EVOLUTION OF VoIP SIGNALING PROTOCOLS1 This chapter reviews the existing and emerging VoIP signaling and call control protocols. In PSTN networks, ISUP (ISDN user part) and TCAP (transaction capabilities application part) messages of the SS7 protocol [1] are commonly used for call control and interworking of services. The first generation (released in 1996) of VoIP signaling and media control protocols, such as ITU-T’s H.225/H.245—defined under ITU-T’s H.323 umbrella protocol [2]—was intended to o