DetermineRoamingFromHlr

This feature’s source code is available in the Sentinel VoLTE SDK in the volte-determine-roaming-from-hlr module pack. It can be viewed by using the create-module command in the SDK with that module pack, for example:

> create-module new-hlr-module opencloud#volte-determine-roaming-from-hlr#volte/3.0.0;3.0.0.0

This command will prompt you for information needed to create the new module; once completed the original source for the feature can be found in the new module.

The module-pack consists of a single module, volte-determine-roaming-from-hlr, containing the feature’s code. It does rely on the volte-map-event-handler which contains the shared event handler for MAP features and also publishes a module pack, however the event handler will not require modification unless a new feature name is introduced.

Note: The default values for both RoamingStatus and RoamingIndicator are UNKNOWN and false respectively. If this feature is unable to determine the roaming status for any reason, it will leave the pre-set values.

The feature uses configuration data from both the HLR MAP Configuration and SIP Sentinel Configuration.

DetermineRoamingFromHlr statistics are tracked by the DetermineRoamingFromHlr feature and can be found under the following parameter set:
SLEE-Usage ▶ sentinel.volte.sip service ID ▶ sentinel.volte.sip SBB ID ▶ DetermineRoamingFromHlr.

This feature uses the CGIN MAP RA to query the HLR with an ATI for subscriber location information.

Each time the feature is invoked, it checks the call type and determines the subscriber number that it should use to query the HLR.

When invoked on a SIP response the feature checks whether a request to the HLR has not already been made and whether there is an OC-Terminating-Domain present in the SIP responses with value CS. If either is not the case then the feature finishes execution.

The feature attempts to extract "phone number digits" from the CMSISDN session state field set by FetchCMSISDN, and if it cannot, from the Subscriber field set by SubscriberDetermination. If the feature cannot form a MSISDN it raises a Feature Error and finishes execution.

The feature then requests subscriber location info by sending a AnyTimeInterrogation request to the configured HLR.

In order to form the ATI request the feature:

If a successful result is received, it retrieves location information from the ATI result. The location information can be in either of the CellGlobalIdOrServiceAreaIdFixedLength or LaiFixedLength fields. If neither field is present, the feature increments the RoamingDataMissingFromHlrResponse stat and finishes.

If the location information is found, the MCC and MNC are evaluated using the PLMN ID Analyser Component to determine whether the subscriber is roaming or not. The RoamingStatus and RoamingIndicator session state fields are then set accordingly. Their default values in the case of incomplete information or feature failure are UNKNOWN and false respectively.

If found, the location information is also used to generate a discovered network access information. If no other access network information is available, this will be used in charging content AVPs. The format for the generated information is 3GPP-GERAN;cgi-3gpp=<cgi>;network-provided, where <cgi> is the Cell Global ID, made up of the MCC, MNC, Location Area Code (in hex) and Cell Id (in hex) concatenated. If the Cell Id is not provided by the HLR, it will default to 0000.