IntroductionThe expansion of the global Internet has brought an explosion of new communication services in a very short time. Nevertheless, the trusted old telephone and fax still remain key telecommunication devices in our daily lives. Telephony services have been expanding gradually over decades, becoming more versatile, reliable, efficient, and mobile. These services are delivered through high-quality network infrastructures, maintained and operated by wellexperienced service providers.Merging the fast-moving Internet services world with the rigid, quality-focused telephony world is often seen as the future of the telecommunication world. Many companies, including Lucent Technologies, are working to make this convergence a reality. Besides the technical challenges, it is expected to offer many advantages and opportunities. Four major developments are:• Network convergence, which combines and integrates the strengths of data and voice-oriented networks at infrastructure level.• Next-generation services [3], which combine and integrate the strengths of data and voice-oriented networks at the service level. By separating the