(SSP) exchanges. The intelligent peripheral (IP) is a system that provides voice notifications when required, and the service transfer point (STP) is an intermediate exchange, which routes signaling messages between the SSP and STP. A certain range of telephone numbers is reserved for IN services only. When a SSP, which performs the functions of an exchange, detects an IN service number, it requests routing information from the SCP. The SCP then provides information about how that call should be handled. In principle, we could implement all intelligence in the SCP and its database could store all the routing information. This would require heavy signaling between the switching points and the SCP. In practice, the services that do not require a centralized database are implemented in switching points to reduce the load on the SCP and the signaling connections between SCP and SSPs. Introduction to Telecommunications Network Engineering Some examples of IN services follow: Universal access number: A company with several offices in different parts of a country may have the same number throughout the coun- try. Each call is automatically connected to the office closest to the calling subscriber (SSP transfers caller's number to SCP). The cost of the call is the same no matter to which office the call is connected. Premium rate services: Information provision over the phone, for instance, doctor and layer services. The service provider charges sub- scribers via the telephone bill. The charge is dependent on the called service number. Freephone: Companies that want to provide free customer service use this service in which the receiver pays for the call. Credit card call: A service user can pay with his or her credit card by dialing his or her account number and identity code. The modern telecommunications networks using IN technology pro- vide many other services and a few new ones appear annually. An example of these is inexpensive home-to-mobile and mobile-to-home calls for which you dial a specific number given by a