Kohei Watabe

Intrusiveness-aware Estimation for high quantiles of a packet delay distribution

The active measurement of network quality, in which probe packets are injected into a network, is hindered by the intrusiveness problem, where the load of the probe traffic itself affects network quality. In this paper, we first demonstrate that there exists a fundamental bound on the accuracy of the conventional active measurement of delay. Second, to transcend that bound, we propose INTEST (INTrusiveness-aware ESTimation), an approach that compensates for delays produced by probe packets for wired networks. We show that INTEST enables an accurate high quantile estimation of delay. We do so through two simulations: a single-hop network composed of a router modeled by M/M/1 queuing, and a realistic multi-hop network modeled by a network simulator.

Effect of locality of node mobility on epidemic broadcasting in DTNs

In DTNs (Delay/Disruption-Tolerant Networks) composed of mobile nodes, when the node movement has spatial locality, the nodes repeatedly miss opportunities to forward messages to other nodes, thus lowering communication performance. In this paper, we analyze the effect of locality of node mobility on message dissemination speed in epidemic broadcasting. We represent the locality of node mobility using the positional distribution of nodes in a stationary state, and we present a method for deriving the ratio of infected nodes from the positional distribution. Based on the results of a numerical experiment where the positional distribution of nodes obeys a two-dimensional normal distribution, we show that the message dissemination speed is heavily restricted by the locality of node mobility. Moreover, we clarify that a heavy-tailed positional distribution leads to a low locality of node mobility and entails mostly unrestricted message dissemination speed.

Analysis on the fluctuation magnitude in probe interval for active measurement

Active measurement, which can provide end-to-end measurements of network performance, is critical since the Internet is managed by multiple organizations. Recently, on the active measurement of delay and loss, Baccelli et al reported that many probing policies can be used to provide appropriate estimation in addition to the traditional policy based on PASTA property if the volume of probe stream is negligible compared to the traffic stream. Probing schemes with fixed probe packet intervals suffer from the phase-lock phenomenon due to synchronization against the network performance; they do, however, provide superior accuracy. A remaining issue is how to decide the optimal probing policy while taking the phase-lock phenomenon into consideration. In this paper, we propose the probing policy that randomly fluctuates the probe packet interval to avoid the phase-lock phenomenon. We start by clarifying the relationships among the fluctuation magnitude, the properties of the target network, and estimation accuracy, and we discuss the optimal probing policy with regard to the properties of the target network.

Accuracy improvement of CoMPACT monitor by using new probing method

CoMPACT monitor that we have proposed is new technique to measure per-flow quality of service (QoS). CoMPACT monitor provide scalable measurement of one-way delay distribution by the combination of active and passive measurement. Recently, a new probing method for improving the accuracy of simple active measurement have been proposed. In this paper, we adopt the new probing method as active measurement of CoMPACT monitor, and show that the combination improves the accuracy of measurement remarkably for UDP flows.

Reduction of response time by data placement reflecting co-occurrence structures in structured overlay networks

We propose a method to accelerate a response of structured overlay networks by reducing the number of hops required to answer multi-queries. In the proposed method, by copying data items to the redundant storage spaces in other storages, a good data placement reflecting co-occurrence structures in the structured overlay network is achieved. We formulate the optimization problem of the data placement in the limited redundant space of the storages as an integer programming. A greedy approach to solve the optimization problem is also proposed. Through several simulations, it is confirmed that the proposed method can reduce the average number of hops required to answer multi-queries by about 30% at the maximum in our simulation settings. The reduction rate of the average number of hops depends on the level of co-occurrence. Further, the reduction of the computation time to solve the optimization problem with the greedy approach is evaluated. We also confirm that the proposed method does not affect load balancing of structured overlay networks.

A Proposal of an Efficient Traffic Matrix Estimation Under Packet Drops

Traffic matrix (TM) estimation has been extensively studied for decades. Although conventional estimation techniques assume that traffic volumes are unchanged between origins and destinations, packets are often discarded on a path due to traffic burstiness, silent failures, etc. This paper proposes a novel TM estimation method that works correctly even under packet drops. The method is established on a Boolean fault localization technique; the technique requires fewer counters though it only determines whether each link is healthy. This paper extends the Boolean technique so as to deal with traffic volumes with error bounds just by a small number of counters. Along with submodular optimization for the minimum counter placement, we evaluate our method with real network datasets.

On the Search Algorithm for the Output Distribution That Achieves the Channel Capacity

We consider a search algorithm for the output distribution that achieves the channel capacity of a discrete memoryless channel. We will propose an algorithm by iterated projections of an output distribution onto affine subspaces in the set of output distributions. The problem of channel capacity has a similar geometric structure as that of smallest enclosing circle for a finite number of points in the Euclidean space. The metric in the Euclidean space is the Euclidean distance and the metric in the space of output distributions is the Kullback-Leibler divergence. We consider these two problems based on Amaris α-geometry [1]. Then, we first consider the smallest enclosing circle in the Euclidean space and develop an algorithm to find the center of the smallest enclosing circle. Based on the investigation, we will apply the obtained algorithm to the problem of channel capacity.

A Method at Link Layer to Improve the Fairness in Multi-hop Wireless Ad Hoc Networks

Using the protocol IEEE 802.11, multi-hop wireless ad hoc networks yield only a poor performance, especially in throughput and fairness. When the offered load becomes large, i.e. the system is in saturation state, long-distance flows suffer a high degree of throughput deterioration. These problems not only come from medium contention at the MAC layer but are due to the link layer. In this paper, we propose a method to solve the throughput degradation and unfairness problem by providing fair treatment between flows at the link-layer. In our proposed method, a fair scheduling algorithm using round robin queue and the estimation for the average interval of packet enqueueing is applied to alleviate the unfairness problem at both MAC layer and link layer. The simulation results reveal that our proposed method is able to achieve better throughput and fairness compared to the standard IEEE 802.11.

An epidemic broadcasting mechanism in delay/disruption-tolerant networks utilizing contact duration distribution

Epidemic broadcasting, in which an infected node repeatedly forwards a copy of a message to other nodes, realizes one-to-many communication in delay/disruption-tolerant networks. In epidemic broadcasting, the key is to control the number of message forwardings among nodes while maintaining a short message delivery time in the network. In this paper, we present a novel idea for improving the performance of epidemic broadcasting: when an infected node encounters a (possibly) susceptible node, the infected node intentionally delays its message forwarding since this may increase the chance of simultaneous transmission to multiple susceptible nodes. On the basis of this idea, we propose HCD-BCAST (History-based Contact Duration aware BroadCAST), which significantly reduces the number of message forwardings. In HCD-BCAST, each node autonomously determines the message forwarding delay based on the contact duration distribution measured by that node. Through simulations, we show that HCD-BCAST achieves a reduction of approximately 10-40% in the number of message forwardings compared with history-based self-adaptive broadcast and k-neighbor broadcast.

Quasi-static approach for retry traffic with different service time

We proposed the “Quasi-static approach” as a method that can analyze the stability of a telecommunication system experiencing retry traffic. This method considers human interaction with the system, and use the difference of timescale between humans and system. Our recent studies evaluated the stability when all traffic including retry traffic has the same holding-time distribution as calls in the data plane. However, it is not natural to assume that all the calls including retries have the same holding-time distribution as those in the data plane. In this report, we consider a generalization of the quasi-static approach for retry traffic with different holding-time distributions.