Lightpath Requests Research Articles

Providing traffic tolerance in optical packet switching networks: a reinforcement learning approach

The servitization of network resources leads to new challenges for optical networks. For instance, to provide on-demand lightpaths as a service while keeping the probability of packet loss (PPL) low, issues such as lightpath setting up, resource reservation and load balancing must be addressed. We present a self-adaptive framework to process lightpath requests on packet switching optical networks that considers and handles the aforementioned issues. The framework is composed of a dimensioning phase that adds up new resources to an initial topology and a learning phase based on reinforcement learning that provides self-adaptation to tolerate traffic changes. The framework is tested on three realistic mesh topologies achieving a PPL between $$1 \times 10^{-1}$$ and $$1 \times 10^{-6}$$ for different traffic loads. Compared to fixed multi-path routing strategies, our framework reduces PPL between $$19\%$$ and up to $$80\%$$ . Furthermore, no packet loss can also be achieved for traffic loads equal to or lower than 0.4.

QoT-aware elastic bandwidth allocation and spare capacity assignment in flexible island-based optical transport networks under shared risk link group constraints

This paper focuses on the problem of provisioning multi-granularity static lightpath connections with fault-tolerant requirements in survivable island-based translucent optical networks with traffic grooming capabilities. The problem is tackled for the first time, to the best of our knowledge, taking into account both Quality of Transmission (QoT) and Shared Risk Link Group (SRLG) constraints. A two phase heuristic algorithm is proposed relying on a novel generic purpose-built auxiliary graph model that may support various factors of network heterogeneity (i.e., network nodes with different wavelength-conversion, regeneration and traffic grooming capabilities), and represent numerous network constraints related mainly to QoT requirements and network-resources. The purpose of the proposed heuristic is to optimize the utilisation of the available network resources and hence the network throughput through the simultaneous use of traffic grooming and two resource sharing techniques namely the Generalized Backup-Backup multiplexing (GBBM) and the Generalized Adaptive Primary-Backup Multiplexing (GAPBM) which are combined for the first time, as far as we know, under a static traffic scenario, and performed in such a way that 100% QoT-aware SRLG-fault recoverability is still guaranteed for all serviced lightpath requests. The performances of the proposed solution are demonstrated through multiple simulation experiments conducted on different network topologies.

Lightpath admission control and rerouting in dynamic flex‐grid optical transport networks

In dynamic flex‐grid optical transport networks, Lightpath Admission Control (LAC) is the task of finding a Routing and Spectrum Assignment (RSA) solution for a current lightpath request; otherwise, the request is blocked if there are not enough free available resources. When rerouting is supported, one or more currently established lightpaths can be rerouted and/or assigned with a different spectrum in order to accommodate the current lightpath request. We propose LAC methods based on mixed integer linear programming that provide a RSA solution for the current request aiming to maximize the acceptance probability of future lightpath requests. When rerouting is supported, we consider that only one currently established lightpath can be rerouted. We compare the proposed methods with the traditional shortest path‐based approach through simulation. Without lightpath rerouting, the blocking probability is significantly improved. With lightpath rerouting, the number of rerouting operations is significantly decreased while the blocking probability is marginally improved. Moreover, the blocking fairness between lightpaths with different spectrum widths is improved both with and without lightpath rerouting. In all cases, the CPU times of the mixed integer linear programming approaches are a few seconds, on average. © 2016 Wiley Periodicals, Inc. NETWORKS, Vol. 69(1), 151–163 2017

Lightpath blocking analysis for optical networks with ROADM intra-node add-drop contention

The contention factor limits the extent to which lightpaths using the same wavelength can be added/dropped in a Reconfigurable Optical Add/Drop Multiplexer (ROADM) when it is operated in a colorless and directionless fashion. This paper presents an analysis to estimate the probability of blocked lightpath requests when a node of this type is used and validates the results for three traffic models. Simulations confirm the validity of the analytical results for lightpath blocking both for various values of the add/drop contention factor C and for changing load distribution in the network. We observe a saturation trend in the lightpath blocking performance as the add/drop port count per bank increases and that a high enough value of C reduces lightpath blocking to levels obtainable from an ideal, comntentionless ROADM. When C is small, limitations on the add/drop port count per bank is observed to be the dominant cause of blocking lightpaths while intra-node contention effects have only a limited impact. With increasing C, blocking is caused more because sufficient link capacity is not available and not because free add/drop ports are not available

Lightpath Admission Control in Dynamic Optical Transport Networks

In dynamic optical transport networks, the Lightpath Admission Control (LAC) is the task that finds a Routing and Wavelength Assignment (RWA) solution for the current lightpath request or blocks it when there are not enough free available resources. We propose a LAC method, based on integer linear programming, that decides the RWA solution for the current request aiming to maximize the acceptance probability of the future lightpath requests. We compare the method with traditional shortest path based approaches. We show that the blocking probability is significantly improved with LAC decision times of a few seconds, on average.

Dispersion-Adaptive First–Last Fit Spectrum Allocation Scheme for Elastic Optical Networks

The quality-of-transmission (QoT) degradation due to the dispersion effect in longer lightpaths is higher than that of shorter lightpaths in a dispersion uncompensated network. To overcome this shortcoming, this letter proposes a dispersion-adaptive first–last fit spectrum allocation scheme for elastic optical networks to decrease the call blocking in the network. The proposed scheme assigns longer lightpath requests from the smallest indexed spectrum slot, where the dispersion effect is less, and shorter lightpath requests from the largest indexed spectrum slot, where the dispersion effect is more. As a result, a less robust modulation technique is used to maintain the QoT threshold level for the longer lightpath requests, and hence a lower number of spectrum slots are required for lightpath establishment. Simulation results show that the proposed scheme outperforms the conventional scheme in terms of blocking probability and contiguous aligned available slot ratio.

Protection lightpath-based hitless spectrum defragmentation for distance adaptive elastic optical networks.

Spectrum defragmentation can improve spectrum utilization for an elastic optical network (EON). However, most of the existing studies have focused on defragmentation for working lightpaths, which may affect upper-layer network services. This paper considers protection lightpath-based hitless spectrum defragmentation for distance adaptive elastic optical networks. Without affecting working lightpaths, but defragmenting spectra for protection lightpaths, we expect to achieve truly hitless spectrum defragmentation for an EON. Shared backup path protection (SBPP) technique is employed as a representative network protection technique to evaluate the benefit of the proposed defragmentation scheme. To smooth the network spectra for future arriving lightpath requests so as to reduce bandwidth blocking probability (BBP), we propose two defragmentation triggering mechanisms, namely, defragmentation upon blocking (BTD) and batch defragmentation (BD). For each of them, we also propose two spectrum defragmentation algorithms, namely, defragmentation with sequentially releasing and re-establishing protection lightpaths (SR-D) and defragmentation with jointly releasing and re-establishing protection lightpaths (JR-D). The performances of these proposed algorithms are evaluated from perspectives of BBP and average number of reconfigurations per successfully established lightpath service (ANR). Simulation results show that compared to the case without defragmentation, the proposed scheme is effective to reduce BBP, which trades off with ANR.

A biased random-key genetic algorithm to maximize the number of accepted lightpaths in WDM optical networks

Given a set of lightpath requests, the problem of routing and wavelength (RWA) assignment in wavelength division multiplexing (WDM) optical networks consists in routing a subset of these requests and assigning a wavelength to each of them, such that two lightpaths that share a common link are assigned to different wavelengths. There are many variants of this problem in the literature. We focus in the variant in which the objective is to maximize the number of requests that may be accepted, given a limited set of available wavelengths. This problem is called max-RWA and it is of practical and theoretical interest, because algorithms for this variant can be extended for other RWA problems that arise from the design of WDM optical networks. A number of exact algorithms based on integer programming formulations have been proposed in the literature to solve max-RWA, as well as algorithms to provide upper bounds to the optimal solution value. However, the algorithms based on the state-of-the-art formulations in the literature cannot solve the largest instances to optimality. For these instances, only upper bounds to the value of the optimal solutions are known. The literature on heuristics for max-RWA is short and focus mainly on solving small size instances with up to 27 nodes. In this paper, we propose new greedy constructive heuristics and a biased random-key genetic algorithm, based on the best of the proposed greedy heuristics. Computational experiments showed that the new heuristic outperforms the best ones in literature. Furthermore, for the largest instances in the literature where only upper bounds to the value of the optimal solutions are known, the average optimality gap of the best of the proposed heuristics is smaller than 4 %.

GMPLS Control Plane With Distributed Multipath RMSA for Elastic Optical Networks

Elastic optical networking (EON) has the constraint that all flows must have contiguous allocated frequency slots across all fiber links end-to-end, hence, the routing, modulation and spectrum assignment (RMSA) is one of the most important considerations in EON. This paper proposes and demonstrates a design of a generalized multiprotocol label switching (GMPLS) control plane for EON with distributed RMSA. The proposed approach uses an extended RSVP-TE to find multipath by broadcasting PATH message, using tentative reservation to avoid setting up multipath for one request. The proposed method also overcomes challenges faced by the previously pursued GMPLS-EON methods which relied on dynamic OSPF-TE where control plane overhead and the collision among lightpath requests caused by signaling latency. Simulation results based on the proposed GMPLS-EON method on different network scenarios reveal that our proposed design reduces the blocking probability by 4.56 and 3.86 when compared with the conventional GMPLS and GMPLS/PCE approaches, respectively, in the NSF topology at the network offered load of 60 Erlang. It also reduces signaling time by a factor of 1.84 compared with conventional GMPLS/PCE approach in the same network condition.

Design based routing and wavelength assignment in WDM networks using link-based multiplexing gain

Design based routing (DBR) is originally proposed for wavelength division multiplexing (WDM) networks with the objective to minimize the total link cost subject to the constraints based on traffic demands in terms of the maximum acceptable end-to-end blocking probability. In DBR, optimized routing is computed off-line based on prior information on traffic demand statistics, and are utilized for on-line routing of dynamic lightpath requests. However, the integer linear programming (ILP) formulation of DBR allocates, on each link, dedicated portions of the link capacity to utilizing source–destination (s–d) pairs without considering the effects of statistical multiplexing. The lack of consideration of the multiplexing gain on transmission links leads to an unnecessary limitation on the applicability of DBR in networks with high traffic loads from a large number of s–d pairs. In such traffic scenarios, the ILP problem of DBR can become infeasible even though the traffic can still be supported without violating the blocking probability constraint. In this paper, we provide an alternative approach to DBR, referred to as link-based DBR (LDBR), by considering the multiplexing gain on each link. Unlike the ILP formulation for DBR, which imposes constraints on end-to-end blocking probabilities, the blocking probability constraints for LDBR are imposed on individual links with the end-to-end blocking probabilities estimated using the union bound. Compared to DBR, LDBR is attractive when individual links carry traffic from a large number of s–d pairs since there are a lot of opportunities for utilizing the multiplexing gain. Simulation results demonstrate that, subject to the same end-to-end blocking probability constraints, the proposed LDBR can extend the applicability of DBR to higher traffic loads when there are a lot of active s–d pairs, which are expected in typical backbone networks.

A Wavelength and Converter Assignment Scheme using Converter Usage History in Wavelength-Routed Networks

In wavelength-routed networks, wavelength conversion improves lightpath blocking probability by eliminating the wavelength-continuity constraint. Because wavelength converters remain expensive in the near future, we need a wavelength and converter assignment scheme that decreases blocking probability with a limited number of converters. In this paper, we propose a wavelength and converter assignment scheme for decreasing blocking probability. Our scheme avoids contention among multiple lightpath requests by making each node-pair to perform wavelength conversion at different intermediate nodes with more idle converters. Simulation results show that 1) our scheme decreases blocking probability by about between 44% and 83% and 2) our scheme needs one or two fewer wavelength converters per node to achieve near-optimal blocking probability compared with conventional schemes.

Design Based Routing with Waveband and Wavelength Assignment in Wavelength Division Multiplexing Networks using Multi-Granular Optical Cross-Connects

In this paper, we extend design based routing (DBR), which is originally proposed for opaque wavelength division mul- tiplexing (WDM) networks without waveband switching (WBS), to transparent WDM networks with WBS. We formulate and solve the corresponding integer linear programming (ILP) prob- lems to facilitate the use of DBR for transparent WDM networks with WBS, referred to as DBR with Waveband and Wavelength Assignment (DBRWWA). The goal of DBRWWA is to minimize the total link cost subject to the constraints on traffic demands and on network resources. DBRWWA guides online routing of dynamic lightpath requests in WDM networks with WBS, where traffic engineered routes are computed offline based on the prior information on traffic demand statistics. We investigate two novel heuristics, called the maximum waveband-wavelength first (MaxWWF) algorithm and the minimum waveband-wavelength first (MinWWF) algorithm, as well as existing first-fit and random-fit algorithms. The proposed heuristics consider all properties of WBS, including waveband and wavelength con- tinuity constraints. We consider end-to-end WBS (ETE-WBS) for lightpath grouping. The online heuristics are combined with shortest path first (SPF) routing, DBR, and DBRWWA to support dynamic traffic. Simulation results show that DBRWWA has on average lower blocking probability compared to DBR, while both DBRWWA and DBR greatly outperform SPF routing in terms of the blocking probability.

Energy-Efficient Translucent Optical Transport Networks With Mixed Regenerator Placement

Translucent networks utilize sparse placements of optical-electronic-optical (O/E/O) 3R (reamplification, reshaping, and retiming) regenerators to improve the cost effectiveness and energy efficiency of wavelength-routed optical transport networks. In this paper, we show that the energy cost of a translucent network can be further reduced by leveraging the energy efficiency of all-optical 2R (reamplification and reshaping) regenerators. We propose a translucent network infrastructure that uses all-optical 2R regenerators to partially replace O/E/O 3R regenerators and implements mixed regenerator placements (MRP). We first consider the problem of MRP along a single given path, and propose three path-based impairment-aware MRP algorithms, based on periodic placement, genetic algorithm (GA), and ant colony optimization (ACO). We then address the offline network planning problem and develop a heuristic algorithm. By incorporating with one of the proposed MRP algorithms, the heuristic can achieve joint optimization of MRP and routing and wavelength assignment for high energy efficiency. We design simulations to compare the performance of different offline network planning scenarios and to see which one can provide the best balance between quality of transmission and energy cost. Simulation results show that the algorithm achieves 58.91-73.62% saving on regeneration energy, compared to the traditional scheme without all-optical 2R regenerators. The results also indicate that the joint optimization using the MRP-GA obtains the best network planning in terms of energy efficiency. Finally, we address the problem of online provisioning, and propose several algorithms to serve dynamic lightpath requests in translucent networks with MRP, and implement them in simulations to compare their performance in terms of blocking probability. Simulation results indicate that the online provisioning algorithm that utilizes the combination of the MRP-GA and a multiple MRP scheme achieves the lowest blocking probability.

A wavelength assignment algorithm for de Bruijn WDM networks

This paper proposes an offline wavelength assignment technique for de Bruijn (d, k) optical wavelength division multiplexing (WDM) networks having nodal degree d and diameter k that can support lightpaths between pair of nodes. Each lightpath uses a channel (wavelength) along each link in its route. An efficient algorithm is proposed that can be used to assign wavelengths to lightpath requests in O(k|V|) time, where |V| represents the number of nodes of the de Bruijn network and V represents the set of nodes. The proposed algorithm can be efficiently used for wavelength assignment in de Bruijn WDM networks having limited wavelength conversion capabilities. This work shows that de Bruijn graph can be expressed as union of edge-disjoint rings. Wavelengths are assigned for the individual rings in the graph thus resulting in the assignment for the graph itself. Results are shown for a given de Bruijn graph and for an arbitrary request. The proposed algorithm is compared with two other algorithms, which use two other known works of wavelength assignment on ring topology. Comparisons of the time complexity and the type of wavelength conversion required for these algorithms clearly show that the proposed algorithm is a faster and more efficient way of assigning wavelengths.

Variable neighborhood descent with iterated local search for routing and wavelength assignment

In this work we treat the Routing and Wavelength Assignment (RWA) with focus on minimizing the number of wavelengths to route demand requests. Lightpaths are used to carry the traffic optically between origin-destination pairs. The RWA is subjected to wavelength continuity constraints, and a particular wavelength cannot be assigned to two different lightpaths sharing a common physical link. We develop a Variable Neighborhood Descent (VND) with Iterated Local Search (ILS) for the problem. In a VND phase we try to rearrange requests between subgraphs associated to subsets of a partition of the set of lightpath requests. In a feasible solution, lightpaths belonging to a subset can be routed with the same wavelength. Thus, the purpose is to eliminate one subset of the partition. When VND fails, we perform a ILS phase to disturb the requests distribution among the subsets of the partition. An iteration of the algorithm alternates between a VND phase and a ILS phase. We report computational experiments that show VND-ILS was able to improve results upon powerful methods proposed in the literature.

Flow Scheduling in Optical Flow Switched (OFS) Networks Under Transient Conditions

Optical flow switching (OFS) has been recently introduced as a potential “green” architecture addressing the power issue of store-and-forward packet switching in future MAN-WAN Terabit networks. One key architectural component of OFS differentiating it from other “green” WAN architectures such as optical circuit switching (OCS), optical packet switching (OPS) and optical burst switching (OBS), is its centralized flow scheduling. Comparing the theoretical network capacity regions of OFS, OCS, OPS and OBS has revealed that the dominating theoretical capacity depends on the hardware as well as on the port configuration. The dominating actual capacity (throughput) that can be achieved also depends on the flow schedulers supported by each architecture. Since centralized scheduling incorporated in OFS is the least restricting between all scheduling methods, OFS is a promising “green” architecture option for future MAN-WAN Terabit networks. For better understanding the actual potential throughput of OFS, we study its scheduling problem in a realistic traffic model where lightpath requests arrive as a time-dependent Poisson process with Pareto distributed lightpath service times. Lightpath schedules are taken at fixed time intervals (larger than 100 ms) in a central node and flows that have already been scheduled cannot be interrupted before their completion. The scheduling problem is represented as a discrete-time Markov decision process where the objective function is given by the flow blocking probability over a finite time horizon. We derive three lower bounds to the objective function and propose several schedulers, with and without fairness requirements. The performance of our OFS schedulers are evaluated under both static and limited dynamic routing, by emulating the algorithms on random network topologies for two hours. The main result is that our proposed max-min fair scheduler with limited dynamic routing significantly outperforms all other schedulers with static routing. Furthermore, its blocking probability is close to the lower bound for static routing.

Hardware Accelerated Impairment-Aware Control Plane for Future Optical Networks

In this letter, a hardware accelerated GMPLS based and impairment-aware control plane suitable for optical networks with concurrent lightpath requests support is proposed and evaluated. It outperforms the software version by 80 times in the order of sub-seconds. The high acceleration rate, simultaneous requests support, scalability and low computation time variance are the key features of this tool.

Performance Analysis of a Bi-Objective Model for Routing and Wavelength Assignment in WDM Networks

Establishing end-to-end connections on wavelength division multiplexing (WDM) networks requires setting up lightpaths, defining the sequence of optical fibres and the wavelength in each fibre (the routing and wavelength assignment problem) for traffic flow. This paper reviews a bicriteria model for obtaining a topological path (unidirectional or symmetric bidirectional) for each lightpath request in a WDM network, developed by the authors, and presents a performance analysis of the model by considering important network performance measures. An extensive performance analysis of the two bicriteria model is presented, comparing the performance metrics obtained with the monocriterion models using the same objective functions, in five different reference networks commonly used in literature.

Performance Analysis of a Bi-Objective Model for Routing and Wavelength Assignment in WDM Networks

Establishing end-to-end connections on wavelength division multiplexing (WDM) networks requires setting up lightpaths, defining the sequence of optical fibres and the wavelength in each fibre (the routing and wavelength assignmentproblem) for traffic flow. This paper reviews a bicriteria model for obtaining a topological path (unidirectional or symmetric bidirectional) for each lightpath request in a WDM network, developed by the authors, and presents a performance analysis of the model by considering important network performance measures. An extensive performance analysis of the two bicriteria model is presented, comparing the performance metrics obtained with the monocriterion models using the same objective functions, in five different reference networks commonly used in literature.

Performance Analysis of a Bi-Objective Model for Routing with Protection in WDM Networks

The operation of wavelength division multiplexing (WDM) networks involves not only the establishment of lightpaths, defining the sequence of optical fibres and thewavelength in each fibre for traffic flow, but also a fault management scheme in order to avoid the huge loss of data that can result from a single link failure. Dedicated path protection, which establishes two end-to-end disjoint routes between the source–destination node pair, is an effective scheme to preserve customers’ connections. This paper reviews a bicriteria model for dedicated path protection, that obtains a topological path pair of node-disjoint routes for each lightpath request in a WDM network, developed by the authors. An extensive performance analysis of the bicriteria model is then presented, comparing the performance metrics obtained with the monocriterion models using the same objective functions, in four different reference networks commonly used in literature.