The following procedures for a call to a mobile subscriber are
illustrated in Figure B-5.
1. Any call entering the GSM network from the Public Switched Telephony Network/Integrated Services Digital Network (PSTN/ISDN) is routed to the nearest Gateway Mobile services Switching Center (GMSC).
2. The GMSC analyzes the Mobile Station ISDN (MSISDN) to find out which HLR the mobile subscriber is registered in and then sends the MSISDN along with a request for routing information to this HLR. The serving MSC/VLR address is stored in the HLR from location updating. The HLR contains the IMSI that is connected to this MSISDN number.
3. The HLR sends a request for a Mobile Station Roaming Number (MSRN) to the MSC/VLR. Included in the message is the MS’s IMSI. The MSC/VLR allocates an idle MSRN and links it to the IMSI.
4. The MSRN is returned via the HLR to the GMSC.
5. The GMSC, by means of the MSRN, routes the call to the MSC/VLR.
6. When the MSC/VLR receives the call, it uses the MSRN to retrieve the MS’s IMSI. The MSRN is then released.
7. Using the MS’s IMSI, the MSC/VLR identifies the location area in which the phone is currently situated.
8. The MS is paged in all cells within this location area.
9. When the MS responds to the paging message, authentication, cipher mode setting, and an IMEI check are carried out, if defined in the network.
10. If the authentication is confirmed and the ciphering is successful, the call is connected from the MSC to the BSC and the BTS, where a traffic channel is selected on the air path.
illustrated in Figure B-5.
1. Any call entering the GSM network from the Public Switched Telephony Network/Integrated Services Digital Network (PSTN/ISDN) is routed to the nearest Gateway Mobile services Switching Center (GMSC).
2. The GMSC analyzes the Mobile Station ISDN (MSISDN) to find out which HLR the mobile subscriber is registered in and then sends the MSISDN along with a request for routing information to this HLR. The serving MSC/VLR address is stored in the HLR from location updating. The HLR contains the IMSI that is connected to this MSISDN number.
3. The HLR sends a request for a Mobile Station Roaming Number (MSRN) to the MSC/VLR. Included in the message is the MS’s IMSI. The MSC/VLR allocates an idle MSRN and links it to the IMSI.
4. The MSRN is returned via the HLR to the GMSC.
5. The GMSC, by means of the MSRN, routes the call to the MSC/VLR.
6. When the MSC/VLR receives the call, it uses the MSRN to retrieve the MS’s IMSI. The MSRN is then released.
7. Using the MS’s IMSI, the MSC/VLR identifies the location area in which the phone is currently situated.
8. The MS is paged in all cells within this location area.
9. When the MS responds to the paging message, authentication, cipher mode setting, and an IMEI check are carried out, if defined in the network.
10. If the authentication is confirmed and the ciphering is successful, the call is connected from the MSC to the BSC and the BTS, where a traffic channel is selected on the air path.
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