Routing And Spectrum Assignment Research Articles

Attack-Aware Service Provisioning to Enhance Physical-Layer Security in Multi-Domain EONs

It is known that with the multi-domain scenario, elastic optical networks (EONs) can improve network scalability, extend service coverage, and handle the multi-carrier situation. However, as a malicious client can launch cross-domain attacks in the physical layer, the security issues in multi-domain EONs should not be overlooked. In this paper, we consider how to improve the physical-layer security-level of multi-domain EONs. Specifically, we propose to differentiate the routing and spectrum assignment (RSA) schemes of intra- and inter-domain requests with security considerations. To achieve this, we review the physical-layer vulnerabilities due to different clients (especially trusted and untrusted ones) sharing optical components in EONs, analyze the potential attack scenarios to different RSA arrangements, and quantify the corresponding security threats with an attack factor. Then, we define the problem of multi-domain attack-aware RSA and formulate an integer linear programming model to solve it exactly. To reduce the time complexity, a heuristic algorithm is also proposed. The proposed algorithms are evaluated with extensive simulations using both the offline and online provisioning scenarios, and the simulation results verify its effectiveness.

Efficient routing and spectrum assignment in elastic optical networks with time scheduled traffic

Abstract Elastic optical networks (EONs) employ dynamic routing and spectrum assignment (RSA) algorithms to support diverse services and heterogeneous requests. However, these RSA algorithms may possibly induce spectrum fragments when allocating spectrum to accommodate different service requests. Therefore, such induced spectrum fragments should also be regarded as spectrum consumption besides the allocated spectrum by RSA algorithms. In this paper, by additionally considering the holding times of lightpaths and service connections, we first introduce a comprehensive spectrum consumption model to simultaneously investigate both the allocated and the fragmented spectrum consumptions. Then we solve this model in both static and dynamic traffic scenarios, by either formulating the RSA problem with time-scheduled traffic or introducing a time-aware spectrum-efficient heuristics algorithm. Since no defragmentation is executed in spectrum allocation, the proposed RSA algorithm requires no traffic disruption and can be realized more easily in reality. Simulation results show that the proposed algorithm reduces the comprehensive spectrum consumption and has lower bandwidth blocking probability than the typical first-fit RSA algorithm.

An intelligent inter-domain routing scheme under the consideration of diffserv QoS and energy saving in multi-domain software-defined flexible optical networks

Large scale multi-domain software-defined optical networks (SDON) provisioning has become a key area with increased scalable bandwidth services across wider network regions. Although distributed schemes could achieve lightpath routing by the ergodic process of domain boundary nodes, it increases the complexity of the signaling procedure and deployment of the interface. Moreover, the physical impairments are always the main factor of the infrastructure layer in SDON, which affect the transmission quality of the signal. Meanwhile, with increasing energy consumption of the Internet, it is imperative to design energy-efficient networks. To address the above issues, in this paper, an intelligent inter-domain routing scheme, which is supported by hierarchical control plane architecture, is presented based on sub-topology graph under the consideration of diffserv quality-of-service (QoS) and energy saving. The proposed scheme could achieve multi-domain quality of transmission (QoT), energy aware routing and spectrum assignment (RSA). We explore the scenarios where the multi-domain SDON achieve energy efficiency on the basis of meeting the QoT requirement. The blocking, energy consumption and average set up delay performances of the proposed schemes are estimated. The results indicate that the introduction of sub-topology in multi-domain RSA scheme has the better performance comparing with the distributed scheme.

Routing and Spectrum Assignment in Elastic Filterless Optical Networks

Elastic optical networking is considered a promising candidate to improve the spectral efficiency of optical networks. One of the most important planning challenges of elastic optical networks is the NP-hard routing and spectrum assignment (RSA) problem. In this paper, we investigate offline RSA in elastic filterless optical networks, which use a passive broadcast-and-select architecture to offer network agility. Here, an elastic optical network is referred to as the optical network that can adapt the channel bandwidth, data rate, and transmission format for each traffic demand in order to offer maximum throughput. In elastic filterless networks, the presence of unfiltered signals resulting from the drop-and-continue node architecture must be considered as an additional constraint in the RSA problem. In this paper, first, the RSA problem in elastic filterless networks is formulated by using an integer linear program to obtain optimal solutions for small networks. Due to the problem complexity, two efficient RSA heuristics are also proposed to achieve suboptimal solutions for larger networks in reasonable time. Simulation results show that significant bandwidth savings in elastic filterless networks can be achieved compared with the fixed-grid filterless solutions. The proposed approach is further tested in multi-period traffic scenarios and combined with periodical spectrum defragmentation, leading to additional improvement in spectrum utilization of elastic filterless optical networks.

Routing and Spectrum Assignment for Dual Failure Path Protected Elastic Optical Networks

We present the design of a dual failure protected elastic optical network (EON) for different sharing capabilities of protection lightpaths. Routing and spectrum assignment (RSA) is considered for such a network so as to minimize the maximum number of frequency slots (FSs) used. The key principles for protection resource sharing among the first and the second protection lightpaths are identified for dedicated 1:1:1, mixed 1:1:1, 1+1:1, and 1+1+1 protection. Both integer linear programming (ILP) models and spectrum window plane (SWP)-based heuristic algorithms are proposed for RSA in dual failure protected EONs. Simulation results indicate that, apart from being efficient, the proposed SWP-based heuristic algorithm not only performs close to the ILP model but also does much better than a benchmark adaptive routing algorithm. We find that 1:1:1 protection technique performs better in terms of the maximum number of FSs used and the spare capacity redundancy than both the 1+1:1 and 1+1+1 techniques. In addition, the mixed 1:1:1 case outperforms the dedicated 1:1:1 case both in minimizing the maximum number of link FSs used and its spare capacity redundancy.

Routing Code and Spectrum Assignment (RCSA) in Elastic Optical Networks

Elastic optical networks (EONs) are an attractive solution for backbones due to the offered potential flexibility and spectral efficiency. In EONs, an optical connection is allocated by solving the problem of routing and spectrum assignment (RSA). Based on the RSA output, a portion of spectrum—whose width depends on transmission parameters (e.g., bit rate and modulation format)—is assigned to an optical connection along a computed route. New emerging techniques for distance adaptation, that exploit variable code, are under investigation. In this case, the code rate (or redundancy) is tuned depending on the required optical reach. In EONs, transponders supporting distance adaptation permit to trade off between optical reach and required bandwidth (e.g., through the adaptation of modulation format), so that the spectrum occupied by a connection can be minimized while guaranteeing the required optical reach. This paper presents the concept of code selection in RSA for EONs, by proposing a routing, code, and spectrum assignment (RCSA) for dynamic set up. According to RCSA, a path, a code, and a portion of spectrum are selected for a connection request while guaranteeing quality of transmission. RCSA considers transmission impairments (e.g., amplified spontaneous emission) and filtering effects.

Routing, Spectrum, and Transponder Assignment in Elastic Optical Networks

Backbone networks are evolving toward elastic optical network (EON) architecture that allows a flexible and efficient use of spectrum resources. Flexibility in EONs is also guaranteed by emerging sliceable bandwidth variable transponders (SBVTs) that support the simultaneous generation of multiple optical carriers. Such carriers can be used to serve different lightpaths (i.e., slice-ability ), or can be merged into a single high-rate superchannel . SBVTs typically use a dedicated laser to generate each carrier, i.e., multilasers SBVT (ML-SBVT). Alternatively, a multiwavelength source can be used to generate multiple carriers using a single laser, i.e., multiwavelength SBVT (MW-SBVT). MW-SBVT improves the super-channel spectrum efficiency. Indeed, MW-SBVT reduces the intercarrier interference among the subcarriers composing the super-channel; thus, it is possible to reduce the guard bands among subcarriers. With ML-SBVT, each subcarrier suffers from unstableness of the related laser and intercarrier interference may have a huge impact, thus, higher guard bands are needed. On the other hand, the use of a MW-SBVT introduces specific constraints to the routing and spectrum assignment (RSA), because the spacing among the subcarriers is limited to a range of specific values. To take into account the constraints introduced by transponders, this paper integrates the selection of the transponder into RSA; thus, proposing a dynamic routing, spectrum, and transponder assignment (RSTA) scheme supporting both ML-SBVT and MW-SBVT technologies, and aiming to combine the benefits of the two technologies. Simulation results show that the proposed RSTA scheme provides benefits in terms of achieved blocking probability compared to the traditional RSA schemes. Moreover, the achieved results demonstrate that jointly using both SBVT technologies provides significant benefits with respect to the utilization of any single SBVT technology.

Extending light-trail into elastic optical networks for dynamic traffic grooming

A light-trail in a traditional ITU−T fixed wavelength grid optical network is a generalization of a lightpath. Multiple nodes in a light-trail are allowed to communicate each other along the light-trail, leading to sub-wavelength granularity utilized traffic grooming. Architecturally, a light-trail is analogous to a shared wavelength optical bus. Moreover, a new light-trail is always equipped by a guard band for non-interference of optical signals. Therefore, multiple light-trails must be accompanied by multiple guard bands, which indeed is an absolute wastage of optical spectrum resources. In the recent years, besides RWA (Routing and Wavelength Assignment) in WDM (Wavelength Division Multiplexing) optical networks, the Routing and Spectrum Assignment (RSA) algorithm is widely being adopted in many new and emerging elastic optical mesh networks to perform traffic grooming. In such networks, Orthogonal Frequency Division Multiplexing (OFDM) technology is a promising candidate to execute a RSA algorithm and implement an elastic lightpath as a result. The algorithm is capable of transmitting high-speed data stream using multiple low-speed spectrum overlapped sub-carriers (mini-grids). Hereafter, in this paper we have introduced a novel concept (based on our knowledge and belief) elastic light-trail (a variant of an elastic lightpath) in elastic optical networks and proposed an algorithm “Multi-hop Elastic Light-Trail – MELT” that performs an elastic light-trail expansion and/or contraction (in frequency domain), instead of creating a new elastic light-trail where applicable. Otherwise, the algorithm creates a new elastic light-trail that facilitates required data transportation. In this work, we investigate optical spectrum utilization efficiency for proposed elastic light-trail, existing elastic lightpath (Multi-hop Elastic Lightpath algorithm – MEL) and ITU−T wavelength grid fixed lightpath (Multi-hop Lightpath algorithm – ML) and perform comparison measurements.

Fragmentation-aware service provisioning for advance reservation multicast in SD-EONs.

In this paper, we study the service provisioning schemes for dynamic advance reservation (AR) multicast requests in elastic optical networks (EONs). We first propose several algorithms that can handle the service scheduling and routing and spectrum assignment (RSA) of AR multicast requests jointly, including an integrated two-dimensional fragmentation-aware RSA (2D-FMA) that can alleviate the 2D fragmentation caused by light-tree provisioning. Then, we leverage the idea of software-defined EONs (SD-EONs) that utilizes OpenFlow (OF) in the control plane to demonstrate and evaluate the proposed algorithms. Specifically, we build an SD-EON control plane testbed, implement the algorithms in it, and perform control plane experiments on dynamic AR multicast provisioning. The results indicate that 2D-FMA achieves the best blocking performance and provides the shortest average setup delay.

Malleable Reservation Based Bulk-Data Transfer to Recycle Spectrum Fragments in Elastic Optical Networks

In this paper, we propose to facilitate efficient bulk-data transfer in elastic optical networks (EONs) with malleable reservation (MR). The MR scheme performs adjustable routing and spectrum assignment (RSA) for the data-oriented requests that each has certain amount of data to transfer in an EON, where there also exist flow-oriented requests that each requires a fixed bandwidth. We enable RSA reconfigurations for each data-oriented request served by MR, to effectively recycle the 2-D spectrum fragments (i.e, fragments existing in the time and spectrum domains with a correlated manner) generated by the flow-oriented requests. We first formulate a mixed integer linear programming (MILP) model for the MR problem to maximize the percentage of transmitted data using a limited number of RSA reconfigurations. Then, in order to reduce the time complexity, we propose a dynamic programming method (DPM) that can provide the exact solution to the MR problem in polynomial time. Simulation results suggest that compared with the MILP, DPM can provide exact MR solutions for the data-oriented requests with significantly reduced time complexity. The results also verify that without affecting the provisioning of flow-oriented requests, DPM can recycle 2-D spectrum fragments and improve the EON's spectrum utilization effectively.

Distance Adaptive Dynamic Routing and Spectrum Allocation in Elastic Optical Networks with Shared Backup Path Protection

This paper considers distance adaptive dynamic routing and spectrum assignment (RSA) for elastic optical networks with shared backup path protection (SBPP). Efficient heuristic algorithms based on spectrum window planes are proposed for implementing distance and modulation format adaptive RSA so as to maximize spare capacity sharing among multiple protection lightpaths. A differentiated sharable frequency slot cost was also defined for the first time to more efficiently share protection resource. Network performance is evaluated in terms of bandwidth blocking probability (BBP) through simulations. The proposed SBPP technique is effective in reducing BBP and improving spectral efficiency compared to conventional SBPP schemes and 1+1 path protection. The impact of transponder tunability on bandwidth blocking performance is also evaluated to show that a limited tuning range is sufficient to achieve a BBP performance close to that with full tunability.

Time-Spectrum Consecutiveness Based Scheduling With Advance Reservation in Elastic Optical Networks

Novel advance reservation (AR) requests, such as user data replication and grid computing, which are different from immediate reservation requests, allow certain initial-delay during setting up, as long as the resources are allocated before a preset deadline. Empowered by the optical orthogonal frequency-division multiplexing (O-OFDM) technology, the elastic optical networks (EON) support channels operating at heterogeneous line rates by allocating spectral resources in a flexible and dynamic manner. However, in a dynamic traffic scenario, dynamic path setup and teardown operation will inevitably lead to spectral fragmentation. In this paper, to effectively allocate the spectrum in a suitable duration along a better route, we introduce a notion of available time-spectrum consecutiveness (TSC) to describe the spectrum fragmentations along frequency axis and time axis. Based on TSC, three time-aware routing and spectrum assignment (RSA) algorithms are proposed. The novel algorithms retain the TSC as much as possible when establishing a lightpath and reduce the spectrum fragmentation. Simulation results indicate three proposed algorithms achieve lower blocking probability and higher spectrum efficiency.

A multi-domain control scheme for diffserv QoS and energy saving consideration in software-defined flexible optical networks

The software-defined networking has emerged as an efficient network technology. It is capable of supporting the dynamic nature of future network functions and intelligent applications to provide the customized services. However, the physical impairments are still the main factor affecting the transmission quality of the signal. Meanwhile, the future network design should also take the growing energy consumption into account. To address the above issues, we first present an impairment-energy aware control plane for single domain management based on the extended OpenFlow protocol in software-defined flexible optical networks. Then, a service-oriented multi-domain control scheme is designed for the network scalability requirement. To implement our scheme, a multi-domain quality of transmission (QoT) and energy aware routing and spectrum assignment (RSA) algorithm is proposed for the diffserv quality of service (QoS) and energy saving consideration. The experimental works validate that our proposed RSA scheme makes a better balance between the QoT and the energy efficiency and also improves the spectrum resources utilization with the acceptable average set up delay.

On Routing and Spectrum Assignment in Rings

We present a theoretical study of the routing and spectrum assignment (RSA) problem in ring networks. We first show that the RSA problem with fixed-alternate routing in general-topology (mesh) networks (and, hence, in rings as well) is a special case of a multiprocessor scheduling problem. We then consider bidirectional ring networks and investigate two problems: 1) the spectrum assignment problem under the assumption that each demand is routed along a single fixed path (e.g., the shortest path), and 2) the general case of the RSA problem whereby a routing decision along the clockwise and counter-clockwise directions must be made jointly with spectrum allocation. Based on insights from multiprocessor scheduling theory, we derive the complexity of the two problems and develop new constant-ratio approximation algorithms with a ratio that is strictly smaller than the best known ratio to date.

Minimum- and Maximum-Entropy Routing and Spectrum Assignment for Flexgrid Elastic Optical Networking [Invited

We present two complementary routing and spectrum assignment (RSA) algorithms that use a quantitative fragmentation metric using the concept of Shannon entropy in flexgrid networks. Applying the minimum-entropy (MinEnt) approach to the BT network, support for almost 10% more demands in a static growth scenario is shown. We also present results for a maximum-entropy (MaxEnt) RSA approach, implemented using a genetic algorithm, and operated on the same real BT network topology. The MaxEnt approach avoids fragmentation problems, and it is anticipated that this can increase network utilization.

OpenFlow-Assisted Online Defragmentation in Single-/Multi-Domain Software-Defined Elastic Optical Networks [Invited

Spectrum fragmentation limits the efficiency of spectrum utilization in elastic optical networks (EONs). This paper studies how to take advantage of the centralized network control and management provided by software-defined EONs (SD-EONs) for realizing OpenFlow-assisted implementation of online defragmentation (DF). We first discuss the overall system design and OpenFlow protocol extensions to support efficient online DF and conduct DF experiments with routing and spectrum assignment (RSA) reconfigurations in a single-domain SD-EON. Then, we propose to realize fragmentation-aware RSA (FA-RSA) in multi-domain SD-EONs with the cooperation of multiple OpenFlow controllers. In order to provision inter-domain lightpaths with restricted domain visibility on intradomain resource utilization, we design and implement an inter-domain protocol to facilitate FA-RSA in multi-domain SD-EONs and demonstrate controlling the spectrum fragmentation on inter-domain links with FA-RSA. Our experimental results indicate that the OpenFlow-controlled DF systems perform well and can improve the performance of SD-EONs effectively.

Spectrum-efficient anycast in elastic optical inter-datacenter networks

With the rapid development of cloud computing, optical inter-datacenter (inter-DC) networks have attracted intensive research attentions. Meanwhile, recent advances on the flexible-grid elastic optical networks (EONs) have demonstrated agile spectrum management in the optical layer. Therefore, we expect EONs to become a promising underlying infrastructure for optical inter-DC networks. In this paper, we investigate offline and online routing and spectrum assignment (RSA) problems for anycast requests in elastic optical inter-DC networks. For the offline problem, we formulate an integer linear programming (ILP) model and propose several heuristics based on single-DC destination selection. The optimal solutions for small-scale problems are obtained by solving the ILP, and we compare them with those from the heuristics for measuring the optimization gaps. For the online problem, we design several heuristics to consider the computing and bandwidth resources jointly for efficient service provisioning, including an algorithm that uses multi-DC destination selection. Our simulation results demonstrate that the anycast algorithm with multi-DC destination selection can fully utilize the bandwidth resources in the elastic optical inter-DC network, make computing resources become the bottleneck, and reduce the bandwidth blocking probability of anycast requests effectively.

Hybrid routing and spectrum assignment algorithms based on distance-adaptation combined coevolution and heuristics in elastic optical networks

By adopting the orthogonal frequency division multiplexing technology, spectrum-sliced elastic optical path networks can offer flexible bandwidth to each connection request and utilize the spectrum resources efficiently. The routing and spectrum assignment (RSA) problems in SLICE networks are solved by using heuristic algorithms in most prior studies and addressed by intelligent algorithms in few investigations. The performance of RSA algorithms can be further improved if we could combine such two types of algorithms. Therefore, we propose three hybrid RSA algorithms: DACE-GMSF, DACE-GLPF, and DACE-GEMkPSF, which are the combination of the heuristic algorithm and coevolution based on distance-adaptive policy. In the proposed algorithms, we first groom the connection requests, then sort the connection requests by using the heuristic algorithm (most subcarriers first, longest path first, and extended most k paths’ slots first), and finally search the approximately optimal solution with the coevolutionary policy. We present a model of the RSA problem by using integral linear programming, and key elements in the proposed algorithms are addressed in detail. Simulations under three topologies show that the proposed hybrid RSA algorithms can save spectrum resources efficiently.

Dynamic and Adaptive Bandwidth Defragmentation in Spectrum-Sliced Elastic Optical Networks With Time-Varying Traffic

Elastic optical networks (EONs) enable network operators to have agile bandwidth management in the optical layer. In this paper, we investigate dynamic and adaptive bandwidth defragmentation (DF) in EONs with time-varying traffic using connection reconfigurations. We consider how to design DF procedure in a systematic way, and study the problems that have not been fully explored so far. Basically, we divide the procedure design into four subproblems: “How to reconfigure?,” “ How to migrate traffic?,” “When to reconfigure?,” and “What to reconfigure?,” and solve them sequentially. For “How to reconfigure?,” we investigate the combination of routing and spectrum assignment (RSA) algorithms for DF, i.e., the RSA algorithm that the connections are originally served with and the algorithm that they are re-optimized with. For “ How to migrate traffic?,” we propose to construct a dependency graph to represent the relations among the selected connections and to use it to assist the best-effort traffic migration. A move-to-vacancy method is also proposed to further reduce the traffic disruptions. For “When to reconfigure?” and “ What to reconfigure?,” we propose intelligent timing selection and adaptive DF ratio selection methods to tackle the tradeoff between the bandwidth blocking probability (BBP) performance and operational complexity. Simulation results show that the algorithm with both methods implemented (DF-AT-AR) achieves better tradeoff between BBP performance and operational complexity, when compared with existing algorithms.

Exact performance analytical model for spectrum allocation in flexible grid optical networks

Dynamic flexible grid optical networks have gained much attention because of the advantages of high spectrum efficiency and flexibility, while the performance analysis will be more complex compared with fixed grid optical networks. An analytical Markov model is first presented in the paper, which can exactly describe the stochastic characteristics of the spectrum allocation in flexible grid optical networks considering both random-fit and first-fit resource assignment policies. We focus on the effect of spectrum contiguous constraint which has not been systematically studied in respect of mathematical modeling, and three major properties of the model are presented and analyzed. The model can expose key performance features and act as the foundation of modeling the Routing and Spectrum Assignment (RSA) problem with diverse topologies. Two heuristic algorithms are also proposed to make it more tractable. Finally, several key parameters, such as blocking probability, resource utilization rate and fragmentation rate are presented and computed, and the corresponding Monte Carlo simulation results match closely with analytical results, which prove the correctness of this mathematical model.