Traffic CasesinterWAVE COMMUNICATIONS
Location Update
Location Updating keeps the network informed of the Mobile Station’s whereabouts
Location Updating involving the HLR is invoked when the MS moves to a new location area or when the MS tries to access the network and is not known to the VLR
This is called location updating
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MSC updates VLR to LA A2
Still same serving MSC
2. MS location updates to MSC B via BSS
3. MSC updates VLR from MS: LA B1
LA B1
LA A2
MSC/VLR B
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Only sent to HLR if this is the first time the MS has location updated in this VLR
Chan. Req.
Chan. Estab.
(RAND/SRES/Kc)
SDCCH
(RAND)
if authentication was successful the VLR will request the MSC to start the ciphering process. If fails the HLR will be notified and an “Authentication Reject” message will be sent to the mobile
6. Cipher mode
MS Originate Req
1. The subscriber presses the send key initiate a “Channel Request” message from the MS to the BSS.
2. This is followed by the assignment of dedicated control channels and the establishment of the signaling link between the MS and BSS
3. The “request for service “ is passed to the MSC which relays to the VLR. The VLR carries out the authentication process. HLR checked if if the MS was not previously registered.
4. The set-up message is sent to the MSC accompanied by the call information( type off call, and number being called.
5. The MSC may invoke the MS IMEI check(to see if it is a valid subscriber)
6. The MSC then assigns a traffic channel to the BSS (Assignment command), which in turn assigns an air- interface channel to the BTS
7. Ring tone is applied at the MS in response to “alerting” which the MSC sends when the PSTN responds.
8. When answered the message “connect” is forwarded to the MS by the MSC, stopping the ringing. The MSC then connects the GSM traffic channel to the PSTN circuit
Handshake
Assgn complete
Alert, Connect
MSC
VLR
HLR
Gateway
MSC
1. Call arrives from PSTN, ISDN, or PLMN. MSISDN is passed to Gateway MSC (G-MSC)
2. G-MSC inquires HLR serving the called MSISDN
3. HLR looks up MSISDN and gets corresponding IMSI and serving MSC
4. HLR sends request with IMSI to the serving MSC/VLR for MS roaming number (MSRN)
5. MSC/VLR assigns MSRN and associates it with IMSI
6. MSRN is passed to HLR, which passes it to G-MSC
7. G-MSC uses MSRN to route traffic call to serving MSC (possibly via PSTN exchanges)
8. Serving MSC receives call at MSRN and looks up the corresponding IMSI
MSISDN
IMSI
MSC
VLR
IMSI
BSC
BTS
BTS
1. MSC inquires VLR for Location Area (LA) of IMSI
2. MSC looks up serving BSC corresponding to Location Area
3. MSC initiates paging procedure for IMSI (or TMSI, if VLR sent TMSI)
4. BSC sends paging command to BTS
5. BTSs send paging requests over the air
6. Mobile responds to page and initiates page response procedure
page
page
page
IMSI
IMSI
Page Command
Page Req
Chan Req
RR Connection
Paging Response
Power budget
To avoid losing a call in progress when a mobile station leaves the radio coverage of the cell in charge or when the radio link as seen by the MS is better by another serving cell without leaving the coverage area.
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Handover between two BTSs that are controlled by different BSCs.
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Handovers
Intra-BTS
Intra-BSC
Inter-BSC
Inter-MSC
Handover between two BTSs that are controlled by different BSCs, which are controlled by different MSCs.
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(1/2 second) reported to BSC (SACCH)
Uplink channel (MS to BTS) measured by BTS:
RxLev (power level)
RxLev (of serving BTS)
RxQual (of serving BTS)
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interWAVE COMMUNICATIONS
Handover Algorithm
BSC decides when handover is required, as well as list of best target BTS’s.
GSM TS 05.08 : generic HO algorithm
Manufacturer specific
Depends on :
1. Activate a new traffic channel at new BTS
2. HO command to MS
3. MS sends HO Access on new traffic channel
4. MS & new BTS establishes reliable link
5. HO complete
6. Call routed to new BTS
7. Old traffic channel is released
Note: (2) TCH channels are active until the HO process is complete
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information
exchange
SACCH
FACCH
FACCH
FACCH
SACCH
measure
measure