GSM Call Setup
Transcript of GSM Call Setup
Call setup to/from a GSM subscriber
Technology for executives, Moscow - 13 September 2004Author: Hans Myhre
How does the network know where the subscribers are?
The radio network consists of a large number of BTSs. Each of these is given an identity.
The BTSs are grouped in Location Areas, which also are given an identity.
Each MSC/VLR (Mobile Services Switching Center/Visitor Location Register) serves the BTSs in an number of Location Areas
The GSM phones reports to the network (VLR) when it moves from a BTS in one Location Area to a BTS in another Location Area.
How does the network know where ths subscribers are?
VLR always knows in which Location Area the GSM subscriber is located in at the moment
HLR always knows in which MSC/VLR the GSM subscriber is just now
The GSM subscriber’s telephone number tells the network to which HLR the actual GSM subscriber belongs.
Location update HLRA
MSC/VLR1
Location Area 1 info1
2 3
4
Mobile A
1) Mobile A is staying in Location Area 1. MSC/VLR1 has reported this to Mobile A’s HLR.
2),3) Mobile A moves to Location Area 2, and identifies a new Location Area info (LA2). It reports its arrival to MSC/VLR2.
4) MSC/VLR2 informs HLRA, and receives sets of Authentication Data for Mobile A.
MSC/VLR2
Location Area1
Location Area2
Mobile A
1
Call to a mobile telephone
HLRB
MSC/VLR
Calling9212345
Where is 9212345?
9212345 is in MSC/VLRB
MSC/VLRB1
2 3
4
5
1) The call is routed through the telephone network to the MSC closest to the called GSM subscriber (”Gateway” MSC)
2), 3)Gateway MSC checks with HLRB ”Where is the GSM subscriber?”
4) The call is established to the actual MSC/VLR (Visiting MSC) either directly or through the fixed or international telephone network
5) The request for mobile 9212345 is transmitted over all BTSs in the actual Location Area of the called GSM subscriber. Mobile B recognises its own identity, and ringing is generated.
Mobile B 9212345
Physical connection which must be remain connected during the whole call
Gateway MSC (GMSC)
Visiting MSC
Call to a GSM phone which has activated Unconditional Call Forward
HLRB
MSC/VLR
9212345
Where is 9212345?
9212345 shall be forwarded to number xxxxxxx
MSC/VLRB1
2 30
0) The GSM subscriber has activated the service ”Forward all calls to another number (Unconditional call Forward)”.
3) When calling GSM subscriber 9212345, the HLRB request the call to be forwarded to the desired number.
4) ”Gateway MSC” ensures call forwarding of the call, e.g. to the GSM subscriber’s Voice Mailbox.
4
0
VMS
Mobile B 9212345Gateway MSC
(GMSC)
Calling9212345
Call from a GSM phone to a fixed phone
HLRA
MSC/VLRA
Calling2212345
Request for authentication data
Authentication data
1
2 3
4
Mobile A
1) Via the radio path and the base station network a call request for Fixed subscriber B 2212345 is sent to the MSC/VLRA.
2-3) MSC/VLRA collects authentication data from HLRA (if such data has not been collected earlier) .
4) The connection is established via the closest telephone switch in the fixed telephone network, and are treated further as a normal connection in the national/international fixed telephone network.
4 Subscriber B 2212345
Call from a GSM phone to another GSM phone
HLRA
MSC/VLRA
Calling9212345
Authentication data
MSC/VLRB1
2 3
6 7
1) Via the radio path and the base station network a call request for GSM subscriber B 9212345 is sent from Mobile A to MSC/VLRA.
2-3) MSC/VLRA collects authentication data from HLRA (if such data has not been collected earlier) . Normally a bulk of such data is transferred, thus avoiding repeating authentication requests to HLRA.
4-7) MSC/VLRA requests HLRB of the actual location of GSM subscriber B, and the call is establised as described earlier.
HLRB
Mobile AMobile B 9212345
Where are 9212345?
9212345 is in MSC/VLRB
4
5
NOTE:
The four MSCs/HLRs can be everything from one integrated node to four network elements being in four different countries belonging to four different mobile operators, everything dependent of the identity and location of the two GSM mobiles.
Request for authentication data
Roaming- Call setup
- Accounting
Example: Call from Norwegian GSM mobile visiting Thailand, and calling a Malayan GSM mobile who also are visiting Thailand
Mobile A Mobile B
+6016***
HLRA
MSC/VLRA
Calling+6016**
Request of authentication data
Authentication data
1
2 3
MSC/VLRB
MSC/VLR
HLRB
Where is +6016**?+6016** is in MSC/VLRB
5
47
6
Norway
Malaysia
Thailand
National/ internationaltelephone network
+6016**
Physical connection which must be established during the whole call
Note:
Mobile A and B can either be in same or different mobile networks in Thailand.
A pays for international connection Thailand – Malaysia
B pays for international connection Malaysia - Thailand
Example: Call from Norwegian GSM mobile visiting Thailand, and calling a Malayan GSM mobile who also are visiting Thailand.
Call data flow
TnM
DiGi
DTAC
Billing
system
Mobile A (TnM)
Mobile B (DiGi)
Note:
The responsibility for paying DTAC (Thailand) is the GSM operators (TnM and DiGi)!
TnM and DiGi has the responsibility to collect money from their GSM subscribers
Clearing house X
Billing
system
Billing
system
MSC/VLR
Clearing house Roameo
MO CDR $
MT CDR $
MT TAP $ MO TAP $
MT TAP $
MO TAP $
MO TAP $
Roaming and accounting
GSM Association has defined standard format on call/billing data which shall be transferred between the operators
Eariler: All operators transferred data to all => chaos! Now: All operators utilises Data Clearing Houses
– Largest actors: MACH, Roameo, EDS– Single point of contact for data float between operators– Doesn ot change the responsibilities between the operators! (Acts as
the extended arm of the operator…)
Data Clearing House services:– Can convert data formats (local format to TAP-format, TAP2 to TAP3…)– Checks invoices and call records– Fraud control– Etc
Revenue Assurance - an exampe
Control
Switch configuration
EDR errors
CommissionsData accuracy
Tariff accuracy
Inventory management
Interconnect reconciliations
Fraud management
Prepaid controls Mediation rules
Tariff settingsInvoice
production
Least cost routing
Credit controlPayments
Acess Network
Revenue Assurance- example: SMS, TnM
HLR
MSC/TSC
SMSC
IN
EPPBilling
GatewayVAS-Rating
Geneva
NA S212 (CABS)
2
1
3 5 6 7
12 11
13
49
10
8
Production/traffic collections Charging Invoicing