TCP congestion control is receiving increased attention in recent years due to their usefulness for network stability, robustness use of network buffer and bandwidth resources on an end-to-end per-connection basis. The RED scheme was designed for a network where a single dropped packet is sufficient to signal the presence of congestion to the TCP protocol. This paper applies matrix-analytic approach to analyze both the long-term and the short-term drop behaviors of a queue with RED scheme and uses this model to quantify the benefits brought about by RED. The result shows that the drop probability between RED and Drop-Tail is very close under heavy load conditions. This indicates that RED not only can resolve the synchronization problem but also has the same loss performance with Drop-Tail scheme under the heavy load circumstances. Our findings also show that the rate oscillation behavior of RED is better than Drop-Tail when TCP applies the additive-increase and multiplication-decrease mechanism. As a consequence, it can help reduce the required buffer capacity in the RED router.

In this paper, we propose and evaluate a new channel assignment scheme for a micro-cellular network integrating data and conversational services. The channel assignment scheme combines handover processing depending on terminal speed with a preemptive scheme. High-speed terminals take over the channels of data terminals upon entering a full cell, while the data terminals are put in a queue until new resources are available. Simulating several variations of the scheme, allowing both fast moving data and voice terminals to preempt data terminals yielded the best result. Suspension time for fast moving data terminals was reduced dramatically, reducing the disadvantage caused by a high number of handovers. The cost was a small increase in blocking probability for new terminals.

This letter presents a new approach for obtaining the expected waiting time for packets under the drop-head (also called a drop-from-front) scheme for buffer management. The results show that the drop-head scheme is more effective in reducing queueing delays than the drop-tail scheme.

The surface film of a slip ring is important for the sliding contact phenomenon. The surface film is affected by atmospheric temperature, humidity and air pressure. The main objective of our study is to examine the effect of oxygen gas on the sliding contact phenomenon. In the present experiment, we examined the contact voltage drop for continuous sliding when the atmosphere is changed from low pressure to atmospheric pressure by introducing oxygen (O2 20%+N2 80%) or nitrogen gas. As a result, the contact voltage drop increases rapidly with increasing gas pressure, and its fluctuation also becomes large. These phenomena are observed in both cases of oxygen (O2 20%+N2 80%) and nitrogen introduction. The results clearly show that the sudden increase of contact voltage drop is affected by factors other than the oxide film. Actually, the oxide film is not formed in the nitrogen atmosphere. Furthermore, the frictional coefficient of carbon and copper ring is changed at ambient atmosphere. It is inferred from these data that the contact voltage drop may be affected by the frictional coefficient. When the gas pressure decreases again, the contact voltage drop does not suffer from the effect of ambient gas. Therefore, only the resistance of the oxide film appears to affect contact voltage drop. In this paper, the effect of sliding contact phenomenon on the contact voltage drop by gas adsorption and film generation was examined.

An on-chip, 64-Mb, embedded, DRAM MPEG-2 encoder LSI with a multimedia processor has been developed. To implement this large-scale and high-speed LSI, we have developed the hierarchical skew control of multi-clocks, with timing verification, in which cross-talk noise is considered, and simple measures taken against the IR drop in the power lines through decoupling capacitors. As a result, the target performance of 263 MHz at 1.5 V has been successfully attained and verified, the cross-talk noise has been considered, and, in addition, it has become possible to restrain the IR drop to 166 mV in the 162 MHz operation block.

This paper presents a high resolution long array thermal ink jet (TIJ) printhead which has been developed and demonstrated to operate successfully by combining two functional Si wafers, a bubble generating heater plate fabricated using LSI process and a channel plate fabricated using Si bulk micromachining technology. The heater plate consists of logic LSIs, high voltage MOS transistor, polycrystalline Si (Poly Si) heating resistor and polyimide protective layer. The polymide layer is patterned by O2 plasma reactive ion etching (RIE) and is applicable to high resolution heater array. The Si channel plate consists of an ink chamber and an ink inlet formed by KOH etching, and a nozzle formed by inductively coupled plasma RIE (ICP RIE). The nozzle formed by RIE has squeezed structures which contribute to high energy efficiency of drop ejector and therefore successful ejection of small ink drop. These two wafers are directly bonded by using a novel electrostatic bonding of full-cured polyimide to Si. The adhesive-less bonding provided an ideal shaped small nozzle orifice. And also, the bonding method enabled to use an on-chip LSI wafer because of the contamination free material and the suitable processing conditions (low temperature). The bonded wafer is diced to form printhead chip. No delamination or displacement of the chip was observed even though the chip was subjected to thermal stress during assembly process. This is because of no difference in thermal expansion coefficient between both chips (Si and Si). And therefore it is suitable for long chip concept. With the above technologies, we have fabricated a 1.3" long printhead with 1024 nozzles having a 800 dots per inch (dpi) resolution, a 2.7 pl. ink drop volume, 14 m/sec. ink drop velocity and 18 kHz jetting frequency. And we have confirmed high speed printing and high quality printing.

We propose a novel optical add/drop multiplexer (OADM) utilizing free spectral range (FSR) periodicity of an arrayed-waveguide multiplexer (AWG). In this OADM, wavelength-division multiplex (WDM) signal is multiplexed and/or de-multiplexed in two steps. Power penalty due to coherent crosstalk is drastically reduced compared with that of conventional OADM where AWG multiplexers are opposite to each other. The calculated power penalty due to the coherent crosstalk is about 0.7 dB after the 16 OADMs in the case of 128 wavelengths. It was confirmed through a computer simulation that more than one hundred channels at 10 Gbps data rate could be accommodated in an OADM network with 16 nodes. These results show that the OADM network with over 1 Tbps capacity and 16 nodes could be constructed.

A fully integrated Low Dropout (LDO), low quiescent current regulator has been fabricated in a 0.6 µm CMOS technology. It is stable with low and high effective series resistance (ESR) capacitors. A dynamic feedback (DNFB) bias technique is used to bias the error amplifier in the LDO such that good current efficiency is achieved while maintaining a good transient response. In order to compare the performance of the LDO regulators with and without dynamic feedback, the error amplifiers are configured to have a large bias current (LC), a small bias current (SC) and a bias with dynamic feedback current using switches. The measurement results show that DNFB's line and load regulations are 0.145%/V and 11 ppm/mA, respectively. Besides, there is about 33% reduction in settling time and voltage drop compared with SC LDO when load current is switching from 0 mA to 50 mA. In order to reduce the dropout voltage, a dropout reduction circuitry based on DNFB is also designed to reduce the threshold voltage of LDO's output PMOS. The measured dropout reduction is 8.1 mV which can be further reduced by a larger feedback ratio in DNFB. The quiescent current of this LDO is measured to be 59.4 µ A and this LDO can provide a maximum output current of 250 mA at an input voltage of 3.6 V. The active area of this LDO is 760 µ m 714 µ m.

We propose a novel optical add/drop multiplexer (OADM) utilizing free spectral range (FSR) periodicity of an arrayed-waveguide multiplexer (AWG). In this OADM, wavelength-division multiplex (WDM) signal is multiplexed and/or de-multiplexed in two steps. Power penalty due to coherent crosstalk is drastically reduced compared with that of conventional OADM where AWG multiplexers are opposite to each other. The calculated power penalty due to the coherent crosstalk is about 0.7 dB after the 16 OADMs in the case of 128 wavelengths. It was confirmed through a computer simulation that more than one hundred channels at 10 Gbps data rate could be accommodated in an OADM network with 16 nodes. These results show that the OADM network with over 1 Tbps capacity and 16 nodes could be constructed.

A "dual-ring" network configuration is proposed in wavelength-division multiplexing (WDM) metropolitan area network (MAN). In the proposed architecture, a "sub-ring" using two fibers is added to the existing metropolitan WDM ring for flexible and cost effective addition of new nodes.

The non-collision packet reservation multiple access (NC-PRMA) protocol has been proposed for wireless voice communications. In that protocol, although it can avoid any collision by using control minislot, the terminal which generates its talkspurt in a current frame has to wait till a next frame to transmit an asking packet to obtain reservation. Furthermore, under integrated voice and data traffic, in the conventional NC-PRMA the voice packet dropping probability becomes worse, because of the number of slots that voice terminals can access are limited. In this paper, we propose the NC-PRMA with random transmission to idle slots. First, we evaluate the mean access delay and the voice packet dropping probability under only voice traffic by the theoretical analysis and the computer simulation. It is shown that the proposed scheme attains lower mean access delay than the conventional NC-PRMA. Next, we evaluate the data packet delay and the voice packet dropping probability under integrated voice and data traffic by the computer simulation. It is shown that the proposed scheme attains lower packet dropping probability than the PRMA and the conventional NC-PRMA.

At the sliding contact of brush and rotating slip-ring or commutator, it has been recognized that the brush wear is influenced by brush pressure, current density and atmosphere nearby contact part. However, little is known about the relation between brush wear and atmosphere condition in detail. In this paper, the experiments are carried out with a great attention to the effect of surrounding temperature and humidity on brush wear. The sliding part of brush and slip-ring is put on the sealed box and the atmosphere in the sealed box is kept on the specified condition by temperature and humidity control system. The brush wear, contact voltage drop and slip-ring surface morphology are observed after the sliding test. From these results, in both cases of the high humidity (nearby 80%) and low humidity (nearby 20%), the brush wear are large. And the brush wear rate is the lowest around 60% relative humidity. However, the characteristics of brush wear under the 15C is not similar to others. When the surrounding temperature is changed, in case of the 20% humidity, the brush wear increases with increasing surrounding temperature. On the other hand, in case of 80% humidity, the brush wear increases with decreasing surrounding temperature. Consequently, the results clearly shows that the temperature and humidity not only affect the brush wear but also change the condition of the film formation on slip-ring.

Characteristics of an FBG hydrophone are described under various conditions. The developed FBG hydrophone detects an acoustic field in water with good performances: linear response,high sensitivity,high stability,wide dynamic range as large as 90 dB and wide operation frequency range from a few kHz to a few MHz. A WDM FBG hydrophone consisting of two FBGs in serial connection can detect simultaneously amplitudes and phases of acoustic fields at different points,which in turn allows a directive measurement of an acoustic field in water.

In this paper, we show that the principle of quantum cryptography can be applied not only to a key distribution scheme but also to a data transmission scheme. We propose a secure data transmission scheme in which an eavesdropping can be detected based on sharing the bases Alice (the sender) and Bob (the receiver) have. We also show properties of this scheme.

This paper discusses global area optical transport ring networks using wavelength division multiplexing (WDM) technologies and proposes a novel optical add/drop multiplexer (OADM) architecture suitable for such an application field. Study on the requirements of a global area ring application elucidates the appropriate ring/protection architecture as the path switched bi-directional ring. The proposed OADM architecture has flexibility in terms of path provisioning and scalability. We conclude that the proposed OADM can effectively configure the large-scale path switched bi-directional rings.

An optical add-drop multiplexer with a grating-loaded directional coupler in silica waveguides is demonstrated. The device for this configuration has a large fabrication tolerance and is small in size. A new scheme, in which the coupling length of the directional coupler is twice the complete coupling length, enables low cross-talk for both add and drop operations. This device is polarization-independent due to its relatively low-temperature process.

This paper discusses global area optical transport ring networks using wavelength division multiplexing (WDM) technologies and proposes a novel optical add/drop multiplexer (OADM) architecture suitable for such an application field. Study on the requirements of a global area ring application elucidates the appropriate ring/protection architecture as the path switched bi-directional ring. The proposed OADM architecture has flexibility in terms of path provisioning and scalability. We conclude that the proposed OADM can effectively configure the large-scale path switched bi-directional rings.

An optical add-drop multiplexer with a grating-loaded directional coupler in silica waveguides is demonstrated. The device for this configuration has a large fabrication tolerance and is small in size. A new scheme, in which the coupling length of the directional coupler is twice the complete coupling length, enables low cross-talk for both add and drop operations. This device is polarization-independent due to its relatively low-temperature process.

By integrating three networks, namely, Public Switched Telephone Network (PSTN), Personal Handy-Phone System (PHS) and Intelligent Network (IN) to work together as a Personal Communication Telephone (PCT) service to be offered in the Bangkok metropolis area, the PCT service enables the advent of three new concepts, first, using the same telephone number as that of the fixed line to become a "Personal Number," second, a cell coverage designed to cover larger areas than that of the PHS (by changing hand-out threshold level from 33 dBµV to 30 dBµV and hand-in threshold level from 30 dBµV to 25 dBµV) in order to reduce the muting time during the handover process and provide higher mobility at up to 60 kilometers per hour, and third, a technique of "2 carriers per area" to reduce "call drop." All these techniques will be described in this paper.

We propose and demonstrate a simple polarization-independent construction of a local node for optical WDM ring networks using a centralized multiwavelength light source (MWLS). The node is simply composed of a 4-port optical circulator, an add/drop multiplexing (ADM) filter, a reflective modulator, and a drop fiber Bragg grating (FBG). A Faraday rotator mirror (FRM) is used to enable an LiNbO3 intensity modulator to operate in the polarization-independent mode. We examine three ADM filters, an interference filter, a fiber Fabry-Perot (FP) filter, and a set of FBG's. An optical WDM system experiment is performed to demonstrate the feasibility of the proposed node construction.