Routing And Spectrum Assignment Algorithms Research Articles

Pre- and post-processing techniques for reinforcement-learning-based routing and spectrum assignment in elastic optical networks

Research on the routing and spectrum assignment (RSA) problem has long been conducted with the aim of efficiently utilizing the frequency resources of optical networks. Given the recent progress in machine learning (ML) technology, it has been reported that the application of ML in various areas of optical network design, operation, and management has the potential to bring about new innovations such as autonomous optical network operation and highly accurate estimation of network conditions. With regard to the RSA problem, it is expected that an algorithm that achieves better accommodation efficiency than conventional heuristic methods can be realized by applying reinforcement learning (RL), which well supports training in a simulation environment. In this paper, we introduce and evaluate three techniques devised to apply RL more effectively to elastic optical networks (EONs): two pre-processing techniques called link-axis positional encoding (LPE) and slot-axis positional encoding (SPE) and a post-processing technique named the assignable boundary slot mask. First, we build a simple model in which the state data of the optical network, including frequency slot utilization, are input to the neural network of the RSA agent in RL and show that this model has difficulty outperforming the conventional heuristic RSA algorithm. Next, we build an RSA agent model with the proposed techniques and simulate the accommodation of dynamic optical paths to quantitatively demonstrate that the blocking probability can be reduced by 17% compared to the conventional heuristic.

Evaluation of Network Blocking Probability and Network Utilization Efficiency on Proposed Elastic Optical Network using RSA Algorithms

AbstractElastic optical networks (EONs) are new generation optical networks that provide flexible bandwidth and spectrum assignment characteristics to accommodate diverse demand range over traditional dense wavelength division multiplexing (DWDM)-based networks. While overcoming spectrum contiguity and continuity constraints, Routing and Spectrum Assignment (RSA) is a challenging task in EONs. In this article, we have proposed an EON network model. Using existing RSA techniques we have analyzed the performance of the proposed model on the basis of Network Blocking Probability (NBP) and Network Utilization Efficiency (NUE) under variable load conditions. It has been found to be working optimally even at a load of 200 Erlangs.

Impact of BER in fragmentation-aware routing and spectrum assignment in elastic optical networks

Routing and spectrum assignment (RSA) in elastic optical network (EON) is a challenging task as an inefficient RSA may result in spectral and spatial fragmentation, leading to under-utilization of spectrum and increased connection blocking. Previous fragmentation-aware RSA algorithms, based on the assumption of an ideal physical layer, are not suitable for the performance evaluation of practical networks, where quality of the optical signal degrades while travelling long distances through the optical fiber links. Therefore, while running a RSA algorithm, it is necessary to consider the impact of all noise components to evaluate receiver bit-error rate (BER) on the fly, so that each connection is setup only when the estimated BER remains below an acceptable limit. This problem, hitherto unexplored in EONs though more significant and complex as compared to the conventional optical networks, is taken into consideration in this paper while framing fragmentation-aware RSA algorithm. In particular, we present a novel BER-cum-fragmentation-aware RSA algorithm, by using online estimates of BER values while executing fragmentation-aware RSA. The simulation results show that awareness of BER increases the connection blocking, which can however be addressed favorably by increasing transmit power, as much as possible from the available transmitter modules. Finally, we present a histogram of number of established connections versus delay-bandwidth product of the connections, leading to an assessment of the proposed algorithm in respect of the ability to allow long-haul connections with large bandwidth requests.

A routing and spectrum assignment algorithm in elastic optical network based on minimizing contiguity reduction

Elastic optical network, due to its flexibility of spectrum assignment, has been the most promising technology in the next generation of backbone transport network. Routing and spectrum assignment (RSA) is one of its key issues. Several RSA algorithms have been proposed in recent years. In the spectrum assignment process, the more contiguous the idle frequency slices, the more likely it is to find available spectrum blocks for connection requests. Therefore, in this paper, we first give the concept of link/path contiguity reduction (LCR/PCR) to express the change of spectrum contiguity on a link/path after a spectrum block is used. Then, we propose a RSA algorithm named Min-PCR-LCR, which always chooses a spectrum block with the minimum path contiguity reduction to a connection request, and if there is a tie, the one with the minimum sum of link contiguity reductions is finally chosen. Simulation results show that the Min-PCR-LCR algorithm can get lower blocking probability than the existing well-performed RSA algorithms.

Performance analysis of elastic optical networks (EONs) switches under unicast traffic

Bandwidth variable-wavelength cross connect switches (BV-WXCs) play an important role in the routing and spectrum assignment (RSA) problem in elastic optical networks (EONs). These switches, whose structure has been derived from micro electro mechanical systems technology, aim to switch the incoming traffic flexibly such that the existing resources are not wasted and more requests can be served. There exist different quality of service parameters which have to be provided in EON, such as delay, loss, jitter, and so forth. Among these parameters, blocking probability (BP) has been always taken into account in EON and several researches have been done to address it. The main objective of most RSA algorithms is to alleviate BP of requests through efficient usage of resources, such as frequency slots and BV-WXC ports. To show the importance of BV-WXC in routing and resource assignment in EON, its performance is analyzed in this paper. The BP of the BV-WXC is evaluated by means of an analytical model under unicast traffic and the obtained results are compared to the blocking probability results acquired from simulations for different number of input/output ports and available resources. The obtained results show that the analytical model has a good agreement with the simulation results.

Analysis Framework of RSA Algorithms in Elastic Optical Rings

With flexibility in optical layer, elastic optical network (EON) has been considered as a competitive candidate to architect next-generation backbone networks. Routing and spectrum assignment (RSA) is a key problem for the service provisioning in EONs. The RSA problem is $\mathcal {NP}$ -hard even in elastic optical rings. Numerous heuristics have been proposed, and they can generally be categorized into two types: Route-First (RF) and Spectrum-First (SF). Although most previous work demonstrated by numerical simulations that the SF algorithms always outperform the RF ones, there is a lack of theoretical analysis on the reasons causing the performance difference between the two types of RSA algorithms. In this paper, we aim at proposing a unified theoretical framework for the performance analysis of RSA algorithms by leveraging conflict graphs, which offers a new perception on the optimality of RSA algorithms. To validate the proposed framework, we apply it in elastic optical rings (with cycle topology), and theoretically analyze the number of edges of the conflict graphs for RF and SF algorithms. Different from the literature, we obtain an interesting observation that neither the RF nor the SF can surpass the other in elastic optical rings under different traffic distributions, and their performances have a strong correlation to the edge count of their conflict graph. This observation provides a new perspective, i.e., conflict graph, to explore the property of RSA algorithms.

De-multiplexing the required spectrum in a traffic demand into multiple non-adjacent granular spectrums for dynamic traffic grooming in EON

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 {b1, b2, … bn} 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.

Dynamic routing and spectrum assignment based on multilayer virtual topology and ant colony optimization in elastic software-defined optical networks

Elastic software-defined optical networks greatly improve the flexibility of the optical switching network while it has brought challenges to the routing and spectrum assignment (RSA). A multilayer virtual topology model is proposed to solve RSA problems. Two RSA algorithms based on the virtual topology are proposed, which are the ant colony optimization (ACO) algorithm of minimum consecutiveness loss and the ACO algorithm of maximum spectrum consecutiveness. Due to the computing power of the control layer in the software-defined network, the routing algorithm avoids the frequent link-state information between routers. Based on the effect of the spectrum consecutiveness loss on the pheromone in the ACO, the path and spectrum of the minimal impact on the network are selected for the service request. The proposed algorithms have been compared with other algorithms. The results show that the proposed algorithms can reduce the blocking rate by at least 5% and perform better in spectrum efficiency. Moreover, the proposed algorithms can effectively decrease spectrum fragmentation and enhance available spectrum consecutiveness.

Leveraging Game Theory to Achieve Efficient Attack-Aware Service Provisioning in EONs

Multidomain elastic optical networks (MD-EONs) help to improve network scalability, extend service coverage, and facilitate good interoperability to orchestrate administrative domains managed by different carriers. Since the users in other domains can launch cross-domain physical-layer attacks to a domain, this paper studies the problem of attack-aware service provisioning in one domain of an MD-EON. We consider a realistic scenario that does not treat all the interdomain lightpaths as malicious ones, and try to arrange the lightpaths' routing and spectrum assignment (RSA) schemes with the help of the game theory to balance the spectrum utilization and security-level of the domain well. Specifically, we define a two-player Bayesian game to represent the provisioning procedure for each interdomain request, and design the game strategies and utility functions for the players (i.e., the domain manager and the user from other domains). Then, we formulate a nonlinear programming model, solve the game with it to obtain a Bayesian Nash equilibrium (BNE), and determine the best strategies for the players based on the BNE. Finally, with the game model, we propose a game-assisted RSA algorithm to achieve attack-aware service provisioning efficiently. The proposed algorithm is evaluated with extensive simulations and the results confirm its effectiveness.

Static Routing and Spectrum Assignment for Deadline-Driven Bulk-Data Transfer in Elastic Optical Networks

Inter-datacenter services such as data replication and virtual machine migration contribute significantly to the underlying network traffic. These bulk-data transfer services can tolerate certain delay if the completion time is guaranteed with a pre-defined deadline. In this paper, we propose joint frequency- and time-domain optimization algorithms of static routing and spectrum assignment (RSA) for these deadline-driven bulk-data transfer requests in elastic optical networks. We formulate the problem as an integer linear program (ILP) and then propose six scheduling schemes, which combine three request ordering strategies with two RSA algorithms. Simulation results show that compared with ILP, our schemes can achieve the same performance in terms of spectrum utilization with efficient time complexity. Furthermore, based on the numerical results and computational efficiency, we provide a guideline on choosing scheduling schemes.

An efficient spectrum assignment algorithm based on variable-grouping mechanism for flex-grid optical networks

Flex-grid optical networks (FONs) employ dynamic routing and spectrum assignment (RSA) algorithms to support diverse services with heterogeneous bit-rates. Although these RSA algorithms can increase the flexibility and efficiency of spectrum allocation, they may also possibly induce spectrum fragments when allocating spectrum to accommodate different service requests. The generated spectrum fragments may exhaust the available spectrum resources and degrade networking performances. Therefore, many schemes referred as defragmentation algorithms have been proposed to reduce spectrum fragments at the cost of traffic disruption or extra components, which are usually required to handle the fragmented spectrum via resource re-optimization. Although some grouping RSA algorithms have been proposed to prevent the generation of spectrum fragments with no traffic disruption or extra components, the pre-divided fixed spectrum groups reduce the flexibility in a dynamic spectrum assignment and thus degrade the blocking performance of the network. In this paper, we propose a RSA algorithm based on variable-grouping mechanism, namely Minimized Variable Grouping (MVG) RSA algorithm, which can not only efficiently restrain the generation of spectrum fragments, but also improve the blocking performance compared to the typical ungrouped and the conventional grouping RSA algorithms. By employing variable grouping mechanism, the proposed algorithm sorts services into different kinds according to their bandwidth requirements and then divides the spectrum resources into several variable groups according to the kinds of services. And the generation of the spectrum fragments is restricted in the spectrum intervals between two adjacent groups. In this way, the proposed algorithm can dramatically restrain the generation of fragments. In addition, the proposed algorithm can reduce the blocking probability by minimizing the grouped spectrum resources to maximize the remained vacant spectrum resources in the spectrum intervals between two adjacent groups for future service requests and thus helps improve the blocking performance. The simulation results show that the proposed MVG RSA algorithm can dramatically reduce the fragments with no traffic disruption while exhibiting a low blocking probability.

Routing and Spectrum Assignment Algorithm with Most Fragmented Path First in Elastic Optical Networks

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.

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.

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.

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.

Spectral and Spatial 2D Fragmentation-Aware Routing and Spectrum Assignment Algorithms in Elastic Optical Networks [Invited

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 O(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 K-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.