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Global System for Mobile Communications (GSM)

•Designed to be a digital (wide area) wireless network.

• Driven by European telecom manufacturers, operators, and standardization committees

• Very widely used around the world

GSM Features

1.Service portability

• Mobile can be used in any of the participating countries with international roaming and
standardized numbering & dialing (but possibly at different rates!)
• Usable for both wire line services and for mobile service
• Usable when: walking, driving, boating, … (up to 250 km/h)

2. Quality of service and Security

• Quality at least as good a previous analog systems
• Capable of offering encryption

3. Good radio frequency utilization

• High spectrum efficiency
• Co-existence with earlier systems in the same bands

4. Modern network

• Following ITU recommendations – to allow efficient inter- operation with ISDN
networks
• Supporting voice and low rate data.
• Standardized mobility and switching support.
• Standardized interfaces between the sub-systems, to allow a mix-and-match system.

5. System optimized to limit cost of mobiles (and to a lesser extent to limit the cost of the whole system)

• GSM required higher complexity mobiles than earlier analog systems
• Subscriber cost less than or equal to existing analog systems

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Incoming Call

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1.Incoming call is passed from the fixed network to the GMSC (Gateway Mobile Switching Center).

2.Based on the IMSI(International Mobile Subscriber Identity) numbers of the called party, HLR (Home Location Register) is determined

3.HLR checks for the existence of the called number, then the relevant VLR (Visitor Location Register) is requested to provide a Mobile Station Roaming Number (MSRN).

4.Reply transmitted back to the GMSC.

5.Connection is switched through to the responsible MSC

6.VLR is queried for the location range and reach ability status of the mobile subscriber.

7. If the MS (Mobile Station) is marked reachable, then a radio call is enabled

8. Radio call is executed in all radio zones assigned to the VLR

9. Reply from the MS in its current radio cell

10. When mobile subscriber telephone responds to the page, then complete all necessary security procedures

11. If this is successful, the VLR indicates to the MSC that call can be completed

12. Call can be completed

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