CONCLUSIONS AND CHALLENGES1 The technologies and standards required to implement VoIP service are currently well established and mature. Many equipment manufacturers are presently marketing interoperable products—such as IP phones, call servers or managers, MGWs and SGs, and so on—to realize and manage the VoIP service. Advances in digital signal processing and networking software, hardware, and protocol technologies—as discussed in Chapters 2 and 3—have stimulated the development of plug-and-ta