As a part of Roaming a raft of parameters are sent from the HPLMN (HLR) to the VPLMN (VLR). This assumes that a Roaming agreement is in place with the co-operating CSPs (operators). GSM MAP V3 or above is the key protocol that is used to convey InsertSubscriberData() to the VPLMN.
Below are some parameters that are conveyed:-
-MSISDN. The ISDN number assigned to the roamer.
-IMSI. The IMSI of the roamer.
-Category. This refers to the calling party category. It is included either at location updating or when it is changed.
-Subscriber status. This parameter is set to service granted if no operator-determined barring (ODB) is required. To apply, remove, or update ODB, the subscriber status is set to operator-determined barring. In this case, the ODB parameter is present.
-Forwarding information list. This includes the SS code for an individual call forwarding supplementary service.
-Call barring information list. This includes the SS code for an individual call barring supplementary service.
-Bearer service list. This lists the codes of all bearer services subscribed to by the roamer.
-Teleservice list. This lists the codes of all the teleservices subscribed to by the roamer.
-Operator-determined barring HPLMN data. This includes all the operator-determined barring categories that may be applied to a roamer in a VPLMN.
Recommend that you look at 3GPP’s MAP Specification.
Error codes exists that will help you to understand the nature of the failure. Below are some examples:-
-Unknown subscriber. No such subscriber.
-Roaming not allowed. The diagnostic code provides further information.
-PLMN not allowed