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. | 1 GSM Switching Services and Protocols . Second Edition. Jôrg Eberspâcher Hans-Jorg Vogel and Christian Bettstetter Copyright 2001 John Wiley Sons Ltd Print ISBN 0-471-49903-X Online ISBN 0-470-84174-5 Introduction 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
