الفهرس 
Overview of the PSTNOnly 14 pages are availabe for public view
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Abstract
)1oice over IT is one of the quickest deve[oying Internet services and s[ow[y rey[aces traditiona[ tefeyhony. J-fowever, whi[e moving te[eyhony to the yu/Jfic IT y(atform /Jroadens its service caya/Jifities, some security yro/J(ems may occur. It is /Jecause the amount of threats existing in IT networks is much bigger than in case of traditiona[ te[eyhone networks.
In this work we wire begin the first yart by the PSTN history, te chno [ogy, signaCing, services, arui its draw /Jacks. The second yart is the ’VOlT techno{ogy discussing the OSI reference mode£; some ’VOlT techno[ogy /Jasics, and the Iy signafing yrotoco{S. Then in the fast yart we wire exy[ain the security cha[[enges of ’VOlT yu/JCic network in more detai{S and how to secure ’VOlT networks.