The rising demand for mobile communication is increasing the importance of efficient use of limited radio frequency resources. The assignment of radio channels to the cells of current cellular mobile radio systems, specifically, to each base station, has been much studied to increase efficiency in radio frequency use. Dynamic Channel Assignment (DCA) is one approach to this problem. This paper compares the basic characteristics of DCA with Fixed Channel Assignment (FCA) and describes the main DCA strategies. The most important current research topics on DCA are discussed, focusing on micro-cellular systems, which are considered indispensable in meeting the huge demand for future mobile communications.

In order to increase the flexibility and the extensibility for packet transmission, the active network approach, that makes network nodes programmable, is very promising. Every packet includes a program specifying behavior of the packet at network nodes, and the network nodes only have the functions to execute programs of the packet. In an active network, network congestion management is achieved more flexibly and intelligently than that in the conventional internet. A number of mechanisms for congestion management are easily developed because various network functions such as QoS routing and congestion detection are easily combined in the same network nodes. By executing different routing protocols that use different levels of the link information, a congestion management scheme can be customized by users. This paper shows how QoS routing and congestion detection achieve a congestion management over an active internetwork system.

Ultrahigh-speed all-optical label processing method is proposed and experimentally demonstrated. This processing method dramatically increases the label processing capability. Optical packet switch (OPS) systems and networks based on OPS nodes are applications of optical processing technologies. For the experiment, we constructed the world's first 40 Gbit/s/port OPS prototype with an all-optical label processor, optical switch, optical buffer, and electronic scheduler. Three-hop optical packet routing using OPS nodes was experimentally demonstrated with it, verifying the feasibility of OPS networks.

Using ultrafast nonlinear-optical response of organic dye films, a train of picosecond optical pulses can be converted into a space pattern of a mm scale. As applications of this technique we demonstrate a single-shot multichannel optical switching for 1 Tbit/s pulse trains, and a timing jitter suppression of pulse trains using a control system with femtoseconds time resolution.

The demand for mobile communications is continuing to grow, but there is a limit on the radio frequency resources. Micro cellular systems are a strong solution to this problem. However, Forced Call Termination (FCT) and Channel Changing (CC) occur frequently in these systems because of their small cell size. This paper proposes a new Dynamic Channel Assignment (DCA) strategy which uses information of moving direction of Mobile Stations (MSs) to reduce FCT and CC. This strategy, the MD (Moving Direction) strategy, is compared with other major DCA strategies by simulating a one-dimensional service area covering a road, such as an expressway. The simulation shows that the MD strategy performs better than the other strategies with regard to FCT, CC, and carried load. FCT is an especially important factor in the quality of service. The MD strategy reduces FCT and has the largest carried load of the strategies, which means that it has the most efficient channel usage. This is an attractive characteristic of the MD strategy for micro cellular systems.

We approach nanophotonic computing on the basis of optical near-field interactions between quantum dots. A table lookup, or matrix-vector multiplication, architecture is proposed. As fundamental functionality, a data summation mechanism and digital-to-analog conversion are experimentally demonstrated using CuCl quantum dots. Owing to the diffraction-limit-free nature of nanophotonics, these architectures can achieve ultrahigh density integration compared to conventional bulky optical systems, as well as low power dissipation.

QoS restoration, a new approach to keep QoS of end-to-end ATM connections for failures is proposed. In a network with QoS restoration, each end-to-end connection's customer pre-defines the minimum QoS requirements such as minimum throughput. When a failure occurs, resources such as bandwidth of working connections are reallocated for restoration if they are dispensable to keep the minimum requirements along with the pre-assigned spare resources. This resource reallocation is done in a distributed manner and the result of the modification of a connection is notified to the customer of the connection to help him adjust the way of using it. The effect of the reallocation is mathematically evaluated. It is shown that the reallocation enables to achieve high restoration ratio with insufficient pre-assigned spare resources, such as to restore double-link failures with spare resources prepared for single-link failures, or even to restore single-link failures with no spare resources. It is also shown that pre-assigned spare resources can be reduced if the reallocation is considered in network design phase. The performance of the proposed distributed algorithm is evaluated with an event-driven simulator. The result shows that regardless of whether or not pre-assigned spare resources exist, a restoration ratio which is close to the theoretical maximum can be achieved. A proof-of-concept experimental system is developed by controlling commercial ATM switches via SNMP. The system shows it can effectively manage failures in WAN environment.

As the Internet has become the infrastructure for the global communication, the quality degradation due to network failures and illegal traffic such as DDoS (Distributed Denial of Service) have become a serious problem. In order to solve the problem, a network monitoring system that monitors the traffic of Internet in real time is strongly desired. Traffic monitors that collect the statistics from captured packets play a key roll in the system; however, they are not flexible enough for being used in the rapidly changing Internet. The traditional approach such that a new traffic monitor is developed for a new requirement results in a long turn around time of the development. Therefore, we have proposed a flexible network monitoring system that consists of programmable traffic monitors. Traffic monitors are made programmable by introducing active network techniques; therefore, we call the network monitoring system as the programmable monitor network. This paper describes the implementation of the programmable monitor network and its application to DDoS (Distributed Denial of Service) attack detection.

We study photonic packet switches to support asynchronously arriving variable-length packets. A scheduler for contention resolution is operated in electrical domain even when data street of the buffer is provided in optical domain. In this scheme, the scheduler may be a bottleneck. To compensate the gap of high-speed optical transmission and slow-speed electronic processing, we propose a multi-stage fiber delay line (FDL) buffer architecture that forms a tree structure in which each node has a block of FDLs and a scheduler. This is especially useful for output-buffer switches in which scheduling complexity is proportional to the number of ports of the packet switch. Through a newly-developed approximate analytical method, we show the optimum unit length of the fiber delay lines to decrease packet loss probability. We also show the sufficient number of FDLs in the two-stage buffer.

The forwarding speed of IP routers must grow to accommodate the skyrocketing amount of traffic on the Internet. MPLS, which relies on the high processing power of lower layers, is a solution and it is under developing. On the other hand, a WDM network has been expected as a high-speed network, but it is also called a stupid network because of lacking its traffic granularity. In order to bridge between these two layers, an IP over WDM network by a concept of MPLS has been proposed. This network has a potential to effectively use large transmission capacity provided by WDM technology. In this paper, we design IP over WDM networks that reconfigure IP routing and lightpaths each day or month. We formulate a problem that maximizes the network throughput based on integer linear programming. Through numerical examples, we show that the increase of the network throughput in IP over WDM networks is larger than that of IP networks. We also show the area where this method is applicable to the reconfigurable network.