【作者】 沈可；

【导师】 甘育裕；

【作者基本信息】 重庆大学 ， 电路与系统， 2002， 硕士

【摘要】 在传统的IP网络中，人们主要关心如何使网络能尽量满足用户需求，网络所能提供的服务质量（Quality of Service , QoS）并没有得到足够的重视。IP网络中没有专门的机制保证服务质量，只提供“尽力而为”或“不可靠”的服务。其最大的特点就是：为IP网络提供不可靠，无连接的数据报服务。然而近年来，网络用户的不断增加，网络应用范围的不断扩大，各种实时性新型业务在传输的时候对网络提出了更高的要求。传统的IP网络在处理新业务的时候会显得力不从心。只有IP 网络中具备了 QoS保障机制才能够有效地解决IP新业务以及实时业务推广应用中碰到的问题。文章第一部分首先给出了QoS的定义，随后详细分析了传统IP网络无法满足数据传输QoS的原因。接着在文章的第二部分介绍了现在流行的三种研究QoS的模型（IntServ模型, DiffServ模型，集成和区分混合模型）。比较三种模型在解决QoS时的优缺点之后，确定重点研究DiffServ模型。文章的第三部分对DiffServ模型中QoS确保机制进行了研究。首先分析了DiffServ模型下数据分类的实现机制。在分类的基础上提出通过建立多个路由转发表，让不同类的数据通过各自合适的转发路径进行传输的方案。软件仿真的结果证明新方案比采用单一路由表的方式更适合传输具有不同QoS要求的数据。接着，文章重点分析了现有网络节点中所采用队尾丢弃策略的不足，认为只有采用随机早期探测（Random Early Detection: RED）这种动态队列管理机制才能有效避免网络出现拥塞。在分析了多种RED实现算法之后，文章认为采用RIO( RED IN/OUT)算法能够对符合规范的数据提供更好的保护，并通过软件仿真验证了这个结论。随后，文章对影响QoS的调度机制进行了分析。在常规的调度方式下，不同类的数据无法得到公平的对待，数据之间缺乏有效的隔离。如果要确保数据传输时QoS可以满足用户要求，就必须提供具有公平性的调度机制。为此文章分析了多种具有公平性的算法。并提出一种适合具有不同优先级特性数据传输的新算法：结合优先级实现具有公平性的DRR(Deficit Round Robin)算法。通过实验可以验证这种新算法不仅可以满足具有高QoS约束的数据传输的需要，还能够节省带宽。在文章的最后，对全文进行了总结。文章认为：DiffServ模型在不对传统IP机制进行大的改动（相对于IntServ模型）的前提下，可以在一定程度上满足用户对数据传输QoS的要求。同时提出：采用多个路由转发表，使用RIO算法管理队列，使用结合优先级的DRR算法进行调度，可以最大限度地保证高QoS要求数据传输的需要更多还原

【Abstract】 In the classical IP networks, the QoS(Quality of Service) provided by the networks was not given much attention. People only concerned about the ways to provide services as soon as possible. So there is no special method to insure the quality of service in the networks , and they can only provide "best effort" or "unreliable" services. The most important characteristic of those networks is that they only offer unreliable and connectionless services. Recently, the subscribers of networks increase quickly. At the same time, the domain in which the networks apply expands very fast. Stricter requirement is demanded by some modern real-time services. The classical IP networks can not meet those requirements very well. This problem will not be solved completely until the networks have some means that can guarantee QoS. In the first part of this thesis, the definition of QoS is given at the beginning , then the reasons why the classical IP networks can not insure packets transmission QoS are analyzed . Then three popular QoS network models (they are IntServ model, DiffServ model and IntServ & DiffServ integration model)are introduced separately in the second part of the thesis.The QoS guarantee mechanisms in the DiffServ model are studied in the third par of this thesis. The classification of data in the DiffServ model is analyzed firstly. On this classification base, thesis bring advance a route mean which hold many different forwarding information tables in single router , each classification data is forwarded according to different forwarding information table. This means which is validated by software emulation prove that it can provide much better QoS behavior in data transmission than classical forwarding mean. Then the deficiencies of DFE(Dorp From End) mechanism in a router’s input queue are studied. After that, the thesis figure out that RED (Random Early Detection) active queue management mechanism can be used to prevent networks from congestion collapse. After analyzing different RED method, the thesis confirm that the RIO( RED IN/OUT) can protect data better than other method. This conclusion is testified by software emulation. At last of this part, the scheduling mechanisms are studied. By common scheduling mechanism , different data can not be insulated distinctly and they can not be handled fairly . if the networks want<WP=6>to solve this problem, there must be some fair scheduling mechanisms in them. So this paper analyzes many fair-scheduling mechanisms. On this base, a new scheduling method is put forward. The new method proved by emulation is priority-based DRR(Deficit Round Robin) which can not only meet the requirement of the data with strict QoS restriction but also save the bandwidth. The last part is the conclusion for whole paper. DiffServ model can fulfil the request of data transmission a certain extent without changing classical IP mechanism much. On the other hand , the thesis consider that if the new route method , RIO and priority-based DRR are used at one time in a network, the transmission requirements of data with high QoS demand can be satisfied well更多还原