ie634 wireless high speed networks
TRANSCRIPT
IE634 Wireless High Speed Networks
Lecture 5. GSMMobility Management andInternational Roaming for GSM (Ch 11, 13)
GSM Mobility Management
GSM Location Area hierarchy LA(location area); a group of
BTSs Registration Permanent record; HLR
Location update procedure
Two issues of GSM MM Fault tolerance Database overflow
GSM Location Update
Location update procedure Case 1: Inter-LA movement Case 2: Inter-MSC movement Case 3:Inter-VLR movement
Step 1; TMSI(temporary mobile subscriber identity), alias of IMSI
Step 2: MAP_UPDATE_LOCATION_AREA Address of MSC, TMSI, LAI, Target
LAI, etc
Step 3 and 4; Acknowledgement
GSM Location Update
Location update procedure Case 2: Inter-MSC
movement
Step 1-2; Location update request sent to VLR1
Step 3: VLR1 sends MAP_SEND_LOCATION to HLR. The message includes IMSI of MS, addresses of MSC2 and VLR1.
Step 4; by using IMSI, HLR identifies MS’s record. MSC number field updated.
Step 5-6: Acknowledgement to MS
GSM Location Update
Location update procedure Case 3: Inter-VLR movement
Step 1; Location update request sent to VLR2
Step 2-3: From MAP_UPDATE_LOCATION_AREA message, VLR2 identifies VLR1’s address. Sends MAP_SEND_IDENTIFICATION to VLR1 -> TMSI of MS retrieved by VLR1 and used to get MS’s IMSI by VLR1 and IMSI sent to VLR2 by VLR1.
Step 4-5; VLR2 sends registration message to update HLR
Step 6: VLR2 generates new TMSI and sends it to MS
Step 7-8 : obsolete record of MS in VLR1 deleted
Basic Call Origination Procedures
Step 1; MS sends call origination request
Step 2: MSC forwards MAP_SEND_INFO_FOR_OUTGOING_CALL to VLR
Step 3; VLR sends MAP_SEND_INFO_FOR_OUTGOING_CALL_ack to MSC to grant call request.
Step 4: MSC sets up trunk according to standard PSTN call setup procedure
Call Termination Procedures
Step 1; MSISDN -> SS7 ISUP IAM message
Step 2: GMSC->HLR, MAP_SEND_ROUTING_INFORMATION to HLR.
Step 3: HLR sends MAP_PROVIDE_ROAMING_* to VLR to obtain MSRN.
Step 4 and 5: VLR creates MSRN by using MSC number -> it is sent back to GMSC through HLR
Step 6: MSRN provides the address of the target MSC where MS resides. SS7 ISUP IAM
Mobility Databases
HLR : HLR record consists of three types of information
Mobile station information, IMSI, MSISDN (phone of an MS)
Location information : ISDN number (address) of VLR where MS resides and ISDN number of MSC where MS resides.
Service information: service subscription, service restrictions, supplementary services.
VLR : VLR record consists of three parts:
Mobile station information: IMSI, MSISDN, TMSI Location information: MSC number, LAI Service information : a subset of service
information stored in HLR
Failure Restoration
VLR Failure Restoration MS registration
VLR record recovered as in inter-VLR movement. IMSI over the air.
MS call origination Unidentified subscriber.
MS call termination MAP_SEARCH_FOR_MOBILE_SUBS
CRIBER : expensive operation. Step 9-11 : Target MSC
interrogates VLR, but in vain. VLR asks MSC to determine LA of MS by sending above message.
HLR Failure Restoration
For a GSM HLR, Save updates into nonvolatile storage. Location information periodically transferred from HLR into the backup.
After HLR failure, data in the back reloaded into HLR. -> uncovered period
HLR restoration procedure Step 1: HLR sends SS7 TCAP messa
ge MAP_RESET to the VLRs where its MSs are located.
Step 2 : MAP_UPDATE_LOCATION to HLR
VLR Identification Algorithm (VIA)
Describe an algorithm to identify the exact VLRs to be contacted by HLR after HLR failure. After HLR failure, HLR only needs to send the MAP_RESET message to the VLRs listed in VLR_List*.
HLR record has two extra fields. ts field : last time of location update PVLR filed : address of the VLR where
MS resides at the last check-pointing time. HLR*[p].VLR=HLR[p].PVLR
VLR Identification Algorithm (VIA)
Two extra data structures TS : last check-pointing or
back up time VLR_Counter : set of (VLR,
Count) pairs
VLR Identification Algorithm (VIA)
VIA Procedure 1: Check-pointing HLR[p]*.VLR<- HLR[p].VLR TS<- current time HLR[p].ts <-TS; HLR[p].PVLR<-HL
R[p].VLR VLR_Counter<-0, VLR_List*<-0;
VLR Identification Algorithm (VIA)
VIA Procedure 2: Registration Step 1: Update HLR
Vold <- HLR[p].VLR; HLR[p].VLR<-Vnew; Told <- HLR[p].ts; HLR[p].ts<-ts;
Step 2: Update Vnew Count field in VLR_Counter
If HLR[p].VLR is not equal to HLR[p].PVLR then
If VLR_Counter[Vnew] exists, then VLR_Counter[Vnew].Count <- VLR_Counter[Vnew].Count+1;
Else create VLR_Counter[Vnew] and VLR_List*[Vnew]; VLR_Counter[Vnew]<-1;
VLR Identification Algorithm (VIA)
VIA Procedure 3: Restore Step 1; TS <- current time Step 2: HLR[p].PVLR<- HLR[p].VL
R<-HLR[p].VLR; HLR[p].ts<-TS; For every VLR entry V in VLR_List
*, send an SS7 TCAP MAP_RESET message to V.
VLR Overflow Control
# of records in VLR can change dynamically. -> VLR overflow.
Overflow control scheme presented.
Extra flag (1 bit) required. Algorithm O-I: Registration
Step 1: Registration Request Step 2: Registration Response
u3V2*
VLR Overflow Control
Algorithm O-IV: Call termination
Step 1 : Location Query Step 1.1 Calling party dials
u1 Step 1.2 location query
message to HLR Step 1.3 u1 is overflow user.
Step 2 : Location Response V2 creates the routable address of
u1 HLR returns routable address to
originating switch Setup trunk to MSC MSC pages MS and call path
established
CH 13. International Roaming for GSM
International call setup procedure
Call setup message flow : (1)->(1.1)->(1.2)->(1.3)->(2 : HLR E)->(3.1)->(3.2)->(3.3 : VLR F)-> (4.1 : ISC B)->(4.2: ISC C)->(4.3) ->(5 : GMSC D)->(6.1) ->(6.2)->(6.3 : MSC C) -> MS
Voice circuit path is : (1) -> (1.2) -> (1.3)->(6.1)->(6.2)->(6.3)
Reducing the International Call Delivery Cost
Roamer Location Cache (RLC) : Contains the records of all international r
oamers who are presently in that visited system.
For home HLR, RLC is like a VLR For visited VLR, RLC is like a HLR
Solution 1 : RLC colocated with ISC Location update procedure Step 2. VLR sends MAP_UPDATE_LOCATI
ON to roamer’s HLR Step 5. MSISDN required, MAP_RESTORE
_DATA, MAP_INSERT_SUBSCRIBER_DATA
Reducing the International Call Delivery Cost
Call Delivery (solution 1)
Reducing the International Call Delivery Cost
Solution 2 GSM service provider builds its
own RLC Registration procedure
Reducing the International Call Delivery Cost
Solution 2 Caller must dial Switch D : Sophisticated billing : can be
charged either with GSM call or with international call.
Reducing the International Call Delivery Cost
Solution 3 Extractor
Reducing the International Call Delivery Cost
Solution 4 Dial
NDC1+IRAC+CC+NDC2+SN