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Taking a standards-based approach to converged services, Architecting the Telecommunications Evolution lays a foundation for a service-oriented architecture in telecommunications. After outlining the development of Internet telephony, the book focuses on how to use the respective benefits of the PSTN and the Internet to create and implement more value-added services. It then examines services that originate in the Internet and take advantage of PSTN services followed by PSTN-originating services using the Internet. It concludes with a discussion on how this convergence creates smart spaces in the telecoms domain. Here's Chapter 2, Internet Telephony: The Evolution to a Service-Oriented Architecture.