Spectrum fragmentation issue in flexible optical networks: analysis and good practices

Amar, Djamel; Rouzic, Esther Le; Brochier, Nicolas; Augé, Jean-Luc; Lepers, Catherine; Perrot, Nancy

doi:10.1007/s11107-015-0487-1

Cited by 36 publications

(22 citation statements)

References 15 publications

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“…Network fragmentation has been widely studied in EONs (see survey papers [5,12]), while it is only considered in a few papers in the case of SS-FONs. Ref.…”

Section: Related Workmentioning

confidence: 99%

“…To the best of our knowledge, even though several fragmentation metrics have been proposed in EON (e.g., external fragmentation, Shannon entropy or access blocking probability [5,12,22]), there is lack of investigation on the definition of network fragmentation metrics in SS-FONs, except our recent work [11]. SS-FONs introduce the additional spatial dimension, and it should be addressed in the fragmentation metrics.…”

Section: Related Workmentioning

confidence: 99%

“…In this section, we present the SS-FON model and the notation required to define fragmentation metrics. Then we introduce several fragmentation metrics (many of them are adapted from EONs) to evaluate link fragmentation in SS-FONs [11], namely, External Fragmentation (EF), Shannon Entropy (SE), access blocking probability (ABP) [5,12,22], root of sum of squares (RSS), root mean square factor (RMSF) [23].…”

Section: Fragmentation Metricsmentioning

confidence: 99%

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Fragmentation metrics and fragmentation-aware algorithm for spectrally/spatially flexible optical networks

Lechowicz

Tornatore

Włodarczyk

et al. 2020

J. Opt. Commun. Netw.

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Spectrally/spatially-flexible optical networks (SS-FONs) are a promising solution to cope with future traffic requirements in optical backbone networks. SS-FONs exploit the spatial dimension to increase network capacity while preserving resource management flexibility, as they still operate within a flex-grid composed of small frequency slots (slices). Flex-grid allows realizing transmission using super-channels (SChs) that comprise a set of contiguous slots. In this paper, we focus on spectral SChs, i.e., a SCh realized only on one spatial mode on each fiber. In SS-FONs, setting up and tearing down multiple lightpath requests within flex-grid may result in spectrum fragmentation, and, in turn, blocking of requests. In this work, we investigate several fragmentation metrics in SS-FON. The problem of identifying appropriate metrics to measure fragmentation has been investigated in single-core elastic optical networks (EONs), but, to the best of our knowledge, there is lack of such investigation for SS-FONs. Therefore, we propose several fragmentation metrics for SS-FON. We introduce the concept of bordering super-channels (B-SChs), i.e., SChs whose spectrum is allocated at the "border" of already allocated spectrum slots that are promising SChs to be chosen to minimize fragmentation. The investigation of all candidate B-SCh for a request allows us to find the one which minimizes network fragmentation, and, in turn spectrum waste. Hence, we propose a fragmentation-aware algorithm with bordering super-channels (FA-BSC) that assigns optical resources to dynamic requests utilizing information from the proposed fragmentation metrics and the set of candidate B-SChs. Experiments on a representative network topology show that the investigation of multiple B-SChs in the fragmentation-aware algorithm reduces the blocking probability when compared to the reference fragmentation-aware algorithms. Finally, we analyze the impact of a spatial continuity constraint on the network fragmentation.

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“…Network fragmentation has been widely studied in EONs (see survey papers [5,12]), while it is only considered in a few papers in the case of SS-FONs. Ref.…”

Section: Related Workmentioning

confidence: 99%

Section: Related Workmentioning

confidence: 99%

Section: Fragmentation Metricsmentioning

confidence: 99%

See 1 more Smart Citation

Fragmentation metrics and fragmentation-aware algorithm for spectrally/spatially flexible optical networks

Lechowicz

Tornatore

Włodarczyk

et al. 2020

J. Opt. Commun. Netw.

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show abstract

“…Let us first define a spectral fragmentation metric (or FI), similar to [23] and [5], as the ratio between the sum of the set of bandwidth requests that can be accepted in a fragmented link and the set of bandwidth requests that can be accepted in a non-fragmented link. In addition to that, let us take into account all possible ways that a bandwidth request b i with demand of i slots can be allocated in a free spectrum block of size n, i.e., n − i 1 number of possible ways in which spectrum can be allocated to this request b i .…”

Section: A Fragmentation Metric-spectral Domainmentioning

confidence: 99%

Efficient Spectrum Defragmentation With Holding-Time Awareness in Elastic Optical Networks

Jukan¹

2017

J. Opt. Commun. Netw.

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Elastic optical networks are prone to spectrum fragmentation, resulting in poor resource utilization and often higher blocking probability. To overcome the spectrum fragmentation, a defragmentation (DF) of the spectrum can be applied by reconfiguring some or all active connections. However, reconfiguration is generally not desirable, as it can interrupt the services of the existing connections. In this paper, we propose two novel connection reconfiguration schemes to efficiently address spectrum DF: (i) a reactive-disruptive scheme and (ii) a proactivenon-disruptive scheme. Both schemes utilize the information of holding times of the existing connections in order to reduce fragmentation and thus improve resource utilization and minimize connection blocking. The reactivedisruptive reconfiguration scheme tries to allocate an incoming connection, which could not be accepted otherwise, by reconfiguring some existing connections. The proactive-non-disruptive reconfiguration method, on the other hand, allows us to reconfigure only such connections, which can be shifted without crossing over the spectrum of other connections. This paves the way for a non-disruptive DF when setting up a new connection, which is a desirable feature. Simulation results show that the reconfiguration schemes with holding-time awareness can be effectively utilized to reduce the spectrum fragmentation and, hence, result in better resource utilization and overall lower connection blocking probability.

show abstract

“…Let us first define a spectral fragmentation metric (or FI), similar to [10], as the ratio between the sum of the set of bandwidth requests that can be accepted in a fragmented link and the set of bandwidth requests that can be accepted in a non-fragmented link. In addition to that, let us take into account all possible ways that a bandwidth request b i with demand of i slots can be allocated in a free spectrum block of size n, i.e.…”

Section: A Fragmentation Metric -Spectral Domainmentioning

confidence: 99%

Non-disruptive spectrum defragmentation with holding-time awareness in optical networks

Jukan

2016

2016 International Conference on Optical Network Design and Modeling (ONDM)

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Generally, an elastic optical network (EON) under a dynamic connection (non-uniform bandwidth) set up and termination scenario leads to spectrum fragmentation, and results in higher blocking probability. To overcome this problem, a defragmentation of the spectrum can be applied by reconfiguring some or all connections in the network. However, reconfiguration can interrupt the services of the existing connections if it is not performed in a non-disruptive manner, meaning that no data is lost or interrupted during reconfigurations. In this paper, we propose a different non-disruptive proactive reconfiguration scheme that utilizes the information of holding times (HT) of the connections in order to reduce fragmentation and thus improve resource utilization and minimize the connection blocking. Our reconfiguration method utilizes the HT information, and we allow to reconfigure only such connections, which can be shifted in parallel and without crossing-over the spectrum of other connections. This paves the way for a non-disruptive defragmentation when setting up a new connection. Simulation results show that the reconfiguration with holding time awareness can be effectively utilized to reduce the spectrum fragmentation, and hence results in lower connection blocking probability.

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Spectrum fragmentation issue in flexible optical networks: analysis and good practices

Cited by 36 publications

References 15 publications

Fragmentation metrics and fragmentation-aware algorithm for spectrally/spatially flexible optical networks

Fragmentation metrics and fragmentation-aware algorithm for spectrally/spatially flexible optical networks

Efficient Spectrum Defragmentation With Holding-Time Awareness in Elastic Optical Networks

Non-disruptive spectrum defragmentation with holding-time awareness in optical networks

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