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The next generation network (NGN) is the inevitable direction in which the telecommunication network will transform. And with the incessant expansion of the NGN experiment and the commercial network, Quality of Service (QoS) of the comprehensive service provided by NGN will be more and more prominent. NGN uses the IP technology to take on multiple tasks (Everything over IP), while the traditional IP network only provides sole service, therefore it frequently appears as unable to fulfill the requirement of the real-time data transmission in large-scale business multimedia such as audio, video and so on, and even the basic voice QoS that NGN provides is worse than traditional Public Switch Telephone Network (PSTN). In this case, the QoS research of NGN would be of great theoretical and the practical significance, and it has already become one of hot research issues in this field.This dissertation, based on the media gateway (MG) of the voice quality function, studied how to guarantee and enhance the voice QoS of the media gateway in the NGN framework. The dissertation first simply introduced the current development of NGN comprehensively, defined the basic concept of the NGN, and described the four levels of NGN framework: the access layer, the transmission layer, the control layer and the service layer, and it also analyzed the fundamental characteristics and the privilege of NGN development. Afterwards, it analyzed several kinds of commonly used QoS models: IntServ, DiffServ, MPLS, CAC and VPN and so on, and detailedly discussed about the QoS guarantee mechanism of NGN from several aspects in terms of the access layer, the transmission layer, and the control layer. Then, rooted upon the role MG played, it introduced the function MG needed to provide to guarantee voice quality, and on the basis of analyzing H.248 and Q.931 protocol, explained how media gateway controller (MGC) realized basic calling flow and media capacity match by controlling the MG, proposed a kind of QoS guarantee mechanism grounded on the media match policy by expanding H.248 protocol, and utilized the call controlling and resource management of MGC, to provide dynamic negotiation process of voice QoS capacity, including voice encoding, RTP attribute, voice enhancing attribute and so on, and realized mechanism of traffic control in NGN. And then, according to the feature of NGN, based on not increasing the hardware resources and not influencing the original function, the dissertation proposed an initiative testing method of QoS in NGN, which expanded H.248 protocol, and simulated real calling flow totally and reflected real network state and voice QoS in NGN. Finally, this dissertation put forward a summary to the current research and advanced the prospect to the development trend of voice quality in NGN.
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