The Internet real-time applications are growing rapidly, and available bandwidth estimation is required. Available bandwidth estimation methods by end host have been studied e.g. Pathload and pathChirp. These methods parameterize probe packet volume and observe the delay variation to estimate available bandwidth. In these methods, the probe packets impose heavy overhead loads on the network. In this paper, we propose a new available bandwidth estimation method based on the frequency of minimum RTT of probe packets in multi hop links. This method estimates bandwidth utilization and available bandwidth of a bottleneck link without significantly increasing network overhead. Estimation accuracies are evaluated for available bandwidth by implementing the proposed method. The proposed method shows better performance than pathChirp or Pathload, requiring fewer probe packets and less estimation time simultaneously.

Recent research on overlay networks has revealed that user-perceived network performance could be improved by an overlay routing mechanism. The effectiveness of overlay routing is mainly a result of the policy mismatch between the overlay routing and the underlay IP routing operated by ISPs. However, this policy mismatch causes a "free-riding" traffic problem, which may become harmful to the cost structure of Internet Service Providers. In the present paper, we define the free-riding problem in the overlay routing and evaluate the degree of free-riding traffic to reveal the effect of the problem on ISPs. We introduce a numerical metric to evaluate the degree of the free-riding problem and confirm that most multihop overlay paths that have better performance than the direct path brings the free-riding problem. We also discuss the guidelines for selecting paths that are more effective than the direct path and that mitigate the free-riding problem.

Recent research on overlay networks has revealed that user-perceived network performance, such as end-to-end delay performance, could be improved by an overlay routing mechanism. However, these studies consider only end-to-end delay, and few studies have focused on bandwidth-related information, such as available bandwidth and TCP throughput, which are important performance metrics especially for long-lived data transmission. In the present paper, we investigate the effect of overlay routing both delay and bandwidth-related information, based on the measurement results of network paths between PlanetLab nodes. We consider three metrics for selecting the overlay route: end-to-end delay, available bandwidth, and TCP throughput. We then show that the available bandwidth-based overlay routing provides significant gain, as compared with delay-based routing. We further reveal the correlation between the latency and available bandwidth of the overlay paths and propose several guidelines for selecting an overlay path.

With the spread of broadband and wireless Internet access, there is a growing need for a nomadic network environment that enables the use of network services anywhere, via various access media. In a nomadic network environment, however, the connectivity is decreased because users move among different access networks, and the bandwidth is narrow and fluctuating, especially for radio propagation in wireless networks. To solve these problems, we propose a multilink system with three key functions: IPinIP tunneling, dynamic distribution of packets, and reordering of distributed packets. In particular, our distribution function includes a novel algorithm based on available bandwidth estimation. A prototype of our system was evaluated through experiments using real wireless environments and its efficiency is discussed.

We previously proposed a new version of TCP, called Inline measurement TCP (ImTCP), in [2],[3]. The ImTCP sender adjusts the transmission intervals of data packets and then utilizes the arrival intervals of ACK packets for available bandwidth estimation. This type of active measurement is preferred because the obtained results are as accurate as those of other conventional types of active measurement, even though no extra probe traffic is injected onto the network. In the present research, we develop a new capacity measurement function and combine it with ImTCP in order to enable simultaneous measurement of both capacity and available bandwidth in ImTCP. The capacity measurement algorithm is a new packet-pair-based measurement technique that utilizes the estimated available bandwidth values for capacity calculation. This new algorithm promises faster measurement than current packet-pair-based measurement algorithms for various situations and works well for high-load networks, in which current algorithms do not work properly. Moreover, the new algorithm provides a confidence interval for the measurement result.

In the present paper, ImTCP-bg, a new background TCP data transfer mechanism that uses an inline network measurement technique, is proposed. ImTCP-bg sets the upper limit of the congestion window size of the sender TCP based on the results of the inline network measurement, which measures the available bandwidth of the network path between the sender and receiver hosts. ImTCP-bg can provide background data transfer without affecting the foreground traffic, whereas previous methods cannot avoid network congestion. ImTCP-bg also employs an enhanced RTT-based mechanism so that ImTCP-bg can detect and resolve network congestion, even when reliable measurement results cannot be obtained. The performance of ImTCP-bg is investigated through simulations, and the effectiveness of ImTCP-bg in terms of the degree of interference with foreground traffic and the link bandwidth utilization is also investigated.

We propose a real-time measurement method, DPDC (Detection of Packet-Delay Correlation), which models both available bandwidth and the averaging time scale. In this method, measurement periods are short and constant, while the theoretical measurement error is reduced. DPDC is established based on the discussion of the systematic error of the packet pair/train measurement. We evaluate through simulations its accuracy and robustness against the multihop effect. We also verify the feasibility of real-time measurements through testbed experiments using a tool called Linear that implements DPDC. Efficiency is demonstrated through simulations and testbed experiments by analyzing accidental and systematic errors. Finally, we discuss the available bandwidth variation in an Internet path using real-time data produced by Linear measurements and passive monitoring.

We propose a probing-based channel adaptive video streaming method to provide seamless video transmission over the wireless 3G network. In the proposed method, the available bandwidth (AB) of the end-to-end path is estimated by analyzing RTP packets at the streaming client and the network/client buffer status (NCBS) is predicted by examining the RTCP receiver report (RR) and the application defined packet (APP) including the AB information. Using the estimated AB, the NCBS, and the stored multirate bitstream information, the proposed streaming method determines the next transmission bitrate precisely. Experimental results indicate that the proposed method can be effectively used for video streaming.

This paper proposes ABdis, a new active measurement method for estimating the available bandwidth on a communication network path. Due to the recent explosion in multimedia applications, it is becoming increasingly important to manage network QoS, and tools that can measure network quality precisely are necessary to do this. Many conventional active measurement methods/tools, however, can measure/estimate only the average of the available bandwidth in a given period but cannot measure its distribution. If the distribution of the bandwidth over short intervals can be measured, the information would be useful for network management, proxy selection, and end-to-end admission control. We propose an end-to-end active measurement method called ABdis, which can estimate the distribution of the available bandwidth in a network path. ABdis employs multiple probes having different rates and a parameter-matching technique for estimating distribution. Furthermore, we present the results of simulations and verify ABdis's performance under various conditions by changing probe parameters, amount of cross traffic, and network models.