USSD in MSC-VLR

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  • IT 12 063

    Examensarbete 30 hpNovember 2012

    GSM MSC/VLR Unstructured Supplementary Service Data(USSD) Service

    Egemen Taskin

    Institutionen fr informationsteknologiDepartment of Information Technology

  • Teknisk- naturvetenskaplig fakultet UTH-enheten Besksadress: ngstrmlaboratoriet Lgerhyddsvgen 1 Hus 4, Plan 0 Postadress: Box 536 751 21 Uppsala Telefon: 018 471 30 03 Telefax: 018 471 30 00 Hemsida: http://www.teknat.uu.se/student

    Abstract

    GSM MSC/VLR Unstructured Supplementary ServiceData(USSD) Service

    Egemen Taskin

    Although the Unstructured Supplementary Service Data (USSD) service is one of the most used GSM services such as checking the balance of prepaid cards, it is not well known by subscribers and it is so oftenconfused with a popular GSM service, Short Message Service (SMS). While SMS is based on the characteristics of storing and forwarding data, USSD is session based and real-time.

    Technically, USSD service allows the Mobile Station (MS) user and a Public Land Mobile Network (PLMN) operator defined application to communicate in a way which is transparent to the MS and to intermediate network entities.[6]

    This master thesis specifies all the phases in the development of USSD service in Mobile Switching Center (MSC)/Visitor Location Register (VLR) and its integration with an USSD Gateway. Meanwhile, it shows how a message passing functional programming language (Erlang) fits to develop a highly concurrent, available, fault-tolerant and distributable telecommunication system.

    Tryckt av: Reprocentralen ITC

    Sponsor: Mobile Arts ABIT 12 063Examinator: Lisa Kaatimnesgranskare: Ping WuHandledare: Martin Kjellin

  • Acknowledgements

    There are some special people who have helped me in the preparation of thisthesis.

    Firstly, I would like to thank Martin Kjellin, Product Manager at MobileArts AB, for supervising my thesis. I would like to thank Mobile Arts ABfor providing an invaluable sponsorship.

    Also, I would like to thank Ping Wu, Associate Professor at Department ofEngineering Sciences / Uppsala University, for reviewing my thesis.

    Finally, I would like to thank my big hearted aunt Hatice Taskin for beingmy angel investor and my family for supporting me with an invaluable trustand patience.

    5

  • Contents

    1 Introduction 131.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131.2 Purpose & Tasks . . . . . . . . . . . . . . . . . . . . . . . . . 141.3 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.4 Related Works . . . . . . . . . . . . . . . . . . . . . . . . . . . 161.5 Overview of the thesis . . . . . . . . . . . . . . . . . . . . . . 16

    2 Background 182.1 Basics of GSM . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

    2.1.1 Introduction to GSM . . . . . . . . . . . . . . . . . . . 182.1.2 GSM Networks . . . . . . . . . . . . . . . . . . . . . . 18

    2.1.2.1 GSM Architecture . . . . . . . . . . . . . . . 192.1.2.2 Geographical Network Structure . . . . . . . 19

    2.1.2.2.1 Cell . . . . . . . . . . . . . . . . . . 192.1.2.2.2 Location Area . . . . . . . . . . . . . 202.1.2.2.3 MSC Area . . . . . . . . . . . . . . . 202.1.2.2.4 PLMN Area . . . . . . . . . . . . . . 21

    2.1.2.3 Components . . . . . . . . . . . . . . . . . . . 212.1.2.3.1 Switching System . . . . . . . . . . . 21

    2.1.2.3.1.1 MSC . . . . . . . . . . . . . . 222.1.2.3.1.2 HLR . . . . . . . . . . . . . . 222.1.2.3.1.3 VLR . . . . . . . . . . . . . . 232.1.2.3.1.4 EIR . . . . . . . . . . . . . . 232.1.2.3.1.5 G-MSC . . . . . . . . . . . . 23

    2.1.2.3.2 Base Station System . . . . . . . . . 232.1.2.3.2.1 BTS . . . . . . . . . . . . . . 232.1.2.3.2.2 BSC . . . . . . . . . . . . . . 232.1.2.3.2.3 TRAU . . . . . . . . . . . . . 23

    2.2 Erlang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242.2.1 General consideration . . . . . . . . . . . . . . . . . . . 242.2.2 OTP(Open Telecom Platform) . . . . . . . . . . . . . . 24

    7

  • 2.2.2.1 Supervisor . . . . . . . . . . . . . . . . . . . . 252.2.2.2 gen server . . . . . . . . . . . . . . . . . . . . 252.2.2.3 gen fsm . . . . . . . . . . . . . . . . . . . . . 25

    2.2.3 Mnesia . . . . . . . . . . . . . . . . . . . . . . . . . . . 262.3 USSD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

    2.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 262.3.1.1 Why USSD? . . . . . . . . . . . . . . . . . . 262.3.1.2 Areas of Use . . . . . . . . . . . . . . . . . . 272.3.1.3 USSD vs. SMS . . . . . . . . . . . . . . . . . 27

    2.3.2 Architecture & Communication . . . . . . . . . . . . . 282.3.2.1 MS initiated . . . . . . . . . . . . . . . . . . 292.3.2.2 NW initiated . . . . . . . . . . . . . . . . . . 32

    3 Requirements 373.1 Functional Requirements . . . . . . . . . . . . . . . . . . . . . 37

    3.1.1 Mobile Initiated USSD . . . . . . . . . . . . . . . . . . 373.1.2 Network Initiated USSD . . . . . . . . . . . . . . . . . 38

    3.2 Non-functional Requirements . . . . . . . . . . . . . . . . . . 39

    4 Design 404.1 System Overview . . . . . . . . . . . . . . . . . . . . . . . . . 404.2 Network Design . . . . . . . . . . . . . . . . . . . . . . . . . . 404.3 Software Design . . . . . . . . . . . . . . . . . . . . . . . . . . 42

    4.3.1 Available Architecture . . . . . . . . . . . . . . . . . . 424.3.1.1 Components . . . . . . . . . . . . . . . . . . . 42

    4.3.1.1.1 TCP server . . . . . . . . . . . . . . 424.3.1.1.2 MUS . . . . . . . . . . . . . . . . . . 434.3.1.1.3 HLR . . . . . . . . . . . . . . . . . . 434.3.1.1.4 VLR . . . . . . . . . . . . . . . . . . 434.3.1.1.5 Application Platform . . . . . . . . . 434.3.1.1.6 Media Gateway Host . . . . . . . . . 43

    4.3.1.2 Communication . . . . . . . . . . . . . . . . . 444.3.2 Architecture with USSD support . . . . . . . . . . . . 44

    4.4 Decomposition Description . . . . . . . . . . . . . . . . . . . . 454.4.1 USSD MSC Component . . . . . . . . . . . . . . . . . 45

    4.4.1.1 Overview . . . . . . . . . . . . . . . . . . . . 454.4.1.2 Processes . . . . . . . . . . . . . . . . . . . . 45

    4.4.2 USSD VLR Component . . . . . . . . . . . . . . . . . 474.4.2.1 Overview . . . . . . . . . . . . . . . . . . . . 474.4.2.2 Processes . . . . . . . . . . . . . . . . . . . . 48

    4.5 Communication Design . . . . . . . . . . . . . . . . . . . . . . 49

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  • 4.5.1 MUS Controller - USSD MSC . . . . . . . . . . . . . . 494.5.2 Indirect Communication with USSDGW . . . . . . . . 49

    4.5.2.1 USSD MSC to/from USSD VLRUSSD VLR to/from USSD HLRUSSD HLR to/from USSDGW . . . . . . . . 49

    4.5.3 Direct Communication with USSDGW . . . . . . . . . 494.5.3.1 USSD MSC to/from USSDGW . . . . . . . . 49

    4.5.4 Messages . . . . . . . . . . . . . . . . . . . . . . . . . . 494.5.4.1 BSSAP . . . . . . . . . . . . . . . . . . . . . 49

    4.5.4.1.1 BSSMAP . . . . . . . . . . . . . . . 504.5.4.1.2 DTAP . . . . . . . . . . . . . . . . . 50

    4.5.4.1.2.1 Supplementary services . . . . 504.5.4.1.2.2 The ones already implemented

    . . . . . . . . . . . . . . . . . 504.5.4.2 MAP . . . . . . . . . . . . . . . . . . . . . . 51

    4.5.4.2.1 MAP Overview . . . . . . . . . . . . 514.5.4.2.2 Common MAP services . . . . . . . 514.5.4.2.3 USSD MAP services . . . . . . . . . 524.5.4.2.4 MAP paging and search services . . 53

    4.6 Design Rationale . . . . . . . . . . . . . . . . . . . . . . . . . 53

    5 Implementation & Test 555.1 Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

    5.1.1 Initial Implementation & Test Plan . . . . . . . . . . . 555.1.2 Problems Regarding the Initial Plan . . . . . . . . . . 555.1.3 The Solutions . . . . . . . . . . . . . . . . . . . . . . . 56

    5.2 Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

    6 Results 576.1 Technical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576.2 Software Development Method . . . . . . . . . . . . . . . . . . 586.3 Company . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586.4 Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586.5 Personal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

    7 Conclusions 60

    8 Future Work 62

    9

  • Abbreviations

    (=) Corresponding field carries the same field in incoming request

    3GPP The 3rd Generation Partnership Project

    BS Base Station

    BSC Base Station Controller

    BSS Base Station Subsystem

    BSSAP Base Station System Application Part

    BSSMAP Base Station System Management Application sub-Part

    BTS Base Transceiver Station

    C Conditional

    DETS Disk-Based Erlang Term Storage

    DTAP Direct Transfer Application Part

    ETS Erlang Term Storage

    G-MSC Gateway Mobile service Switching Centre

    GSM Global System for Mobile Communication

    HLR Home Location Register

    HPLMN Home Public Land Mobile Network

    IMSI International Mobile Subscriber Identity

    M Mandatory

    MAP Mobile Application Part

    11

  • MGC Media Gateway Controller

    MG Host, M-MGW Media Gateway Host, Mobile Media Gateway

    MMI Man-Machine Interface

    MS Mobile Station

    MSC Mobile service Switching Centre

    MSISDN Mobile Subscriber Integrated Services Digital Network

    MUS Mobile User Service

    MUS Con Mobile User Service Controller

    O Optional

    PLMN Public Land Mobile Network

    SS7 Signalling System 7

    SCCP Signalling Connection Control Part

    SIM Subscriber Identity Module

    SSN Subsystem Number

    TCAP Transaction Capabilities Application Part

    TMSI Temporary Mobile Subscriber Identity

    USSD Unstructured Supplementary Servi