 planners and engineers to validate designs and resolve problems quickly. 8 A cellular telephone also can be locked to prevent others from making calls, but it can still receive incoming calls. This is the electronic equivalent of the lock and key we used to put on a rotary-dial phone, and it does not really change the call-state space. 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. Source: CDMA CAPACITY AND QUALITY OPTIMIZATION Key Data Concepts Today's and tomorrow's cellular networks rely on digital technology and offer services that carry user data. However, engineers with a telephony or radio engineering background may not have a deep familiarity with the data standards and protocols that have developed over the last 30 years. "Key Data Concepts" provides the background in information technology (IT) networking needed to plan and grow cellular systems as the convergence of voice and data systems continues and as third- generation (3G) cellular systems are being deployed. In Chap. 17, "Quality of Service (QoS)," we address the most fundamental challenge facing engineers who are developing systems that will carry both voice and data: the different quality requirements of each service and how to manage those different requirements on a single network. In Chap. 18, "Speech Coding," we provide the details of a key application of data technology to telephony and cellular systems: the process of digitizing voice signals. Starting in Chap. 19, we turn to the world of IT. In Chap. 19, "Hybrid Voice-Data Networks," we take a look at existing and emerging solutions for carrying both voice and data on the same transport. After an extensive discussion of voice over Internet Protocol (VoIP), we look at the use of VoIP on cellular networks and its implementation in the process of upgrading the backhaul network from base stations to mobile switching c