 error-correcting procedures; recovery from outages of components in the transit path; control to avoid congestion on the Internet; detection of the status of peer entities (i.e., in service, out of service); support for security mechanisms to protect the integrity of the signaling information; and extensions to support security and future requirements. The characteristics of next-generation networks are very different from what the traditional PSTN was aiming at. Next-generation networks are not designed for just voice, data, or video. They are designed for multimedia and streaming media, and this requires capacities that are broadband in nature, networks that are engi- neered for extremely low and controllable latencies, and infrastructures that pro- vide the ability to administer quality of service on a very granular level. This book has talked about the explosion of bandwidth that's occurring because of developments in optics. As the availability of bandwidth increases, bandwidth becomes cheaper and cheaper. When bandwidth becomes very inex- pensive or almost free, a carrier needs to find other ways to generate revenue, such as by offering a large variety of value-added services (e.g., reliability, priority, cus- tomer service, and encryption or security). But to administer all these services and to provide differentiated pricing, which can result in handsome revenue streams, there must be mechanisms for controlling, monitoring, and billing. The next-generation network infrastructure has a number of important fea- tures that are covered in detail in later chapters: It has very fast packet switching, with capacities that we're beginning to need to measure in terabits per second (Tbps) and soon in petabits per sec- ond (1Pbps = 1,000Tbps), and on its heels, in exabits per second (1Ebps = 1 billion Gbps). (See Chapter 10.) It places great emphasis on optical networking elements to take advantage of the abundant bandwidth inherent in the visible light spectrum. (See Chapter 11, "Optical Networking.") Multiservice