Research Topics

Measurement / Estimation Techniques of Dynamic Characteristics

There are “local state of the network” in various time granularity (scale), “global state of the network”,”communication quality to flow experience” as the measurement target. If difficult to direct / overall measurement of the subject property from large-scale and dispersibility of management, we need estimates from indirect / partial measurement. In particular, we are working on “Network Tomography”, statistical estimation of the difficult characteristics measured by the direct measurement from  the correlation between measurement data at multiple points simultaneously.The tomography is the method of seeing through from a plurality of directions by using X-rays, and refers the three-dimensional diagnosis of internal without incision. “Network tomography” are also using the same theory, for example, “estimation of characteristics about a certain flow through the multiple point by using measurement of the aggregate flow rate (the sum of several flows that pass through the point) ” and “estimation of characteristics about certain internal section shared by a plurality of paths, by using  the simultaneous measurement of the characteristics of the end-to-end of each path”.Currently, about the former, we researching the method to estimate the flow rate statistics of flow between each pair of multiple entrance and exit router of large networks, about the latter, we developing the method to estimate the packet loss rate and delay variation in one way part interval of network (e.g. from WWW server of router to our PC).

Active network technology

In the Internet, as a result of the emphasis on flexibility and economy, simplifies the functionality of the relay node, providing an alternative to the information service is performed end-node, also the estimated end nodes of the network state based on the end-to-end protocol by performing the optimization of delivery to and the network, and has been working to ensure the quality required for the service.It is said that a large-scale Internet, such as of today has become feasible thanks to this end-to-end principle. However, in accordance with an increase in the diversity of services provided and use environment-connection form, cooperation between end node and the relay node also has become important.The individual flow characteristics and required quality which occurs, depending on a variety of services and environments knows end node, whereas, since the variety of internal network state knows relay nodes, each of the requirements and to satisfy the, immediately adapted to the changes, and to do the whole of efficiency and fairness also take into account the control and management, both of cooperation because it is essential Active Network (Active Network), in order to answer such a request has been proposed as a framework which can be dynamically and flexible changed the function of the relay node, and aimed a programmable network is the future technique.Here, in particular, it is said to be encapsulated model among them, in each packet to include information for indication of the end node, and based on it to work on applications of the mechanism for changing the flexible processing at the relay node is fine-grained, it is now within the framework of lightweight AN that eliminates the “aggressive” behavior that inconvenience to the communication of others, we are developing the application in the measurement, control and time synchronization, etc..

DTN(Delay/Disruption/Disconnected Tolerant Network)

Today, with the development of information and communication technology, it has become to allow a stable communication at high speed in many places. However, such communication environment you want to move to radio waves is hard to reach and high speed, such as high-speed behind a building and underground shopping center, communication There is also a place that does not stabilize (poor communication environment). In poor communication environment, you can slow it is to receive the data (packet), communications or become intermittent, and prone to a problem that can happen to data loss. Therefore, studies such DTN have been made in order to allow a stable communication even in poor communication environments.

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