ard for cellular communications. Data transmissions in the past were slow across the radio interfaces due to many propagation and reception problems. To create a broadband communica- tions interface, GPRS was developed as a stepping-stone approach to other services like the Enhanced Data for a Global Environment (EDGE). Regardless of the names we place on these services, the real issues are how much (cost) and how fast (speed) we need to meet the demands for data transmission now and in the future. Before delving directly into the GPRS systems and services, it is prudent to have common ground on the use of the radio-based systems. Therefore, a review (or introduction) of GSM is appropriate. After all, if GPRS is an over- lay to GSM, we should at least understand how and why GSM works. History of Cellular Mobile Radio and GSM The idea of cell-based mobile radio systems appeared at Bell Laboratories in the early 1970s. However, the commercial introduction of cellular sys- tems did not occur until the 1980s. Because of the pent-up demand and newness, analog cellular telephone systems grew rapidly in Europe and North America. Today, cellular systems still represent one of the fastest growing telecommunications services. Recent studies indicate that three of four new phones are mobile phones. Unfortunately, when cellular systems Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Introduction to GSM Introduction to GSM were first being deployed, each country developed its own system, which was problematic because The equipment only worked within the boundaries of each country. The market for mobile equipment manufacturers was limited by the operating system. Three different services had emerged in the world at the time. They were Advanced Mobile Phone Services (AMPS) in North America Total Access Communications System (TACS) in the United Kingdom Nor