communication protocol engineering lab. taek-su shin 1 gsm mobility management april, 15, 2003...

Taek-su Shin 1CommunicationProtocolEngineering Lab.

GSM Mobility Management

April, 15, 2003 Taek-su Shin

([email protected])Communication Protocol Engineering Lab.


Contents Overview GSM Location Update Mobility Databases Failure Restoration VLR Identification Algorithm VLR Overflow Control


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


LA2

Basic Location Update Procedure(1/3)

Case 1: Inter-LA Movement

HLR

VLR1 VLR1

MSC1 MSC2

LA1 MS

HLR: Home Location RegisterVLR: Visitor Location RegisterMSC: Mobile Switching CenterLA: Location AreaMS: Mobile Station

A location update request messageMAP_UPDATE_LOCATION_AREAMAP_UPDATE_LOCATION_AREA_ackA location update request message_ack



Case 2: Inter-MSC Movement

LA2

HLR

VLR1 VLR1

MSC1 MSC2

LA1 MS

A location update request messageMAP_UPDATE_LOCATION_AREAMAP_UPDATE_LOCATIONMAP_UPDATE_LOCATION_ackMAP_UPDATE_LOCATION_AREA_ackA location update request message_ack



Case 3: Inter-VLR Movement

LA2

HLR

VLR1 VLR1

MSC1 MSC2

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


Basic Call Origination Procedure Call origination operation

VLR

u1

MSC

MSu1

PSTN

the call origination requestMAP_SEND_INFO_FOR_OUTGOING_CALLMAP_SEND_INFO_FOR_OUTGOING_CALL_ackIAM


Basic Call Termination Procedure Call termination message flow

MSCMSu1

PSTN HLR VLR1GMSC

ISUP IAMMAP_SEND_ROUTING_INFORMATIONMAP_PROVIDE_ROAMING_NUMBERMAP_PROVIDE_ROAMING_NUMBER_ackMAP_SEND_ROUTING_INFORMATION_ackISUP IAM


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


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


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


VLR Failure Restoration(2/2) MS call termination

MSCMSu1

PSTN HLR VLRGMSC

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


HLR Failure Restoration Uncovered period

HLR restoration procedure

HLR VLR

MAP_RESETMAP_UPDATE_LOCATIONMAP_UPDATE_LOCATION_ack


VIA VLR Identification Algorithm

HLR architectureMS VLR

VLRV1

V2

V3

V4

MS PVLR VLRtsVLRV1

V2

V3

V4

Count3147

TS

HLR*VLR_List*

HLRVLR_Counter

Backup (Nonvolatile Storage)


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;


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: IfHLR[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;


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];


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;


Algorithm O-I Registration

VLR V2

u3

HLRu1u3

V1V2 MS

Request

u1

V2

Response


Algorithm O-II Cancellation

HLR* u1 V1V2


Algorithm O-III Call Origination

VLR V2 MS

MAP_SEND_INFO_FOR_OUTGOING_CALLMAP_SEND_INFO_FOR_OUTGOING_CALL_ack(deny_reason: no record)

MAP_UPDATE_LOCATION_AREAMAP_UPDATE_LOCATION_AREA_ackMAP_SEND_INFO_FOR_OUTGOING_CALLMAP_SEND_INFO_FOR_OUTGOING_CALL_ack


Algorithm O-IV Call Termination

Originatingswitch

VLR V2

u3

HLR**

u1u3

V2V2

Location query

u1

Location response

MSC MSu1

communication protocol engineering lab. taek-su shin 1 gsm mobility management april, 15, 2003...

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