e.g., T-carrier and J-carrier operate at 56Kbps, E-carrier operates at 64Kbps). SS7 is an entire architecture that performs out-of-band signaling (i.e., signaling in which the conversation and the signaling take place over different paths) in sup- port of the information-exchange functions necessary in the PSTN, such as call establishment, billing, and routing. Database access messages convey information between toll centers and centralized databases to permit real-time access to billing- Signaling Systems related information and other services. The SS7 architecture defines the procedures for the setup, ongoing management, and clearing of a call, and it enables the passing along of customer-related information (e.g., the identity of the caller, the primary carrier chosen) that helps in routing calls. The efficiency of the network also results in faster call setup times and provides for more efficient use of the circuits when car- rying the voice or data traffic. In addition, SS7 supports services that require signal- ing during a call as it is occurring-not in the same band as the conversation. SS7 permits the telephone company to offer one database to several switches, thereby freeing up switch capacity for other functions, and this is what makes SS7 the foundation for intelligent networks (INs) and advanced intelligent networks (AINs). (INs and AINs are discussed later in this chapter.) It is also the foundation for net- work interconnection and enhanced services. Without SS7, we would not be able to enjoy the level of interoperability we have today. SS7 is also a key to the development of new generations of services on the Internet, particularly those that support tradi- tional telephony services. To be able to accommodate features such as call forward- ing, call waiting, and conference calling, you must be able to tap into the service logic that delivers those features. Until quite recently, the Internet has not been able to do this, but the year 2000 saw the introduction of SS7 gateways, which allow an inter