lled by the customer for features such as area code routing, time of day routing, etc. were implemented using software that controlled the switches. An entire multibillion dollar industry grew out of the simple concept of reversing the charges and the power of letting the customer decide which data center to route the call to, for reducing their agent costs or providing better service to their end customers. For enterprise customers, AT&T provided a trademarked service called AT&T SDN ONENET, which provided private dialing plans, authentication codes and departmental charging capability as a virtual Time-Division Multiplexing (TDM) network for enterprise customers. With or with- out a Private Branch Exchange (PBX), the service exposed a programmable virtual network to enterprises. The DSDC network also provided the ability to add or remove resources to the call for advanced functions and mechanisms for dealing with federated controllers. Service Assist was a mechanism to service-chain an announcement and digit collection node into a call; this grew into Interactive Voice Response (IVR) technology with speech recognition but it was an early form of service chaining for virtual networks. When more than one controller was needed to handle the load Building the Network of the Future (or to perform the entire set of desired features) NCP transfer was used, which today we would see as controller-to-controller federation. Many variations of these types of service were created, across the globe, as both the ability for software control and the availability of computing to do more pro- cessing, allowed the service providers to let their customers manage their business. These SDN-like networks in the circuit-switched world were followed by a similar capability of providing network-level intelligent control in the packet-routed world, where the routers replace the switches. The development and implementation of SDN for AT&T's IP/MPLS network-generally known as the Intelligent Routing Service Control Platform (IRSCP)-was lau