| Along with the involvement of some famous equipment manufacturers, organization for standardization and telecoms operators, VoIP is more and more widely used. There are two main development trends of VoIP, which are H.323 and SIP. With its own advantage, each of them has occupied comparative market share, and would continue a long time. Hence, devices which support both SIP and H.323 are the main stream of VoIP products.In this paper, firstly, we introduce the VoIP system developed by BUPT-Vanlink laboratory. Secondly we analyze H.323 and SIP protocols separately. H.323 protocol is standardized by ITU for audio, video and packet data network for sharing data, and SIP protocol developed by IETF is simple with good expansibility and closely linked with the existing internet. In this paper we make a comparison between the two protocols on complexity, scalability and expandability and so on.More especially, we discuss the problems of interworking between the H.323 and SIP protocols, such as addressing and locating issues between different networks, message mapping preprocessing, address transformation of signaling terminals, and so on. Then, we propose the corresponding solutions to those problems, based on which we design the structure and functional modules of signaling gateway for conversation layer, as well as the external communication flow and the internal message procedure.Finally, we test the two main functions of signaling gateway---registration and basic communication function. The testing result demonstrates that the gateway we present in this paper is able to support the basic communication between SIP terminals and H.323 terminals successfully. |
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