What it does

When CAP online charging is in use, the Rhino VoLTE TAS functions as an IM-SSF (IP Multimedia Service Switching Function) and communicates with an SCP in a GSM network. At various points in the SIP signalling for the call the Rhino VoLTE TAS will translate the SIP to the equivalent CAP signalling towards the SCP, to give it the opportunity to intervene in call processing. Through this the SCP can provide a charging service. The exact details of how and when the Rhino VoLTE TAS will signal the SCP is determined by subscriber specific IM-CSI data in the HLR.

CAP online charging requires that integration with an SCP is set up. To do this, the SCCP (Signalling Connection Control Part) address of the SCP must be set in the scf-address field.

Note CAMEL Application Part (CAP) is a GSM protocol, so naturally can only be used with GSM networks.

The Rhino VoLTE TAS supports CAP phase 2 and phase 3 triggers.

IM-CSI

The IM-CSI (IP multimedia CAMEL subscription information) is subscriber data retrieved from the HLR that is used to determine when and how to do SIP to CAP translation. There are different versions of the IM-CSI for the originating and terminating legs of the call; they are the O-IM-CSI and the VT-IM-CSI respectively. The Rhino VoLTE TAS can be configured to retrieve either the O-IM-CSI or the VT-IM-CSI independently of whether it is acting as an originating or terminating TAS.

The IM-CSI that is fetched on:

Both fields can take the same values, which are numbers that correspond to CAP TDPs (trigger detection points).

The following values are valid for these fields.

Table 1. TDPs for IM-CSI retrieval
TDP number TDP name IM-CSI retrieved

2

 
Collected_Info

O-IM-CSI

3

 
Analysed_Info

O-IM-CSI

12

 
Terminating_Attempt_Authorised

VT-IM-CSI

Location information

Information about a subscriber’s current country and access network can be sent to the SCP in the form of a charging GT (global title).

The format of the charging GT is configured in the format field, and it is made up from any combination of: fixed digits, the mobile country code (MCC), the mobile network code (MNC), and/or the two letter ISO country code. The value of the field should match any fixed digits to be included in the charging GT, with {mcc}, {mnc}, and/or {iso} tags inserted where those values should be substituted in. For example, 12345{mcc}{mnc} results in a charging GT that always starts with 12345 and has the current MCC and MNC for the subscriber appended on the end.

The unknown-location field can be used to set a default charging GT, which is used when a subscriber’s location cannot be determined.

When a subscriber receives a call, the CAP charging service is always invoked. This can be changed so that the service is only used for terminating calls when the charging GT data indicates that the subscriber is roaming in a foreign country.

Configuration

Note CAP based charging is only available on GSM networks.

The example for sentinel-volte-gsm-config.yaml shows example configuration relevant to CAP charging in the sentinel-volte/charging section.

What you need

  • ❏ The SCCP address of the GSM charging SCP.

  • ❏ The TDP(s) to use when retrieving IM-CSI data from the HLR.

  • ❏ Whether or not to send location information to the SCP.

If sending location information to the SCP:

  • ❏ The format to sent the information in (see Location information).

  • ❏ A default value to send when a subscriber’s location cannot be determined.

Setting up CAP based online charging

I want to…​

Enable CAP charging

In the charging section, set the gsm-online-charging-type to either cap or cap-ro for mixed CAMEL/Ro deployments:

        gsm-online-charging-type: cap

Also in the charging section:

        cap-charging:
            imssf:
                scf-address: "type=C7,ri=pcssn,pc=6,ssn=156"

  • Ensure there is a cap-charging section.

  • Ensure there is an imssf section.

  • Set the scf-address to the SCCP address of the SCP that the Rhino VoLTE TAS should communicate with.

Disable CAP charging

In the charging section, set the gsm-online-charging-type to disabled:

        gsm-online-charging-type: disabled

Comment out the entire cap-charging section:

#        cap-charging:
#            imssf:
#                imcsi-fetching:
#                    originating-tdp: 2
#                    terminating-tdp: 12
#                charging-gt:
#                    format: "6422142{iso}"
#                    unknown-location: "64221429090"
#                    only-charge-terminating-call-if-international-roaming: false
#                scf-address: "type=C7,ri=pcssn,pc=6,ssn=156"
Change the SCP that the CAP charging service communicates with

In the imssf section, set the scf-address to the SCCP address of the new SCP:

                scf-address: "type=C7,ri=pcssn,pc=6,ssn=156"
Generate and send a charging GT containing location information for a subscriber to the SCP

In the imssf section:

                charging-gt:
                    format: "6422142{iso}"
                    unknown-location: "64221429090"

  • Add a charging-gt section. Inside it add:

    • a format field specifying how the location information should be delivered. It can be made up from fixed digits and any of these tags: {mcc}, {mnc}, and/or {iso}; which will substitute in the MCC, MNC, and ISO two letter country code respectively.

    • a unknown-location field indicating what to send to the SCP if location information cannot be obtained.

Related section: Location information

Disable sending of the charging GT to the SCP

In the imssf section, comment out the entire charging-gt section:

#                charging-gt:
#                    format: "6422142{iso}"
#                    unknown-location: "64221429090"

Related section: Location information

Only invoke the CAP charging service for terminating subscribers when they are roaming in a foreign country

In the charging-gt section, set the only-charge-terminating-call-if-international-roaming to true:

                    only-charge-terminating-call-if-international-roaming: true

Related section: Location information

Always invoke the CAP charging service for terminating subscribers regardless of their location

In the charging-gt section, set the only-charge-terminating-call-if-international-roaming to false:

                    only-charge-terminating-call-if-international-roaming: false

Related section: Location information

Use O-IM-CSI data from the HLR on originating calls

In the charging section:

        cap-charging:
            imssf:
                imcsi-fetching:
                    originating-tdp: 2

Related section: IM-CSI

Use VT-IM-CSI data from the HLR on originating calls

In the charging section:

        cap-charging:
            imssf:
                imcsi-fetching:
                    originating-tdp: 12

Related section: IM-CSI

Use O-IM-CSI data from the HLR on terminating calls

In the charging section:

        cap-charging:
            imssf:
                imcsi-fetching:
                    terminating-tdp: 2

Related section: IM-CSI

Use VT-IM-CSI data from the HLR on terminating calls

In the charging section:

        cap-charging:
            imssf:
                imcsi-fetching:
                    terminating-tdp: 12

Related section: IM-CSI

Disable retrieval of IM-CSI data from the HLR

In the imssf section, remove or comment out the entire imcsi-fetching section:

            imssf:
#               imcsi-fetching:
#                   originating-tdp: 2
#                   terminating-tdp: 12

To disable retrieval for only:

Related section: IM-CSI

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Rhino VoLTE TAS Version 4.2