Design And Implementation Of The H.323 Gatekeeper

With Internet growing more and more fast and getting widely used, packetization based on IP has become the main trend of the evolution of telecommunication networks, and VoIP technology is being developed very rapidly. Various VoIP products are sold in markets, which have changed human life style; meanwhile, VoIP protocols and standards, the currently researching hotspots, are continuously renovated. In spite of the impact of SIP, H.323, as one of the most important VoIP protocol system, seems to have a dim future. But in practice, it has been nearly supported by all of VoIP manufacturers, and has a mass of loyal users. Comparing with other standards such as SIP, MGCP, H.248/MEGACO and soft switch, the most advantage of H.323 is its maturity, and highest market share. With the development of VoIP technology, H.323 is assimilating advantages (like fast start) of other relevant standards, making self-improvement, becoming more mature and sturdy, and showing a strong vitality. Many people believe that H.323 will continue to be the de facto VoIP standard.In this thesis, we discuss the structure of the H.323 stack, and analyze its key implementation technologies in detail, such as ASN.l encoding and partition of the functions of primary protocol entity. It is very important for us to master these technologies, which are significant to modify, customize and enhance H.323 stack in order to make it accorded with national standards and to design it with full intellectual property.In this thesis, we also describe the implementation of a gatekeeper based H.323. This gatekeeper is designed for small telecom operators or business customs. It is conformed to the H.323v4 and relevant national standards and ensures interoperability. Besides the functions specified in H.323, such as Address Translation, Admissions Control, Zone Management, Call Management and Bandwidth Control, it can satisfied with the requirements defined by users, such as Web management, dynamic modification of running parameters, NAT environment and fees calculation.Firstly, according to the requirements mentioned above, we provide the module partitions of the gatekeeper, introduce its total design scheme, and explain the functions and interfaces of each module in detail. Secondly, we particularly describe some modules such as gatekeeper kernel module (GKCore), web communication module and authorization module, and provide some parts of implementing detailsand important workflows. Lastly, we describe the testing environment for the gatekeeper, provide the testing result cooperating with Cisco gateway, Microsoft Netmeeting, Dialogic gateway and Palm IP phone, and give suggestions for the future research. Because the gatekeeper is fully conformed to the object oriented design technology, it has good scalability and code reusability.