INSURED approach to S-UMTS

The paper introduces an S-UMTS concept based on the presence of InterWorking Function (IWF) modules at the interface between already existing terrestrial networks, or satellite systems (underlying networks). The insertion of these IWF modules requires a minimum interaction with the underlying networks, since each underlying network sees these modules as entities belonging to its network. The introduction of the IWF modules permit one to obtain, even if sometimes in a downgraded way, many of the UMTS features. In this respect, the IWF approach can be considered as a first migration step toward UMTS; the second step being the introduction of UMTS protocols common to all the underlying networks. It is stressed, that due to its simplicity the UMTS IWF approach is particularly attractive for manufacturing. In light of the above, the INSURED project has proposed a demonstrator aiming to obtain the interworking between the GSM network and the IRIDIUM system, by the introduction of two IWF modules: the INSURED adapter, to be placed in the dual mode terminal at the interface between the GSM terminal and the IRIDIUM terminal, and the INSURED network testbed, to be placed at the interface between the GSM MSC and the SS 7/PSTN/ISDN. The paper shows that, by means of these IWF modules, two important UMTS features are achieved, namely the inter-segment handover (from the GSM network to the IRIDIUM system) and the inter-segment roaming (including the system capability to set-up the call on the most convenient link and to reach the mobile by a single INSURED number).