Web APIs are offered in many Web sites for Ajax and mashup, but they have been developed independently since no reusable database component has been specifically created for Web applications. In this paper, we propose WAPDB, a distributed database management system for the rapid development of Web applications. WAPDB is designed on Atom, a set of Web API standards, and provides several of the key features required for Web applications, including efficient access control, an easy extension mechanism, and search and statistics capabilities. By introducing WAPDB, developers are freed from the need to implement these features as well as Web API processing. In addition, its design totally follows the REST architectural style, which gives uniformity and scalability to applications. We develop a proof-of-concept application with WAPDB, and find that it offers great cost effectiveness with no significant impact on performance; in our experiments, the development cost is reduced to less than half with the overhead (in use) of response times of just a few msec.

Current Web authentication frameworks have well-known weaknesses. HTTP provides an access authentication framework, but it is rarely used because it lacks presentational control. Forms and cookies, which are most commonly used, have the long-standing privacy issue raised by tracking. URI sessions, which are used in some mobile services like i-mode 1.0, disclose session identifiers unintentionally. This paper proposes iAuth, which integrates better parts of the existing frameworks and fixes their problems; iAuth allows servers to provide log-in forms, and introduces a session header to avoid servers' tracking and unintentional disclosure. Since iAuth has backward compatibility with the major legacy browsers, developers can freely introduce iAuth into their Web sites or browsers as needed. Experiments confirm its correct operation; an iAuth server is shown to support not only an iAuth client but major legacy browsers. We believe that iAuth will resolve the long-standing issues in Web authentication.

For subgraph enumeration problems, very efficient algorithms have been proposed whose time complexities are far smaller than the number of subgraphs. Although the number of subgraphs can exponentially increase with the input graph size, these algorithms exploit compressed representations to output and maintain enumerated subgraphs compactly so as to reduce the time and space complexities. However, they are designed for enumerating only some specific types of subgraphs, e.g., paths or trees. In this paper, we propose an algorithm framework, called the frontier-based search, which generalizes these specific algorithms without losing their efficiency. Our frontier-based search will be used to resolve various practical problems that include constrained subgraph enumeration.

Source routing multicast has been gathering much more attention rather than traditional IP multicast, since it is thought to be more scalable in terms of the number of groups at the cost of higher traffic loads. This paper introduces a mathematical framework to analyze the scalability of source routing multicast and IP multicast by leveraging previous multicast studies. We first analyze the amount of data traffic based on the small-world nature of networks, and show that source routing multicast can be as efficient as IP multicast if a simple header fragmentation technique (subgrouping) is utilized. We also analyze scalability in terms of group numbers, which are derived under the equal budget assumption. Our analysis shows that source routing multicast is competitive for low bit-rate streams, like those in the publish/subscribe service, but we find some factors that offset the advantage. This is the first work to analytically investigate the scalability of source routing multicast.

In this paper, we discuss the efficiency of tunneling techniques which are expected to accelerate multicast deployment. Our motivation is that, despite the proposal of many tunneling techniques, no paper has studied their impact on multicast efficiency. Through detailed computer experiments, we find that there is a critical size of multicast island, above which the loads imposed on tunneling endpoints are suddenly diminished. In addition, multicast islands equaling or exceeding the critical size reduce the overhead of forwarding states on routers. We also find a scaling law between the critical size and group size. Based on these findings, we present simple guidelines on using tunneling when deploying multicast systems. A possible explanation for our findings is uncovered by a simple analysis. Our work is the first to evaluate the impact of tunneling and clarify conditions in which multicast deployment is well supported by tunneling.

Several web sites providing disaster-related information failed repeatedly after the Great East Japan Earthquake, due to flash crowds caused by Twitter users. Twitter, which was intensively used for information sharing in the aftermath of the earthquake, relies on URL shorteners like bit.ly to offset its strict limit on message length. In order to mitigate the flash crowds, we examine the current Web usage and find that URL shorteners constitute a layer of indirection; a significant part of Web traffic is guided by them. This implies that flash crowds can be controlled by URL shorteners. We developed a new URL shortener, named rcdn.info, just after the earthquake; rcdn.info redirects users to a replica created on a CoralCDN, if the original site is likely to become overloaded. This surprisingly simple solution worked very well in the emergency. We also conduct a thorough analysis of the request log and present several views that capture user behavior in the emergency from various aspects. Interestingly, the traffic significantly grew up at previously unpopular (i.e., small) sites during the disaster; this traffic shift could lead to the failure of several sites. Finally, we show that rcdn.info has great potential in mitigating such failures. We believe that our experience will help the research community tackle future disasters.

Virtual network embedding has been intensively studied for a decade. The time complexity of most conventional methods has been reduced to the cube of the number of links. Since customers are likely to request a dense virtual network that connects every node pair directly (|E|=O(|V|2)) based on a traffic matrix, the time complexity is actually O(|E|3=|V|6). If we were allowed to reduce this dense network to a sparse one before embedding, the time complexity could be decreased to O(|V|3); the time saving would be of the order of a million times for |V|=100. The network reduction, however, combines several virtual links into a broader link, which makes the embedding cost (solution quality) much worse. This paper analytically and empirically investigates the trade-off between the embedding time and cost for the virtual network reduction. We define two simple reduction operations and analyze them with several interesting theorems. The analysis indicates that an exponential drop in embedding time can be achieved with a linear increase in embedding cost. A rigorous numerical evaluation justifies the desirability of the trade-off.

Autonomous mobility machines, such as self-driving cars, transportation robots, and automated construction machines, are promising to support or enrich human lives. To further improve such machines, they will be connected to the network via wireless links to be managed, monitored, or remotely operated. The autonomous mobility machines must have self-status based on their positioning system to safely conduct their operations without colliding with other objects. The self-status is not only essential for machine operation but also it is valuable for wireless link quality management. This paper presents self-status-based wireless link quality prediction and evaluates its performance by using a prototype mobility robot combined with a wireless LAN system. The developed robot has functions to measure the throughput and receive signal strength indication and obtain self-status details such as location, direction, and odometry data. Prediction performance is evaluated in offline processing by using the dataset gathered in an indoor experiment. The experiments clarified that, in the 5.6 GHz band, link quality prediction using self-status of the robot forecasted the throughput several seconds into the future, and the prediction accuracies were investigated as dependent on time window size of the target throughput, bandwidth, and frequency gap.

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 lost on a path due to traffic burstiness, silent failures, etc. Counting every path at every link, we could easily get the traffic volumes with their change, but this approach significantly increases the measurement cost since counters are usually implemented using expensive memory structures like a SRAM. This paper proposes a mathematical model to estimate TMs including volume changes. The method is established on a Boolean fault localization technique; the technique requires fewer counters as it simply determines whether each link is lossy. This paper extends the Boolean technique so as to deal with traffic volumes with error bounds that requires only a few counters. In our method, the estimation errors can be controlled through parameter settings, while the minimum-cost counter placement is determined with submodular optimization. Numerical experiments are conducted with real network datasets to evaluate our method.

In this paper, we examine the efficiency of tunneling techniques since they will accelerate multicast deployment. Our motivation is that, despite the many proposals focused on tunneling techniques, their impact on multicast efficiency has yet to be assessed sufficiently. First, the structure of multicast delivery trees is examined based on the seminal work of Phillips et al. [26]. We then quantitatively assess the impact of tunneling, such as loads imposed on the tunnel endpoints and redundant traffic. We also formulate a critical size of multicast island, above which the loads are suddenly diminished. Finally, a unique delivery tree model is introduced, which is so simple yet practical, to better understand the performance of the multicast-related protocols. This paper is the first to formulate the impact of tunneling.

The routing efficiency of structured overlay networks depends on the consistency of pointers between nodes, where a pointer maps a node identifier to the corresponding address. This consistency can, however, break temporarily when some overlay nodes fail, since it takes time to repair the broken pointers in a distributed manner. Conventional solutions utilize “backpointers” to quickly discover any failure among the pointing nodes, which allow them to fix the pointers in a short time. Overlay nodes are, however, required to maintain backpointers for every pointing node, which incurs significant memory and consistency check overhead. This paper proposes a novel light-weight protocol; an overlay node gives a “living will” containing its acquaintances (backpointers) only to its successor, thus other nodes are freed from the need to maintain it. Our carefully-designed protocol guarantees that all acquaintances are registered via the living will, even in the presence of churn, and the successor notifies the acquaintances for the deceased. Even if the successor passes away and the living will is lost, the successor to the successor can identify the acquaintances with a high success ratio. Simulations show that our protocol greatly reduces memory overhead as well as the detection time for node failure with the cost being a slight increase in messaging load.

Communication networks are now an essential infrastructure of society. Many services are constructed across multiple network domains. Therefore, the reliability of multi-domain networks should be evaluated to assess the sustainability of our society, but there is no known method for evaluating it. One reason is the high computation complexity; i.e., network reliability evaluation is known to be #P-complete, which has prevented the reliability evaluation of multi-domain networks. The other reason is intra-domain privacy; i.e., network providers never disclose the internal data required for reliability evaluation. This paper proposes a novel method that computes the lower and upper bounds of reliability in a distributed manner without requiring privacy disclosure. Our method is solidly based on graph theory, and is supported by a simple protocol that secures intra-domain privacy. Experiments on real datasets show that our method can successfully compute the reliability for 14-domain networks in one second. The reliability is bounded with reasonable errors; e.g., bound gaps are less than 0.1% for reliable networks.

The exciting goals of ubiquitous computing and communication services can only be achieved if we can increase the efficiency with which the location of mobile terminals can be managed; current mobile infrastructures are not efficient since they treat all mobile terminals uniformly despite that fact that many mobiles often move together (i.e. passengers on the same train or a group of cars on a road). This paper presents a hierarchical location management scheme that handles such grouped mobiles collectively and so reduces the overhead costs of location management. In our scheme, mobiles that move together for long enough form a mobile network and make a hierarchy in the wireless access network. The scheme also adjusts the number of mobile networks to keep communication overhead low. We apply the scheme to Mobile IPv6 and evaluate the resulting performance improvement. Simulation results confirm that our hierarchical approach can greatly reduce the overhead costs of location management, and that it is very practical since it can flexibly develop suitable mobile networks.

Network virtualization is one of the promising technologies that can increase flexibility, diversity, and manageability of networks. Building optimal virtual networks across multiple domains is getting much attention, but existing studies were based on an unrealistic assumption, that is, providers' private information can be disclosed; as is well known, providers never actually do that. In this paper, we propose a new method that solves this multi-domain problem without revealing providers' private information. Our method uses an advanced secure computation technique called multi-party computation (MPC). Although MPC enables existing unsecured methods to optimize virtual networks securely, it requires very large time to finish the optimization due to the MPC's complex distributed protocols. Our method, in contrast, is designed to involve only a small number of MPC operations to find the optimal solution, and it allows providers to execute a large part of the optimization process independently without heavy distributed protocols. Evaluation results show that our method is faster than an existing method enhanced with MPC by several orders of magnitude. We also unveil that our method has the same level of embedding cost.