Chul Geun Park

Packet Delay Analysis of Symmetric Gated Polling System for DBA Scheme in an EPON

In this paper, we analyze the mean packet delay of a dynamic bandwidth allocation (DBA) scheme in an Ethernet passive optical network (EPON). We propose the interleaved polling system with a gated service discipline and a two-stage queue in order to investigate the delay performance of DBA scheme in an EPON. We assume that input packets arrive at an optical network unit (ONU) according to a Poisson process from several types of users. We use a continuous time queueing model in order to find the mean packet delay and the mean cycle time of an arbitrary packet. We obtain the closed form solution for the mean packet delay of the proposed gated polling system with a two-stage queue. We obtain another result on the mean packet delay by solving a system of linear equations derived from the moments of the queue length distribution. We give some numerical results to investigate the delay performances for the symmetric polling system with statistically identical stations. In addition, we compare numerical results on the closed form solution with numerical results on a system of linear equations.

Performance analysis of MAC layer protocols in the IEEE 802.11 wireless LAN

In recent years, WLANs (Wireless Local Area Networks) based on the IEEE 802.11 standard have been taken a growing interest and developed widely all over the world. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocols are the most popular MAC (Medium Access Control) protocols for WLANs. The performance of CSMA/CA protocols over wireless channels has been investigated over the past years. In this paper, we obtain the probability distribution function of the MAC layer packet service time, and we present the comprehensive performance analysis of IEEE 802.11 MAC protocol by investigating the queue dynamics of a wireless station based on the MAC layer packet service time. We adopt an MMPP(Markov Modulated Poisson Process) as the input traffic model that describes well the bursty nature of Internet traffic. The analysis on the throughput and the delay performance has been carried out by using the MMPP/G/1/K queueing model. We have some numerical results that represent the system throughput and the queue dynamics including the mean packet waiting time and packet blocking probability.

Queueing Analysis of IEEE 802.11 MAC Protocol in Wireless LAN

In this paper, we present the performance analysis of IEEE 802.11 MAC(Medium Access Control) protocol by investigating the queue dynamics of a wireless station based on the general probability distribution of packet sizes. We use the MMPP(Markov Modulated Poison Process) as the input traffic model well describing the bursty nature of Internet traffic. Thus we have the MMPP/G/1/K queueing model with the MAC layer service time to analyze the throughput and the delay performance of IEEE 802.11 MAC protocol in wireless LAN.We take some numerical examples for the queue dynamics including the mean packet delay and the packet blocking probability.

Packet delay analysis of dynamic bandwidth allocation scheme in an ethernet PON

In this paper, we deal with the packet delay of a dynamic bandwidth allocation(DBA) scheme in an Ethernet passive optical network(EPON). We focus on the interleaved polling system with a gated service discipline. On the access side, input traffic may be aggregated from a number of users. So we assume that input packets arrive at an optical network unit(ONU) according to Poisson process. We use a continuous time queueing model in order to find the mean waiting time of an arbitrary packet. We give some numerical results to investigate the delay performances for the symmetric polling system with statistically identical stations.

A High-speed Digital Laser Grating Projection System for the Measurement of 3-dimensional Shapes

In the non-contact 3-dimensional (3D) shape measurements, the fringe pattern projection method based on the phase-shifting technique has been considered very effective for its high speed and accuracy. The digital fringe projector in particular has great flexibility in generating fringe patterns since the patterns can be controlled easily by the computer program. In this work, we have developed a high-speed digital laser grating projection system using a laser diode and a polygon mirror, and evaluated its performance. It has been demonstrated that all the optical measurements required to find out the profile of a 3D object could be carried out within 31 ms, which confirmed the validity of our 3D measurement system. The result implies the more important fact that the speed in 3D measurement can be enhanced remarkably since, in our novel system, there is no device like a LCD or DMD whose response time limits the measurement speed.

Performance analysis of DBA scheme with interleaved polling algorithm in an Ethernet PON

We investigate the mean queue length and the mean packet delay of a dynamic bandwidth allocation (DBA) scheme in an Ethernet passive optical network (EPON). We focus on the interleaved polling system with a gated service discipline. We assume that input packets arrive at an optical network unit (ONU) according to Poisson process. We use a continuous time queueing model in order to find the queue length distribution of the gated interleaved polling system with the first stage input queue and the second stage transmission queue. We give some numerical results to show the mean queue lengths and mean packet delays for the symmetric polling system.

Performance analysis of an AAL multiplexer with dynamic bandwidth allocation in an IP/ATM environment

In this paper, we present a discrete-time queueing model with a Markov modulated batch Bernoulli process (MMBBP) as a bursty input traffic model of internet protocol packets in order to investigate the performance of a ATM adaptation layer (AAL) multiplexer with a finite buffer and a threshold-based dynamic bandwidth allocation scheme (DBAS): As a deterministic service time, we use the segmentation processing time devoted to a cell payload in the AAL multiplexer. This service time consists of several slot times and varies in line with threshold levels of the buffer contents. In an MMBBP process, the arrivals during a slot time occur as batch Bernoulli processes with a general distribution of batch sizes varying according to the phases of a Markov chain. We obtain the loss probability and the mean delay of an arbitrary packet. We present some numerical results to show the effects of the burstiness and thresholds on the performance of the AAL multiplexer with a DBAS.

Study on the Precise Alignment of Micro-Lenses in the Microcolumn by Using the Laser Diffraction Pattern

The alignment precision of the electron lenses is one of the most critical factors that determine overall performance of the microcolumn system including the image resolution and aberration. Since the lens apertures are usually as small as 5 ~ 300 μm, the alignment is difficult to carry out, even if the expensive and complicated aligner is used. In this work, we have developed a novel alignment method using laser diffraction pattern, with which we can easily obtain high-precision alignment. The images of Cu grid (mesh# 1000) and carbon nanotubes (200-nm diameter) taken by the microcolumn fabricated by the new alignment scheme has confirmed that the new method was very simple and useful.

Investigation on the LPCVD LTO Thin Film as a New Dielectric Layer for the Future ULSI Devices

As the design rule goes down sub-70 nm for the ULSI devices, the total thermal budget that the device can take during the fabrication is also reduced very much. Hence, in this work, we propose a novel low-temperature LPCVD process for formation of thin dielectric oxide film which does not need SiH2Cl2 gas. We have also evaluated the electrical reliability of the film by making the capacitors with oxide-nitride-oxide (ONO) structure. The leakage current of the new oxide was similar to that of the high-temperature wet oxide until the electric field is lower than 5 MV/cm. When the film was annealed by N2 gas, however, it has shown much better characteristics over the entire range.

Comparison of loss formulas for a circuit group with overflow traffic

Many articles have dealt with the loss formulas for determining the required number of circuits in a transit circuit group with overflow traffic. Traditionally, ERM (Equivalent Random Method) is used to determine number of circuits in a final circuit group with rough overflow traffic which has vmr (variance to mean ratio) greater than one. Recently, IPP (Interrupted Poisson Process) approximate method which represents the collective feature of the overflow have been introduced. The negative binomial loss formula can be applied to determine the required number of circuits. In this paper, we deal with the negative binomial loss formula and determination method of number of circuits. We also analyze and compare these three loss formulas. To apply these formulas to the capacity planning of circuit networks, we need more effective algorithm for the accurate numerical calculation.