12.053GPPSubscriber Related Call and Event DataTS
Figure B.4 illustrates an incoming call from a fixed network subscriber "A" to a PLMN subscriber "B" who is currently roaming in another PLMN.
The call is first routed to a GMSC (1) and the GMSC shall create an incoming gateway record for accounting purposes as described in subclause B.4.2. The GMSC interrogates the HLR of the called subscriber in order to determine his current location (2). The HLR shall create an Interrogation event record.
The GMSC routes the call to the VPLMN in which subscriber "B" is currently located (3). The GMSC shall create an outgoing gateway record for accounting purposes. The GMSC shall also create a roaming record. This record includes the IMSI of the "B" subscriber and may be used as a cross-check for the TAP information received from the VPLMN.
The call is then routed by the VPLMN to the MSC at which the subscriber is currently located (4). The GMSC of the VPLMN shall produce an incoming gateway record and the terminating MSC shall create an MTC record for the call to "B".
The records generated are subsequently transferred to the OS of the appropriate PLMN (A). The MTC record generated by the terminating MSC shall be employed to create the appropriate MTC TAP record. The TAP records shall be included in a TAP file and transmitted to the HPLMN (B).
Figure B.4: Incoming call to a roaming subscriber