Takeo Abe

A method of detecting performance degradation at TCP flow level from sampled packet streams

Managing the performance at the flow level through traffic measurement is crucial for effective network management. On the other hand, with the rapid rise in link speeds, collecting all packets has become difficult, so packet sampling has been attracting attention as a scalable means of measuring flow statistics. We have therefore established a method of detecting performance degradation at the TCP flow level from sampled flow behaviors. The proposed method is based on the following two flow characteristics: (i) sampled flows tend to have high flow-rates and (ii) when a link becomes congested, the performance of high-rate flows becomes degraded first. These characteristics indicate that sampled flows are sensitive to congestion, so we can detect performance degradation of flows that are sensitive to congestion by observing the rate of sampled flows. We also show the effectiveness of our method using measured data.

Method of Bandwidth Dimensioning and Management for Aggregated TCP Flows with Heterogeneous Access Links

We propose a method of dimensioning and managing the bandwidth of a link on which flows arriving on access links that have heterogeneous bandwidths are aggregated. We start by developing a formula that approximates the mean TCP file-transfer time of a flow in such a situation. This only requires the bandwidth of the access link carrying the flow and the bandwidth and utilization of the aggregation link, each of which is easy to set or measure. We then extend the approximation to handle various factors that affect actual TCP behavior, such as round-trip time and restrictions other than the access-link bandwidth and congestion of the aggregation link in the end-to-end path of the flow. To do this, we define the virtual access-link bandwidth as the file-transfer speed of the flow when utilization of the aggregation link is negligibly small. We apply the virtual access-link bandwidth in the approximation to estimate the TCP performance of the flow with increasing utilization of the aggregation link. We use this method of estimation as the basis for a method of dimensioning the bandwidth of the link such that TCP performance is maintained and a method of managing bandwidth by comparing measured link utilization with the estimated threshold that indicates degradation of TCP performance. We also use simulation to analyze the accuracy of the estimates produced by our method.

A Method of Bandwidth Dimensioning and Management Using Flow Statistics

We develop a method of dimensioning and manag- ing the bandwidth of a link on which TCP flows from access links are aggregated. To do this, we extend the application of the processor-sharing queue model to TCP performance evaluation by using flow statistics. To handle various factors that affect actual TCP behavior besides the access-link bandwidth, such as round-trip time, window-size, and other bottlenecks, we extend the model by replacing the access-link bandwidth with the actual file-transfer speed of a flow under a low utilization of the aggregation link. We only use the number of active flows and the link utilization to estimate the file-transfer speed. Unlike previous studies, the extended model based on the actual transfer speed does not require any assumptions/predeterminations about file- size, packet-size, and round-trip times, etc. Using the extended model, we predict the TCP performance when the link utilization increases. We also show a method of dimensioning the bandwidth needed to maintain TCP performance. We show the effectiveness of our method through simulation analysis. I. INTRODUCTION

QoS control to handle long-duration large flows and its performance evaluation

A method of controlling the rate of long-duration large flows and its performance evaluation is described in this paper. Most conventional QoS controls allocate a fair-share bandwidth to each flow regardless of its duration. Thus, a long-duration large flow (such as a P2P flow) is allocated the same bandwidth as a short-duration flow (such as data from a Web page) in which the user is more sensitive to response time. As a result, long-duration flows will occupy the bandwidth over the long period and worsen response times of short-duration flows, and the conventional QoS methods do nothing to prevent this. We have, therefore, proposed a new form of QoS control that takes flow duration into account and assigns higher priority to the acceptance of shorter-duration flows. In this paper, we show through simulation that our method achieves high performance for short-duration flows without degrading the performance of long-duration flows. We also explain how to set parameters used in our method. Furthermore, we discuss the applicability of a packet-sampling technique to improve the methods scalability.

A method of bandwidth dimensioning and management for aggregated TCP flows with heterogeneous access links

We propose a method of dimensioning and managing the bandwidth of a link on which flows arriving on access links that have heterogeneous bandwidths are aggregated. We start by developing a formula that approximates the mean TCP file-transfer time of a flow in such a situation. This only requires the bandwidth of the access link carrying the flow and the bandwidth and utilization of the aggregation link, each of which is easy to set or measure. We then extend the approximation to handle various factors that affect actual TCP behavior, such as round-trip time and restrictions other than the access-link bandwidth and congestion of the aggregation link in the end-to-end path of the flow. To do this, we define the virtual access-link bandwidth as the file-transfer speed of the flow when utilization of the aggregation link is negligibly small. We apply the virtual access-link bandwidth in the approximation to estimate the TCP performance of the flow with increasing utilization of the aggregation link. We use this method of estimation as the basis for a method of dimensioning the bandwidth of the link such that TCP performance is maintained and a method of managing bandwidth by comparing measured link utilization with the estimated threshold that indicates degradation of TCP performance. We also use simulation to analyze the accuracy of the estimates produced by our method.

Special Section on Networking Technologies for Overlay Networks

Overlay networks are expected to be a promising technology for the realization of QoS (Quality of Service) control. Overlay networks have recently attracted considerable attention due to the following advantages: a new service can be developed in a short duration and it can be started with a low cost. The definition and necessity of the overlay network is described, and the classification of various current and future overlay networks, particularly according to the QoS feature, is attempted. In order to realize QoS control, it is considered that routing overlay and session overlay are promising solutions. In particular, session and overlay networks are explained in detail since new TCP protocols for QoS instead of current TCP protocols that control congestion in the Internet can be used within overlay networks. However, many open issues such as scalability still need further research and development although overlay networks have many attractive features and possess the potential to become a platform for the deployment of new services. key words: overlay network, QoS, quality, routing, session, transport, TCP/IP, relay

Replication scheme for traffic load balancing and its parameter tuning in pure P2P communication

A replication scheme is an effective method for maintaining a high hit rate for target files. This paper proposes a new replication scheme that scatters replicas of files to other servants on a P2P network for the purpose of dispersing query and download traffic. First, the details of this proposed scheme are described and its parameter tuning is discussed by introducing rating functions. Second, the effectiveness of this scheme is evaluated by simulation. The simulation results demonstrate that the proposed scheme has superior performance for some characteristic values, such as the hit rate and the number of mean hops to the target servant, compared with other schemes. Finally, the influence of departure rate is discussed.