ific service IN. They depend also on the implementation of security mechanisms (e.g., PIN, strong authentication, place- ment of authentication, management of key, etc). Manufacturers as well as the standardization groups carry out analysis of risks in order to improve the security of systems IN. Although a lot of improve- ments have already been realized concerning the security of access to SCP and SMP, new services and new architectural concepts necessitate supplementary improvements. Figure 21.8 presents areas of different threats. Intelligent networks are distributed by nature. This distribution is realized not only to the superior level where the services are described as a collection of service feature (SF), but also to lower levels, where the functional entities (FE) can be propagated on different physical entities (PE). As communication Modification data Service provider Modification data SCP author provider Listen PIN Threats of SS7/INAP communication SCP(SDF, SRF) IP phone SS7/ISUP local switch Modification data listen keys 00000000 Listen PIN Switch IP phone service node author FIGURE 21.8 Areas of potential threats. © 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security of various elements of the network are realized on the open and uncertain environments, security mechanisms need to be applied. A responsible system can prevent these threats of security by using the various mechanisms. The authentication has to be applied in order to prevent unauthorized users gain access to the distribution of services. 21.4.2 Secure the Intelligent Network with SIP SIP communication is susceptible to several types of attack. The simplest SIP attack permits assailants access to information on users identities, services, media and topology of distribution. This information can be employed and executed in other types of attack. The modification of attack occurs when an assailant intercepts the effort, covers the signal and modifies the SIP message in order to change a certain service c