According to a new kind of permanent contactor, this paper analyses the dynamic behavior of the contactor with and without current-feedback system. And it presents a method to obtain the dynamic characteristics of the contactor with current-feedback system. The experiments prove that the method is correct. Then, it compares the contactor without current-feedback system with the one with current-feedback system. The result shows that the contactor with current-feedback system can avoid this flaw of the contactor without current-feedback system.

Cell losses due to statistical multiplexing of bursty traffic in ATM networks tend to be in clusters rather than uniformly scattered. Since the quality of service for users is quite sensitive to such bursty losses, it is necessary to characterize the temporal behavior of cell loss. This paper reports results obtained from investigating overload period and underload period in an ATM multiplexer with heterogeneous burst traffic input, using a bufferless model. The overload period is defined as the time interval when the instantaneous bit rate exceeds the output link capacity. With the bufferless model, we assume that all the instantaneous bit rate exceeding the link capacity is lost, and the loss rate is called "virtual cell loss probability". The virtual cell loss probability during the overload period, average overload period and underload period durations are analyzed. Numerical results show that the cell loss probability in overload periods and the average duration of overload periods (normalized by burst duration) are not very sensitive to link load or average rate/peak rate ratio of the burst, and that they are approximately on the order of peak bandwidth/link capacity ratio for the multiplexed burst. Furthermore, it is also shown that the mean underload duration is simply given as the inverse of the overall cell loss probability multiplied by the constant value inherently determined by peak bandwidth and link capacity. With these observations, applications to the call acceptance control using these measures are also presented.

Rate based control is a promising way to achieve an efficient packet transmission especially in high speed packet switching networks where round trip delay is much larger than packet transmission time. Although inappropriate tuning for the parameters, increasing and decreasing factors, of the rate control function causes the performance degradation, most of the previous works so far have not studied the effect of the parameters on the performance. In this paper, we investigate the effect of the rate control parameters on the throughput under the condition that the packet loss probability is kept below a specific value, say 10-6. For this purpose, we build a queueing model and carry out a transient analysis to examine the dynamic behavior of the queue length at an intermediate node in a high speed network suffering from large propagation delay. Numerical examples exploit the optimal value of the parameters when one or two source-destination pairs transmit packets. We also discuss the effect of the propagation delay on the performance. Our model can be applicable to investigate the performance of various kinds of rate-based congestion control when the relation between the congestion measure and the rate control mechanism is given explicitly.

Rate-based congestion/flow control is a promising way to achieve high throughput in high speed packet-switching networks. We consider a rate-based congestion control to aim at obtaining high throughput and fair sharing of the communication resources. In the scheme, each intermediate node informs its congestion status to the source node. Two kinds of control packets are used for this mechanism. One (a choke packet) is to throttle the rate and another (a loosen packet) is to allow increase of the rate. The source node initiates transmission with a low rate and increases the rate slowly to avoid a rapid increase of the packet queueing at an intermediate node. When the source node receives a choke packet, it decreases the rate rapidly to relieve congestion as soon as possible. The source node upon receipt a loosen packet increases the rate slowly again. We develop a queueing model to investigate the parameter settings to provide a good performance via simulation. The increasing and decreasing parameters of the rate control function are first investigated in various load conditions. We next examine the effect of the queue-length threshold value for the indication of congestion at the intermediate node. The numerical results indicate that the threshold value should be small to obtain a good performance. We finally introduce a technique which accurately recognizes congestion and inhibits an acceptable queueing of the packets at intermediate nodes.