How it works

The Rhino VoLTE TAS determines if a session is roaming and if it represents an international call based on:

  • the location of the calling party, and

  • the destination address.

Determining international status

The Rhino VoLTE TAS uses the home network configuration to determine the international status of a subscriber.

If the checked address is not in an international format and non-international-format-number-is-national is set to true, the Rhino VoLTE TAS determines the number is not an international or international-exHC number.

Otherwise, the Rhino VoLTE TAS analyzes the call alongside the home network information to determine international status.

The Rhino VoLTE TAS determines the call’s international status according to the definitions given by 3GPP 24.611:

international: This condition evaluates to true when the request URI of the outgoing SIP request:

  • corresponds to a telephone number, i.e. a SIP URI with a “user” URI parameter set to “phone” or a tel URI; and

  • does not point to a destination served by a network within the country where the originating user is located when initiating the call.

international-exHC: This condition for international barring, excluding the home country, evaluates to true when the request URI of the outgoing SIP request:

  • corresponds to a telephone number, i.e. a SIP URI with a “user” URI parameter set to “phone” or a tel URI;

  • does not point to a destination served by a network within the country where the originating user is located when initiating the call; and

  • does not point to a destination served within the served users home network.

Determining roaming status

The Rhino VoLTE TAS determines roaming status of a subscriber by checking the following:

  • Firstly, the home-plmn-ids MCCs and MNCs are checked with the subscriber address’s respective MCC and MNC.

    • If a home network MCC and MNC (PLMN ID) match with the address’s MCC and MNC respectively, the call is NOT-ROAMING.

    • If a home network MCC and address’s MCC match, but there is no MNC match, the call is NATIONAL roaming.

    • If a home network MCC does not match with the address’s MCC, the call is INTERNATIONAL roaming.

  • If the address has no MCC present, the ISO country code of the party is compared with the network’s configured home-network-iso-country-code.

    • If the ISO country codes match, the call is NOT-ROAMING, otherwise, it is INTERNATIONAL roaming.

  • If there is no ISO country code present, the Visited Network ID of the party is compared with the network’s configured home-domain.

    • If the network IDs match, the call is NOT-ROAMING, otherwise it is INTERNATIONAL roaming.

  • Finally, if the call’s visited MCC nor visited network are not present, the roaming status is UNKNOWN.

Using the visited network ID

The Rhino VoLTE TAS determines the visited network ID on an incoming request with the following techniques:

  • Firstly, if the Rhino VoLTE TAS has already loaded on the visited network ID for the session, it uses that.

  • Otherwise, the Rhino VoLTE TAS uses the P-Visited-Network-Id header for originating sessions or OC-Term-P-Visited-Network-Id for terminating sessions on the incoming request.

  • Finally, the Rhino VoLTE TAS will query for the third party registration data stored in subscriber data.

Interactions with other services

Call Barring

The Rhino VoLTE TAS uses the roaming and international status for MMTel communication barring features. For further information on barring feature configuration, see Call barring.

International Call Management

The outcome of international status determination is used to decide whether the International Call Management service should run.

Configuration

Roaming determination depends on number normalization and home network dialing configurations.

It is possible to configure a list of addresses that will have roaming determination skipped. Contact Metaswitch support for more information on how to configure roaming determination skip lists.

What you need

  • ❏ Whether to treat non-international numbers as national numbers.

  • ❏ Whether to end a call if there is no visited network information on the incoming call request.

  • ❏ The minimum length of the destination address required to set international and roaming status.

  • ❏ For a GSM network, whether to use the HLR to determine roaming.

Setting up roaming and international status

I want to …​

Treat any non-international format number as a national number

To set the Rhino VoLTE TAS to treat any non-international format number as a national number for roaming, in the international-and-roaming section, set non-international-format-number-is-national to true:

            non-international-format-number-is-national: true
End a call if no visited network can be determined

To set the Rhino VoLTE TAS to end an incoming call if the P-Visited-Network-Id cannot be determined, in the international-and-roaming section, set end-call-if-no-visited-network to true:

            end-call-if-no-visited-network: true
Not determine roaming and international status for dialed digits below a certain length

To set the Rhino VoLTE TAS to not determine roaming or international status for short dialed digit strings (such as any length below 7 for example), in the international-and-roaming section, set min-length to 7:

            min-length: 7
Use the HLR for determining roaming with the GSM network

To set the Rhino VoLTE TAS to query the HLR for determining roaming using GSM network information, in the mmtel section, set determine-roaming-from-hlr to true:

        determine-roaming-from-hlr: true
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Rhino VoLTE TAS Version 4.1