Communication between people has changed with the invention of the telephone. The ability to communicate across continents in real-time has also helped our society in several dimensions including entertainment, trade, finance, and defense. But this new capability did not come without an investment. Building an international telephony infrastructure has required the cooperation of both commercial and government organizations to evolve into what it is today. It has also led to the formation of international standard bodies that both direct and support the industry towards an interoperable communication networks.

IP networks are the next step from the traditional telecommunications. For a while, IP family of protocols was only used in the Internet, and the main applications were file transfers and e-mail. With the World Wide Web, the Internet changed into a global and always open information distribution channel. And finally with the advent of VoIP, the Internet is becoming a real-time communication media that integrates with all the earlier multimedia capabilities.

Traditional telecommunication networks are critical to the survival of our society. The PSTN is a closed network and its operational intricacies are known to a few select individuals who have devoted much of their lives to building it. Although operations in PSTN are not entirely a secret, they were and still remain proprietary for several reasons such as competitive advantage and national defense. The PSTN was and remains a closed infrastructure that concentrated its intelligence in its core network elements and left the edge devices very simplistic. The equipment and resources to operate a TDM network require a substantial financial investment. This lack of direct access to core network elements from subscribers and the high price of connectivity alleviated the risk for attacks. Ergo, subscribers demonstrate greater trust for communications through the PSTN compared to the Internet. This is a misconceived trust once you start analyzing the PSTN components and protocols and realize the lack of protection mechanisms.

In the earlier days of the Internet, security was appalling. The Internet was an open network where anyone could attack anyone anonymously and many of the attack tools were, and still are, available. As such, security research became a standard practice in government, commercial, and academic worlds with globally known research groups in organizations such as DARPA, DISA, CERIAS, MIT CIS, Bellcore, Bell Labs, and many others. Things became a bit more complicated with the transition of critical services such as telephony on the Internet along with other multimedia applications such as video and gaming. And due to the performance, availability, and privacy requirements of these applications, their security requires new approaches and methods compared to traditional IP security. Nevertheless the traditional security objectives apply such as confidentiality, integrity, and availability of services.