Voip security in public networks

VoIP over public networks is just a specialized internet service. In today?s world, VoIP is preferred since it utilizes the existing computer networks and thus reduces costs for long-distance calls and in-company telephony network?s initial setup and maintenance. As an expected result of lower costs with more features VoIP usage increases day by day.In this thesis work, VoIP technology, infrastructure, threats to VoIP and possible precautions and solutions to these threats are researched. Among these threats, most of the technical ones have already been studied many times and certain, somewhat effective solutions to these threats are developed. Unlike many others, the weight is on non-technical attacks in this thesis and a speaker and text dependent biometric speaker verification / identification system is prototyped and successfully tested to prevent impersonation attacks.To build the system, a collection of users sound-print files is formed from the collected samples from users and an initial voice authentication (speaker verification) before calls is aimed to be performed by means of this system. Any following work is advised to focus on integration of this system to commonly deployed production level VoIP services and a text independent version of the speaker verification system.