Optical Switching and Networking最新文献

Issues of high energy costs and a time delay factor currently pose a considerable challenge to the success of the Internet of Things (IoT). Accordingly, fog computing (fog-C) has been introduced as a new paradigm to address both the high bandwidth cost and time delay issues that can result from transmitting sensing data all the way to centralized cloud servers. In addition, the optical fog-C network has been introduced to improve packet transmission among a group of connected fog nodes to support services to the end-user, with a minimum time delay. However, since network traffic management issues, such as building a network topology for supporting network traffic rules, have not been systematically recognized in optical or wireless fog-C, the fog-C network system itself is still not sufficiently dynamic to completely address these energy costs and latency issues. Thus, many studies have been suggested to integrate a software defined network (SDN) into the fog-C network system to present a software defined fog-C (SDFC) network architecture in order to eliminate the aforementioned issues associated with IoT applications. However, integrating the SDN with the fog-C system may generally result in introducing specific security and privacy challenges to the fog-C network topology system due to its distinctive features. This paper will review the overall promising advantages of SDFC networks, with a consideration of security and privacy threats associated with the fog-C network topology as well as possible solutions.

Optical networks are vulnerable to failures due to targeted attacks or large-scale disasters. The recoverability of optical networks refers to the ability of an optical network to return to a desired performance level after suffering topological perturbations such as link failures. This paper proposes a general topological approach and recoverability indicators to measure the network recoverability for optical networks for two recovery scenarios: 1) only the links which are damaged in the failure process can be recovered and 2) links can be established between any pair of nodes that have no link between them after the failure process. We use the robustness envelopes of realizations and the histograms of two recoverability indicators to illustrate the impact of the random failure and recovery processes on the network performance. By applying the average two-terminal reliability and the network efficiency as robustness metrics, we employ the proposed approach to assess 20 real-world optical networks. Numerical results validate that the network recoverability is coupled to the network topology, the robustness metric and the recovery strategy. We further show that a greedy recovery strategy could provide a near-optimal recovery performance for the robustness metrics. We investigate the sensitivity of network recoverability and find that the sensitivity of the recoverability indicators varies according to different robustness metrics and scenarios. We also find that assortativity has the strongest correlation with both recoverability indicators.

This work presents optimization algorithms on attack-aware routing and spectrum allocation (Aa-RSA) in conjunction with spectrum selective switch (SSS) placement, taking into account variations in traffic demands. The objectives of the algorithms are to minimize the required number of SSSs, as well as the number of lightpath re-allocations between different demand scenarios, taking into account the crosstalk interactions that could potentially be utilized during a jamming attack to facilitate the spread of the attack to additional lightpaths throughout the network. To solve the offline network design problem, first the proposed Aa-RSA algorithm is modeled as a mathematical formulation that jointly considers all the design parameters. Then, integer linear program (ILP)-based decomposition techniques and graph-based heuristics are also proposed to address large-sized networks. Additionally, it is shown through a dynamic time-varying Aa-RSA scenario, that the offline pre-calculated network configurations are a good fit for the traffic demand variations, eliminating the computational time required in the path computation element (PCE) for dynamically reconfiguring the network. The benefits of each of the proposed algorithms with respect to the network's operating and capital expenditures (measured in terms of performance metrics such as the number of SSSs deployed, the spectrum utilization, and the number of re-allocations) are reported and validated through extensive simulation results.

An Upper Physical layer functional Split (UPS) for an Ethernet fronthaul network is modelled, and the frame delay and Frame Delay Variation (FDV) limitations are investigated. The results show that contention in Ethernet switch ports can cause an increase in the delay and FDV beyond proposed specifications for the UPS and other time-sensitive traffic types such as I/Q-type traffic. Time Aware Shaping (TAS) can significantly reduce or even remove FDV for UPS traffic and I/Q-type traffic, but it is shown that TAS design aspects have to carefully consider the transmission pattern of the contending traffic in the Ethernet fronthaul network switches. Taking into account the transmission pattern of the UPS traffic, different time allocations within TAS window sections are proposed in conjunction with both receiver and transmitterside buffering. Further, it is proven that using TAS with higher link rates for example, 10 Gbps link rates or beyond makes it possible to transport the UPS and time sensitive traffic within its specification over fronthaul fiber spans, more than 10 km length, and/or more hops as TAS can potentially eliminate any increase in the FDV of the UPS traffic.

Reconfigurable optical networks have emerged as a promising technology to efficiently serve the fast-growing traffic produced by the digital society. This paper provides a survey of the field. We first review enabling optical hardware technologies in general and then consider technologies that are specific to data center networks and wide-area networks in more detail. We further provide an overview of the cost models used in the literature as well as the algorithmic problems introduced by these technologies, their first solutions, and discuss systems and implementation aspects. We conclude with a discussion of open challenges.

Elastic Optical Networks (EONs) are extensively accepted promising solution for future ultra-high-speed optical transmission, due to their capability of efficient and flexible assignment of immense optical bandwidth to the heterogeneous traffic demand. However, it undergoes through an aggravated form of the spectrum fragmentation problem due to the heterogeneous bandwidth requirements, spectrum continuity and contiguity constraints. Several techniques have been presented in the literature to get the optimal solution of this problem while multi-path provisioning comes out to be very compelling among them. Although, it creates further challenges due to high hardware requirement and more spectrum consumption due to guard-bands. In this paper, we propose a novel scheme, called optimal spectrum defragmentation (DF) strategy with split spectrum approach (OSDSSA), to tackle this limitation of multi-path provisioning by utilizing minimum number of spectral paths, which improves the scalability, reduces the extra spectrum consumption by guard-bands and avoids the exhaustion of transponders at nodes. The proposed scheme initially serves a connection request using k-shortest routing paths and first-fit spectrum allocation policy in a best possible way. In case, if a connection request cannot be served then the proposed mechanism proceeds with the triggering of Process Defragmentation on the link disjoint shortest paths followed by splitting of traffic demand on corresponding link-disjoint paths. The Process Defragmentation is triggered on the active connections at the immediate right and left of the largest continuous available spectrum block on the link-disjoint shortest paths sequentially until the requested amount of frequency slots (FSs) are achieved. In this work, reconfiguration includes spectrum re-tuning without changing the routing paths, thereby reducing the unnecessary service disruption, DF complexity and cost, leading to improvement in quality of service (QoS) of the network. The performance of the proposed scheme has been assessed through simulation results where single path and multi-path provisioning algorithms have been considered as benchmarks. Through our proposed scheme bandwidth blocking performance, spectrum utilization ratio, and degree of fragmentation have also been improved significantly.

This paper proposes a static Routing and Spectrum Allocation (RSA) method to design low-power elastic optical networks. In the elastic optical networks, data are transmitted via lightpaths, which are routes flexibly assigned frequency resources according to transmission distances and traffic demands. When designing the elastic optical networks with a static lightpath establishment policy, lightpaths are generally established so as to minimize frequency bandwidth allocated in order to save frequency resources necessary for constructing the networks. The proposed method focuses on not only this performance metric but also the power consumption of optical amplifiers. An optical amplifier in an optical fiber works when any of optical signals pass through it, and thus in multifiber environments where each link consists of multiple optical fibers, lightpaths should be collectively amplified from the view point of the power efficiency. Therefore, the relationship between these two performance metrics is a trade-off. The proposed method develops an Integer Linear Programming (ILP) formulation for the RSA problem taking the trade-off into account. Furthermore, the proposed method provides a heuristic algorithm that performs route selection and frequency spectrum allocation for reducing the total power consumption of optical amplifiers while saving necessary frequency resources. Through numerical experiments, we show the performance of the proposed method.

Advanced modulation formats like dual-polarization quadrature phase-shift keying (DP-QPSK) along with the digital coherent receiver are enabling optical networks to provide high spectral efficiency (SE) over long-haul transmission reach. The DP-QPSK based dense wavelength division multiplexing (DWDM) system with 37.5 GHz channel spacing can provide extra throughput of 33% compared to 50 GHz channel spacing. However, at 37.5 GHz channel spacing, optical add-drop multiplexers (OADMs) at intermediate nodes, impact the performance of WDM based optical networks in terms of increased BER, thereby reducing transmission reach drastically. In this paper, we have analyzed with the help of numerical simulations, the performance of a differentially encoded eight-channel 112 Gb/s, OADM based DWDM optical network with a channel spacing of 37.5 GHz. We propose that the selection of optimum values of system parameters can result in reducing the impact of crosstalk propagation and narrowband optical filtering introduced by a chain of OADMs at 37.5 GHz channel spacing. The paper exhibited that the selection of optimum values of parameters like filter order of multiplexer and demultiplexer, launch power per channel and filter taps of adaptive equalizer (AE) result in achieving minimum BER on all the channels over a long transmission reach up to 3600 km.

The proposed adaptive power control based on the chaotic hurricane search optimization (A-CHSO) for elastic optical networks (EON)s dynamically and efficiently adjusts the power increasing (r₀) parameter taking into account the quality of transmission (QoT), which is measured by the optical performance monitors (OPM)s. For sake of comparison, three alternative power assignment methods are analyzed, the analytical gradient descent (GD), as well as two low-complexity methods, namely the egoistic power allocation (EPA) and the enough power allocation (EnPA). Numerical results demonstrate a promising performance-complexity trade-off for the A-CHSO regarding the GD, EPA and EnPA methods, as well as a substantial network margin reduction, energy efficiency increasing, and cost reduction. The A-CHSO has been proved to be an efficient power allocation (PA) method for operation in EONs, corroborating the dynamical and flexible aspects of the EONs.

Passive optical networks (PONs) are the most successful broadband access solutions for its wide bandwidth, low-cost deployment worldwide, and maintenance. In the last decade, the diverse and prevalent research related to PONs sustains 330+ science citation index (SCI) articles per year, with 9.18 average citations per article, making it "big literature data". This article, for the first time, presents the graphical representation of knowledge base, knowledge domain, and knowledge evolution of PON research using co-citation analysis based on 3381 SCI publications worldwide from 2010 to 2019 in bibliometric visualization tool- CiteSpace. The bibliographic analysis focused on 528 important research articles, 34 hotspots, 155 research frontier keywords, 481 core authors, 185 cited authors, 58 countries, 254 institutions, and 118 journals. Based on the frequency of keywords, Modulation, WDM PON, Transmission, Semiconductor optical amplifier, and Dynamic bandwidth allocation are the dominant and turning points in the structural basis of PON research. The most prominent research hotspots appearing in recent years are Energy efficiency, NG-EPON, and Chaotic encryption. The trend of future research on PONs is from TWDM PON issues, fronthaul implementation in NG-PON2, 5G-PON and encryption methods for physical layer security. The leading core authors, institutes, countries, and journals were also identified related to the PON research. This analysis would serve as a comprehensive guide on the status and future research trends on PONs for the aspirant researchers.