charging Characteristics" is present, a default charging profile shall be applied.

The Partial Record generation trigger thresholds are GSN configuration parameters defined by the operator through O&M means.

In the event that the S-CDR is closed and the PDP context remains active, a further S-CDR shall be opened with an incremented Sequence Number in the SGSN.

5.6.2 Triggers for M-CDR Charging Information Collection

An M-CDR is used to collect charging information related to the mobility management of a GPRS mobile in the SGSN.

An M-CDR shall be opened for each GPRS mobile upon GPRS Attach, and record details such as Record Type, Served IMSI, Sequence Number etc. Not all of the charging information to be collected is static, and other charging information is directly dependent on the mobility of the MS as provided by the Radio Access Network (RAN). Subsequent partial records may be opened if the M-CDR is closed and the MS is still attached to the network.

The subsequent subclauses identify the conditions for adding information to, and closing of the M-CDR for generation towards the CGF.

NOTE: In case of a 3G or a combined 2G/3G SGSN, the specified mobility management handling implies that not every routing area update is captured by the core network, depending on the mobility management state of the UE. This may result in e.g. not every change of Routing Area being recorded in the M-CDR. For more information about mobility management procedures in GPRS, see TS 23.060 [8].

5.6.2.1 Triggers for M-CDR Charging Information Addition

The "Change of Location" attribute of the M-CDR consists of a set of containers, which are added when specific trigger conditions are met, and identify the time stamped routing area on encountering that trigger condition.

Table 3: Triggers for M-CDR Charging Information Addition

Trigger Conditions

Description/Behaviour

Mobility Change

A change in the Routing Area shall result in a "Change of Location" container being added to the M-CDR.

5.6.2.2 Triggers for M-CDR Closure

The M-CDR shall be closed on encountering some trigger conditions. Table 4 identifies which conditions are supported to permit closures of the M-CDR.

Table 4: Triggers for M-CDR closure

Closure Conditions

Description/Behaviour

End of MM Context within SGSN

Deactivation of the MM context in the SGSN shall result in the CDR being closed. The trigger condition covers:-

– SGSN change (inter-SGSN routing area update including system handover),

– GPRS detach,

– any abnormal release.

Partial Record Reason

O&M reasons permit the closure of the CDR for internal reasons. The trigger condition covers:-

– time (duration) limit,

– maximum number of mobility changes, and

  • Management intervention,
  • Intra system handover (change of radio interface from GSM to 3G or visa versa).

In the event that the M-CDR is closed and the GPRS mobile is still known to the SGSN, a further logical M-CDR shall be opened with an incremented Sequence Number in the SGSN.

5.6.3 Triggers for G-CDR Charging Information Collection

A G-CDR is used to collect charging information related to the packet data information for a GPRS mobile in the GGSN.

If, according to the Charging Characteristics of a PDP context, CDR generation is activated a G-CDR shall be opened at PDP context activation, and record includes details such as Record Type, Served IMSI, Sequence Number etc. Not all of the charging information to be collected is static, and other charging information is directly dependent on dynamic GPRS usage.

A G-CDR shall be opened for each activated PDP context, and record details such as Record Type, Served IMSI, Sequence Number etc. Not all of the charging information to be collected is static, and other charging information is directly dependent on dynamic GPRS usage.

The "List of Traffic Data Volumes" attribute of the G-CDR consists of a set of containers, which are added following specific trigger conditions, and identify the volume count on encountering that trigger condition. The trigger conditions are as for the S-CDR (see subclause 5.6.1 on "Triggers for S-CDR Charging Information Collection") with the following exceptions:

  1. an SGSN change will not close the G-CDR;
  2. an inter-PLMN SGSN change causes the closure of a partial record.

Subsequent partial records may be opened if the G-CDR is closed and the PDP context is still active.

The Partial Record generation trigger thresholds are those associated to the Charging Characteristics of the related PDP context determined as follows:

  • If a "PDP context Charging Characteristics" is present in the PDP context data, it shall be used;
  • Otherwise a default charging profile shall be applied.

The Partial Record generation trigger thresholds are GSN configuration parameters defined by the operator through O&M means.

In the event that the G-CDR is closed and the PDP context remains active, a further G-CDR is opened with an incremented Sequence Number in the GGSN.

5.7 Examples of charging scenarios

This subclause contains a number of example scenarios illustrating the purpose and practical usage of the various types of records defined in the previous subclauses. These examples are by no means exhaustive.

For the purpose of these examples the following assumptions have been made:

– the CDR records are sent to a CGF;

– the generation of all of the CDR record types has been enabled.

The following conventions have been used for the Figures 5, 6, 7 and 8, contained within this subclause:

1) Network connections and signalling transactions are illustrated by means of solid lines and referenced by number e.g. (1).

2) Operation & Maintenance actions, such as the transfer of call records, are represented by means of dotted lines and referenced by letter e.g. (A).

5.7.1 GPRS Mobile to PDN Context

Figure 5 illustrates a simple outgoing GPRS context from a PLMN GPRS subscriber "A" to a mainframe "B" via a PDN (1).

The respective PDP context is activated in the SGSN and GGSN and PDP PDUs are routed in MO and MT direction. The SGSN shall create an S-CDR and the GGSN shall create a G-CDR for subscriber "A".

The records generated are subsequently transferred to the CGF (A). The CGF transfers the CDRs to the BS.

Figure 5: GPRS Mobile to PDN Context

5.7.2 GPRS Mobile to Mobile Context

Figure 6 illustrates a simple GPRS mobile to mobile context within the same HPLMN.

The respective A-party related PDP context is activated in the SGSN-A and the GGSN (1).

After the location of subscriber "B" is determined, the B party related PDP context is activated (2) in the SGSN-B and the GGSN and PDP PDUs are routed in MO and MT direction. The SGSN-A shall create an S-CDR and the GGSN shall create a G-CDR for subscriber A, the SGSN-B shall create an S-CDR and the GGSN shall create a G-CDR for subscriber "B".

If subscriber "A" and subscriber "B" use the same GGSN, both G-CDRs are produced at that GGSN.

If session leg (2) requires a PDP context activation the respective PDP records will contain a network initiated PDP context activation-flag.

The records generated are subsequently transferred to the CGF (A). The CGF transfers the CDRs to the BS.

Figure 6: GPRS Mobile to Mobile Context

5.7.3 PDN to GPRS Mobile Context

Figure 7 illustrates a simple incoming GPRS context from a mainframe "A" to GPRS mobile subscriber "B" via a PDN (1). After the location of subscriber "B" is determined, the PDP context is activated (2).

The GGSN receiving the PDUs shall generate a G-CDR whereas the SGSN currently serving subscriber "B" creates an S-CDR. These records contain a flag that the PDP context is activated due to network request.

The records generated are subsequently transferred to the CGF (A). The CGF transfers the CDRs to the BS.

Figure 7: PDN to GPRS Mobile Context

5.7.4 GPRS Mobile to PDN Context while roaming, GGSN in HPLMN

Figure 8 illustrates an outgoing GPRS context from a roaming GPRS mobile subscriber "A" to mainframe "B" via Boarder Gateway, inter PLMN backbone and GGSN of the HPLMN (1).

The respective a-party related PDP context is activated in the SGSN and GGSN and PDUs are routed in MO and MT direction. The SGSN shall create an S-CDR (VPLMN) and a G-CDR is generated at the used GGSN (HPLMN) for subscriber "A". From the GGSN the packets are sent via the PDN to the mainframe "B".

The records generated in the HPLMN and the VPLMN are subsequently transferred to the CGFs (A). The CGFs transfer the CDRs to the BS. (B)

Later on the records created in the VPLMN are transferred from the BS to the BS of the HPLMN via TAP procedure (C).

Figure 8: GPRS Mobile to PDN Context whilst roaming via BG

5.8 Charging support for CAMEL

CAMEL GPRS interworking can be activated for GPRS session, SGSN PDP context and mobile originated SMS based on subscription information stored in HLR. Control point for all CAMEL interactions in GPRS network domain reside at gprsSSF typically co-located with SGSN. GGSN is not aware of CAMEL service at all. For more information about CAMEL interworking (see 3GPP TS 23.078 [9]).

An M-CDR, S-CDR and S-SMO-CDR include basic information about CAMEL service information, such as service key and SCF address, and service usage, such as CAMEL modification information and amount of signalling. CAMEL service may also send transparent free format data in one or several messages to be stored in the CDR. Each received free format data indicates whether it is overwritten or appended to previously received free format data.

CAMEL service may deny the GPRS attach, PDP context activation or sending of short message. CAMEL service may also change the APN determined by SGSN before activating PDP context or it may change the destination information of short message.

CAMEL feature to download advice of charge parameters does not need to be supported because sending of these parameters down to MS and usage in the MS is not standardised for GPRS terminals. The message itself shall however be supported and in case of a relative tariff switch is received, then at that tariff switch time volume counts shall be reported to CAMEL service.
Tariff switch times configured in GSN and those received from CAMEL service are independent. Tariff time switches reported in CDRs must not be influenced by tariff time switches provided via CAMEL. In the context of CDRs only tariff time switches defined on GSN level are valid.