so worked with service providers and enter- prise customers who use CUBE to implement SIP Trunks into both CUCM and CUCME solutions. ATM holds an M.S. degree in computer science from Texas A&M University and a B.S. degree in computer science and engineering from Bangladesh University of Engineering and Technology (BUET). About the Technical Reviewers Maulik Shah has been with Cisco Systems for the past nine years. He has worked with Unified Communications and Voice over IP (VoIP) systems for the last seven years as part of the Cisco Technical Assistance Center and Technical Marketing Team. He has helped design, deploy, and troubleshoot multiple customer VoIP networks. In his current role as Technical Marketing Engineer, he is focused on Cisco Small Business Solutions including Cisco SBCS and SIP trunking deployments. He also is a CCIE in Routing and Switching and Voice. Vinay Pande is a technical leader at Cisco, where he is the subject matter expert for SIP trunking architectures. He works with customers to identify new features and designs network architectures with a focus on delivering end-to-end solutions. Prior to joining Cisco, Vinay was a VoIP interop and test lead for Lucent Technologies. He has filed seven patents in the areas of SIP and NAT transversal for SIP. He has over 12 years of experi- ence in the field of voice, data, and video network integration. Dedications From Christina Hattingh: To Robert Verkroost and my parents for their unfailing encour- agement and support. From Darryl Sladden: To Melissa Brown and my mom, sisters, and friends for their patience and support. From ATM Zakaria Swapan: To my parents for their great contribution that brings me here today. vi SIP Trunking Acknowledgments We would like to extend special thanks to Mike Wood, Sibrina Shafique, and Syed Rahman who were coauthors on some early SIP trunk white papers, the content of which were adjusted, updated, and reused in this book. These white papers, available on Cisco.com as of early 2008, represent some of the earliest w