 and other signaling information are transmitted via the radio path and BSS to the MSC. The telephone number of subscriber B is transmitted to the MSC/VLR. 2. The MSC recognizes mobile B (in this example) as a subscriber of its own network and requests the roaming number from the HLR of subscriber B. The roaming number is a temporary telephone number that is used for call establishment via a PSTN. 3. The HLR of subscriber B knows the identification of the "visited" VLR where mobile B is currently located. When mobile B was switched on, the MSC/VLR of network Y sent its address to the HLR (location update). The HLR builds up a signaling message that includes the identification of called subscriber B together with the address of the visited MSC/VLR. 4. The HLR requests the visited VLR to provide a roaming number. The MSC/VLR of network Y has a pool of roaming numbers that look like the ordinary telephone numbers of that country. The vis- ited MSC/VLR then allocates one roaming number to subscriber B, stores it in its database, and sends it to the HLR, which then for- wards it to the MSC/VLR in network X. 6. The MSC/VLR of network X routes the call toward the MSC/VLR in network Y using the roaming number for dialing digits and the call is then routed the same way as any other telephone call. 7. When the MSC/VLR in network Y receives the call identified by the previously allocated roaming number, it associates this with subscriber B and initiates paging toward MS B. The roaming number is then released for reuse. To keep Figure 5.12 simple, the GMSCs at the border of networks X and Y are not shown as separate network elements. There is always at least one GMSC in each individual GSM network. The GMSC is a signaling interface point to other networks and it is able, for example, to route signal- ing messages toward the right HLR inside its own network. The telephone call to a roamed subscriber is currently always connected via the GMSC of the home network, and the roamed subscriber pays for the connection from the home 