Defragmentation Technique Research Articles

Penalty-method based impairment-aware performance of Elastic Optical Networks with spectrum conversion

In Elastic Optical Networks (EONs), fragmentation is a major bottleneck which affects the spectral efficiency significantly. Many defragmentation techniques have been proposed to tackle this issue and often, these schemes involve complex operations at the controllers and various sophisticated devices. Moreover, the amount of defragmentation achieved is also limited. In this regard, recently, spectrum conversion is gaining attention as a potential solution for the fragmentation issue in EONs. On the other hand, physical-layer impairments such as non-linear interference, amplified spontaneous emission (ASE) noise, beat noises due to coherent detection, etc. aggravate the fragmentation issue significantly. In this paper, we propose a novel impairment-aware routing and spectrum allocation (RSA) scheme with allowable spectrum conversion at intermediate nodes. We also propose a novel node architecture involving spectrum conversion with full switching flexibility. We first formulate a mixed integer linear program (MILP) optimization framework based on the proposed architecture in presence of impairments for a sample network and propose a penalty-method-based heuristic algorithm for realistic networks. Within our optimization framework, we ensure that a minimum end-to-end bit error rate (BER) for each demand is provisioned.

On analyzing graphs with motif-paths

Path-based solutions have been shown to be useful for various graph analysis tasks, such as link prediction and graph clustering. However, they are no longer adequate for handling complex and gigantic graphs. Recently, motif-based analysis has attracted a lot of attention. A motif, or a small graph with a few nodes, is often considered as a fundamental unit of a graph. Motif-based analysis captures high-order structure between nodes, and performs better than traditional "edge-based" solutions. In this paper, we study motif-path , which is conceptually a concatenation of one or more motif instances. We examine how motif-paths can be used in three path-based mining tasks, namely link prediction, local graph clustering and node ranking. We further address the situation when two graph nodes are not connected through a motif-path, and develop a novel defragmentation method to enhance it. Experimental results on real graph datasets demonstrate the use of motif-paths and defragmentation techniques improves graph analysis effectiveness.

Countering Fragmentation in an Enterprise Storage System

As a file system ages, it can experience multiple forms of fragmentation. Fragmentation of the free space in the file system can lower write performance and subsequent read performance. Client operations as well as internal operations, such as deduplication, can fragment the layout of an individual file, which also impacts file read performance. File systems that allow sub-block granular addressing can gather intra-block fragmentation, which leads to wasted free space. Similarly, wasted space can also occur when a file system writes a collection of blocks out to object storage as a single large object, because the constituent blocks can become free at different times. The impact of fragmentation also depends on the underlying storage media. This article studies each form of fragmentation in the NetApp ® WAFL ® file system, and explains how the file system leverages a storage virtualization layer for defragmentation techniques that physically relocate blocks efficiently, including those in read-only snapshots. The article analyzes the effectiveness of these techniques at reducing fragmentation and improving overall performance across various storage media.

Study of Snort performance in counteracting port scanning techniques

Snort Intrusion Detection System became the de-facto standard among the software-based Intrusion Detection Systems because of the high level of customization and the relative ease of use. However, it is essential for an Intrusion Detection System not only to prevent the known attacks, but also to detect zero-day attacks and their preceding steps, such as port scans. A lot of companies neglect the security measures, associated with the prevention of the steps, preceding the attack, such as port scans. This article analyzes the performance of Snort in relation to detecting various port scanning methods and common evasion techniques, as well as the configurations that lead to the best performance. Port scanning prevention is discussed in the context of the nmap service and all the scanning techniques associated with it. Moreover, a packet defragmentation technique is discussed as the evasion technique, as well as the ways of the evasion detection. The article includes the recommendations for configuration of the Snort Intrusion Detection System for effective detection of the port scanning attacks.

On the comparative efficiency of non-disruptive defragmentation techniques in flexible-grid optical networks

The presence of dynamic traffic in optical networks can lead to spectrum fragmentation, which significantly reduce the network performance. This problem is exacerbated in flexible grid optical networks, since the heterogeneity of channel spectral widths increases the misalignment of the available slots along the optical connections. To overcome this problem, several techniques have been devised for providing defragmentation in these networks. Spectral defragmentation aims to create large contiguous free areas in optical spectrum through rerouting or spectral reassignment of existing connections. In this paper, we revisit the push-pull and hop tuning techniques, assessing them over an unified framework under equal conditions to properly evaluate their comparative efficiency in releasing network resources. This framework also includes the re-planning technique as a lower bound benchmark for the push-pull and hop tuning. To this effect, we propose Integer Linear Programming (ILP) models and heuristic algorithms to study the effectiveness of these techniques and present a performance analysis based on spectrum usage. The relative performance of the different defragmentation techniques was validated under varying network scenarios, including an assessment of how different planning methods and policies impact the effectiveness of each defragmentation technique. Aside from benchmarking the potential spectrum efficiency gain in each non-disruptive defragmentation technique, this analysis also revealed that the gains associated with them are greatly influenced by how the networks were originally planned.

Software-Defined Defragmentation in Space-Division Multiplexing With Quasi-Hitless Fast Core Switching

Multicore fibres (MCF) offer the opportunity of both increasing communication capacity as well as offering enhanced flexibility in the network scenario. Software-defined networks (SDN) are capable of handling novel functionalities coming from physical layer with the aim of better exploit overall connectivity. In this paper, network defragmentation is considered combined with space-division multiplexing (SDM). In particular, SDN-driven effective defragmentation technique on a seven-core MCF is demonstrated. This paper includes a networking view about defragmentation principle exploiting SDN control plane. At the same time, an accurate model and numerical investigations reveal feasibility and system constraints. Push–pull operation for a coherent DQPSK transmission has been experimentally demonstrated together with full dynamic defragmentation. By using a high-speed-integrated dual-output intensity modulator switch for core adaptation in combination with hitless frequency shift, quasi-hitless SDN-driven reconfiguration performances are shown. Defragmentation for $40\,\text{Gb/s}$ DQPSK and $80\,\text{Gb/s}$ 16QAM signals is demonstrated. Switching from core 2 to core 1, $100\text{-}\text{GHz}$ frequency shift, and switching back to core 2 is obtained losing just $1800$ and $2600$ symbols, respectively.

Integrity Enhancement of Flexible/Semi-Flexible Grid Networks That Minimizes Disruption in Spectrum Defragmentation and Bitrate-Dependent Blocking

We propose a novel disruption-minimized dynamic rerouting and spectrum defragmentation algorithm that addresses blocking ratio equalization on different bandwidth signals in flexible grid networks and our recently proposed semi-flexible grid networks. The blocking ratio inequality among channels stems from nonuniform frequency bandwidth allocation to different channels, which is unique to flexible/semi-flexible grid networks. The nonuniform assignment also causes more frequent channel setup blocking due to the severe fragmentation that is possible in the frequency domain. To resolve these issues, a dedicated bandwidth reservation technique for the broadest bandwidth paths is introduced to cope with the inequality issue, and the path blocking ratio is reduced by applying rerouting and a spectrum defragmentation technique. Numerical evaluations verify that combining these techniques can achieve a maximum improvement in the network performance including blocking ratio and equality. The results also confirm that semi-flexible grid networks can achieve almost the same performance as the currently studied flexible grid solution. Since the former have much relaxed hardware requirements, this novel approach is expected be a viable solution to realizing future flexible bandwidth networks cost-effectively.

Improvement of Crack-Detection Accuracy Using a Novel Crack Defragmentation Technique in Image-Based Road Assessment

AbstractA common problem of crack-extraction algorithms is that extracted crack image components are usually fragmented in their crack paths. A novel crack-defragmentation technique, MorphLink-C, is proposed to connect crack fragments for road pavement. It consists of two subprocesses, including fragment grouping using the dilation transform and fragment connection using the thinning transform. The proposed fragment connection technique is self-adaptive for different crack types, without involving time-consuming computations of crack orientation, length, and intensity. The proposed MorphLink-C is evaluated using realistic flexible pavement images collected by the Florida Department of Transportation (FDOT). Statistical hypothesis tests are conducted to analyze false positive and negative errors in crack/no-crack classification using an artificial neural network (ANN) classifier associated with feature subset selection methods. The results show that MorphLink-C improves crack-detection accuracy and reduces...

Control of Frequency Conversion and Defragmentation for Super-Channels [Invited

Super-channel (or multi-carrier) transmission is today one of the most promising techniques for the support of high line rates, which are required to satisfy the massive increase of Internet traffic. Moreover, flex-grid optical networks seem to be the candidates for backbone networks by enabling high spectral efficiency thanks to the adoption of the ITUT flex-grid. Such networks may suffer from spectrum fragmentation, which can prevent the establishment of new connections. For this reason, defragmentation techniques (i.e., reoptimization) have been widely studied, especially considering single-carrier transmission. Inparallel, the software defined networking (SDN) paradigm and the active stateful path computation element (PCE) are emerging as candidates for the control of next-generation optical networks. Such architectures are also particularly suitable in the case of defragmentation since they enable the controller to trigger reoptimization procedures. In this paper, we investigate defragmentation in the presence of super-channels, at both the control and data planes. We propose and experimentally demonstrate a technique based on a periodically poled lithium niobate waveguide to achieve both frequency conversion and defragmentation in elastic (or flex-grid) optical networks. Its peculiarity is that it is suitable for super-channels because it avoids detrimental subcarrier overlapping during a frequency shift. SDN with the OpenFlow protocol is discussed for the control of such operations, as well as the active stateful PCE and generalized multi-protocol label switching (GMPLS). The frequency conversion and defragmentation techniques are demonstrated in a lab trial considering a 200 Gb/s super-channel and extended OpenFlow for the control plane. No loss of data is experienced.

Improved ROADM Architecture for Network Defragmentation Comprising a Broad-Band Wavelength Converter

We report on an all-optical spectrum defragmentation technique using an optoelectronic broad-band wavelength converter. The defragmentation of a 50-GHz wavelength slot is shown in a ROADM at half-distance transmission of up to 9 DP-16QAM 28 GBd channels over six spans of 80-km length single mode fiber. all-optical broad-band wavelength converter

Feasibility demonstration of spectrum defragmentation in flexigrid optical network employing multi‐format and multi‐rate transmitter/receiver

The feasibility of spectrum defragmentation is demonstrated in a flexigrid optical network employing the multi-format and multi-rate transmitter and receiver. For efficient defragmentation, the push-pull defragmentation technique is improved with additional functionality, which tunes the occupied frequency slots as well as the centre frequency.

Push-Pull Defragmentation Without Traffic Disruption in Flexible Grid Optical Networks

In flexi-grid optical networks, fragmentation of spectrum resources may significantly affect the overall network efficiency. Effective techniques for defragmentation (i.e., re-optimization) are then required to limit the wasting of spectrum resources. However, current defragmentation techniques can only be implemented thanks to the presence of additional resources, such as spare expensive transponders. In this study, we propose, discuss and evaluate a novel defragmentation technique called push-pull. The technique is based on dynamic lightpath frequency retuning upon proper reconfiguration of allocated spectrum resources. It does not require additional transponders and does not determine traffic disruption. All the relevant technological limitations that may affect the push-pull applicability are discussed in the context of both optically-amplified direct and coherent detection systems. The technique is then successfully demonstrated in two different flexi-grid network testbeds, reproducing the two aforementioned scenarios. In particular, the reoptimization of a 10 Gb/s OOK lightpath is safely completed in few seconds (mainly due just to node configuration latencies) without experiencing any traffic disruption. Similarly, the push-pull is successfully performed on a 100 Gb/s PM-QPSK lightpath, providing no traffic disruption.

Adaptive Spectrum Control and Management in Elastic Optical Networks

Elastic optical networking (EON) has emerged in recent years as a promising solution for implementing flexible bandwidth channels (flexpaths) that efficiently match the allocated bandwidth with the traffic demand using agile granularities of spectrum allocation. However, the additional flexibility in such networks raises challenges in terms of efficient control and management of spectrum resources. Among them, three important issues are (1) mitigation of spectral fragmentation, (2) implementation of impairment awareness and enhancement of robustness against impairments for potentially large-bandwidth flexpaths, and (3) design of an efficient restoration scheme to combat network failures. This paper presents an adaptive spectrum control and management scheme, which includes: dynamic on-demand spectral defragmentation, adaptive combinational quality of transmission (QoT) restoration (ACQR) and supervisory channel-assisted active restoration, to account for the three issues above. We present scalable networking algorithms and experimental demonstrations that address these issues in an EON testbed. Simulation results show that the defragmentation technique is capable of reducing the provisioning blocking probability by half with only one defragmentation module on each link. Then, we also show that the ACQR can efficiently restore many degraded flexpaths on the same impaired link while reducing the restoration blocking probability by a factor of 10 compared with the conventional rerouting method. At last, we show via simulation the advantages of using supervisory channels to determine restoration path quality and selection in EON restorations. This paper also presents experimental demonstrations to corroborate the effectiveness and feasibility of implementing these capabilities in next generation optical networks.

Rapid and complete hitless defragmentation method using a coherent RX LO with fast wavelength tracking in elastic optical networks

This paper demonstrates a rapid and full hitless defragmentation method in elastic optical networks exploiting a new technique for fast wavelength tracking in coherent receivers. This technique can be applied to a single-carrier connection or each of the subcarriers forming a super-channel. A proof-of-concept demonstration shows hitless defragmentation of a 10 Gb/s QPSK single-carrier connection from 1547.75 nm to 1550.1 nm in less than 1 µs. This was obtained using a small (0.625 kB) link-layer transmitter buffer without the need for any additional transponder. We also demonstrated that the proposed defragmentation technique is capable of hopping over an existing connection, i.e. 10 Gb/s OOK at 1548.5 nm, without causing any degradation of its real-time Bit Error Rate (BER) value. The proposed scheme gives advantages in terms of overall network blocking probability reduction up to a factor of 40.

Space defragmentation for packing problems

One of main difficulties of multi-dimensional packing problems is the fragmentation of free space into several unusable small parts after a few items are packed. This study proposes a defragmentation technique to combine the fragmented space into a continuous usable space, which potentially allows the packing of additional items. We illustrate the effectiveness of this technique using the two- and three-dimensional bin packing problem, where the aim is to load all given items (represented by rectangular boxes) into the minimum number of identical bins. Experimental results based on well-known 2D and 3D bin packing data sets show that our defragmentation technique alone is able to produce solutions approaching the quality of considerably more complex meta-heuristic approaches for the problem. In conjunction with a bin shuffling strategy for incremental improvement, our resultant algorithm outperforms all leading meta-heuristic approaches based on the commonly used benchmark data by a significant margin.

A Secure Mobile Agent System against Tailgating Attacks

Problem statement: A lot of real time applications have extended their hands towards Mobile Agents to accomplish various tasks, due to its flexibility in its functionalities. Since Mobile Agent Systems are used in a distributed environment, it is obvious that they may be vulnerable to various security threats. Most of the security threats faced by the mobile agent systems are overcome by existing security algorithms and architectures. One of the major threats which are not of much focus in a mobile agent system is the Tailgating attack. Approach: In this study, mobile agent system architecture has been proposed to overcome Tailgating. The proposed architecture uses the mechanism of Dual Check-point to preclude Tailgating attacks. Also, to support the mechanism, we use fragmentation and defragmentation techniques. This assures a free flow of data within the system. Results: The results obtained prove that the system is much efficient in its operations as well is immune to Tailgating attacks. Conclusion: The security of the system is improved with the implementation of the Dual Check-point method.