the layer IN such that the acceptance of call and the routing is executed by the basic states. The service machine is accessed by IN layers with the call IN model [7]. The model of service programming with SIP consists of an add-on SIP server and an IN layer, that manages the interconnection with the IN called SIP Intelligent Network (SIN) [8]. This operation necessitates Service logic Programming interface Request Request SIP server Response Response function FIGURE 21.1 Model for programming SIP services. (From Schweizer, L. 2001. Scripts et APIs pour la gestion de serveurs SIP. www.tcom.ch; 23/12/2001. With permission.) C 2009 by Taylor & Francis Group, LLC Secure Intelligent SIP Services O-SIP T-SIP FIGURE 21.2 Interconnection SIP-IN. the definition of a correspondence between the call IN and call SIP models, it is to tell a correspondence between the state machine of the SIP protocol (SIP defines the header Record Route that allows to order the SIP server to function in mode with states until liberation of the call) and the state machine of IN. A call will be processed by the two machines, the state machine SIP processes the initiation of call and the final reply deliverance, and the IN layer communicates with the intelligent point SCP to provide services during call processing [8]. Figure 21.2 illustrates the integrated SIP-IN. Similarly to the machine of states IN, one defines the quoted calling and called the entity (O-SIP) and (T-SIP) these entities correspond, respectively, to the O-BCSM and T-BCSM of the model IN. In the basic SIP system, the SIP proxy with control of intelligent call is designed to interconnect with IN, this IN is realized by the utilization of sig- nificant control calls called 'state' that can synchronize with the model of call IN (BCSM). According to RFC 2543 (SIP) one can define calls of the state machine of the SIP client and SIP server [8,9]. The 11 PICs of O_BCSM come into play when a call request (SIP INVITE message) arrives from an upstream SIP client to an originating SIN-en