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Communication Protocol Engineering Lab. Taek-su Shin 1 GSM Mobility Management April, 15, 2003 Taek-su Shin (piercer@kw.ac.kr) Communication Protocol Engineering Lab.
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Communication Protocol Engineering Lab. Taek-su Shin 2 Contents Overview GSM Location Update Mobility Databases Failure Restoration VLR Identification Algorithm VLR Overflow Control
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Communication Protocol Engineering Lab. 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
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Communication Protocol Engineering Lab. Taek-su Shin 4 Contents Overview GSM Location Update Mobility Databases Failure Restoration VLR Identification Algorithm VLR Overflow Control
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Communication Protocol Engineering Lab. Taek-su Shin 5 LA2 Basic Location Update Procedure(1/3) Case 1: Inter-LA Movement HLR VLR1 MSC1MSC2 LA1 MS HLR: Home Location Register VLR: Visitor Location Register MSC: Mobile Switching Center LA: Location Area MS: Mobile Station A location update request messageMAP_UPDATE_LOCATION_AREAMAP_UPDATE_LOCATION_AREA_ackA location update request message_ack
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Communication Protocol Engineering Lab. Taek-su Shin 6 Basic Location Update Procedure(2/3) Case 2: Inter-MSC Movement LA2 HLR VLR1 MSC1MSC2 LA1 MS A location update request messageMAP_UPDATE_LOCATION_AREAMAP_UPDATE_LOCATIONMAP_UPDATE_LOCATION_ackMAP_UPDATE_LOCATION_AREA_ackA location update request message_ack
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Communication Protocol Engineering Lab. Taek-su Shin 7 Basic Location Update Procedure(3/3) Case 3: Inter-VLR Movement LA2 HLR VLR1 MSC1MSC2 LA1 MS A location update request messageMAP_UPDATE_LOCATION_AREAMAP_SEND_IDENTIFICATIONMAP_SEND_IDENTIFICATION_ackMAP_UPDATE_LOCATIONMAP_UPDATE_LOCATION_ack MAP_UPDATE_LOCATION_AREA_ack MAP_CANCEL_LOCATIONMAP_CANCEL_LOCATION_ack A location update request message_ack
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Communication Protocol Engineering Lab. Taek-su Shin 8 Basic Call Origination Procedure Call origination operation VLR u1 MSC MS u1 PSTN the call origination requestMAP_SEND_INFO_FOR_OUTGOING_CALLMAP_SEND_INFO_FOR_OUTGOING_CALL_ackIAM
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Communication Protocol Engineering Lab. Taek-su Shin 9 Basic Call Termination Procedure Call termination message flow MSC MS u1 PSTN HLR VLR1 GMSC ISUP IAMMAP_SEND_ROUTING_INFORMATIONMAP_PROVIDE_ROAMING_NUMBERMAP_PROVIDE_ROAMING_NUMBER_ackMAP_SEND_ROUTING_INFORMATION_ackISUP IAM
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Communication Protocol Engineering Lab. Taek-su Shin 10 Contents Overview GSM Location Update Mobility Databases Failure Restoration VLR Identification Algorithm VLR Overflow Control
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Communication Protocol Engineering Lab. 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
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Communication Protocol Engineering Lab. 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
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Communication Protocol Engineering Lab. Taek-su Shin 13 Contents Overview GSM Location Update Mobility Databases Failure Restoration VLR Identification Algorithm VLR Overflow Control
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Communication Protocol Engineering Lab. 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
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Communication Protocol Engineering Lab. Taek-su Shin 15 VLR Failure Restoration(2/2) MS call termination MSC MS u1 PSTN HLR VLR GMSC ISUP IAMMAP_SEND_ROUTING_INFORMATIONMAP_PROVIDE_ROAMING_NUMBER MAP_PROVIDE_ROAMING_NUMBER_ack MAP_RESTORE_DATAMAP_RESTORE_DATA_ackMAP_INSERT_SUBSCRIBER_DATAMAP_INSERT_SUBSCRIBER_DATA_ack MAP_SEND_ROUTING_INFORMATION_ackISUP IAMMAP_SEND_INFO_FOR_INCOMING_CALLMAP_SEARCH_FOR_MOBILE_SUBSCRIBERMAP_PROCESS_ACCESS_REQUESTMAP_PROCESS_ACCESS_REQUEST_ack
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Communication Protocol Engineering Lab. Taek-su Shin 16 HLR Failure Restoration Uncovered period HLR restoration procedure HLR VLR MAP_RESETMAP_UPDATE_LOCATIONMAP_UPDATE_LOCATION_ack
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Communication Protocol Engineering Lab. Taek-su Shin 17 Contents Overview GSM Location Update Mobility Databases Failure Restoration VLR Identification Algorithm VLR Overflow Control
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Communication Protocol Engineering Lab. Taek-su Shin 18 VIA VLR Identification Algorithm HLR architecture MSVLR V1V1 V2V2 V3V3 V4V4 MSPVLR VLRts VLR V1V1 V2V2 V3V3 V4V4 Count 3 1 4 7 TS HLR* VLR_List* HLR VLR_Counter Backup (Nonvolatile Storage)
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Communication Protocol Engineering Lab. 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;
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Communication Protocol Engineering Lab. Taek-su Shin 20 VIA Procedure(2/4) Registration Step 1. Update HLR: V old ← HLR[p] · VLR; Send message, MAP_CANCEL_LOCATION, to cancel the VLR entry of p at V old : HLR[p] · VLR ← V new ; t old ← HLR[p] · ts; HLR[p] · ts ← t; Step 2. Update the V new Count field in VLR_Counter: If HLR[p] · VLR ≠ HLR[p] · PVLR then: Step 2.1. If VLR_Counter[V new ] exists, then: VLR_Counter[V new ] · Count ← VLR_Counter[V new ] · Count + 1; Step 2.2 Else create VLR_Counter[V new ] and VLR_List*[V new ]; VLR_Counter[V new ] ← 1;
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Communication Protocol Engineering Lab. Taek-su Shin 21 VIA Procedure(3/4) Registration Step 3. Update the V old counter entry: If t old > TS and V old ≠ HLR[p] · PVLR then: Step 3.1. VLR_Counter[V old ] · Count ← VLR_Counter[V old ] · Count – 1; Step 3.2. If VLR_Counter[V old ] · Count = 0 then: Step 3.2.1. Delete VLR_Counter[V old ] and VLR_List*[V old ];
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Communication Protocol Engineering Lab. 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;
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Communication Protocol Engineering Lab. Taek-su Shin 23 Contents Overview GSM Location Update Mobility Databases Failure Restoration VLR Identification Algorithm VLR Overflow Control
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Communication Protocol Engineering Lab. Taek-su Shin 24 Algorithm O-I Registration VLR V2 u3 HLR u1 u3 V1 V2 MS Request u1 V2 Response
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Communication Protocol Engineering Lab. Taek-su Shin 25 Algorithm O-II Cancellation HLR *u1V1V2
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Communication Protocol Engineering Lab. Taek-su Shin 26 Algorithm O-III Call Origination VLR V2 MS MAP_SEND_INFO_FOR_OUTGOING_CALL MAP_SEND_INFO_FOR_OUTGOING_CALL_ack (deny_reason: no record) MAP_UPDATE_LOCATION_AREA MAP_UPDATE_LOCATION_AREA_ackMAP_SEND_INFO_FOR_OUTGOING_CALLMAP_SEND_INFO_FOR_OUTGOING_CALL_ack
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Communication Protocol Engineering Lab. Taek-su Shin 27 Algorithm O-IV Call Termination Originating switch VLR V2 u3 HLR * * u1 u3 V2 Location query u1 Location response MSC MS u1
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