Chuan Ching Sue

Robust Design for Reconfigurable Coder/Decoders to Protect Against Eavesdropping in Spectral Amplitude Coding Optical CDMA Networks

This paper presents an enhanced security mechanism to protect spectral-amplitude-coding optical code-division multiple-access networks against eavesdropping. This study proposes an alternative to huge code-space size techniques such as wavelength hopping/time spreading or spectral-phase coding for network protection against eavesdropping by exploiting the cyclic properties of arrayed-waveguide-grating routers and maximal-length sequence code (M-sequence code). In addition, the network is protected using a dynamic reconfigurable coding/decoding scheme based on optical switches and a dynamic code matrix assignment scheme implemented using simple electrical shift registers. The signal-to-beat noise ratio is evaluated for various data bit rates to provide an indication of the confidentiality of the power level for a specified bit error rate (Pe<10-9). To further verify the effectiveness of the proposed scheme, this paper investigates a weighted load balance problem based on the power distribution of each transmitted wavelength under various eavesdropping abilities. A dynamic codeword modification is proposed which identifies the code matrix assignment that minimizes the degree of weighted load balance (DWLB). The evaluation results show that the reconfiguration policy outperforms one class of static policies in terms of two performance metrics, namely, the DWLB and the number of register shifts required to reconfigure the code matrix assignment.

A fitting report position scheme for the gated IPACT dynamic bandwidth algorithm in EPONs

In EPONs using the gated Interleaved Polling with Adaptive Cycle Time (IPACT) scheme, the position of the report message within the granted transmission window has a direct effect on the average packet delay within the network. In this paper, this delay is minimized by using a fitting report position (FRP) scheme to adaptively adjust the position of the report message within the transmission window in accordance with the current network load. In the proposed approach, the optimal position of the report message is determined analytically for various system loads. The optical line terminal (OLT) then uses a heuristic algorithm to estimate the load of the optical network units (ONUs) in accordance with their report messages and determines the report message position that minimizes the average packet delay within the network. Finally, the OLT informs the ONUs of the optimal report position through an optional field in the gate message. The performance of the proposed FRP scheme is evaluated for three different network models, namely Poisson traffic with a uniform ONU load, Poisson traffic with a nonuniform ONU load, and self-similar traffic, respectively. The simulation results show that the FRP scheme achieves a lower average packet delay than fixed-report-position schemes such as fixed-report-front (FRF) or fixed-report-end (FRE) for both Poisson and self-similar traffic. The performance improvement is particularly apparent in networks with a nonuniform ONU load distribution.

A new IPTV channel zapping scheme for EPON

This paper proposes a new IPTV channel zapping scheme in EPON, and defines two users operation behavior for channel zapping. Based on such users operation behavior, this paper defines two channel zapping types that are intra- and inter-stream channel zapping. In addition, we propose two analysis models to evaluate channel zapping time for both channel zapping types, respectively. According to simulation results, our proposed scheme can reduce channel zapping time and satisfy quality criteria (500ms). In addition, some further works are described in this work.

Software reliability growth models incorporating fault dependency with various debugging time lags

Software reliability is defined as the probability of failure-free software operation for a specified period of time in a specified environment. Over the past 30 years, many software reliability growth models (SRGMs) have been proposed and most SRGMs assume that detected faults are immediately corrected. Actually, this assumption may not be realistic in practice. In this paper we first give a review of fault detection and correction processes in software reliability modeling. Furthermore, we show how several existing SRGMs based on NHPP models can be derived by applying the time-dependent delay function. On the other hand, it is generally observed that mutually independent software faults are on different program paths. Sometimes mutually dependent faults can be removed if and only if the leading faults were removed. Therefore, here we incorporate the ideas of fault dependency and time-dependent delay function into software reliability growth modeling. Some new SRGMs are proposed and several numerical examples are included to illustrate the results. Experimental results show that the proposed framework to incorporate both fault dependency and time-dependent delay function for SRGMs has a fairly accurate prediction capability

A novel 1:N protection scheme for WDM passive optical networks

This paper presents a 1:N protection scheme based on the cyclic property of an array waveguide grating and a specific connection pattern among the optical network units (ONUs). The proposed scheme requires half the number of wavelengths of existing schemes presented in the literature. Although the current scheme requires more fiber links among the ONUs than previous schemes, the network resource demands are greatly reduced and the protection performance is improved

Design and analysis of accelerative preallocation protocol for WDM star-coupled networks

For a wavelength division multiaccess (WDMA) system, the reservation (R-WDMA) and the preallocation (P-WDMA) protocols are two major media access methods to support packet-switched traffic. In this paper, a new media access control (MAC) protocol, accelerative preallocation WDMA (AP-WDMA), is proposed to overcome the disadvantages of P-WDMA and retain its advantages. AP-WDMA relieves the technology constraints by restricting the wavelength tunability at only one end of the communication link, removes the channel and station status tables required by R-WDMA, and uses simple arithmetics to allocate channels. Although it uses a dedicated control channel to send control-acknowledge packets, AP-WDMA employs a network management mechanism to make full use of idle time slots under different propagation and tuning delays. In addition, it is well suited to wavelength-limited networks. Three heuristic methods for channel sharing, interleaved (I), neighborhood (N), and weighted-balanced (WBH), are evaluated. Through analytical evaluations, AP-WDMA is shown to be able to improve the channel utilization and system throughput much more significantly than I-TDMA*, which is a P-WDMA protocol. We also evaluate the impact on the performance of AP-WDMA by the number of channels, the four traffic types (mesh, disconnected, ring, and uniform), the degree of channel sharing, and the unbalanced load among channels. The results show that the utilization is scalable in terms of the number of channels. Furthermore, the utilization of channels is best for the ring-traffic type and worst for the disconnected-traffic type, and the system throughput decreases as the degree of channel sharing increases. Finally, using heuristics I or WBH instead of N can resolve the unbalanced load problem under various traffic types and degrees of channel sharing.

Wavelength routing with spare reconfiguration for all-optical WDM networks

This study presents a wavelength-routing scheme with spare reconfiguration (SR) to construct dependable all-optical wavelength-division-multiplexing (WDM) networks. Path protection using shared spare lightpaths is a general wavelength-routing method for reducing blocking probability while minimizing demand for spare resources. However, in a dynamic traffic environment, this method may still yield a poor performance because a wavelength on a link is very likely to be continuously held by a spare lightpath and to be unable to be assigned to the working lightpath of a new connection. This study develops a spare reconfiguration mechanism with wavelength reassignment (SR/spl I.bar/WR) and path reassignment (SR/spl I.bar/PR) to make the spare dynamic and thus further reduce the blocking probability. The proposed wavelength routing with SR proceeds in three stages and has polynomial time complexity. Extensive simulation experiments were conducted on the NSFNET and the K5 fully connected network to investigate the performance of the proposed wavelength routing with SR. Results of this study show that the proposed wavelength routing with SR can reduce the blocking probability compared with the general wavelength routing with just shared spare lightpaths by choosing a positive tuning cost. In addition, the improvement of the blocking performance is maximized when using SR/spl I.bar/WR followed by SR/spl I.bar/PR.

Capacity-efficient strategy for 100% dual-failure restorability in optical mesh networks utilising reconfigurable p-cycles and a forcer filling concept

The problem of achieving 100% dual-failure restorability utilising reconfigurable p-cycle mechanisms has been investigated via three different p-cycle mechanisms derived from the integer linear programming model; complete-repair (CRP), incremental-repair (IRP) and dynamic-repair (DRP). An enhanced 100% dual-failure restoration mechanism is proposed, designated as modified DRP with forcer filling concept (MDRP/wFF), in which network protection is achieved using only reconfigurable span-protecting p-cycles without the addition of path-segment-protecting p-cycles as in DRP. As a result, the overhead incurred in differentiating between the two p-cycles becomes non-existent upon network restoration. Furthermore, a FF concept is employed to reduce the amount of spare capacity required to restore the network. The performance of the MDRP/wFF scheme was benchmarked against that of the CRP, IRP and DRP mechanisms. The simulation results show that MDRP/wFF achieves a performance tradeoff among CRP, IRP and DRP in terms of its spare capacity requirements and average number of reconfigured spans during the reconfiguration process [designated as average reconfiguration overhead (ARO)]. The MDRP/wFF scheme was found to have a lower spare capacity requirement but incurs some additional ARO compared with DRP.

Software Reliability Prediction and Assessment Using both Finite and Infinite Server Queueing Approaches

Over the past 30 years, many software reliability growth models (SRGMs) have been proposed for estimation of reliability growth of software. In fact, effective debugging is not easy because the fault may not be immediately obvious. In the past, some researchers ever used an infinite server queueing (ISO) model to describe the software debugging behavior. An infinite-server queueing model is considered where access of customers to service is controlled by a gate and the gate is open only if all servers are free. However, the finite server queueing (FSQ) model is first advantageously modeled as an infinite-server system. Thus, in this paper, we show how to incorporate both FSQ and ISQ models into software reliability estimation and prediction. In addition, we also consider the factor of perfect/imperfect debugging. Experimental results show that the proposed framework to incorporate both fault detection and correction processes for SRGM has a fairly accurate prediction capability

OPN01-1: 1:N Protection Scheme for AWG-based WDM PONs

This paper presents a 1:N protection scheme based on the cyclic property of an array waveguide grating (AWG) and a specific connection pattern among the optical network units (ONUs). A self-protecting architecture for WDM passive optical networks (PONs) has been proposed in previous studies, and a novel centrally controlled protection scheme has recently been proposed with reduced network resources. However, previous studies focused only on 1:1 protection and developed schemes in which the number of required wavelengths was twice the number of ONUs. Furthermore, these studies located the protection scheme either at the ONU end or at the optical line terminal (OUT) end. By contrast, this study distributes the controlled protection scheme to both the ONU end and the optical line terminal (OLT) end. The proposed scheme provides an automatic traffic restoration capability in the event of a single distribution fiber cut between the remote node and the ONU through its specific design of the OLT and ONU and the cyclic property of the AWG. The cost and performance of the current protection scheme are evaluated and compared with those of previous schemes. Although the current scheme expenses more fiber links among the ONUs than previous schemes, the network resource demands are greatly reduced (i.e. the number of wavelengths is reduced) and the protection performance is improved (i.e. a 1:N protection capability is achieved.).