GSM switching services and protocols P1

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GSM Switching, Services and Protocols: Second Edition. Jorg Eberspacher, È È Hans-Jorg Vogel and Christian Bettstetter È È Copyright q 2001 John Wiley & Sons Ltd Print ISBN 0-471-49903-X Online ISBN 0-470-84174-5 1 Introduction 1.1 Digital, Mobile, Global: Evolution of Networks Communication everywhere, with everybody, and at any time ± we have come much closer to this goal during the last few years. Digitalization of communication systems, enormous progress in microelectronics, computers, and software technology, inventions of ef®cient algorithms and procedures for compression, security, and processing of all kinds of signals, as well as the development of ¯exible communication protocols have been important prerequisites for this progress. Today, technologies are available that enable the realization of high-performance and cost-effective communication systems for many application areas. In the ®eld of ®xed networks ± where the end systems (user equipment) are connected to the network over a line (two-wire copper line, coaxial cable, glass ®ber) ± new network technologies (such as xDSL and cable modem) have been introduced, providing broadband access to the Internet. The largest technological and organizational challenge is, however, the support of subscri- ber mobility. It can be distinguished between two kinds of mobility: terminal mobility and personal mobility. In the case of terminal mobility, the subscriber is connected to the network in a wireless way ± via radio or light waves ± and can move with his or her terminal freely, even during a communication connection. The degree of mobility depends on the type of mobile radio network. The requirements for a cordless in-house telephone are much less critical than for a mobile telephone that can be used in a car or train. If mobility is to be supported across the whole network (or country) or even beyond the network (or national) boundaries, additional switching technology and administrative functions are required, to enable the subscribers to communicate in wireless mode outside of their home areas. Such extended network functions are also needed to realize personal mobility and univer- sal reachability. This is understood to comprise the possibility of location-independent use of all kinds of telecommunication services ± including and especially in ®xed networks. The user identi®es himself or herself (the person), e.g. by using a chip card, at the place where he or she is currently staying and has access to the network. There, the same communication services can be used as at home, limited only by the properties of the
2 1 Introduction local network or terminal used. A worldwide unique and uniform addressing is an impor- tant requirement. In the digital mobile communication system GSM (Global System for Mobile Commu- nication), which is the subject of this book, terminal mobility is the predominant issue. Wireless communication has become possible with GSM in any town, any country, and even on any continent. GSM technology contains the essential ``intelligent'' functions for the support of personal mobility, especially with regard to user identi®cation and authentication, and for the localization and administration of mobile users. Here it is often overlooked that in mobile communication networks by far the largest part of the communication occurs over the ®xed network part, which interconnects the radio stations (base stations). Therefore it is no surprise that in the course of further development and evolution of the telecommunication networks, a lot of thought is given to the convergence of ®xed and mobile networks. Today, GSM is used mainly for speech communication, but its use for mobile data communication is growing steadily. The GSM Short Message Service (SMS) is a great success story: several billion text messages are being exchanged between mobile users each month. The driving factor for new (and higher bandwidth) data services is the wire- less access to the Internet. The key technologies that have been introduced in GSM, the General Packet Radio Service (GPRS) and the Wireless Application Protocol (WAP), are also explained in this book. The next generation of mobile communications is known as Universal Mobile Telecom- munication System (UMTS) in Europe and as International Mobile Telecommunication System 2000 (IMT-2000) worldwide. The standardization has already progressed quite far, such that the ®rst networks are expected to start operation in 2002. Despite the differences to GSM (in particular with regard to transmission technique and capacity), it is a clear goal of this future network technology to keep the newly introduced GSM technologies and make them essential components of UMTS/IMT-2000. 1.2 Classi®cation of Mobile Communication Systems This book deals almost exclusively with GSM; however, GSM is only one of many facets of modern mobile communication. Figure 1.1 shows the whole spectrum of today's and ± as far as can be seen ± future mobile communication systems. For the bidirectional ± and hence genuine ± communication systems, the simplest variant is the cordless telephone with very limited mobility (in Europe especially the DECT stan- dard). This technology is also employed for the expansion of digital PBXs with mobile extensions. A related concept is Radio in the Local Loop (RLL) or Wireless Local Loop (WLL). Both concepts require only limited mobility. Local Area Networks (LANs) have also been augmented with mobility functions: Wireless LANs have been standardized and are now offered by several companies. WLANs offer IP- based, wireless data communication with very high bit rates but limited mobility. IEEE 802.11 systems transmit up to 11 Mbit/s, and HIPERLAN will offer up to 25 Mbit/s. Both systems form pico-cellular networks. They are installed, for example, in of®ce environ-
1.2 Classi®cation of Mobile Communication Systems 3 ments and airports, as supplement or alternative to wired LANs, and they are also consid- ered to be a good supplement to UMTS access technologies. The efforts to ``mobilize'' the Internet are also worth mentioning in this context. A new routing protocol called Mobile IP [48,49] has been developed, which allows a mobile computer to change its point of attachment to the Internet. A further strong innovation impulse for mobile data and multi- media communication is the development of wireless Mobile ATM systems based on the exchange technology Asynchronous Transfer Mode (ATM). Figure 1.1: Overview of contemporary and future mobile communication systems Another emerging class of wireless networks is used for short-range communication. Bluetooth, for example, replaces cables by enabling direct wireless information exchange between electronic devices (e.g. between cellular phones, Personal Digital Assistants (PDAs), computers, and peripherals). These networks are also called Body Area Networks or Personal Area Networks. Unlike the mobile technologies mentioned above, they are not based on a ®xed network infrastructure (e.g. base stations). The possibility of building up
4 1 Introduction such networks in a spontaneous and fast way gave them the name ad hoc networks. WLAN technologies also include the capability for peer-to-peer ad hoc communication (besides the classical client-to-base station transmission modus). GSM belongs to the class of cellular networks, which are used predominantly for public mass communication. They had an early success with analog systems like the Advance Mobile Phone System (AMPS) in America, the Nordic Mobile Telephone (NMT) in Scan- dinavia, or the C-Netz in Germany. Founded on the digital system GSM (with its variants for 900 MHz, 1800 MHz, and 1900 MHz), a market with millions of subscribers world- wide was generated, and it represents an important economic force. A strongly contribut- ing factor to this rapid development of markets and technologies has been the deregulation of the telecommunication markets, which allowed the establishment of new network operators. Another competing or supplementing technology is satellite communication based on Low Earth Orbiting (LEO) or Medium Earth Orbiting (MEO) satellites, which also offers global, and in the long term even broadband, communication services. Trunked radio systems ± in digital form with the European standard Trans European Trunked Radio (TETRA) ± are used for business applications like ¯eet control. They offer private services that are only accessible by closed user groups. Besides bidirectional communication systems, there also exists a variety of unidirectional systems, where subscribers can only receive but not send data. With unidirectional message systems (paging systems) users may receive short text messages. A couple of years ago, paging systems were very popular, since they offered a cost-effective reach- ability with wide-area coverage. Today, the SMS in GSM has replaced the function of paging systems. Some billion SMS messages are being exchanged between mobile GSM users each month. Digital broadcast systems, such as Digital Audio Broadcast (DAB) and Digital Video Broadcast (DVB), are very interesting for wireless transmission of radio and television stations as well as for audio- and video-on-demand and broadband transmission of Internet pages. The path to the future universal telecommunication networks (UMTS/IMT-2000) has been opened with the realization of the personal communication services, Universal Personal Telecommunication (UPT), based on intelligent networks. During the last few years, the huge success of GSM as well as the exploding number of Internet users gave the design and development of third generation mobile systems a new orientation: One of the most important goals in the evolution from GSM to UMTS is to offer an ef®cient and powerful mobile access to the Internet. GSM and its enhancements, however, will remain for many years the technological base for mobile communication, and it continues to open up new application areas. At the moment, the area of mobile e-commerce (e.g. mobile payment with cellular phones, mobile banking) is particularly attractive. Also text-based news services, locating, ¯eet management, telemetry applications, and automatic emergency call systems are of great interest. The techniques and procedures presented in this book are the foundation for such innovative applications.
1.3 Some GSM History and Statistics 5 1.3 Some GSM History and Statistics In 1982 the development of a pan-European standard for digital cellular mobile radio was Â Â Â started by the Groupe Special Mobile of the CEPT (Conference Europeenne des Admin- ÂÂ istrations des Postes et des Telecommunications). Initially, the acronym GSM was derived from the name of this group. After the founding of the European standardization institute ETSI (European Telecommunication Standards Institute), the GSM group became a Tech- nical Committee of ETSI in 1989. After the rapid worldwide proliferation of GSM networks, the name has been reinterpreted as Global System for Mobile Communication. After a series of incompatible analog networks had been introduced in parallel in Europe, e.g. Total Access Communication System (TACS) in the UK, NMT in Scandinavia, and the C-Netz in Germany, work on the de®nition of a Europe-wide standard for digital mobile radio was started in the late 1980s. The GSM was founded, which developed a set of technical recommendations and presented them to ETSI for approval. These proposals were produced by the Special Mobile Group (SMG) in working groups called Sub Tech- nical Committees (STCs), with the following division of tasks: service aspects (SMG 01), radio aspects (SMG 02), network aspects (SMG 03), data services (SMG 04), and network operation and maintenance (SMG 06). Further working groups were mobile station testing (SMG 07), IC card aspects (SGM 09), security (SGM 10), speech aspects (SMG 11), and system architecture (SMG 12) [18]. SGM 05 dealt with future networks and was respon- sible for the initial standardization phase of the next generation of the European mobile radio system, the UMTS. Later, SMG 05 was closed, and UMTS became an independent project and Technical Body of ETSI. In the meantime, the Third Generation Partnership Project (3GPP) has been founded in cooperation with other standardization committees worldwide. Its goal is the composition of the Technical Speci®cations for UMTS. Finally, in July 2000, ETSI announced the closure of the SMG which has been responsible for setting GSM standards for the last 18 years. Their remaining and further work has been transferred to groups inside and outside ETSI; most of the ongoing work has been handed over to the 3GPP. After the of®cial start of the GSM networks during the summer of 1992 (Table 1.1), the number of subscribers has increased rapidly, such that during the fall of 1993 already far more than one million subscribers made calls in GSM networks, more than 80% of them in Germany. On a global scale, the GSM standard also received very fast recognition, as evident from the fact that at the end of 1993 several commercial GSM networks started operation outside Europe, in Australia, Hong Kong, and New Zealand. Afterward, GSM has also been introduced in Brunei, Cameroon, Iran, South Africa, Syria, Thailand, USA and United Arab Emirates. Whereas the majority of the GSM networks operate in the 900 MHz band (GSM900), there are also networks operating in the 1800 MHz band (GSM1800) ± Personal Communication Network (PCN), Digital Communication System (DCS1800) ± and in the United States in the 1900 MHz band (GSM1900) ± Personal Communication System (PCS). These networks use almost completely identical technol- ogy and architecture; they differ essentially only in the radio frequencies used and the pertinent high-frequency technology, such that synergy effects can be taken advantage of, and the mobile exchanges can be constructed with standard components. In parallel to the standardization efforts of ETSI, already in 1987 the then existing prospec-
6 1 Introduction Table 1.1: Time history ± milestones in the evolution of GSM Year Event 1982 Â Groupe Special Mobile established by the CEPT. 1987 Essential elements of wireless transmission are speci®ed, based on prototype evaluation (1986). Memorandum of Understanding (MoU) Association founded in September with 13 members from 12 countries. 1989 GSM becomes an ETSI Technical Committee (TC). 1990 The Phase 1 GSM900 speci®cations (designed 1987±1990) are frozen. Adaptation to DCS1800 commences. 1991 First GSM networks launched. The DCS1800 speci®cations are ®nalized. 1992 Most European GSM networks turn commercial by offering voice communication services. Some 13 networks in 7 countries are ``on air'' by the end of the year. 1993 First roaming agreements in effect. By the end of 1993, 32 networks in 18 countries are operational. 1994 Data transmission capabilities launched. The number of networks rises to 69 in 43 different countries by the end of 1994. 1995 MoU counts 156 members from 86 countries. After the GSM standardization Phase 2 including adaptations and modi®cations for the PCS1900 (Personal Communication System) is passed, the ®rst PCS1900 Network is launched in the USA. Facsimile, data and SMS roaming starts. Video signals are transmitted via GSM for demonstration purposes. An estimated 50 000 GSM base stations are in use all over the world. 1996 January: 120 networks in 71 countries operational. June: 133 networks in 81 countries operational. 1997 July: 200 GSM networks from 109 countries operational, amounting to 44 million subscribers worldwide. 1998 January: 268 GSM networks with 70 million subscribers worldwide. End of 1998: 320 GSM networks in 118 countries with 135 million subscribers worldwide. 1999 Wireless Application Protocol (WAP). End of 1999: 130 countries, 260 million subscribers. 2000 August: 362 million users. General Packet Radio Service (GPRS). tive GSM network operators and the national administrations joined in a group whose members signed a common Memorandum of Understanding (MoU). The MoU Associa- tion was supposed to form a base for allowing the transnational operation of mobile stations using internationally standardized interfaces. In August 2000, the GSM MoU had 394 members which operated GSM networks in 150 countries (see Figure 1.2). Figure 1.2 illustrates the impressive growth in the number of GSM networks and GSM subscribers. In 1997, 6 years after the commercial start of the ®rst GSM networks, GSM
1.4 Overview of the Book 7 had 68 million users and thus a share of approx. 28% of the worldwide mobile market. In the following year, the subscriber number almost doubled, and it doubled again by the beginning of 2000. At the time of writing, in September 2000, there were about 380 million subscribers in all three frequency bands (900 MHz, 1800 MHz, 1900 MHz). In total, there were 373 networks in 142 countries in operation. The share of GSM in the worldwide radio communication market has thus grown up to 60% (of 635 million users) and is still rising. If we consider only digital systems, GSM is even more successful; its market share was over 68% in the middle of 2000. The largest market is Europe with 64% of all subscribers, followed by the Asian Paci®c region with 28%. Moreover, China and many African and South-American countries are operating GSM networks, which opens up a market with substantial growth possibilities. It is expected that in the year 2003 over 600 million people will be using GSM. Relevant numbers can be obtained from the Web page of the GSM Association at http://www.gsmworld.com. Figure 1.2: GSM network and subscriber statistics. Source: GSM Association, EMC World Cellular Database All of these networks have implemented Phase 1 of the GSM standard, or the later de®ned PCN/PCS version of it. In many places, additional services and service characteristics of GSM Phase 2 have also been realized. Phase 1 is essentially the basis for this book, but we will also go into important developments of Phase 2 and Phase 21. 1.4 Overview of the Book The remainder of this book is as follows. In Chapter 2, we give an introduction to radio channel characteristics and the cellular principle. The understanding of duplex and multi- ple access schemes serves as the basis for understanding GSM technology. Chapter 3 introduces the GSM system architecture and addressing. It explains the basic structure and elements of a GSM system and their interfaces as well as the identi®ers of users, equipment, and system areas. The GSM services are covered in Chapter 4. Next, Chapter 5 deals with the physical layer at the air interface (How is speech and data transmitted over the radio channel?). Among other things, it describes GSM modulation, multiple access, duplexing, frequency hopping, the logical channels, and synchronization. In Chapter 6, we discuss GSM coding (source coding, speech processing, and channel coding) and mechan- isms for authentication and encryption. Chapter 7 covers the entire protocol architecture of GSM (payload transport and signaling). For example, communication protocols for radio
8 1 Introduction resource management, mobility management, connection management at the air interface are explained. Chapter 8 describes in detail three main principles that are needed for roaming and switching: location registration and update (i.e. How does the network keep track of the user and ®nd him or her when there is an incoming call?), connection establishment and termination, and handover. In Chapter 9 we give an overview of data communication and networking, and Chapter 10 deals with some aspect of network opera- tion. Finally, Chapters 11 and 12 present the latest developments in GSM technology. Chapter 11 explains in detail GPRS which can be used for wireless Internet access. Chapter 12 gives an overview of some more services recently introduced in GSM Phase 21. It covers new speech services, high-rate data services, supplementary services for speech and location services, service platforms, WAP, and Advanced Speech Call Items (ASCI). We conclude this book with an outlook to UMTS.