We propose an algorithm for finding heavy hitters in terms of cardinality (the number of distinct items in a set) in massive traffic data using a small amount of memory. Examples of such cardinality heavy-hitters are hosts that send large numbers of flows, or hosts that communicate with large numbers of other hosts. Finding these hosts is crucial to the provision of good communication quality because they significantly affect the communications of other hosts via either malicious activities such as worm scans, spam distribution, or botnet control or normal activities such as being a member of a flash crowd or performing peer-to-peer (P2P) communication. To precisely determine the cardinality of a host we need tables of previously seen items for each host (e.g., flow tables for every host) and this may infeasible for a high-speed environment with a massive amount of traffic. In this paper, we use a cardinality estimation algorithm that does not require these tables but needs only a little information called the cardinality summary. This is made possible by relaxing the goal from exact counting to estimation of cardinality. In addition, we propose an algorithm that does not need to maintain the cardinality summary for each host, but only for partitioned addresses of a host. As a result, the required number of tables can be significantly decreased. We evaluated our algorithm using actual backbone traffic data to find the heavy-hitters in the number of flows and estimate the number of these flows. We found that while the accuracy degraded when estimating for hosts with few flows, the algorithm could accurately find the top-100 hosts in terms of the number of flows using a limited-sized memory. In addition, we found that the number of tables required to achieve a pre-defined accuracy increased logarithmically with respect to the total number of hosts, which indicates that our method is applicable for large traffic data for a very large number of hosts. We also introduce an application of our algorithm to anomaly detection. With actual traffic data, our method could successfully detect a sudden network scan.

We present the development of a VoIP quality of service (QoS) measurement system that enables operators to diagnose a QoS degradation segment. Our system uses a flow-based passive measurement method to fulfill the requirement for QoS measurement in large-scale IP networks. In particular, we adopt an access control list (ACL)-based filtering function that selects traffic to monitor and develop a function for correlating signals and media data records. This correlation function is required to dynamically configure ACL-based filtering for monitoring media streams whose port numbers are determined by a signaling protocol. To improve the scalability of existing measurement systems, we also develop a hardware-based filtering engine on a commercial switch as well as a mediation box that performs QoS calculation based on traffic records exported by the engine in a distributed manner. We demonstrate the feasibility of the measurement system by evaluating a prototype system.

Crystalline GaN films can be grown even on amorphous substrates with the use of graphene buffer layers by pulsed sputtering deposition (PSD). The graphene buffer layers allowed us to grow highly c-axis-oriented GaN films at low substrate temperatures. Full-color GaN-based LEDs can be fabricated on the GaN/graphene structures and they are operated successfully. This indicates that the present technique is promising for future large-area light-emitting displays on amorphous substrates.

This paper presents a method of measuring the traffic of IP multicast streaming, such as IPTV, by using IPFIX and PSAMP. The IP multicast streaming service has recently become one of the popular network services, but no IP multicast operation method has been established yet. In particular, traffic measurement of IP multicast streaming encounters two challenges: as monitoring a multicast path tree and QoS measurement. There is no method to monitor them continuously in large-scale networks. Hence, we explore measurement structure suitable for large-scale networks, and then using IPFIX and PSAMP, we propose an efficient a network-level quality measurement method for IPTV and a method to extract multicast path tree data. In addition, we demonstrate the feasibility of the measurement method by evaluating a prototype system.

IP multicast technology is highly advantageous for various applications and future needs in the Internet. Yet, it is generally recognized that the IP multicast routing protocol is fairly complex and non-scalable and requires additional maintenance and operational cost to network administrators. Although there has been much research related to IP multicast and most router vendors already support basic IP multicast routing protocols, there is still a big gap between what is reported as the state-of-the-art in the literature from what is implemented in practice. In this paper, we clarify the complexities of traditional multicast communication and describe possible solutions using the one-to-many multicast communication model called Source-Specific Multicast (SSM). We explain this communication model and the corresponding routing architecture and examine the statistics obtained for the number of multicast routing entries in our backbone router, which is connected to the international backbone. We also introduce our international collaboration activities that are contributing to the deployment and promotion of IP multicast services in the Internet.

Luminescent characteristics of BaGd4Si3O13:Tb phosphor powder including fluorine, which is synthesized at about 1000, have been investigated. This phosphor shows the green emission due to Tb3+ under VUV excitation. By incorporation of F ion based on low-temperature synthesis, the photoluminescence excitation band lying in the wavelength region from 130 to 170 nm increases drastically in comparison to BaGd4Si3O13:Tb phosphor synthesized at 1550. This phosphor is a candidate for a green PDP phosphor for both 147 nm resonance line and 172 nm excimer band of Xe plasma.

An anomalous change in traffic distributions caused by an external inter-domain routing change leads to congestion of some network links, which then affects the network quality or disrupts traffic. Thus, network operators need to promptly deal with these problems by changing the routing policy or by soliciting the help of an involved or neighboring network operator through operator channels. In addition, they need to diagnose situations in which customers are affected by the incident or in which destinations become unreachable. Although this task is indispensable, understanding the situation is difficult since the cause lies outside the operators' network domains. To alleviate the load on operators, we developed a system for monitoring traffic shifts and the disruptions caused by BGP routing changes. It is challenging to extract information that is more valid from a large amount of BGP update messages and traffic flow records. By correlating these data, the system provides meaningful reports and visualized traffic statistics, and it enables operators to easily detect the cause of traffic changes and to investigate the extent of damage. We demonstrate the effectiveness of the system and evaluate its feasibility by applying it to an ISP backbone network. In addition, we present a case study of traffic changes that the system detected.