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 prerequisite Extract Network Info Feature attempts to parse the P-Access-Network-Info and P-Visited-Network-Identifier headers to obtain the visited MCC and MNCs, and stores them in session state. The feature first checks if the session state field PaniMccsMncs (obtained from P-Access-Network-Info) contains any entries. If so, it takes the first entries for both the MCC and MNC. Otherwise, the visited MCC and MNCs are retrieved from the session state field PvniMccMnc, obtained by parsing the P-Visited-Network-Identifier according to IETF RFC 3455.

The feature first checks if the session state field 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.

The addresses in the list will be used to determine the international status based on the MCC. For originating calls the called party address is used to find the destination MCC, and for terminating calls the calling party address is used to define the MCC from the originating party. This list allows the operator to define how the international status will be resolved by setting the field isVisitedNetwork.

For a session processed by VoLTE:

The prefix address list to use is now determined as follows:

If no prefix 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:

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 finds a non-empty MCC for the visited network, it compares that value with the home MCC present in the 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 does 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 feature sets the RoamingStatus to NOT_ROAMING and the RoamingIndicator session state field is set to true.

If neither the visited MCC nor the visited network are present, the feature sets the RoamingStatus to UNKNOWN.