ABSTRACT
Until the early 1990s telecommunication providers were employing dedicated closed networks, like the Public Switch Telephone Network (PSTN), for transmitting voice. By this way the establishment of communication and voice transmission in PSTN was exploiting only 10-25% of the total available resources [1]. Even though significant effort has been devoted to improve resource utilization and to minimize the cost of the provided services, very little has been achieved to date. The Internet has supported the revolution in telecommunications and specifically in the provision of voice services, voice is transmitted over the Internet Protocol (VoIP) utilizing the Internet as a backbone network. Despite the fact that a plethora of novel, sophisticated, low-cost services can be offered in this way (e.g., conference rooms, click to dial etc), telecommunication providers are now facing security problems that have not been previously encountered.
