GSM: Switching, Services and Protocols

• Authors: Joerg Eberspaecher;Christian Bettstetter;Hans-Jhorg Vhogel
• Venue: GSM: Switching, Services and Protocols
• Year: 2001

From the Book:1: Introduction1.1 Digital, Mobile, Global: Evolution of NetworksCommunication everywhere, with everybody, and at any time - we have come much closer to thisgoal during the last few years. Digitalization of communication systems, enormous progress inmicroelectronics, computers, and software technology, inventions of efficient algorithms andprocedures for compression, security, and processing of all kinds of signals, as well as thedevelopment of flexible communication protocols have been important prerequisites for thisprogress. Today, technologies are available that enable the realization of high-performance andcost-effective communication systems for many application areas.In the field of fixed networks - where the end systems (user equipment) are connected to thenetwork 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 theInternet.The largest technological and organizational challenge is, however, the support of subscribermobility. It can be distinguished between two kinds of mobility: terminal mobility and personalmobility.In the case of terminal mobility, the subscriber is connected to the network in a wireless way - viaradio or light waves - and can move with his or her terminal freely, even during a communicationconnection. The degree of mobility depends on the type of mobile radio network. The requirementsfor a cordless in-house telephone are much less critical than for a mobile telephone that can beused in a car or train. If mobility is to be supported across the whole network (or country) or evenbeyond the network (or national) boundaries, additional switching technology and administrativefunctions are required, to enable the subscribers to communicate in wireless mode outside of theirhome areas.Such extended network functions are also needed to realize personal mobility and universalreachability. This is understood to comprise the possibility of location-independent use of all kindsof telecommunication services - including and especially in fixed networks. The user identifieshimself or herself (the person), e.g. by using a chip card, at the place where he or she is currentlystaying and has access to the network. There, the same communication services can be used asat home, limited only by the properties of the local network or terminal used. A worldwide uniqueand 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. Wirelesscommunication has become possible with GSM in any town, any country, and even on anycontinent.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 andadministration of mobile users. Here it is often overlooked that in mobile communication networksby far the largest part of the communication occurs over the fixed network part, whichinterconnects the radio stations (base stations). Therefore it is no surprise that in the course offurther development and evolution of the telecommunication networks, a lot of thought is given tothe convergence of fixed and mobile networks.Today, GSM is used mainly for speech communication, but its use for mobile data communicationis growing steadily. The GSM Short Message Service (SMS) is a great success story: severalbillion text messages are being exchanged between mobile users each month. The driving factorfor new (and higher bandwidth) data services is the wireless access to the Internet. The keytechnologies that have been introduced in GSM, the General Packet Radio Service (GPRS) andthe Wireless Application Protocol (WAP), are also explained in this book.The next generation of mobile communications is known as Universal Mobile TelecommunicationSystem (UMTS) in Europe and as International Mobile Telecommunication System 2000 (IMT-2000)worldwide. The standardization has already progressed quite far, such that the firstnetworks are expected to start operation in 2002. Despite the differences to GSM (in particularwith regard to transmission technique and capacity), it is a clear goal of this future networktechnology to keep the newly introduced GSM technologies and make them essential componentsof UMTS/IMT-2000.1.2 Classification of Mobile Communication SystemsThis book deals almost exclusively with GSM; however, GSM is only one of many facets ofmodern mobile communication. Figure 1. 1 shows the whole spectrum of today's and - as far ascan be seen - future mobile communication systems.For the bidirectional - and hence genuine - communication systems, the simplest variant is thecordless telephone with very limited mobility (in Europe especially the DECT standard). Thistechnology is also employed for the expansion of digital PBXs with mobile extensions. A relatedconcept is Radio in the Local Loop (RLL) or Wireless Local Loop (WLL). Both concepts requireonly limited mobility.Local Area Networks (LANS) have also been augmented with mobility functions: Wireless LANshave 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 systemstransmit up to 11 Mbit/s, and HIPERLAN will offer up to 25 Mbit/s. Both systems form pico-cellularnetworks. They are installed, for example, in office environments and airports, as supplement oralternative to wired LANs, and they are also considered to be a good supplement to UMTS accesstechnologies. The efforts to "mobilize" the Internet are also worth mentioning in this context. A newrouting protocol called Movile IP (48,49) has been developed, which allows a mobile computer tochange its point of attachment to the Internet. A further strong innovation impulse for mobile dataand multimedia communication is the development of wireless Mobile ATM systems based on theexchange technology Asynchronous Transfer Mode (ATM).Another emerging class of wireless networks is used for short-range communication. Bluetooth, forexample, replaces cables by enabling direct wireless information exchange between electronicdevices (e.g. between cellular phones, Personal Data Assistants (PDAs), computers, andperipherals). 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 networkinfrastructure (e.g. base stations). The possibility of building up such networks in a spontaneousand fast way gave them the name ad hoc networks. WLAN technologies also include the capabilityfor peer-to-peer ad hoc communication (besides the classical client-to-base station transmissionmodus).GSM belongs to the class of cellular networks, which are used predominantly for public masscommunication. They had an early success with analog systems like the Advance Mobile PhoneSystem (AMPS) in America, the Nordic Mobile Telephone (NMT) in Scandinavia, or the C-Netz inGermany. Founded on the digital system GSM (with its variants for 900 MHz, 1800 MHz, and 1900MHz), 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 andtechnologies has been the deregulation of the telecommunication markets, which allowed theestablishment of new network operators.Another competing or supplementing technology is satellite communication based on Low EarthOrbiting (LEO) or Medium Earth Orbiting (MEO) satellites, which also offers global, and in the longterm even broadband, communication services. Trunked radio systems - in digital form with theEuropean standard Trans European Trunked Radio (TETRA) - are used for business applicationslike 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 systemswere 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 arebeing exchanged between mobile GSM users each month. Digital broadcast systems, such asDigital Audio Broadcast (DAB) and Digital Video Broadcast (DVB), are very interesting for wirelesstransmission of radio and television stations as well as for audio - and video - on-demand andbroadband transmission of Internet pages.The path to the future universal telecommunication networks (UMTS/IMT-2000) has been openedwith the realization of the personal communication services, Universal PersonalTelecommunication (UPT), based on intelligent networks. During the last few years, the hugesuccess of GSM as well as the exploding number of Internet users gave the design anddevelopment of third generation mobile systems a new orientation: One of the most importantgoals in the evolution from GSM to UMTS is to offer an efficient and powerful mobile access to theInternet.GSM and its enhancements, however, will remain for many years the technological base formobile communication, and it continues to open up new application areas. At the moment, thearea of mobile e-commerce (e.g. mobile payment with cellular phones, mobile banking) isparticularly attractive. Also text-based news services, locating, fleet management, telemetryapplications, and automatic emergency call systems are of great interest. The techniques andprocedures presented in this book are the foundation for such innovative applications.