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.

This study develops a quantum switching device with fully nonblocking properties. Although previous studies have also presented quantum-based solutions for the blocking problem, the proposed schemes are characterized by an increased packet loss, a large number of quantum SWAP gates and an increased propagation delay time complexity. The current study overcomes these drawbacks by designing an N x N fully nonblocking quantum switch, in which the packet payload is passed through quantum SWAP gates while the packet header is passed through quantum control gates designed by applying a modified quantum Karnaugh mapping method. The allocation of quantum SWAP gates to the different layers within the switch is solved using a Perfect Matching in Complete Graph (PMiCG) algorithm with a time complexity of O(N!/(2N/2(N/2)!)). A symmetry-based heuristic method is proposed to reduce the time complexity of the search process for all the perfect matching pairs to a time complexity of O(N2). The performance of the proposed quantum switch is compared with that of a quantum self-routing packet switch and a quantum switching/quantum merge sorting scheme, respectively, in terms of the hardware complexity, the propagation delay time complexity, the auxiliary qubit complexity, and the packet loss probability.

In the past decade, several rate-based simulation approaches were proposed to predict software failure process. But most of them did not take the number of available debuggers into consideration and this may not be reasonable. In practice, the number of debuggers is always limited and controlled. If all debuggers or developers are busy, the new detected faults should be willing to wait (for a long time to be corrected and removed). Besides, practical experiences also show that the fault removal time is non-negligible and the number of removed faults generally lags behind the total number of detected faults. Based on these facts, in this paper, we will apply queueing theory to describe and explain the possible debugging behavior during software development. Two simulation procedures are developed based on G/G/ infin and G/G/m queueing models. The proposed methods will be illustrated with real software failure data. Experimental results will be analyzed and discussed in detail. The results we obtained will greatly help to understand the influence of size of debugger teams on the software failure correction activities and other related reliability assessments.

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.).

The logical ring topology is a simple protection scheme in WDM networks. The failure of a single physical fiber link may cause the failure of multiple lightpaths. The service becomes unprotected if the failure propagates to the logical ring topology. In this paper, we focus on the elimination of failure propagation from the physical WDM network to the logical topology. We propose a method to make the augmented logical ring topology survivable. The augmented survivable edges (ASE) is based on the connectivity problem of the logical topology. Our method makes the modification of logical ring topology cost-effective, i.e., with the minimal number of the additional edges to the original logical ring topology. Finally, we show the results on various network cases

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

This paper studies the issues arising when reconfiguring coded-WDM networks to provide protection against eavesdropping and it proposes a tradeoffs involved in carrying out this reconfiguration process. It commences by showing that the degree of confidentiality (DOC) and the traffic loss are two important, but conflicting, objectives in the design of reconfiguration policies. The reconfiguration problem is formulated as a Markovian decision process (MDP). The results obtained from MDP theory are applied to establish optimal reconfiguration policies for coded-WDM networks with various system parameters

Due to the dynamic nature of the network topology and resource constraints, designing an efficient routing in MANETs is challenging. To tolerate communication faults, this study explores the network redundancy through multipath routing. The designated on-demand hybrid multipath routing (OHMR) features two novel characteristics; it establishes multiple node-disjoint and braided routing paths between a source-destination pair and it maintains an end-to-end transmission for a longer period than other multipath routing schemes. Through simulation results, we show OHMR can reduce the frequency of route discoveries and achieve a higher packet delivery ratio

Since the early 1970s tremendous growth has been seen in the research of software reliability growth modeling. In general, software reliability growth models (SRGMs) are applicable to the late stages of testing in software development and they can provide useful information about how to improve the reliability of software products. For most existing SRGMs, most researchers assume that faults are immediately detected and corrected. However, in practice, this assumption may not be realistic and satisfied. In this paper we first give a review of fault detection and correction processes in SRGMs. We show how several existing SRGMs based on NHPP models can be comprehensively derived by applying the time-dependent delay function. Furthermore, we show how to incorporate both failure dependency and time-dependent delay function into software reliability growth modeling. We present stochastic reliability models for software failure phenomenon based on NHPPs. Some numerical examples based on real software failure data sets are presented. The results show that the proposed framework to incorporate both failure dependency and time-dependent delay function into software reliability modeling has a useful interpretation in testing and correcting the software.

This paper addresses the problem of achieving full restoration and tolerating as many faults as possible in wavelength division multiplexing (WDM) networks without the capability of wavelength conversion. The problem of finding the maximum number of faults that can be tolerated is modeled as a constrained ring cover set problem, which is a decomposition problem with exponential complexity. The face decomposition algorithm (FDA) that can tolerate one or more faults is proposed. From the results, we know that the maximum number of faults tolerated can be extended from one significantly under various network topologies.

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. 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.

For the wavelength division multi-access system (WDMA), the reservation approach and the pre-allocation approach are two major media access protocols to support the packet-switched traffic. In this paper, a new media access control (MAC) protocol, the AP-WDMA (accelerative pre-allocation), is proposed for the WDMA. Although implemented on a simple basic architecture, it does provide a better media access protocol which can be easily extended to all the WDMA. Through evaluations, the AP-WDMA is shown to be able to overcome the wavelength limitation through a channel sharing mechanism and enable efficient transmission with the accelerative mechanism. The AP-WDMA relieves these technology constraints restricting the tunability to only one end and the table size to only n+2 memory spaces, where n is the number of stations.

This paper presents the analysis of multicasting performance in broadcast-and-select wavelength division multiplexing (WDM) networks from two aspects: multicast session length and multicast group size. The protocol analyzed in this paper is based on an existing protocol which can schedule unicast and multicast traffic. The packet distance, determined by the Euclidean distance of session length and the group size of a multicast distance is compared with the multicast distance to select the most appropriate scheduling method for multicast packets. Further comparisons on channel utilization and packet delay show that the session length affects the channel dominance significantly and the group size determines the range of multicast distance such that the performances will remain the same. In addition, multicast traffic with larger mean session length or mean group size will make some specific scheduling strategies fail to achieve optimal performance. If the multicast distance is properly chosen, performance tradeoffs can be made under multicasting environments with large session length or large group size.

In this paper, we propose a synchronous flow control mechanism in wormhole routed optical networks. It is expected that the benefit of shorter routing delay and smaller buffer size requirement in wormhole routing will be significant in optical networks. Different from the traditional bi-directional asynchronous back-pressure flow control, the flow control is modified to be unidirectional and synchronous. The size of synchronized control slot does not depend on the routing path length and the number of bits is a constant which is equal to the total number of virtual channels and nodes. The proposed flow control takes advantage of the restricted order of accessing channels in deadlock-free routing to broadcast their control information in a corresponding restricted order. Furthermore, in order to reduce the buffer size to only one unit, the virtual channels which share the same physical channel must be able to simultaneously transmit data. The low channel utilization induced by such mechanism is overcome by our modified source routing. In summary, this paper introduces a flow control mechanism which easily incorporates the benefit of wormhole routing into the limited-resource optical networks.