nd the ability for several independent applications to be applied to a given call leg were among other important required characteristics. There was no single network architecture supporting voice, video, and multimedia services. Telecom operators had several separate, standalone, unconnected network islands supporting voice, video, and multimedia services for its various entities. Any traffic between these networks was done via the public switched telephone network (PSTN). The vision for a common architecture for real-time services combined these various networks into a single IP-based network to provide end-to-end IP connectivity, thus improving both network and capital efficiency as well as enabling interoperability and next-generation services. With IMS standards and the associated architecture specifications reaching a level of acceptance in the telecommunications industry and becoming the de facto standard for real-time, multimedia services over wired and wireless networks, tele- com operators adopted IMS as the basis for their network architecture, and started to deploy IMS- compliant functions supplemented with additional functions in the network as appropriate and as business needs required. Service Platforms The current architecture for real-time services over IP is based on a layered framework with the following basic concepts: 1. Infrastructure core for session control and management on top of a converged IP/MPLS (Multiprotocol Label Switching) network Each access technology communicates via a border controller, which provides a uniform internal view 3. Packet core infrastructure that supports packet processing gateway functions 4. To provide a service, the corresponding application server (AS) is plugged in 5. Once a new access technology is supported, it can be used by all existing and future AS 6. Once a new AS is deployed, it can support all existing and future access technologies 7. Application programming interfaces (APIs) expose key network capabilities for applica- tion developers Figure 14.1 