IT602 • Wireless and Mobile Computing

Unit 2 GSM, GPRS and Mobile Standards

Complete exam-oriented notes on GSM services, architecture, radio interface, logical channels, protocols, localization, handover, security, HSCSD, GPRS, DECT, TETRA and UMTS.

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1. Introduction to GSM

GSM stands for Global System for Mobile Communications. It is a digital cellular standard for mobile voice and data communication.
  • Digital voice communication
  • International roaming
  • SIM-based identity
  • SMS support
  • Authentication and encryption

2. GSM Services

Teleservices

  • Voice calls
  • Emergency calls
  • SMS
  • Fax

Bearer Services

Provide data transmission between a mobile user and an external network.

Supplementary Services

  • Call forwarding
  • Call waiting
  • Call barring
  • Caller identification
  • Multiparty calls

3. GSM System Architecture

Mobile Station | BTS | BSC | MSC -------- HLR | VLR | AuC | EIR Public Networks
  • BTS: communicates with mobile stations.
  • BSC: controls BTS units and radio resources.
  • MSC: switching and mobility management.
  • HLR: permanent subscriber database.
  • VLR: temporary subscriber information.
  • AuC: authentication data.
  • EIR: equipment identity records.

4. GSM Radio Interface

GSM uses FDMA and TDMA together. Each carrier is divided into eight time slots, with separate uplink and downlink frequency bands.

| Slot 0 | Slot 1 | Slot 2 | Slot 3 | Slot 4 | Slot 5 | Slot 6 | Slot 7 |

5. GSM Logical Channels

GroupExamplesPurpose
BroadcastBCCH, FCCH, SCHNetwork information and synchronization
Common ControlRACH, PCH, AGCHAccess, paging and assignment
Dedicated ControlSDCCH, SACCH, FACCHUser-specific signaling
TrafficTCH/F, TCH/HVoice and data

6. GSM Protocol Architecture

  • Radio Resource Management: channel allocation and handover.
  • Mobility Management: location update, authentication and roaming.
  • Connection Management: call control, SMS and supplementary services.
Connection Management | Mobility Management | Radio Resource Management | Physical Layer

7. Localization and Calling

Location Update

The mobile informs the network when it enters a new location area.

Outgoing Call

  1. Mobile requests a channel.
  2. Network authenticates the user.
  3. MSC establishes the call.
  4. A traffic channel is assigned.

Incoming Call

  1. HLR identifies the serving MSC.
  2. The mobile is paged.
  3. Authentication occurs.
  4. A traffic channel is assigned.

8. GSM Handover

Handover transfers an active call from one channel or cell to another without disconnecting it.
  • Intra-cell handover
  • Inter-cell, intra-BSC handover
  • Inter-BSC, intra-MSC handover
  • Inter-MSC handover

9. GSM Security

  • IMSI: permanent subscriber identity.
  • TMSI: temporary identity.
  • Ki: secret authentication key.
  • AuC: generates authentication parameters.
  1. Network sends a challenge.
  2. SIM computes a response.
  3. Network compares the response.
  4. Access is granted if valid.

10. HSCSD

HSCSD means High-Speed Circuit-Switched Data.

It assigns multiple time slots to one user for a higher data rate.

Advantages

  • Higher data rate
  • Continuous connection
  • Useful for real-time data

Limitations

  • Consumes several time slots
  • Less efficient for bursty data

11. GPRS Architecture

GPRS adds packet-switched data capability to GSM.
Mobile Station | BSS | SGSN | GGSN | External Packet Network
  • SGSN: mobility management, authentication and packet delivery.
  • GGSN: connects GPRS with external packet networks.

12. GPRS Interfaces and Channels

InterfaceConnectionPurpose
UmMobile–BSSRadio interface
GbBSS–SGSNPacket transfer
GnSGSN–GGSNBackbone communication
GiGGSN–External networkInternet access
GrSGSN–HLRSubscriber data

Important packet channels include PDTCH, PACCH, PBCCH, PRACH, PAGCH and PPCH.

13. GPRS Mobility Management

  • Idle: mobile is not attached.
  • Standby: attached; location known at routing-area level.
  • Ready: location known more precisely.

Procedures

  • Attach and detach
  • Routing area update
  • PDP context activation
  • Authentication
  • Packet routing

14. DECT, TETRA and UMTS

StandardMain UseFeature
DECTCordless communicationShort range
TETRAEmergency and professional radioGroup calls and reliability
UMTS3G mobile communicationHigher data and multimedia support

Unit 2 Summary

  • GSM offers digital voice, SMS, roaming and SIM-based identity.
  • GSM architecture includes MS, BTS, BSC, MSC, HLR, VLR, AuC and EIR.
  • Logical channels carry traffic and control information.
  • Handover maintains calls during movement.
  • GPRS adds packet data using SGSN and GGSN.
  • DECT, TETRA and UMTS serve different wireless needs.

Important RGPV Exam Questions

Long Answer Questions

  1. Explain GSM services and features.
  2. Draw and explain GSM architecture.
  3. Explain GSM radio interface and logical channels.
  4. Explain GSM protocol architecture.
  5. Explain localization and calling procedures.
  6. Explain GSM handover and security.
  7. What is HSCSD?
  8. Draw and explain GPRS architecture.
  9. Explain GPRS interfaces, channels and mobility management.
  10. Write notes on DECT, TETRA and UMTS.

Short Answer Questions

  1. Define GSM.
  2. What is HLR?
  3. What is VLR?
  4. What is BCCH?
  5. Define TMSI.
  6. What is SGSN?
  7. What is GGSN?
Exam Strategy: Expand abbreviations, draw architecture diagrams and explain each network element.

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Frequently Asked Questions

GSM is a digital cellular standard supporting voice, SMS, data and roaming.
GPRS adds packet-switched data services to GSM.
SGSN handles mobility and packet delivery, while GGSN connects to external packet networks.
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