# GSM switching services and protocols P1

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## GSM switching services and protocols P1

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Truyền thông khắp nơi, với tất cả mọi người, và tại bất kỳ thời gian ± chúng tôi đã đến khá gần với mục tiêu này trong vài năm qua. Kỹ thuật số của các hệ thống thông tin liên lạc, tiến bộ rất lớn trong vi điện tử, máy tính, và công nghệ phần mềm, phát minh của EF ® cient thuật toán nén, thủ tục, an ninh, và chế biến của tất cả các loại tín hiệu, cũng như sự phát triển của giao thức truyền thông ¯ exible đã được quan trọng điều kiện tiên quyết cho...

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## Nội dung Text: GSM switching services and protocols P1

1. 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. 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-
3. 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
6. 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