This book covers all aspects of telephony over IP networks, known as Voice over IP (VoIP). VoIP hit the headlines during the mid-1990's amid claims concerning its impact upon existing Switched Circuit telephony services. Whilst VoIP has clearly provided a focus for much debate within the telecommunications industry, there has been a clear gulf between hype and reality. This book examines VoIP as a technology and its consideration within the industry, the motivations for VoIP networks, a review of the status of the major components of a VoIP network and their development, and both current and emerging applications. This makes for essential reading for those with a technical or business interest in this rapidly developing area of telecommunications.