摘要： 设计并实现了基于USB接口的低成本网络可视电话系统，描述了其内嵌的QoS控制机制。基于区分服务体系，对IP数据包的ToS字段进行不同的编码设置，以区别服务的优先级；采用双向链表结构的抖动缓冲区进行时延抖动的平滑，链表的节点位数据帧或空闲帧，二者可动态切换，输入线程和输出线程互斥地对其进行读写操作。实验证明，在多数应用场合下，系统的通信时延小于30ms，丢包率低于10%。

关键词: 区分服务, 抖动缓冲区, 双向链表, H.323协议

Abstract: This paper presents the design and implementation of an Internet video phone system based on ITU-T H.323. It is a USB-based low-cost Internet communication terminal system. Its QoS guarantee mechanism is also presented. By filling the ToS field of each data packet with different code, it classifies different services’ priorities. The paper designs a doubly linked list jitter buffer to smooth the delay variation. The nodes in the list are data frames and free frames that can dynamically transform each other. An input and a play thread access the list exclusively. A series of tests show that the average delay is less than 30ms and the loss rate is below 10%.

Key words: Differentiated services, Jitter buffer, Doubly linked list, H.323 protocol