riting on the start of the industry transition from TDM to SIP trunking. We would also like to extend special thanks to the many Cisco employees on whose expertise, advice, laboratory work, configurations, and examples we drew from for the technical accuracy of this book. Specifically, to Vinay Pande who is an undisputed expert in the area of SIP trunking and Francisco Sedano Crippa, one of the many enterprising Cisco engineers who developed a novel Tcl-based Cisco Unified Border Element (CUBE) script solution for his customer, which is reused in this book. Special thanks also go to Tony Banuelos of the Cisco Unified Communication interoper- ability laboratory, whose unfailing dedication generates countless working configurations to ease customer network implementations and to the unfailing support and cooperation of Patty Mertz Medberry who manages the interoperability lab. Special thanks also go to David Hanes for his expertise on topics involving fax and modem traffic; to Charles Ganzhorn for video expertise; to Dan Wing and Paul Kyzivat for their knowledge of SIP and the SIP standards; and to Ed Curry, Charles Demaret, and Tim Cabeceiras for their expertise on specific SP SIP trunk service offerings. Thanks also go to various experts who helped with the case studies contained in this book, including Kees Gerritsen, Zulfi Anees, Kevin Whelan, Mike Haag, and Spencer Lawes. Thanks also to Kim Haugan Cook for documentation support; to John Heaton for help in the cost analyses; and to Vivek Bhargava and James Stormes for general expertise in enterprise SIP trunk design. Lastly, thanks go to Mike Wood, David Sauerhaft, and Teresa Newell for their leadership and executive support. Contents at a Glance Introduction Part I: From TDM Trunking to SIP Trunking Chapter 1 Overview of IP Telephony Chapter 2 Trends in IP Telephony 11 Chapter 3 Transitioning to SIP Trunks 31 Chapter 4 Cost Analysis 45 Part II: Planning Your Network for SIP Trunking Chapter 5 Components of SIP Trunks Chapter 6 SIP Trunking Models Chapter 7 Des