Elsevier

Computer Networks

Volume 177, 4 August 2020, 107317
Computer Networks

Defragmentation based on route partitioning in 1 + 1 protected elastic optical networks

https://doi.org/10.1016/j.comnet.2020.107317Get rights and content

Abstract

In survivable elastic optical networks (EONs), spectrum fragmentation is one of the major obstacles to efficiently use spectrum resources. Efficient defragmentation approaches are indispensable to reduce spectrum fragmentation in survivable EONs, where both full 1 + 1 protected and quasi 1 + 1 protected services exist. The full 1 + 1 protected service offers full reliability without causing any traffic disturbance, where the backup path is not allowed to be reallocated, i.e., 1 + 1 path protection is always maintained. Whereas, the quasi 1 + 1 protected service compromises the reliability if any failure occurs on a primary path while its corresponding backup path is being reallocated. When full 1 + 1 protected and quasi 1 + 1 lightpaths are mixed in EONs, the network operators need to consider them to achieve thorough defragmentation carefully. This paper presents and investigates defragmentation based on route partitioning intending to reduce the spectrum fragmentation and blocking probability in 1 + 1 protected EONs, where both full 1 + 1 protected and quasi 1 + 1 protected services exist. A defragmentation scheme that focuses on minimizing the retuning interference on the full 1 + 1 protected lightpaths is introduced; the retuning interference occurs when a full 1 + 1 protected lightpath cannot be retuned to fill in a gap left by an expired lightpath due to the interference of another lightpath that prevents it from being moved further. We define a route partitioning optimization problem to minimize the interference on full 1 + 1 lightpaths in 1 + 1 protected EONs considering both full 1 + 1 protected and quasi 1 + 1 protected lightpaths. We formulate the problem as an integer linear programming (ILP) problem. The decision version of route partitioning problem in 1 + 1 protected EONs is proved as an NP-complete problem. We develop a heuristic algorithm for the case where the ILP is not tractable. We provide an online defragmentation algorithm for dynamic traffic. The effectiveness of the introduced defragmentation scheme with route partitioning is demonstrated through a simulation study.

Introduction

Elastic optical networks (EONs) [1], [2] transmit highly sensitive data, and any obtrusion of the data flow causes tremendous data loss. Thus, survivability against any failure has become a key requirement for EONs [3]. To improve reliability, several techniques have been considered for survivable EONs, which are 1 + 1/1:1 protection considering end-to-end path [4], shared protection of backup path (SBPP) [5], p-cycles [6], and span restoration [7]. Among them, 1 + 1 path protection techniques are considered the best one in terms of reliability, which provide instantaneous recovery by utilizing additional network resources.

In 1 + 1 path protected EONs, bandwidth fragmentation [8], [9], [10] is a serious issue, which degrades the spectrum utilization. To enhance spectrum utilization, bandwidth fragmentation is reduced by incorporating proper spectrum management techniques [10], which can consider either non-defragmentation approaches [11], [12], [13], [14], [15] or defragmentation approaches [16], [17], [18], [19], [20], or both.

As defragmentation approaches reduce blocking probability, which is defined as a ratio of the number of blocked lightpath requests to the number of served lightpath requests, than non-defragmentation approaches, researchers prefer to use defragmentation approaches for 1 + 1 protected EONs to reduce bandwidth fragmentation. Taking this direction, a defragmentation approach was introduced in [18] for 1 + 1 path protected EONs, which explores the defragmentation advantages offered by the backup paths without causing any interruption of traffic flow. The work in [18] considers that the backup paths can be reallocated as they are only used when their corresponding primary paths are failed. Thus, hitless defragmentation is achieved by executing spectrum defragmentation on them.

In [19], the path exchanging scheme was introduced for 1 + 1 protected EONs. The approach is to exchange the function of corresponding primary and backup lightpaths. Lightpaths that are in the primary state are toggled to the backup state, while their corresponding backup lightpaths are toggled to become primary lightpaths. This allows the inclusion of both 1 + 1 protection lightpaths into the defragmentation process.

The works in Wang et al. [18] and Ba et al. [19] consider that a backup lightpath is disconnected for a short time to be reallocated without impeding the data transfer, which continues through the corresponding primary lightpath. Nevertheless, this approach removes the 1 + 1 protection during the reallocation of backup lightpaths, as the protected lightpath is not available during the reallocation process. To reflect this, we refer to the 1 + 1 protection where backup lightpaths can be reallocated as quasi 1 + 1 protection.

Quasi 1 + 1 protection introduced in Ba et al. [19] offers more flexibility in the defragmentation process as it uses the path exchanging scheme. However, the repeated breach of protection in quasi 1 + 1 protection constitutes a risk of traffic loss in case of link failure. In that sense, network operators should offer the possibility to opt for 1 + 1 protection to clients requiring high-reliable data transmission. We refer such 1 + 1 protection where the effect is high and backup lightpaths cannot be reallocated as full 1 + 1 protection. With full 1 + 1 protection, both working and protected lightpaths transmit the data without disconnection as long as the signal is active. Therefore, the inclusion of full 1 + 1 protected lightpaths limits the opportunity of defragmentation process as full 1 + 1 protected lightpaths do not participate in the path exchanging scheme.

The route partitioning scheme with first-last fit allocation, which was introduced for push-pull retuning in Ba et al. [20], offers a palliative for the defragmentation of unprotected lightpaths. Push-pull retuning performs spectrum defragmentation by gradually moving lightpaths that are still transmitting. With the push-pull retuning, interferences among lightpaths occur as a lightpath can only be retuned until it reaches part of the spectrum being used by another lightpath with which it shares a link. To reduce retuning interference among lightpaths and increase the possibilities of lightpath retuning, the route partitioning sets a bipartition with lightpaths in one partition allocated using the first-fit allocation policy and the lightpaths in the other partition allocated using the last-fit allocation policy. Given that lightpaths that are allocated on different partitions cannot interfere with each other, the route partitioning with the first-last fit allocation minimizes the interference among lightpaths when applying push-pull retuning.

The work in Ba et al. [20] evaluates the effect of route partitioning scheme in unprotected EONs. It does not evaluate the effect in protected EONs, where both full 1 + 1 protected and quasi 1 + 1 protected lightpaths exist. The same route partitioning scheme introduced in Ba et al. [20] cannot be applied for protected EONs as the nature of both lightpaths are different; quasi lightpaths allow reallocation whereas full 1 + 1 lightpaths do not. The presence of both lightpaths involves different network operations, which affects the defragmentation performance. Directly applying the route partitioning to all lightpaths may lead to an unbalanced partitioning, where the overall interferences are minimized but the interferences to full 1 + 1 lightpaths are not. Quasi 1 + 1 lightpaths, which are defragmented using the path exchanging scheme, are not affected by the interferences as they are directly reallocated while in the backup state. No study in EONs has addressed defragmentation considering both full 1 + 1 protected and quasi 1 + 1 protected lightpaths.

This paper investigates the defragmentation scheme based on route partitioning intending to reduce blocking probability in 1 + 1 path protected EONs, where both full 1 + 1 protected and quasi 1 + 1 protected services exist. We introduce a defragmentation scheme that focuses on minimizing the retuning interference on the full 1 + 1 protected lightpaths. We define a route partitioning optimization problem that minimizes the interference on full 1 + 1 lightpaths in 1 + 1 protected EONs with quasi 1 + 1 and full 1 + 1 protected lightpaths. We formulate the problem as an integer linear programming (ILP) problem. We prove that the decision version of route partitioning problem in 1 + 1 protected EONs is NP-complete. We introduce a heuristic algorithm for the case that the ILP is not tractable. We then consider a defragmentation approach for both quasi 1 + 1 and full 1 + 1 protected lightpaths considering dynamic traffic. Varied settings and different networks are used to evaluate the presented scheme and compare it with different approaches. It is indicated from numerical results that it reduces the blocking probability in 1 + 1 protected EONs.

We organize the paper as follows. Section 2 describes the introduced scheme and defines the route partitioning optimization problem. Section 3 presents the approach to defragment the spectrum for both quasi 1 + 1 and full 1 + 1 protected lightpaths. Section 2 is dedicated for a static case, whereas Section 3 deals with a dynamic traffic scenario. Section 4 evaluates the performance of the introduced scheme. Finally, we conclude the paper in Section 5.

Section snippets

Route partitioning in 1 + 1 protected EONs

The defragmentation scheme consists of two phases. In the first phase, it involves the route partitioning optimization problem for minimizing the retuning interference on the full 1 + 1 protected lightpaths, and two partitions of lightpath requests are formed. One partition of lightpath requests is allocated using the first fit and other partition of lightpath requests is allocated using the last fit. In the second phase, the defragmentation scheme handles the operation problem, where

Spectrum defragmentation

The route partitioning scheme in 1 + 1 protected EONs is to be used for dynamic traffic situations. For that purpose, we introduce an online defragmentation approach that considers the two sets of 1 + 1 protected lightpaths, namely quasi 1 + 1 and full 1 + 1 lightpaths, and apply the adequate defragmentation operations to each set. This approach uses two defragmentation processes, namely (i) spectrum retuning, which is used for full 1 + 1 lightpaths and (ii) spectrum reallocation with path

Performance evaluation

The performance of the defragmentation based on path partitioning for 1 + 1 protected EONs is assessed in terms of blocking probability through simulation. For simulation, we consider three networks, which are five-node, National Science Foundation (NSF), and Indian, as shown in Fig. 3. We evaluate the effect of push-pull retuning speed for full lightpaths [20] and hop retuning speed for quasi lightpaths [19] on defragmentation. It is assumed that ϕ [time unit] is required to complete the

Conclusions

This paper introduced defragmentation based on route partitioning to reduce the blocking probability for 1 + 1 path protected EONs, where lightpath can be quasi 1 + 1 or full 1 + 1 protected. A route partitioning optimization problem that minimizes the interference on full 1 + 1 lightpaths in 1 + 1 protected EONs with quasi 1 + 1 and full 1 + 1 protected lightpaths was presented. We formulated the problem as an integer linear programming (ILP) problem. We proved that the decision version of

Declaration of Competing Interest

None.

Acknowledgments

The authors express their gratitude to Dr. Seydou Ba for discussing this research topic. This work was supported in part by the Inspire Faculty Scheme, Department of Science and Technology, New Delhi, India, under grant DST/INSPIRE/04/2016/001316 and in part by JSPS KAKENHI, Japan, under grant number 18H03230.

Bijoy Chand Chatterjee received the Ph.D. degree from the Department of Computer Science & Engineering, Tezpur University in the year of 2014. From 2014 to 2017, he was a Postdoctoral Researcher in the Department of Communication Engineering and Informatics, the University of Electro-Communications, Tokyo, Japan, where he was engaged in researching and developing high-speed flexible optical backbone networks. From 2017 to 2018, he worked as a DST Inspire Faculty at Indraprastha Institute of

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    Bijoy Chand Chatterjee received the Ph.D. degree from the Department of Computer Science & Engineering, Tezpur University in the year of 2014. From 2014 to 2017, he was a Postdoctoral Researcher in the Department of Communication Engineering and Informatics, the University of Electro-Communications, Tokyo, Japan, where he was engaged in researching and developing high-speed flexible optical backbone networks. From 2017 to 2018, he worked as a DST Inspire Faculty at Indraprastha Institute of Information Technology Delhi (IIITD), New Delhi, India. Currently, he is working at South Asian University (An international university established by SAARC nations), New Delhi, India, as an Assistant Professor and DST Inspire Faculty. He is also an Adjunct Professor at Indraprastha Institute of Information Technology Delhi (IIITD), New Delhi. Before joining South Asian University, he was an ERCIM Postdoctoral Researcher at the Norwegian University of Science and Technology (NTNU), Norway. He was a Visiting Researcher at Oki Lab, Kyoto University, Japan, from Jun-July, 2019. Dr. Chatterjee was the recipient of several prestigious awards, including DST Inspire Faculty Award in 2017, ERCIM Postdoctoral Research Fellowship by the European Research Consortium for Informatics and Mathematics in 2016, UEC Postdoctoral Research Fellowship by the University of Electro-Communications, Tokyo, Japan in 2014, and IETE Research Fellowship by the Institution of Electronics and Telecommunication Engineers, India in 2011. His research interests include QoS-aware protocols, cross-layer design, fog networking, optical networks and elastic optical networks. He has published more than 60 journal/conference papers. He has authored of two books Elastic Optical Networking Technologies: Fundamentals, Design, Control, and Management Boca Raton, in 2020, and Routing and Wavelength Assignment for WDM-based Optical Networks: Quality-of-Service and Fault Resilience, published by Springer International Publishing, Cham, in 2016. Currently, he has been serving as an associate editor in IEEE Access. He is a Life Member of IETE and a Senior Member of IEEE.

    Eiji Oki is a Professor at Kyoto University, Japan. He received the B.E. and M.E. degrees in instrumentation engineering and a Ph.D. degree in electrical engineering from Keio University, Yokohama, Japan, in 1991, 1993, and 1999, respectively. In 1993, he joined Nippon Telegraph and Telephone Corporation (NTT) Communication Switching Laboratories, Tokyo, Japan. He has been researching network design and control, traffic-control methods, and high-speed switching systems. From 2000 to 2001, he was a Visiting Scholar at the Polytechnic Institute of New York University, Brooklyn, New York, where he was involved in designing terabit switch/router systems. From 2008 to 2017, he was with The University of Electro-Communications, Tokyo. He joined Kyoto University, Kyoto, Japan, in 2017. He joined Kyoto University, Japan in March 2017. He has been active in standardization of path computation element (PCE) in the IETF. He wrote more than ten IETF RFCs. Prof. Oki was a recipient of several prestigious awards, including the 1999 IEICE Excellent Paper Award, the 2001 Asia-Pacific Outstanding Young Researcher Award presented by IEEE Communications Society for his contribution to broadband network, ATM, and optical IP technologies, the 2010 Telecom System Technology Prize by the Telecommunications Advanced Foundation, IEEE HPSR Paper Awards in 2012, 2014, and 2019, the 2015 IEICE Achievement Award, IEEE Globecom 2015 Best Paper Award, 2016 Fabio Neri Best Paper Award Runner Up, and Excellent Paper Award of 2019 Information and Communication Technology on Convergence. He has authored/co-authored six books, Broadband Packet Switching Technologies, published by John Wiley, New York, in 2001, GMPLS Technologies, published by CRC Press, Boca Raton, FL, in 2005, Advanced Internet Protocols, Services, and Applications, published by Wiley, New York, in 2012, Linear Programming and Algorithms for Communication Networks, CRC Press, Boca Raton, FL, in 2012, Routing and Wavelength Assignment for WDM-based Optical Networks: Quality-of-Service and Fault Resilience, Springer, Cham, in 2016, and Elastic Optical Networking Technologies: Fundamentals, Design, Control, and Management Boca Raton, in 2020. He is a Fellow of IEEE and a Fellow of IEICE.

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