VoIP (voice over IP) networks are currently being deployed by enterprises, governments, and service providers around the globe and are used by millions of individuals each day. Today, the hottest topic with engineers in the field is how to secure these networks. Understanding Voice over IP Security offers this critical knowledge. The book teaches practitioners how to design a highly secure VoIP network, explains Internet security basics, such as attack types and methods, and details all the key security aspects of a VoIP system, including identity, authentication, signaling, and media encryption. What"s more, the book presents techniques used to combat spam and covers the future problems of spim (spam over instant messaging) and spim (spam over internet telephony).