The Design And Implementation Of VoIP Calling Protocol Analysis And Voice Data Decoding

With the rapid development of data communication technology, TCP/IP protocol becomes the dominant network technology. The various types of services which are based on the IP network have become the important trend of communication technology development. VoIP (Voice over IP), also named as IP phone, is an important service on the IP network. Any new technology is a double-edged sword. The rapid development of IP phone brings about tangible benefits and convenience to people's life, at the same time it also becomes a new communication mode in some illegal and criminal activities. It takes a new challenge to the public security, as the traditional means of monitoring can do nothing. Under such circumstances, the public security organs need a new method to monitor VoIP.VoIP monitoring system is a big project, this paper researches on the key technologies of calling signal information analysis and voice decoding. We put forward a method and a process of signal analysis, as well as to restore the voice. And on the base of these researches, we design and implement a VoIP monitoring system, which restores the original calling lists and voice data from IP phone data package effectively.In this paper, we firstly analyze the H.323 protocol stack which is adopted when the Chinese major carriers build their VoIP networks, focusing on core issue H.225.0 calling control signaling and H.245 system control signaling. Then we research on the whole calling process, and voice data decoding technique generally. We put forward entire process of VoIP calling protocol analysis and voice data decoding. In order to solve the authentication information "lose" problem because of the modification of standard access authorization process when UNICOM builds its VoIP network, we propose to obtain the required IP number information from other ways, ensuring the calling signaling integrality.We use the standard voice coding and decoding which ITU commends to accomplish the voice decoding portion. In order to reduce the complication of arithmetic, we modify moderation and adopt it to the voice data decoding in IP monitoring system, and bring forward the means how to associate the voice and calling information. Achieve the voice restore integrity.Finally, based on the pivotal techniques above, we develop the'UNICOM VoIP telephone monitoring system'. The system collects the IP network data from UNICOM via the Spectral way. Monitors the raw data flow particularly, and reverts the information which the public security organs need, it carries out the effective monitoring to data in the UNICOM IP network. It achieves the whole communication lists and authentication information, intercepts and captures the voice selectively according to the user set, then records and plays back, supporting the G.723.1, G.729 and other common voice decoding arithmetic, offering the special real time listen in channels to assure the delay of monitoring less than 200 millisecond. Our practice has shown that this system fills up the VoIP surveillance gap in the public security organs, and improves the efficiency of case detection.