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Communication in open packet-based networks like the Internet must be considered including security aspects. Different approaches exist to realize e.g. confidentiality in IP networks: IPSec at the network layer, TLS/SSL residing on the transport layer and security extensions for applications. Real-time-oriented Internet applications cause different demands on security protocols compared to their counterparts like e.g. HTTP does. It is questionable if the existing mechanisms are suitable for securing multimedia communication. This paper gives an overview of multimedia communication over the Internet. It describes available approaches for enabling confidentiality and analyzes the usability in real-time-oriented environments. Since currently all multimedia applications use RTP to packetize the media stream the newly proposed Internet Draft Secure Real-time Transport Protocol (SRTP) is analyzed as well. SRTP is presented in more detail and an extension to the H.323 protocol family to support SRTP is introduced. This approach enables on the one hand H.323 terminals to use the security services provided by SRTP and on the other hand the application of SRTP even in heterogenous signaling environments. Furthermore our SRTP implementation and its integration into the OpenH323 project is described.