ABSTRACT
Voice over Internet Protocol (VoIP) has rapidly become popular in wireline networks. The evolution of voice service from circuit-switched voice to VoIP has been due to the proliferation of IP networks that can deliver data bits cost-effectively. Similar to the wireline networks, voice in wireless mobile networks started with circuit-switched networks. Since the deployment of the fi rst commercial wireless system, wireless mobile networks have evolved from fi rst-generation analog networks to second-generation digital networks. Third-generation wireless mobile networks that are currently in use offer a highly effi cient circuit-switched service and have double the spectral effi ciency of second-generation systems. After the deployment of the third-generation wireless voice system, however, the number of voice subscribers, having reached a saturation point in many parts of the world, no longer increased. Consequently, the focus on wireless system design shifted to wireless data applications. This resulted in the emergence of high-speed packet-switched data (HSPD) networks, which have been gradually deployed alongside circuit-switched voice networks worldwide.
