MMTel Determine International and Roaming Status

The DetermineInternationalAndRoamingStatus feature analyses a digit string that corresponds to the destination (or called) party. Digit strings may be in a Tel URL, or the user part of a SIP URI.

If the number retrieved from the Tel URI or SIP URI user part contains a + sign, the + sign is removed to leave just the digits.

The DetermineInternationalAndRoamingStatus feature uses different properties of the initial INVITE request for originating and terminating treatment:

Otherwise, the feature execution ends.

If a digit string is not found, then the feature will respond to the sentinel-core with featureCannotStart, and end.

The DetermineInternationalAndRoamingStatus feature may decide to not handle the address if either:

This allows for short codes and specific longer length numbers to avoid DetermineInternationalAndRoamingStatus. The SkipDIRSAddressList is a configurable address list scoped by the Sentinel selection key; it is only given to the component when used by the SIP normalization component.

The visited MCC and MNCs are retrieved from session state field previously populated by the ExtractNetworkInfo feature. Those values will be used when determining the roaming and international statuses.

The feature check first if the session state IMSInformation contains a valid IMS Visited Network Identifier populated by Diameter Per Leg Info Feature.

If no value is present, it extracts the visited network id for the served user as follows:

If the incoming request did not contain the visited network id, and if the served user is logged into the IMS, then Third Party Registration Data is consulted - to find the P-Visited-Network-Id at the time of IMS registration. Third Party Registration data is looked up with an access key of the default public identity for the served user. It is accessed via the Sh Cache.

If a visited network id cannot be determined, the feature checks the configuration in the DetermineInternationalAndRoamingStatusConfigProfileTable to determine if the call should proceed or not. If EndCallIfNoVisitedNetwork is false, then the feature exits without modifying session state. If EndCallIfNoVisitedNetwork is true then the call is terminated.

An important part of this feature is an address list of prefixes for each MCC or each visited network. Each entry in the list states whether an address with this prefix, for a subscriber of the network operator, registered with a subscriber location network, represents a visited or home network.

For a session processed by VoLTE:

If the profile field useMCCSpecificAddressListTables is false then the feature will attempt to use the default address list named DEFAULT. If the profile field useMCCSpecificAddressListTables is true the feature will attempt to use an address list named after the MCC. The feature will use a visited-network-id prefix address list if no MCC could be found or if no address list for the MCC could be found.

If no such address list is found, the feature will respond to the sentinel-core with featureFailedToExecute, and end.

The DetermineInternationalAndRoamingStatus feature does a longest-prefix search of the prefix address list with the address string (extracted in step #1).

If a match is found, then the address starts with a prefix of significance within the scope of the MCC or visited network. The feature can set the International session state field in two ways: * If an MCC has been determined for the served user and there is an MCC present in the prefix address list entry then 'International' is set to 'true' if the MCCs are different. * If either MCC could not be found then 'International' is set to not networkPrefixListEntry.isVisitedNetwork(). The internationalExHC session state field is set to International and not networkPrefixListEntry.isHomeNetwork().

If a prefix address list match is not found, then it must be an international call; so the feature sets the International session state field to true and the internationalExHC session state field to false.

The DetermineInternationalAndRoamingStatus feature uses a single prefix address list named DEFAULT unless useMCCSpecificAddressListTables is configured as true in the feature’s profile.

MCC specific prefix address list tables may be needed for more advanced scenarios where different MCCs are desired to not be treated as international.

The SIP Sentinel SipSentinelConfiguration profile (scoped on the Sentinel selection key) defines the home Mobile Country Code (MCC), the Mobile Network Codes (MNCs) and the home network ids for the network operator. The home network ids define the home network for the subscriber.

If the feature found a non empty MCC for the visited network, it compares that value with the home MCC present in SipSentinelConfiguration profile.

If they are different the feature sets the RoamingStatus to INTERNATIONAL and the RoamingIndicator session state field is set to true.

If they are equal and the visited MNC is present in the home MNCs, the feature sets the RoamingStatus to NOT_ROAMING and the RoamingIndicator session state field is set to false.

If they are equal and the visited MNC is not present in the home MNCs, the feature sets the RoamingStatus to NATIONAL and the RoamingIndicator session state field is set to false.

If no MCC is present then the feature do the roaming analysis based on the visited-network-id. If the visited-network-id is not a member of the set of home network ids, the RoamingIndicator session state field is set to true.

If they are no visited MNC and no visited network was found, the feature sets the RoamingStatus to UNKNOWN.