In ATM networks, two main functions for achieving traffic control and congestion control are Call Admission Control (CAC) and Usage Parameter Control (UPC). Among various UPC schemes, Leaky Bucket is a popular one. In this paper, we study the characteristics of the system in which every traffic source is regulated by an enhanced leaky-bucket before entering the multiplexer at the edge node of the ATM network. In addition to the factor of mean cell rate, peak cell rate is also taken into consideration. Based on the criteria of average waiting time at the multiplexer, we derive the performance bounds expressed as the functions of the LB parameters and numbers of connections.

This paper presents an efficient queue manager chip for controlling a 16 16 shared buffer ATM switch with a 256-cell buffer. Compared to conventional implementations of queue managers for shared buffer ATM switches, our design eliminates the idle address FIFO and the pre-allocated bubbles at the tails of output queues. The former reduces the storage size required for queue management, while the latter improves the effective buffer capacity. Such modular implementation also provides flexibilities in queue management implementation. Back-pressure with soft-full and hard-full flow control for multi-stage expansion and two priority classes with push-out cell discarding are supported without extra hardware overhead. This chip was designed and fabricated using 0.8µm CMOS technology. It has 35,700 transistors in a chip area of 28.3mm², with a core of 10.4mm²and 32,960 transistors. Two test sequences were developed during the design phase to fully verify the queue management functions of the prototype chip. The queue manager chip was tested up to 36 MHz, and is able to control a 16 16 shared buffer switch with a 155 MHz link rate.

In this paper, a new two-level flow control scheme using VP credit-based control and stop-and-go rate control for Asynchronous Transfer Mode (ATM) networks is presented. Since the proposed scheme does not require any information on traffic characteristics, we propose to apply such a flow control scheme to the best effort traffic that requires no band-width guarantee from the network. The proposed flow control scheme can efficiently use the leftover bandwidth after the guaranteed traffic has been satisfied. Therefore, high bandwidth utilization can be achieved. Furthermore, cell loss can completely be avoided by the lower-level credit-flow control done on a per VP basis. On top of this, a higher-level Explicit Congestion Notification (ECN) rate control is employed to avoid any performance degradation. Simulations have been performed to verify the effectiveness of the proposed scheme. It is found that the average end-to-end delay of our proposed scheme is better than that of the original VCFC scheme [1]. In addition, there is also a tremendous saving in the memory required when compared with the VCFC scheme.

Most of the existing analytical models for multistage ATM switching fabric are not accurate in the presence of a non-uniform traffic at the input of the switch. In this paper, we discuss the issues in modeling a multistage ATM switching fabric, and investigate the effect of independence assumptions in two previous analytical models. A highly accurate 4-state Markov chain model for evaluating the performance of ATM switching fabrics based on multistage switches with 22 finite output-buffered SEs is proposed. The proposed model correctly reflects the correlation of cell movements between two subsequent cycles and states of the buffers of two adjacent stages. By comparing the results obtained from the oroposed model, existing models and simulations, it has been shown that the proposed model is much more accurate than existing models in the presence of a non-uniform traffic in the switch. The results from the existing models are unsatisfactory in the presence of an increased blocking in the switch arising from a non-uniform traffic in the switch. On the contrary, the proposed model is very robust even under severe blocking in the switch.

Progress made in the field of high speed networking technology has led to the planning and prototyping of true high-bandwidth applications with very high throughput and low delay requirements. In this study we approach the problem of high throughput demand from the aspect of protocols and introduce the handling of error control in the application layer level as opposed to the transport layer since the eventual destination of data is the application itself. This scheme, called ACER (Application Conscious Error Recovery), is proposed and defined for bulk data transfers. A simple analytic throughput comparison of the sliding window scheme with go-back-N, and ACER is given later, Also, a prototype implementation of ACER for bulk data transfer and experimental measurement results are presented. Besides, we investigate the performance of the scheme by simulation for various network models. Finally, we present a discussion of extending the scheme to different traffic patterns and applications.

The multichannel distortions of direct modulated laser diode were studied from the view point of rate equations. A novel technique for compensating the composite second order distortion (CSO) was proposed. Meanwhile, the related calibration procedures were indicated. After the compensation, 10 dB improvement in CSO was obtained

Optical Frequency Division Multiplexing (OFDM) is an attractive multiplexing approach for exploiting optical communication technology. Although considerable progress has been made in this approach, it still suffers from numerous potential impairments, stemming from several phenomena. (i.e., laser unstability, residual temperature variations, linear and nonlinear cross talk.). Conventional serial coding technique is not practical in lightwave systems, as it changes the system's bit rate that is not desirable. In this paper a new Parallel Coded Optical Multicarrier Frequency Division Multiplexing (PCOM-FDM) technique has been investigated. The strategy of multicarriers, together with Parallel Forward Error Control (PFEC) coding, is a potentially novel approach as in this approach we have, 1) Investigated optical multicarrier communication that is effective in combating dispersion and increasing throughput, 2) Proposed PFEC coding which is different from conventional serial coding in respect that it does not change the system bit rate per carrier and prevents the effects of channel wandering. It is highly desirable in lightwave systems and thus holds a vital importance in practical high speed optical communication systems. Theoretical treatment shows that the proposed approach is promising and practical.

An increase in the system capacity and maximum user bit rate is required for wireless multimedia communications that offer high speed signal transmission such as simultaneous voice and data transmission. This paper proposes a Time Division Multiple Access-Time Division Duplex method combined with an Alternated Frequency Duplexer (TDMA/TDD-AF) for TDMA based wireless personal communications. The newly proposed duplexing method uses the same frequency band and all time slots within a TDMA frame for both up-stream and down-stream transmission. This enables a two-fold increase in the number of time slots within a TDMA frame and the maximum user bit rate compared with the conventional TDMA/TDD method. Transmitter diversity is also applied to improve the transmission quality under multipath fading environments. The traffic performance of the proposed method is approximated theoretically compared with the conventional TDMA/TDD systems on the assumption that an infinite number of terminals are in a cell. The results indicate that the TDMA/TDD-AF method significantly improves the blocking probability when the system is asynchronized among adjacent cells and the number of usable carriers is high.

This paper proposes a novel Doppler frequency shift compensation technique to achieve terrestrial and low earth orbit (LEO) satellite dual mode DS/CDMA terminals robust to high Doppler shift and multipath fading. In order to satisfy the requirements of wide dynamic range and high accuracy simultaneously, the proposed scheme employs two stage compensation scheme, i.e., coarse compensation to keep dynamic range of about 100 kHz and fine compensation to satisfy its resolution of about 30 Hz, using block demodulation technique. Computer simulation results show that the proposed scheme can sufficiently compensate for the offset frequency up to the range of about 100 kHz at the terrestrial and LEO satellite combined mobile communication systems.

A circularly polarized omnidirectional antenna consisting of a vertical sleeve dipole and three pairs of titled parasitic elements set around it is proposed. The antenna is useful to mobile communication because the use of circular polarization allows us to suppress the effect of multi-path reflection waves (inverse rotation) caused by building walls and surface of the ground. The antenna with an omnidirectional pattern has a simple structure without a feeding network for radiating circular polarization. To understand the radiation characteristics of the proposed antenna, an approximation theory using the induced electromotive force method is introduced. As an example, using a fixed spacing of a quarter wave-length between the vertical dipole and the parasitic elements, the possibility of generation of circular polarization is examined. Then the computational results of the axial ratio and the input impedance are compared with the results of the numerical analysis using the moment method and the experimental result. The radiation characteristics of the antenna can be understood by using the approximation theory introduced here. As a summary of the study, the contour map of the axial ratio of circular polarization is depicted using the moment method. For practical design of this antenna, a small correction factor should be multiplied to the calculated results. From the experimental results, the proposed antenna has a gain of 2 dBi and 3 dB band-width with an axial ratio of about 8%.

Recently, several promising window-based policing schemes have been proposed. It is worthwhile to analyze them for performance comparison. In this letter, we formulate numerical equations to evaluate the improved versions of the JW scheme as well as the JW scheme itself. We also show the correctness of our formulation using the simulation results.