Gsm Call Setup

Call setup to/from a GSM subscriber

Technology for executives, Moscow - 13 September 2004 Author: Hans Myhre

How does the network know where the subscribers are? ●

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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

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HLR always knows in which MSC/VLR the GSM subscriber is just now

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The GSM subscriber’s telephone number tells the network to which HLR the actual GSM subscriber belongs.

Location update Location Area 1 info

Mobile A

Location Area 1

1)

4

1

MSC/ VLR1 1

HLRA

2

3

Mobile A

MSC/ VLR2

Location Area 2

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.

Call to a mobile telephone HLRB

Where is 9212345?

2 Gateway MSC (GMSC)

MSC/ VLR

3 9212345 is in MSC/VLRB

5 4

1

Calling9 212345 1)

MSC/ VLRB

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

Visiting MSC

Physical connection which must be remain connected during the whole call

Call to a GSM phone which has activated Unconditional Call Forward Where is 9212345?

Gateway MSC (GMSC)

1

HLRB 2

3

0

9212345 shall be forwarded to number xxxxxxx

MSC/ VLR Calling9 9212345 212345

0

MSC/ VLRB

4

VMS 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.

Mobile B 9212345

Call from a GSM phone to a fixed phone HLR A

Request for 2 authentication data

3

Authentication data

4

MSC/ VLRA

Subscriber B 2212345

4 1

Calling2 212345 1)

Mobile A

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.

Call from a GSM phone to another GSM phone NOTE: HLRA Request for 2 authentication data

3

MSC/ VLRA

Where are 9212345?

4

Authentication data

5

HLRB

9212345 is in MSC/VLRB

6 1

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.

MSC/ VLRB

Calling9 212345 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. Mobile A

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.

7

Mobile B 9212345

Roaming - Call setup - Accounting

Example: Call from Norwegian GSM mobile visiting Thailand, and calling a Malayan GSM mobile who also are visiting Thailand Note: Mobile A and B can either be in same or different mobile networks in Thailand.

HLRA Mobile A

Authentication data

Norway 2

Calling +6016**

3

Request of authentication data

Mobile B +6016***

Thailand

B pays for international connection Malaysia - Thailand

MSC/ VLRB

1

MSC/ VLRA Physical connection which must be established during the whole call

+6016**

6

7

4

MSC/ VLR +6016** is in MSC/VLRB

A pays for international connection Thailand – Malaysia

Malaysia 5

Where is +6016**?

HLRB

National/ international telephone network

Example: Call from Norwegian GSM mobile visiting Thailand, and calling a Malayan GSM mobile who also are visiting Thailand. Billing

Clearing house MO TAP $ Roameo Mobile A (TnM)

system

TnM

DTAC

MO CDR $

MO TAP $

MT CDR $

MSC/ VLR

Billing

Clearing house X MT TAP $

MT TAP $ MO TAP $

system

Note: Billing system

Call data flow

DiGi

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

Mobile B (DiGi)

Roaming and accounting ●

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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…)

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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

Acess Network Switch configuration

Commissions

Prepaid controls

Inventory management

Mediation rules EDR errors Tariff accuracy

Tariff settings Data accuracy

Least cost routing Interconnect reconciliations

Payments

Credit control

Fraud management

Invoice production

Revenue Assurance - example: SMS, TnM Production/traffic collections

SMSC

3

Charging

Billing Gateway

5

Invoicing

VASRating

6

10

2

MSC/ TSC

4

8

9

IN

1

HLR

7

EPP

13 12

NA

11

S212 (CABS)

Geneva