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)