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GSM Mobility Management April, 15, 2003 Taek-su Shin (piercer@kw.ac.kr)

GSM Mobility Management April, 15, 2003 Taek-su Shin (piercer@kw.ac.kr) Communication Protocol Engineering Lab. Contents. Overview GSM Location Update Mobility Databases Failure Restoration VLR Identification Algorithm VLR Overflow Control. Overview. Mobility management

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GSM Mobility Management April, 15, 2003 Taek-su Shin (piercer@kw.ac.kr)

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  1. GSM Mobility Management April, 15, 2003 Taek-su Shin (piercer@kw.ac.kr) Communication Protocol Engineering Lab. Taek-su Shin

  2. Contents • Overview • GSM Location Update • Mobility Databases • Failure Restoration • VLR Identification Algorithm • VLR Overflow Control Taek-su Shin

  3. Overview • Mobility management • Location update (registration) • Call origination • Call termination • Fault tolerance • Location database fail • Can’t GSM service • Failure restoration procedure • Algorithm to speed up the HLR failure recovery procedure • Database overflow • Fail registration • VLR overflow control scheme Taek-su Shin

  4. Contents • Overview • GSM Location Update • Mobility Databases • Failure Restoration • VLR Identification Algorithm • VLR Overflow Control Taek-su Shin

  5. MS Basic Location Update Procedure(1/3) • Case 1: Inter-LA Movement HLR VLR1 VLR1 HLR: Home Location Register VLR: Visitor Location Register MSC: Mobile Switching Center LA: Location Area MS: Mobile Station MSC1 MSC2 A location update request message_ack MAP_UPDATE_LOCATION_AREA_ack A location update request message MAP_UPDATE_LOCATION_AREA LA1 LA2 Taek-su Shin

  6. MS Basic Location Update Procedure(2/3) • Case 2: Inter-MSC Movement HLR VLR1 VLR1 MSC1 MSC2 A location update request message_ack MAP_UPDATE_LOCATION_AREA_ack MAP_UPDATE_LOCATION_AREA A location update request message MAP_UPDATE_LOCATION_ack MAP_UPDATE_LOCATION LA1 LA2 Taek-su Shin

  7. MS Basic Location Update Procedure(3/3) • Case 3: Inter-VLR Movement HLR MAP_CANCEL_LOCATION_ack MAP_CANCEL_LOCATION VLR1 VLR1 MSC1 MSC2 MAP_UPDATE_LOCATION_AREA_ack A location update request message_ack LA1 LA2 MAP_SEND_IDENTIFICATION_ack MAP_UPDATE_LOCATION_AREA A location update request message MAP_UPDATE_LOCATION_ack MAP_SEND_IDENTIFICATION MAP_UPDATE_LOCATION Taek-su Shin

  8. VLR u1 MS u1 Basic Call Origination Procedure • Call origination operation PSTN MSC MAP_SEND_INFO_FOR_OUTGOING_CALL_ack MAP_SEND_INFO_FOR_OUTGOING_CALL the call origination request IAM Taek-su Shin

  9. MS u1 Basic Call Termination Procedure • Call termination message flow PSTN HLR GMSC VLR1 MSC MAP_SEND_ROUTING_INFORMATION_ack MAP_PROVIDE_ROAMING_NUMBER_ack MAP_SEND_ROUTING_INFORMATION MAP_PROVIDE_ROAMING_NUMBER ISUP IAM ISUP IAM Taek-su Shin

  10. Contents • Overview • GSM Location Update • Mobility Databases • Failure Restoration • VLR Identification Algorithm • VLR Overflow Control Taek-su Shin

  11. HLR • Home location register • Mobile station information • IMSI (International Mobile Subscriber Identity) • MSISDN (MS ISDN number) • Location information • ISDN number of the VLR • ISDN number of the MSC • Service information • Service subscription • Service restrictions • Supplementary services Taek-su Shin

  12. VLR • Visitor location register • Mobile station information • IMSI • MSISDN • TMSI (Temporary Mobile Subscriber Identity) • Location information • MSC number • Location area ID (LAI) • Service information • Subset of the service information stored in the HLR Taek-su Shin

  13. Contents • Overview • GSM Location Update • Mobility Databases • Failure Restoration • VLR Identification Algorithm • VLR Overflow Control Taek-su Shin

  14. VLR Failure Restoration(1/2) • MS registration • A case of inter-VLR movement • Recovered by the normal registration procedure • Can’t be recognized TMSI • Be asked to send IMSI • MS call origination • System error : “unidentified subscriber” • Be asked to initiate the location registration procedure Taek-su Shin

  15. MS u1 VLR Failure Restoration(2/2) • MS call termination MAP_PROVIDE_ROAMING_NUMBER_ack PSTN HLR GMSC VLR MAP_INSERT_SUBSCRIBER_DATA_ack MAP_INSERT_SUBSCRIBER_DATA MAP_RESTORE_DATA_ack MAP_RESTORE_DATA MSC MAP_SEARCH_FOR_MOBILE_SUBSCRIBER MAP_SEND_ROUTING_INFORMATION_ack MAP_SEND_INFO_FOR_INCOMING_CALL MAP_PROCESS_ACCESS_REQUEST_ack MAP_SEND_ROUTING_INFORMATION MAP_PROCESS_ACCESS_REQUEST MAP_PROVIDE_ROAMING_NUMBER ISUP IAM ISUP IAM Taek-su Shin

  16. HLR Failure Restoration • Uncovered period • HLR restoration procedure HLR VLR MAP_UPDATE_LOCATION_ack MAP_UPDATE_LOCATION MAP_RESET Taek-su Shin

  17. Contents • Overview • GSM Location Update • Mobility Databases • Failure Restoration • VLR Identification Algorithm • VLR Overflow Control Taek-su Shin

  18. VIA • VLR Identification Algorithm • HLR architecture HLR* VLR_List* MS VLR VLR V1 V2 V3 V4 Backup (Nonvolatile Storage) TS HLR VLR_Counter ts VLR MS PVLR VLR Count V1 3 V2 1 V3 4 V4 7 Taek-su Shin

  19. VIA Procedure(1/4) • Check-pointing Step 1. For every location entry p in HLR* do: HLR[p]* · VLR ← HLR[p] · VLR; Step 2. TS ← current time; Step 3. For every location entry p in HLR do: HLR[p] · ts ← TS; HLR[p] · PVLR ← HLR[p] · VLR; Step 4. VLR_Counter ← Ø, VLR_List* ← Ø; Taek-su Shin

  20. VIA Procedure(2/4) • Registration Step 1. Update HLR: Vold ← HLR[p] · VLR; Send message, MAP_CANCEL_LOCATION, to cancel the VLR entry of p at Vold: HLR[p] · VLR ← Vnew; told ← HLR[p] · ts; HLR[p] · ts ← t; Step 2. Update the Vnew Count field in VLR_Counter: If HLR[p] · VLR ≠ HLR[p] · PVLR then: Step 2.1. If VLR_Counter[Vnew] exists, then: VLR_Counter[Vnew] · Count ← VLR_Counter[Vnew] · Count + 1; Step 2.2 Else create VLR_Counter[Vnew] and VLR_List*[Vnew]; VLR_Counter[Vnew] ← 1; Taek-su Shin

  21. VIA Procedure(3/4) • Registration Step 3. Update the Vold counter entry: If told > TS and Vold ≠ HLR[p] · PVLR then: Step 3.1. VLR_Counter[Vold] · Count ← VLR_Counter[Vold] · Count – 1; Step 3.2. If VLR_Counter[Vold] · Count = 0 then: Step 3.2.1. Delete VLR_Counter[Vold] and VLR_List*[Vold]; Taek-su Shin

  22. VIA Procedure(4/4) • Restore Step 1. TS ← current time; Step 2. For every location entry p in HLR, do: HLR[p] · PVLR = HLR[p] · VLR ← HLR[p]* · VLR; HLR[p] · ts ← TS; Step 3. For every VLR entry V in VLR_List*, send an SS7 TCAP MAP_RESET message to V; Taek-su Shin

  23. Contents • Overview • GSM Location Update • Mobility Databases • Failure Restoration • VLR Identification Algorithm • VLR Overflow Control Taek-su Shin

  24. MS Algorithm O-I • Registration Response Request HLR VLR V2 u1 V1 V2 u3 V2 u1 u3 Taek-su Shin

  25. Algorithm O-II • Cancellation HLR * u1 V1 V2 Taek-su Shin

  26. MS Algorithm O-III • Call Origination VLR V2 MAP_SEND_INFO_FOR_OUTGOING_CALL_ack MAP_SEND_INFO_FOR_OUTGOING_CALL MAP_UPDATE_LOCATION_AREA_ack MAP_SEND_INFO_FOR_OUTGOING_CALL MAP_UPDATE_LOCATION_AREA MAP_SEND_INFO_FOR_OUTGOING_CALL_ack (deny_reason: no record) Taek-su Shin

  27. MS u1 Algorithm O-IV • Call Termination Originating switch Location response Location query HLR VLR V2 * u1 V2 * u3 V2 u3 u1 MSC Taek-su Shin

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