Human need to exchange information on a greater distance brings the development of communication networks to such quality where average user can’t experience any delays or losses in transmission. However,increased need to exchange the content and network possibilities resulted with interoperability issues of networks based on different technologies. The solution was found in protocols and standards that enabled the interoperability of differenty types of networks. Convergence is a step towards in overcoming the current problems in data transmission of different types of networks.Voice over IP is offered as one of the most affordable solutions for replacing an existing PSTN (eng. Public Switched Telephone Network) network that provides voice communication. Also, by expanding the spectrum of communication network capabilities, potential security problems arise, so it is necessary to take into account the level of data integrity in the network. Therefore, the aim of this paper is to describe the basic elements of the VoIP network, define the necessary VoIP protocol protocols, interoperability with other network technologies, and VoIP network security.