The purpose of the MUP-gateway function is to make international roaming with MUP easier and to avoid errors when changes are made in network-configurations and numbering is rearranged between MTX’s.

The gateway function is implemented in the MTX that serves as international signalling point.

Initial international MUP-messages are addressed to the Gateway MTX (by using the Global title of MTXG) where MUP handles the national rerouting. This means that exact national configuration is known only by gateway MTX and not by co-operating networks. In this way international roaming may be addressed by Z of the subscriber Identity.

When a MUP message is received from a co-operating network and the subscriber Identity does not correspond to the MTX's own numbering the MUP re-routes the message to the proper HLR/MTXH.

Figure 3.15: Routing of MUP-messages with MUP-Gateway functionality.