Shoichi Noguchi

Identification of fog with NOAA AVHRR images

The authors attempted to identify fog using image-processing data from the US National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR). AVHRR sensors measure radiation at visible, near-infrared, and infrared wavelengths. Attention is confined to daytime data from channel 1 (CH1), channel 3 (CH3), and channel 4 (CH4) for a detection range of lambda =0.58 approximately 0.68 mu m, lambda =3.55 approximately 3.93 mu m, and lambda =10.5 approximately 11.5 mu m, respectively. The authors have analyzed by image processing the data obtained from CH1, CH3, and CH4 by forming two- and three-dimensional histograms and enhancing them in color. >

An SNMP-based expert network management system for a large-scale OSI-based campus network

The authors examine the design issues of a practical network management system using the simple network management protocol (SNMP) in the context of a large-scale open systems interconnection (OSI)-based campus-network called TAINS. Various design aspects are examined and the importance of time-management is examined. In the proposed design, intelligent, time-synchronized agents are deployed to collect information about the network segments to which they are attached. The manager talks to the agents and gathers relevant network information. This information is used by the expert network manager, in conjunction with a network knowledge base, to reconstruct the overall network-traffic characteristic, to evaluate the status of the network and to take/suggest some action. The introduction of time-labeled composite objects in the MIB provides a means of reducing the load of management-related traffic on the network.<<ETX>>

Heterogeneous ALOHA networks: a sufficient condition for all equilibrium states to be stable

Abstract This paper models and analyzes the stability of a slotted-ALOHA network hosting heterogeneous users. The scheme is modeled by dividing the total user-population into groups of homogeneous users. The behavior of the system is represented by state equations. The stability analysis is carried out by Liapunovs indirect method, in association with the properties of M-matrix, to obtain the sufficient condition for the structural stability of the networks. The analysis also points out the method of hierarchical grouping of the heterogeneous users.

Network management in a large-scale OSI-based campus network using SNMP

The authors expand on their experience in a practical network management system by using the simple network management protocol (SNMP) in the context of a large-scale open systems interconnection (OSI)-based campus-network. Various aspects of network management are examined and the importance of time is shown. The network management infrastructure comprises intelligent, time-synchronized agents and expert managers. Agents are deployed to collect information about the network segments to which they are attached. The expert manager talks to the agents and gathers relevant network information which is used in conjunction with a network knowledge base, to reconstruct the overall network traffic characteristic, to evaluate the status of the network and to take/suggest some action. The model allows some global control, monitoring and management without installing agents on all elements connected to the network. The use of time labels and narrow time windows enables the manager to obtain a reasonably accurate picture of the network status. The introduction of composite time-labeled objects reduces the burden of management traffic on the network.<<ETX>>

Input buffer limiting: behavior analysis of a node throughout the range of blocking probabilities

A numerical method is suggested for estimating the performance parameters of a node with input buffer limiting, throughout the range of blocking probabilities. Congestion is attributed to the sudden increase in the effective service time when the input rate increases. This sudden increase, resulting in the thrashing of the throughput rate, can be related to changes in the shape of the potential function of the node. The methodology of deriving the potential function of the node from its gradient dynamics and dynamic flow conservation considerations is presented. Using the results from catastrophe theory, it is shown that the abrupt changes in the throughput can be expected due to the existence of a catastrophe point in the parameter space. The behavior of a node in a homogeneous network can be characterized by a fold catastrophe. The simulation results are found to agree with the results obtained by the numerical method. >

The MIKB model for intelligent network management

The authors discuss their idea of an intelligent network management system. In order to simulate intelligence, the reasoning and judgement of the human manager are modeled into a knowledge base. The human managers view of the network is limited to the Management Information Base (MIB); thus, the MIB provides the starting point for the design of the knowledge base. The network managers knowledge regarding the objects in the MIB is represented in the Management Information Knowledge Base (MIKB). The authors trace the way this modeling is done.<<ETX>>

On the behavioral aspects of alternate routing in non-hierarchical networks

Abstract The behavior of a node under alternate routing scheme in a homogeneous non-hierarchical network is modeled with respect to the equilibrium states. Under high load intensities, there exist two equilibrium states: one stable and the other unstable. The blocking probability at the stable equilibrium state is higher than that at the unstable one. The evolution of the perturbed system can be found to be dictated by two Liapunov functions. Under one of the Liapunov functions, the system evolves towards the normal state whereas under the other, the system evolves towards the congestion state . Congestion manifests owing to the fold catastrophe in the behavior manifold of the system. Simulation studies indicate that, at certain range of load intensities higher than the rate at the fold point, the throughput exhibits large fluctuations. These fluctuations are interpreted to be resulting from the dynamics of the system specified by the potential function of the system. A performance index, called the Sojourn Ratio (SR), characterizes the behavior of the system beyond the fold point. The ratio SR:(1-SR) is an estimate of the ratio of the duration in which the system is in the domain of the congestion state, to that in which it is in the domain of the normal state. We conjecture that the durations in which the system is in the normal state and in the congestion state are approximately proportional to the height of the potential barriers at the respective states. Accordingly, an analytically obtainable performance index V SR is defined as the ratio of the potential barrier at the congestion state, to the sum of the potential barriers at the normal state and congestion state. Among the characterizations of the system by Maxwell convention, by delay convention and by V SR , it is found that the last one captures best the tendency of SR.

Performance and stability aspects of congestion control by input buffer limiting in store and forward networks

Store-and-forward techniques in computer communication networks are addressed. The performance estimation and the stability aspects of an input buffer limiting (IBL) scheme are presented. The model is formulated with respect to the state-dependent effective input rate and effective service rate. The computation of the performance parameters with respect to the effective service rate yields satisfactory results when blocking probabilities are not restricted to very low values (<<1). The stability aspects are assessed with the results from catastrophe theory; the stability is characterized as fold catastrophe. It is seen that, at higher rates of input, this maximum value of the IBL ratio approaches the capacity law limit proposed by S. Lam and M. Reiser (1979). Further, this method also approximately indicates the no-congestion region.<<ETX>>