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Copyright of Journal of Chongqing University of Posts & Telecommunications (Natural Science Edition) is the property of Chongqing University of Posts & Telecommunications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When circuits are set up and dismantled dynamically in elastic optical networks, the link spectrum becomes fragmented. The fragmentation limits the available path choices and may lead to significant blocking of connection requests. The fragmentation can be link fragmentation due to non-contiguity of available spectral resources on individual links or path fragmentation due to non-continuity of available spectral resources on the paths of the connection requests. The study of fragmentation and its management is essential to operate the networks efficiently. This paper proposes a vectored fragmentation metric for characterizing the fragmentation, which includes both types of fragmentation. We discuss the characteristics of this metric considering different network scenarios, where connection requests arrive and depart dynamically. To establish the functionality of this metric, we also test the utility of the metric in fragmentation management cases. We compare the different link-based fragmentation metrics and a path-based fragmentation metric with our Adapted vectored fragmentation metric to understand the efficacy of the proposed measure. We find the vectored fragmentation metric to be effective in this study. [ABSTRACT FROM AUTHOR]

On designing elastic optical networks, one of the main tasks to be solved is to allocate enough spectrum on the users' paths to achieve communication to all network users, known as the Spectrum Assignment problem (SA). On a static network operation, the order in which the users' spectrum demands are assigned is significant. However, standard approaches do not sort them previous to the spectrum assignment process. In this work, we first sort the users to maximize the spectrum usage based on their bandwidths and path length. Then, we propose a novel topology-based spectrum allocation strategy, which takes advantage of the ring network topology. We called it Spiral Fit, consisting of assigning the frequency spectrum to the users following a spiral (or a concentric rings) order. We compare our strategy's performance and robustness with two optimization models, only in small network topologies (from 5 to 8 nodes) since optimization processes are too expensive on more significant networks. In more extensive networks, we compare the proposed method with the most referenced techniques. The results show that consistently our method obtains near-optimal results in small topologies and outperforms the heuristic solutions found in the literature in terms of network capacity (measured as a number of frequencies slot units and spectrum fragmentation).

• We use the Elman neural network (ENN) to obtain an accurate forecast of future based on historical data. • The proposed crosstalk-aware intra-core resource allocation can reduce the inter-core crosstalk. • The proposed horizon-based inter-core spectrum allocation can reduce the fragmentation and improve spectrum utilization. As network traffic is expected to continue to grow at high rates for the foreseeable future, it becomes imperative to introduce space division multiplexing elastic optical networks (SDM-EONs) into the optical transport network. However, spectrum fragmentation and crosstalk present significant challenges that may negatively impact the performance of SDM-EONs. In this paper, we leverage machine learning techniques to enhance the transmission performance of SDM-EONs, and make two contributions. Specifically, we use an Elman neural network to forecast traffic demands, and use a two-dimensional rectangular packing model to allocate spectrum so as to decrease unnecessary spectrum fragmentation (and, in turn, increase resource utilization). We also present a novel spectrum partition scheme to reduce crosstalk. Our evaluation study confirms that the proposed strategy is effective in improving spectrum utilization while reducing blocking probability and crosstalk. [ABSTRACT FROM AUTHOR]

An elastic light-trail, the advanced version of a traditional light-trail, is one of the most recent dynamic traffic grooming technologies in an elastic optical network. In such networks, Orthogonal Frequency Division Multiplexing (OFDM) is a promising technology to execute the RSA (routing and spectrum assignment) algorithm and implement an elastic light-trail as a result. However, the reconfigurable optical add-drop multiplexers (ROADMs) and bandwidth variable Wavelength Selective Switches (WSSs) are required to implement an optically switched and spectrum varying elastic lightpath. In addition to the hardware equipment mentioned above, Add Drop Couplers (ADC) and optical ON/OFF switches (OS) are required to facilitate elastic light-trail in an elastic optical network. Hereafter, deployment of Add Drop Couplers (ADC) and optical ON/OFF switches incurs a significant network cost to facilitate elastic light-trail implementation. Toward the approach for eliminating this costly hardware setup, we have highlighted the fragmentation problem that occurs in spectrum domain in an optical fiber link. In this problem, the entire spectrum range in an elastic optical link is fragmented into several non-contiguous free spectrum slots at an instance during a data transportation session. In this regard, we have proposed "Multiple multi-hop non-contiguous elastic lightpath - MMNCEL " algorithm, where the required spectrum B of a traffic demand r (s , d , B , T) is sliced into n distinct granular spectrums { b 1 , b 2 , ... b n } according to the current availability and status of fragmented spectrum slots in an elastic optical link. Moreover, to setup an elastic lightpath, the algorithm allocates the same range of spectrum from every optical link in a route to preserve Spectrum Continuity Constraint (SCC), whereas, at each hop in a multi-hop elastic lightpath the algorithm performs opto - electrical conversion. In this paper, our objective is to achieve maximum network throughput in an elastic optical network without deploying ADC and optical ON/OFF switches. However, in this work, we have investigated optical spectrum utilization efficiency for the proposed MMNCEL , existing elastic light-trail (Multi-hop Elastic Light-trail algorithm - MELT) and elastic lightpath (Multi-hop elastic Lightpath algorithm - MEL), and performed comparison measurements preciously. [ABSTRACT FROM AUTHOR]

Flexi-grid technology has emerged as the evolution of fixed-grid DWDM core optical networks, enabling more efficient utilization of spectral resources and leading to higher overall network throughput. However, it suffers from an aggravated form of the spectrum fragmentation problem that affects fixed-grid networks. This work presents a novel path-based metric to better evaluate the fragmentation of spectral resources in flexi-grid optical networks, which considers that not all links of a path may contain enough free frequency slots and the likelihood that an end-to-end spectral void is large enough to house a connection. Furthermore, two families of heuristic routing and spectrum allocation (RSA) algorithms that preventively attempt to minimize the value of an input fragmentation metric are presented. These are used to evaluate the effectiveness of multiple metrics, both introduced in this work and from the existing literature, via simulations. We find that both proposed families can perform better, in terms of blocking probability and achievable network throughput, than the well-known K-shortest paths routing with a first fit spectrum allocation policy, with one of them trading performance for lower complexity, and that the proposed fragmentation metric outperforms the existing ones. [ABSTRACT FROM AUTHOR]

Various research studies have actually explored elastic optical networks with the purpose of broadening the transmission abilities of core networks. To accomplish this goal, it is needed to resolve the range source wastage problem brought on by range fragmentation. In addition, due to the possibly high web traffic needs in future networks, it is necessary to take care of demands that require being reserved immediately in addition to those that can be scheduled ahead of time. In networks that sustain the conjunction of IR and AR demands, IR solution destruction by AR demands is a challenging problem since AR demands often tend to reserve future sources, which creates an absence of present resources to fulfil IR demands. For that reason, we resolve the issue of spectrum fragmentation as well as the service-level control of IR and AR demands by transmitting and also range appropriation (RSA). Initially, we sum up relevant research study right into EONs and also resource-allocation techniques for IR as well as AR demands. Next off, we recommend a unique vibrant RSA technique to decrease spectrum fragmentation and also manage the solution degree of IR and AR demands in regards to data transfer obstructing chance in EONs thinking about the multiplexing impact of spatial networks. Lastly, we review the recommended method based on computer system simulations and also our outcomes demonstrate that the suggested approach can enhance the BBP for the whole web traffic circulation by minimizing range fragmentation, in addition to the solution control of AR demands and also IR requests under numerous network problems. [ABSTRACT FROM AUTHOR]

Due to the accelerated evolution of application services, the sharing of physical network infrastructure among different users and applications can be facilitated by optical network virtualization, which simplifies optical-layer resource management and enables flexibility in spectrum resource allocation. However, fragmentation is one of the great challenges in implementing virtual optical network embedding (VONE) over flexible-grid elastic optical networks (EONs). In this paper, we propose a fragmentation-aware VONE algorithm to reduce spectral fragmentation and improve resource unitization. We first formulate an integer linear programming (ILP) model for multiple static VON requests, while considering the continuity and consecutiveness of the substrate fiber links' (SFLs) optical spectra. Then, to realize the coordinated node and link mapping in the VONE, we constructed a virtual auxiliary graph (VAG) that decomposes the physical infrastructure into several layered graphs, according to the spectrum slot requirement of a VON request. Three different provisioning schemes are designed. The former two benchmark schemes (i.e., spectrum resource traffic balancing and spectrum resource and computing resource traffic balancing) apply a traffic balancing policy on the spectrum resource and computing resource, while another spectrum resource traffic balancing and defragmentation (SR-TB&DF) scheme additionally uses a proactive defragmentation method in the VONE process, with the aid of a novel metric called "fragment block size." The extensive simulations, which consider both static network planning and dynamic service provisioning scenarios, have demonstrated that the proposed fragmentation-aware VONE algorithm with the SR-TB&DF scheme facilitates the reduction of the spectrum slot fragments and improves the request blocking ratio as well, compared with the two other benchmark schemes. [ABSTRACT FROM AUTHOR]

In order to address the problems of spectrum fragmentation and high redundancy of protection resources in the pre‐configured cycle (P‐cycle) protection, a genetic P‐cycle combination protection strategy (GPCPS) based on improved genetic algorithm (IGA) is proposed for elastic optical networks. In GPCPS, an IGA is devised to optimise the basic cycles and find out an efficient P‐cycle protection combination for protecting the whole optical topology. For alleviating the spectrum fragmentation, a P‐cycle configuration strategy, named link spectrum partition and P‐cycle configuration, is introduced to pre‐configure the spectrum resource of P‐cycles. Meanwhile, the least traffic priority and first fit algorithm based on spectrum resources usage and path length aware is designed to select working path effectively. Simulation results show that the proposed GPCPS can reduce the bandwidth blocking probability and improve the spectrum resource utilisation. [ABSTRACT FROM AUTHOR]

The considered problem covers routing and spectrum allocation problem (RSA problem) in Elastic Optical Networks while maintaining the spectrum continuity constraints, non-overlapping spectra constraints for adjacent connections on individual links of the network and spectrum contiguity constraints of the connection. In this article the modified version of the First Fit spectrum slot allocation policy for Fixed Alternate Routing in flexible optical networks has been proposed. The Fixed Alternate Routing with proposed spectrum allocation policy rejects fewer requests, provides less bandwidth blocking probability and less spectrum fragmentation than Fixed Alternate Routing with well-known First Fit and Exact Fit spectrum allocation policies. However, the cost of improving these parameters is a higher computational complexity of the proposed allocation policy. [ABSTRACT FROM AUTHOR]

Spectrum fragmentation, a concept that describes the degree of split for a given portion of spectrum, is a newly emerging issue which can affect productivity and technical efficiency in spectrum use as the telecommunication service paradigm evolves from voice oriented to data oriented services. This paper proposes ten indices, compares them and calculates their values for Korea and Japan. The values of all indices range between zero and one, so one can use them for international comparison of spectrum fragmentation. Out of ten indices, three are Theil indices, comparing the discrepancies between spectrum and subscriber distributions. In addition, this paper discusses policy alternatives to lessen the spectrum fragmentation problem. [ABSTRACT FROM AUTHOR]

Elastic Optical Networks have drawn a lot of attention in recent years because of its ability to transmit different data rates by increasing or decreasing the optical spectrum according to the necessary demand, ensuring a high spectral efficiency. However, establishing and tearing down different connections end up segmenting the spectrum in several small fragments, making it difficult to attend incoming requests. Another recurrent problem in elastic optical networks, called Routing and Spectrum Assignment (RSA), aims to find a path and assign to it a contiguous number of spectrum slots using the smallest possible amount of spectral resources. This paper proposes a novel RSA algorithm to minimize the spectrum fragmentation problem in Elastic Optical Networks by choosing the most fragmented path first. Results obtained through simulations indicate that the proposed algorithm outperforms other conventional algorithms in terms of blocking probability and spectrum fragmentation ratio. [ABSTRACT FROM PUBLISHER]

For addressing the problems of high bandwidth blocking probability and low spectrum utilization caused by spectrum fragmentation in elastic optical networks (EONs), a dynamic EONs node architecture for deploying spectrum slicer is studied to transmit the request in the paper. The spectrum slicer can relax spectrum contiguity and improve spectrum fragmentation utilization for request's lightpath establishing. Then, a fragmentation aware routing and spectrum allocation based on spectrum slicing algorithm (SS-FA-RSA) is put forward. In the routing selection phase of SS-FA-RSA, a path weight value formula is designed to trade-off between path length, normalized fragmentation rate and available spectrum slicer, which reorder the candidate paths to select the most appropriate routing path for the request. Moreover, in the spectrum allocation phase, the spectrum slicing algorithm is proposed to increase the utilization of spectrum fragmentation by reusing spectrum fragmentation in EONs. Comparing with other algorithms, the simulation results show the proposed SS-FA-RSA can get better in bandwidth blocking probability and spectrum utilization. [ABSTRACT FROM AUTHOR]

In Elastic Optical Network (EON), spectrum fragmentation refers to the existence of non-aligned, small-sized blocks of free subcarrier slots in the optical spectrum. Several metrics have been proposed in order to quantify a level of spectrum fragmentation. Approximation methods might be used for estimating average blocking probability and some fragmentation measures, but are so far unable to accurately evaluate the influence of different sizes of connection requests and do not allow in-depth investigation of blocking events and their relation to fragmentation. The analytical study of the effect of fragmentation on requests’ blocking probability is still under-explored. In this work, we introduce new definitions for blocking that differentiate between the reasons for the blocking events. We developed a framework based on Markov modeling to calculate steady-state probabilities for the different blocking events and to analyze fragmentation related problems in elastic optical links under dynamic traffic conditions. This framework can also be used for evaluation of different definitions of fragmentation in terms of their relation to the blocking probability. We investigate how different allocation request sizes contribute to fragmentation and blocking probability. Moreover, we show to which extend blocking events, due to insufficient amount of available resources, become inevitable and, compared to the amount of blocking events due to fragmented spectrum, we draw conclusions on the possible gains one can achieve by system defragmentation. We also show how efficient spectrum allocation policies really are in reducing the part of fragmentation that in particular leads to actual blocking events. Simulation experiments are carried out showing good match with our analytical results for blocking probability in a small scale scenario. Simulated blocking probabilities for the different blocking events are provided for a larger scale elastic optical link. [ABSTRACT FROM AUTHOR]

Flexible grid optical networks allow an efficient utilization of spectrum resources using 12.5-GHz frequency slot multiples instead of a fixed spacing, introducing however spectrum fragmentation (SF). In the literature, SF is often assumed to be a serious problem specifically in a dynamic traffic context. It is mostly related to the bandwidth blocking ratio due to the lack of relevant comparison criteria and efficient metrics. Besides, in operator core network, traffic behavior is instead incremental and it is forecasted for short periods of time in addition to some operational constraints that make of it a specific context. In this work, we present an exhaustive analysis and an accurate evaluation for SF issue in flexible optical networks. We also propose new metric for fragmentation measurements and some approaches to address such a problem. [ABSTRACT FROM AUTHOR]

Radio spectrum for commercial mobile services continues to be scarce. Countries around the world have recognized the importance of efficient utilization of this scarce resource and have initiated regulatory and policy steps towards flexible approaches to spectrum management, including sharing of licensed spectrum, and releasing unlicensed spectrum for mobile services. Technologies for shared access and the associated standardization activities have also progressed towards possible large scale deployments. In this paper, we analyze the evolution of spectrum management policies using a causal model and indicate how the markets can lock in to either centralized or flexible approach. We also cite a use case of a flexible spectrum management approach using "spectrum band fill" option and indicate its suitability to the Indian context. [ABSTRACT FROM AUTHOR]

Elastic optical networks (EONs) facilitate agile spectrum management in the optical layer. When coupling with software-defined networking, they function as software-defined EONs (SD-EONs) and provide service providers more freedom to customize their infrastructure dynamically. In this paper, we investigate how to overcome spectrum fragmentation in SD-EONs with OpenFlow-controlled online spectrum defragmentation (DF), and conduct system implementations to facilitate highly-efficient online DF. We first consider sequential DF, i.e., the scenario that involves a sequence of lightpath reconfigurations to progressively consolidate the spectrum utilization. We modify our previous DF algorithm to make sure that the reconfigurations can be performed in batches and the “make-before-break” scheme can be applied to all of them. The modified algorithm is implemented in an OpenFlow (OF) controller, and we design OF extensions to facilitate synchronous batch reconfiguration. Then, we further simplify the DF operations by designing and implementing parallel DF that can accomplish all the DF-related lightpath reconfigurations simultaneously. All these DF implementations are experimentally demonstrated in an SD-EON control plane testbed that consists of 14 stand-alone OF agents and one OF controller, which are all implemented based on high-performance Linux servers. The experimental results indicate that our OF-controlled online DF implementations perform well and can improve network performance in an efficient way. [ABSTRACT FROM PUBLISHER]

Elastic optical networks (EONs) are considered a very promising solution for next-generation optical networks. Elastic spectral bandwidth allocation promotes spectrum utilization efficiency and thus increases the network capacity. One of the fundamental problemsinEONs is the routing and spectrum allocation (RSA) problem. Since real EONs may provide only a few regular line rates, we comprehensively study in this paper the dynamic RSA problem in EONs with several mixed line rates. To solve the dynamic RSA problem efficiently, we decompose the problem into RSA subproblems. For the routing subproblem, we propose an efficient multiconstrained routing algorithm named sorted feasible paths searching (SFPS) to find the shortest feasible paths for dynamic traffic demands. The completeness, optimality, and complexity of SFPS are proved. For the spectrum allocation subproblem, we propose two spectrum allocation strategies named fixed segmentation and adaptive segmentation to assign spectrum for the noncommensurate traffic demands of EONs with mixed line rates. Simulation results prove that the proposed dynamic RSA algorithms are time efficient and perform better than existing dynamic RSA algorithms in terms of bandwidth blocking probability and spectrum fragmentation ratio in EONs with mixed line rates. [ABSTRACT FROM PUBLISHER]

In this paper we propose two new spectrum allocation (SA) algorithms called Best Fit (BF) and Bit Rate-Aware (BRA), which are applicable to elastic DWDM optical networks under dynamic operation. In addition, we propose a new performance evaluation metric called spectrum fragmentation index, complementing the traditional analysis based on the blocking probability of connections. It evaluates and compares the performance of the algorithms through simulation. The results show that the proposed algorithm BRA presents the best performance compared with the most algorithms cited in the literature. [ABSTRACT FROM PUBLISHER]

Abstract: Flexible bandwidth optical networking (FBON) based on optical orthogonal frequency-division multiplexing (O-OFDM) technology has been proposed to accommodate traffic over 100Gb/s in the future due to its flexibility in spectrum allocation. In FBON, due to the limit of spectrum continuity constraints (SCC), routing and spectrum allocation (RSA) suffers a lot from spectrum fragments. Therefore, a lot of schemes have been proposed to deal with spectrum fragmentation, including spectrum conversion, spectrum sweeping retuning, multi-path routing, and fragmentation-aware RSA algorithm. These schemes are carefully designed to lower blocking probability. However, they usually need extra/high-quality infrastructures, require complex processing, or cause traffic interruption. To reduce spectrum fragmentation, we investigate spectrum allocation approach through utilizing the relationship between spectrum blocks' accommodation capability and traffic bandwidth distribution. Based on this, a fragmentation-aware spectrum allocation (FSA) algorithm is presented. Generally, this algorithm probabilistically optimizes the spectrum resource allocation process. The simulation results show that it is able to achieve a lower bandwidth blocking probability. [Copyright &y& Elsevier]

The need for optical parallelization is driven by the imminent optical capacity crunch, where the spectral efficiency required in the coming decades will be beyond the Shannon limit. To this end, the emerging high-speed Ethernet services at 100 Gbps have already standardized options to utilize parallel optics for data transmission, referred to as multi-lane distribution. OFDM-based optical network is a promising transmission option towards the goal of Ethernet parallelization. It can allocate optical spectrum resource tailored for a variety of bandwidth requirements in a fundamentally parallel fashion, with each sub-carrier utilizing a frequency slot at a lower rate than if serial transmission is used. In this paper, we propose a novel parallel transmission framework designed for elastic (OFDM-based) optical networks to support high-speed Ethernet services, in-line with IEEE and ITU-T standards. We formulate an optimization model based on integer linear programming, with consideration of various constraints, including spectrum fragmentation, differential delay and guard-band constraints. We also propose a heuristic algorithm which can be applied when the optimization model becomes intractable. The numerical results show the effectiveness and high suitability of elastic optical networks to support high-speed Ethernet parallel transmission, especially for connections with high bandwidth requirements. To the best of our knowledge, this is the first attempt to model parallel transmission in elastic optical networks in support of a standardized high-speed Ethernet system. [ABSTRACT FROM PUBLISHER]

Abstract: An efficient channel selection scheme in multi-user cognitive radio networks (CRN) is supposed to address two often conflicting objectives: enhancing the network-wide performance while satisfying the individual quality of service demands of cognitive radios (CRs). In this sense, best-fit channel selection (BFC) inspired from well-known classical bin-packing algorithms achieves better performance compared to the longest-idle time channel selection (LITC). BFC facilitates each CR, with the capability of primary channel idle time estimation, select the channel that is expected to be idle for sufficiently long duration for its traffic request. Unlike BFC, LITC favors the selection of the channel with the longest idle time although the channel is not needed and will not be used for such long duration by this CR. As a generalization of these two approaches, we introduce the p – selfish scheme in which a CR selects the longest channel with probability p. Hence, we also refer to p as degree of selfishness. In [1], we evaluate the performance of BFC and show that it improves performance of the CRN in terms of spectrum opportunity utilization and CR throughput, compared to the LITC. In this work, we present an analytic model for BFC using continuous-time Markov chains (CTMC). The performance improvement achieved by BFC is due the reduced spectrum fragmentation that is achieved by best-fit allocation. BFC can be considered as an implicit solution to spectrum fragmentation in time dimension. We study the CR performance in terms of spectrum opportunity utilization and probability of success under various degree of selfishness through the presented model and compare our results with the simulation results. [Copyright &y& Elsevier]

This paper investigates the spectrum fragmentation issue, which undermines the bandwidth efficiency in elastic optical networks. After categorizing the two-dimensional fragmentation problem as the fragmentation and misalignment subproblems, this paper proposes joint routing and spectrum assignment (RSA) algorithms to alleviate the spectral fragmentation in the lightpath provisioning process. The time complexity of the two proposed algorithms are analyzed in detail, and both algorithms can run in 0(kdnC log C) time, where k is the number of the shortest path in the routing algorithm, d is the maximum node degree in the network, n is the number of nodes in the network, and C is the link capacity expressed as the number of spectral slots. Simulation results indicate that the proposed fragmentation-aware (FA) RSA algorithm and the FA algorithm with congestion avoidance (CA) outperform the existing schemes in terms of blocking probability (BP) reduction. Compared with the benchmark iT-shortest-path routing and first-fit assignment (KSP-FF) algorithm, the proposed FA and FA-CA algorithms can achieve a BP reduction of [100%, 4.43%] and [100%, 6.45%], respectively, according to the traffic load in a sample NSFNET topology. [ABSTRACT FROM PUBLISHER]

SUMMARY Because of the presence of incumbents in cognitive radio networks, the unused spectrum in the TV bands, popularly referred to as 'white spaces', are fragmented with the size of each fragment varying from one TV channel to several TV channels. What is more, because the secondary transmissions adjust their spectrum usage over time, white spaces become increasingly partitioned into a collection of discrete fragments, which decreases the spectral utilization. To improve throughputs, most of the prior researches focused on selecting the best transmission channel in the context of spectrum fragmentation but have rarely involved aggregating the fragmentation to a contiguous channel. In this paper, we present two adaptive spectrum access strategies, both of which not only select the best transmission channel but also efficiently solve the fragmentation problem. The first strategy involves one-agile radios that build a transmission using single fragment of frequency, which partially remedy the fragmentation problem using higher-layer solutions. The second strategy suppresses the impact of spectrum fragmentation successfully at the physical layer by combining k spectrum fragments to form a single transmission. The simulation results show that both of the strategies bring larger throughputs compared with the prior solutions. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we consider the problem of spectrum sharing in CRAHNs and propose a distributed channel selection scheme. The key functionality of our proposal, best-fit channel selection (BFC) is that it accounts both the primary channel traffic activity and CR traffic activity in channel selection. We assume CR nodes have the capability of estimating the primary channel traffic activities. In BFC, each CR selects a channel among the primary user (PU) channels for transmission that best fits to its transmission time requirement. We compare the performance of BFC to the widely known longest idle time channel selection (LITC) scheme. In LITC, a CR selects the channel that has the longest expected idle time independent of its transmission needs. In a multi-user CRN, this may degrade the network performance compared to the non-selfish BFC approach. LITC is considered selfish since each CR aims to maximize its own benefit and thus wastes resources that may be utilized by other nodes in the network. BFC providing an efficient spectrum sharing mechanism implicitly mitigates the effect of spectrum fragmentation which is a significant issue degrading the CR spectrum utilization. In CRNs, spectrum may be fragmented in various dimensions, e.g. time and frequency, such that some parts of the spectrum can not be used although being idle. Our proposal provides a solution to the spectrum fragmentation issue in time dimension at the medium access control (MAC) layer. By a set of simulations, we highlight the performance improvement by BFC over the conventional LITC under various CR/PU traffic, number of CRs, estimation accuracy and buffering capability. Simulation results show that the performance of the proposed BFC is significantly superior to that of LITC in terms of probability of successful transmission, spectrum opportunity utilization and fragmentation. [Copyright &y& Elsevier]

Spatial division multiplexing elastic optical networks (SDM‐EONs) will become the most important form of future optical transport networks, because it can break the physical limit of achievable capacity in single‐mode and single‐core fibre. However, spectrum fragmentation issue becomes more serious in SDM‐EONs compared with in single EON. Crosstalk‐aware cross‐core virtual concatenation (CCVC) scheme is first proposed to solve the spectrum fragmentation issue in SDM‐EONs. Simulation results show that CCVC can achieve lower blocking probability and higher spectrum utilisation compared with single‐core virtual concatenation scheme. [ABSTRACT FROM AUTHOR]

To address the problems of low spectrum utilization and high bandwidth blocking probability of virtual optical network embedding in elastic optical networks, we propose a Survivable virtual optical network Embedding algorithm based on resource awareness of correlation lightpaths (SE-RACL), which can further optimize network resource allocation compared to traditional single lightpath resource allocation algorithms. Firstly, according to the multi-dimensional attributes of nodes, the importance sorting formulas of virtual nodes and physical nodes are designed to increase the cooperation between virtual node embedding and link embedding and reduce the bandwidth consumption of link embedding. Secondly, in the spectrum allocation process of the working lightpath, the spectrum block matching degree formula is designed by combining the spectrum fragmentation degree changes and resource reductions of correlation lightpaths, which is used to optimize the network spectrum resource allocation. Finally, in order to improve the sharing degree of protection resources and the success probability of spectrum allocation under single link failure, a correlation lightpaths spectrum allocation method based on the minimum free frequency slot consumption is proposed. Simulation results show that the SE-RACL algorithm can effectively reduce the bandwidth blocking probability and enhance the spectrum utilization. • Design the ranking formulas for virtual nodes and physical nodes respectively. • Design a spectrum block matching degree formula. • Design a spectrum block selection formula. • Propose a novel virtual node embedding method. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]