.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Speech Coding 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 Chapter Hybrid Voice-Data Networks The basic advantage of a single network carrying both voice and data is clear: If one network carries both, then we incur the expense of creating and maintaining only one network instead of two. When low-speed data transfer was acceptable, hybrid local access and hybrid net- works were easy and common. For local access, we used a modem over the telephone line instead of getting an expensive data line. Back in the early 1990s, Columbia Uni- versity had a hybrid voice-data network for the entire campus. The university installed a telephone system that also supported digital data at 19.2 kbps. Over short distances, the wiring could even be used to support 4-Mbps token ring local area networks (LANs). We find similar examples in wireless with the use of low-speed modems over the cellular system. In the twenty-first century, a hybrid voice-data network that meets the demands of high-speed data is a greater challenge. We have discussed the reasons for this in ear- lier chapters. And we have introduced the technologies that are overcoming these chal- lenges. In this chapter we take a brief look at the status of actual implementations of hybrid voice-data networks, public and private, in the year 2002. 19.1 Quality of Service (QoS) There are three basic approaches to creating a hybrid voice-data network: adding voice on an existing data network, carrying data on an existing voice network, or building the network from the ground up. In the last category, we include any thorough reengi- neering of existing facilities to upgrade the capability of the network. All three approach