KEY TERMS
• IDLE MODE– the MS is ON, but not engaged in a call
• ACTIVE MODE– the MS is ON and engaged in a call
• DETACHED– the mobile station is OFF
• PAGING– message broadcast from MSC/VLR to the MS for an
incoming call
KEY TERMS
• ROAMING– the MS moves around the network, from one cell to
another cell
– it always occurs during idle mode
• HANDOVER– an active call is passed from one cell to another
• REGISTRATION/LOCATION UPDATING– the MS is roaming and must inform the network when it
enters a new Location Area (LA)
REGISTRATION & ROAMING
• both REGISTRATION and ROAMING are always performed in IDLE mode
• MS continuously measures and keeps track the signal strength coming from each of the surrounding cells
• MS will always ‘tune’ to the base station with a better signal strength
HLR GMSCMSC/
VLR
BSC
BTS
BTS
BTS
PSTN
1
2
3
4
5
67
CALL TO MOBILE STATION
• DIFFERENCE with the PSTN network, the MS must be paged since its location is unknown
CALL TO THE MS
• PSTN subscriber dials the mobile subscriber number
• the GMSC receives the call
HLR GMSCMSC/
VLR
PSTN
1
1
CALL TO A MS
• GMSC queries the HLR for routing
• HLR gives back the necessary routing information
2HLR GMSC
PSTN
2
?
CALL TO A MS
• the GMSC routes the call to the serving MSC
3
HLR GMSCMSC/
VLR
3
CALL TO A MS
• MSC checks VLR for the Location Area of the MS
4
GMSCMSC/
VLR
BSC
BTS
BTS
BTS
4
?
CALL TO A MS
• MSC contacts the MS via BSC and
• BTS sends a page request
5MSC/
VLR
BSC
BTS
BTS
BTS
5
?
?
?
CALL TO A MS
• The MS responds
6MSC/
VLR
BSC
BTS
BTS
BTS 6
CALL TO A MS
• BSC selects a traffic channel
• MS tunes to this channel
• The MS generates the ringing signal
7
BSC
BTS
BTS
BTS7
CALL FROM MOBILE STATION
MSC/
VLRPSTN
12
3
4
5BSC
CALL FROM THE MS
• mobile subscriber dials the number
1
1
BSC
CALL FROM THE MS
• MSC/VLR receives a message requesting access
• MSC/VLR checks MS status
2
MSC/
VLR
2
BSC
CALL FROM THE MS
• The number dialed is analyzed by the MSC/VLR
• The MSC/VLR initiates a call set-up to the PSTN
3
MSC/
VLRPSTN
3
?
CALL FROM THE MS
• MSC/VLR directs BSC to allocate a free traffic channel
• this is then forwarded to the BTS and the MS
4
MSC/
VLR
4
BSC
CALL FROM THE MS
• PSTN subscriber answers the call and then connection is established
5
MSC/
VLRPSTN
5BSC
HANDOVER
switching to a new BTS while the MS is in active
mode
again, BTS and MS take measurements and
keeps track of the signal strength per cell
surrounding the MS
the BSC decides if handover is needed
MS’ active role: Mobile Assisted Handover
(MAHO)