 to say, this is a relatively new phenomenon. It used to be that the biggest test for any telephone network was the ability to handle the explosion of calls on Mother's Day. Now, any day can be the busiest for a network-when an entire season of a popular show is released or when the latest smartphone os upgrade goes live. A network today must always be prepared. This paradigm shift requires a new kind of network, one that that can respond and adapt near-real time to constant and unpredictable changes in demand while also being able to detect and deflect all manner of cyber threats. The old network model completely breaks down in the face of this. That's why software-defined networking (SDN) and network function virtualization (NFV) are moving from concept to imple- mentation SO rapidly. This is the network of the future: open-sourced, future-proofed, highly secure, and flexible enough to scale up to meet any demand. This book lays out much of what we have learned at AT&T about SDN and NFV. Some of the smartest network experts in the industry have drawn a map to help you navigate this journey. Their goal is not to predict the future but to help you design and build a network that will be ready for whatever that future holds. Because if there's one thing the last decade has taught us, it's that net- work demand will always exceed expectations. This book will help you get ready. Randall Stephenson Chairman and Chief Executive Officer, AT&T Taylor & Francis Taylor & Francis Group http://taylorandfrancis.com Acknowledgments The authors would like to acknowledge the support from and the following contributions by Mark Austin, Rich Bennett, Chris Chase, John DeCastra, Ken Duell, Toby Ford, Brian Freeman, Andre Fuetsch, Kenichi Futamura, John Gibbons, Mazin Gilbert, Paul Greendyk, Carolyn Johnson, Hank Kafka, Rita Marty, John Medamana, Kathleen Meier-Hellstern, Han Nguyen, Steven Nurenberg, John Paggi, Anisa Parikh, Chris Parsons, Paul Reeser, Brian Rexroad, Chris Rice, Jenifer Robertson, Michael Satterlee, Raj Savoor, I