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GSM was made to provide

connectivity of all local network of

different countries; contributing totodays international Roaming

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Cellular System

MSC

BSC

BTS

BTS

MS

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What is GSM

GSM, the Global System for MobileCommunications, is a digital cellularcommunication system

GSM provides Digital Transmission

ISDN compatibility

Worldwide roaming in other GSM networks

Provides a model for 3G Cellular systems (UMTS)

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Security Threats

Authentication-only valid users are allowed to use the network.

Privacy-Ensure that conversation cannot be listened to

Data and Voice Integrity-Ensure that voice and data traffic cannot

be read or compromised while in transmit

Network and System availability- Networks must be capable of

withstanding Denial of service

Physical protection-The cell sites and equipment are deployed

remotely in untrusted areas, must be protected by firewalls.

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Departments of GSM

MS (Mobile Station) = ME (Mobile Equipment ) +SIM

(Subscriber Identity Module)

BSS (Base Station Subsystem) = BTS (Base Transceiver

Station) + BSC (Base Station Controller)

NSS (Network Switching Subsystem)

MSC (Mobile Switching Center): telephony switching function

and authentication of user

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Principles of cellular networkCellular radio is a technique that was developed to increase the capacity

available for mobile radio telephone service

Each cell is allocated a band of frequencies and is served by the base station,

consisting of transmitter, receiver and control unit.

Each cell has a base transceiver.The transmission power is carefully controlled

to allow communication within the cell using a given frequency while limiting

the power at that frequency that escapes the cell

into adjacent ones.

The objective is to use the same frequencyin other near by cells, thus allowing the

frequency to be used for multiple

simultaneous conversations.

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Frequency Reuse

Frequency usedA1,A2,A3,A4,B1,B2,B3,B4,C1,C2,C3,C4

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Handoff between base station

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Spectrum AllocationFrequency Division Multiple Access(FDMA)-The available spectrum isdivided into channels and each channel can be used for a single conversation.

Advanced mobile phone service (AMPS) uses FDMA.

Limitation: low calling capacity, limited spectrum, poor data communications,

privacy concerns, and vulnerability to fraud

Time Division Multiple Access(TDMA)- TDMA is a digital transmission technologythat allows a number of users to access a single radio frequency without interference by

allocating unique time slots to each user within each channel.

Used by GSM(Europe), JDC(Japan), NADC(North America)

Code Division Multiple Access(CDMA) -CDMA is a "spread spectrum" technology,which means that it spreads the information contained in a particular signal over a much greater

bandwidth than the original signal. CDMA adds a unique code onto each packet before

transmission. Better security without SIM card.

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Diffrance between FDMA TDMA CDMA

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But GSM works on FDMA &TDMA

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Physical Vs. Logical Channel

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Logical Channels in GSM

Two major classes of logical channels

Traffic Channels (TCHs)

Control Channels (CCHs)

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Traffic Channels in GSM

Two types of TCHs

Full-rate traffic channel (TCH/F) 14.4 kb/s

Half-rate traffic channel (TCH/H) 9.6 Kbps

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Control Channels in GSM

Three classes of control channels

Broadcast Channels (BCH)

Common Control Channels (CCCH) Dedicated Control Channels (DCCH)