Studies on congestion control mechanisms realizing various end-to-end communication qualities 多様な通信サービス品質を実現する輻輳制御に関する研究

博士論文

本タイトル (誤植) : Studies on congestion control mechanisms realizing various end-to-end comunication qualities

1 Introduction||2 End-to-end congestion control||3 Controls on intermediate nodes||4 Experiments for High-Speed Transport Protocol of a Single Flow||5 Experiments for High-Speed Transport Protocol of Multiple Flows||6 Quality of Assured Service through Multiple DiffServ Domains||7 Adaptive Early Packet Discarding Scheme to Improve Network Delay Characteristics of Real-Time Flows||8 Concluding Remarks||Bibliography

The Internet has become an important infrastructure and continues to expand. With the ubiquitousness of the Internet in our daily lives, the amount of data, the number of flows, and the types of applications that coexist on the Internet have been increasing. Originally, people used the Internet to realize connectivity between senders and receivers. Currently, however, connectivity that meets a diverse range of requirements for various applications is desired. In a well-provisioned network in which the number of users is limited, it is easy to realize connectivity that meets various requirements with no dedicated controls. On the Internet, however, flows that have various requirements coexist and limited network resources are shared among those flows. Thus, in order to realize connectivity under these environments, congestion controls are important in the network. The present research, therefore, focuses on the congestion control mechanisms in order to realize end-to-end communication qualities that are adequate and suitable for the diversity of the network. Three diversities in the network are considered, i.e., network environments, application types, and the quality of services required by users. In addition, the problems in the current congestion control mechanisms are clarified in order to achieve various levels of end-to-end quality of service in the network and schemes are proposed to solve the problems. The congestion controls in the network can be classified into two categories from an architectural viewpoint: controls conducted between end hosts and controls conducted at all nodes along the path, including intermediate nodes in addition to end hosts. In the following discussion, these two categories of congestion control, working between end-to-end hosts and working at all nodes along the path, are described. Chapter 1 describes the background of the present research and outlines the present approach to target issues. In Chapter 2, the congestion control conducted between end hosts is introduced. Transmission Control Protocol (TCP) is a representative protocol working between end hosts and has been adopted as a transport protocol in the network, which can provide a highly reliable networking environment for non-real time application flows. However, it is well known that TCP cannot achieve efficient data transfer in fast long-distance networks. Therefore, various high-speed transport protocols have been proposed to solve this problem, and these protocols will also be introduced in Chapter 2. In Chapter 3, the congestion control conducted at all nodes along the path is introduced. In Chapter 4, the basic characteristics of a number of existing high-speed transport protocols are presented, which are obtained in testbed network. In this chapter, I primarily observe the throughput characteristics of a single high-speed transport protocol and discuss its efficiency and fairness for a Standard TCP flow. In Chapter 5, a number of experimental results are discussed for various scenarios considering the future high-speed Internet. High-speed transport protocols were originally developed for realizing efficient data transfer in fast long-distance networks. Therefore, in the case of coexisting high-speed transport protocol flows and standard TCP flows, the performance of the standard TCP flow is affected by high-speed transport protocol flows. On the other hand, on the future Internet, the end-to-end network will be faster. Under these circumstances, I believe that users may be interested in transferring their data using high-speed transport protocol instead of the current Standard TCP. Therefore, in Chapter 5, an environment in which high-speed transport protocols are adopted to transfer data by users, and experimental scenarios are considered. In Chapters 6 and 7, I describe the congestion control mechanisms in which intermediate nodes work in conjunction with end hosts. In Chapter 6, I evaluated the performance of end-to-end non-real time flows that pass through multiple DiffServ domains. Research on the quality of service of end-to-end flows achieved by DiffServ technologies focuses primarily on a single DiffServ domain. However, the actual network environment is a network of networks, in which multiple DiffServ domains are connected. Therefore, the end-to-end throughput characteristics of a minimum bandwidth guarantee service flow (AF (Assured Forwarding) service flow) that passes through multiple DiffServ domains in the DiffServ framework are investigated. In the AF service, the packets are marked according to service class in their headers based on the measurement at the ingress edge routers, and are then forwarded to the intermediate nodes. At the border router to another DiffServ domain, the packet arrival rate is measured again and the service classes are re-marked if necessary. I investigate the impact of packet remarking that occurs at edge router on the end-to-end throughput characteristics of AF flow. In Chapter 7, early packet discarding schemes are proposed in order to improve the delay characteristics of real-time application flows. Some real-time applications set limits for acceptable network delay. For example, VoIP defines service classes based on the end-to-end packet delay limit. In these applications, packets delayed longer than an acceptable limit are invalidated by their applications when they reach their destinations, even though they have successfully arrived at the receiver. These packets are considered to be useless by the applications and thus impose an excess load on the network. Therefore, an early packet discarding scheme is proposed as a kind of active queue management scheme, in which packets that do not contribute to the quality of real-time applications are discarded in advance at intermediate nodes. I evaluate the effectiveness of the proposed schemes via network simulation in Chapter 7. Finally, concluding remarks are presented in Chapter 8.

九州工業大学博士学位論文 学位記番号:情工博甲第202号 学位授与年月日:平成19年3月23日

平成18年度

九州工業大学博士学位論文(要旨） 学位記番号:情工博甲第202号 学位授与年月日:平成19年3月23日