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From the Book: 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 efficient algorithms and procedures for compression, security, and processing of all kinds of signals, as well as the development of flexible 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 field of fixed networks - where the end systems (user equipment) are connected to the network over a line (two-wire copper line, coaxial cable, glass fiber) - 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 subscriber 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 universal reachability. This is understood to comprise the possibility of location-independent use of all kinds of telecommunication services - including and especially in fixed networks. The user identifies 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 local network or terminal used. A worldwide unique and uniform addressing is an important requirement. In the digital mobile communication system GSM (Global System for Mobile Communication), 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 identification 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 fixed 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 fixed 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 wireless 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 Telecommunication System (UMTS) in Europe and as International Mobile Telecommunication System 2000 (IMT-2000) worldwide. The standardization has already progressed quite far, such that the first 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 Classification 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 standard). 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 office environments and airports, as supplement or alternative to wired LANs, and they are also considered 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 Movile 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 multimedia communication is the development of wireless Mobile ATM systems based on the exchange technology Asynchronous Transfer Mode (ATM). 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 Data 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 fixed network infrastructure (e.g. base stations). The possibility of building up 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 Scandinavia, 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 worldwide was generated, and it represents an important economic force. A strongly contributing 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 fleet 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 reachability 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 efficient 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, fleet 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.