"Written to address the growth of IP telephony service offerings within the corporate and residential realm, this book discusses technical and regulatory issues related to IP Telephony Interconnection. It describes business and interconnection models and solutions, and provides an overview of emerging architectures such as IMS and TISPAN. The authors offer a detailed overview of the SPPEERMINT activity and proposed architecture, the current work undertaken in DRINKS, the use of ENUM for interconnection, and ENUM implementation status, among others. This text is a first of its kind to offer information on inter-provider communications and interconnect IP telephony clouds"-- "1 The Rise of IP-Based Voice and the Need for Global IP Telephony Reachabi li ty 1.1 Introduction The emergence of VoIP (Voice over IP) as a service that competes directly with PSTN/PLMN (Public Switched Telephony Network/ Public Land Mobile Network) voice services presents a challenge to established voice service providers. Provisioning of VoIP services by new entrants is eroding the revenues enjoyed by PSTN/PLMN voice Service Providers, particularly for long-distance calls. Economic drivers for VoIP offerings over traditional voice include: A packet-switched VoIP connection - is far more efficient in terms of network use than a 64 kb/s nailed-up, traditional, voice call circuit. - An IP network costs less than a PSTN or PLMN, since it can accommodate different services on a single platform and requires only one team for operation, management, and maintenance. - It is possible to provide a VoIP service with little or no network investment by using an "over-the-top" (or OTT) model in which the VoIP Service Provider uses an existing network as a bit-pipe. VoIP usage has increased over the past few years, according to OECD statistics, retail European VoIP subscribers have increased by 183 percent during 2005 (from 1.9 million up to 5.3 million). In addition to substituting traditional voice minutes, the existence of cheaper VoIP services forces traditional Operators to reduce call charges, causing a decrease in revenue. Traditional voice calls have decreased significantly in the PSTN domain"--