Routing And Wavelength Assignment Research Articles

Routing and wavelength assignment in optical networks using Artificial Bee Colony algorithm

This paper presents an intelligent approach for modelling Routing and wavelength assignment (RWA) problem in wavelength-routed Dense-Wavelength-Division-Multiplexing (DWDM) optical networks. A new idea based on Artificial Bee Colony (ABC) algorithm is introduced for solving RWA problem which is known to be an NP-hard problem. In the proposed ABC-RWA approach every food source represents a possible and feasible candidate lightpath between each original and destination node pair in demand matrix. The positions of food sources are modified by some artificial bees in the population where the aim is to discover the places of food sources. The food source with the highest nectar value seems to be a solution which is evaluated by the fitness function. The proposed approach is evaluated for both path length (propagation delay) and hops count optimization schemes for PAN EUROPEAN and NSFNET test bench optical networks. The performance of ABC based approach is compared with the Genetic Algorithm (GA) model for solving RWA problem under random and heavy load traffic models. Simulation results demonstrate the ability and efficiency of proposed ABC model for solving RWA in real-world optical networks. Furthermore a comparison study approves that ABC is faster than GA to hit RWA global optimization solutions due to less complexity and computational processing.

Resource efficient network design and traffic grooming strategy with guaranteed survivability

In WDM networks, path protection has emerged as a widely accepted technique for providing guaranteed survivability of network traffic. However, it requires allocating resources for backup lightpaths, which remain idle under normal fault-free conditions. In this paper, we introduce a new design strategy for survivable network design, which guarantees survivability of all ongoing connections that requires significantly fewer network resources than protection based techniques. In survivable routing, the goal is to find a Route and Wavelength Assignment (RWA) such that the logical topology remains connected for all single link failures. However, even if the logical topology remains connected after any single link fault, it may not have sufficient capacity to support all the requests for data communication, for all single fault scenarios. To address this deficiency, we have proposed two independent but related problem formulations. To handle our first formulation, we have presented an Integer Linear Program (ILP) that augments the concept of survivable routing by allowing rerouting of sub-wavelength traffic carried on each lightpath and finding an RWA that maximizes the amount of traffic that can be supported by the network in the presence of any single link failure. To handle our second formulation, we have proposed a new design approach that integrates the topology design and the RWA in such a way that the resulting logical topology is able to handle the entire set of traffic requests after any single link failure. For the second problem, we have first presented an ILP formulation for optimally designing a survivable logical topology, and then proposed a heuristic for larger networks. Experimental results demonstrate that this new approach is able to provide guaranteed bandwidth, and is much more efficient in terms of resource utilization, compared to both dedicated and shared path protection schemes.

Power-efficient RWA in dynamic WDM optical networks considering different connection holding times

The challenges imposed by environmental issues, such as global warming and the energy crisis, are demanding more responsible energy usage, including in the optical networking field. In optical transmission networks, most of the electrical power is consumed by the optical-electrical-optical conversion in optical repeaters. Modern optical network control plane technologies allow idle optical repeaters to be put into a low-power sleep mode. Inspired by this, we propose a novel power-efficient routing and wavelength assignment (RWA) algorithm, called HTAPE. The HTAPE algorithm exploits the knowledge of the connection holding times to minimize the number of optical repeaters in the active mode, and hence reduce the total electricity consumption of the optical network. We test the new algorithm on the typical CERNET and USNET networks. Compared with traditional RWA algorithms without holding-time-awareness, it is observed that the HTAPE algorithm yields significant reductions in power consumption.

Statistical Approach for Fast Impairment-Aware Provisioning in Dynamic All-Optical Networks

Physical layer impairments (PLIs) need to be considered in the routing and wavelength assignment (RWA) process of all-optical networks to ensure the provisioning of good quality optical connections (i.e., lightpaths). A convenient way to model the impact of PLIs on the signal quality is to use the so-called Q-factor. In a dynamic provisioning environment, impairment-aware RWA (IA-RWA) algorithms include Q-factor evaluation in their on-line decisions on whether to accept a connection request or not. The Q-factor can be computed in either an approximated or an exact way. IA-RWA algorithms using an approximated Q-factor estimation (i.e., worst case) can be very fast and allow for a short setup delay. However, connection request blocking can be unnecessarily high because of the worst-case assumption for the Q-factor parameters. In contrast, an exact Q-factor computation results in a better blocking performance at the expense of a longer setup delay, mainly due to the time spent for the Q-factor computation itself. Moreover, an exact Q-factor approach requires extensions of the generalized multi-protocol label switching suite. To overcome these problems, we propose a statistical approach for fast impairment-aware RWA (SAFIR) computation. The evaluation results reveal that SAFIR improves the blocking probability performance compared to the worst-case scenario without adding extra computational complexity and, consequently, without increasing the connection setup delay.

Review of Dynamic Impairment-Aware Routing and Wavelength Assignment Techniques in All-Optical Wavelength-Routed Networks

Since light-paths are the basic connections in wavelength routed networks, their effective establishment is very important. Routing and Wavelength Assignment (RWA) techniques can be divided into two categories. The first category (pure RWA) concentrates on setting up light-paths under the assumption of an ideal physical layer. However, this assumption could be suitable for opaque networks, where a signal is regenerated at each optical switch along its path. On the other hand, as an optical signal propagates along a light-path to its destination in a transparent (all-optical) network, the signal's quality degrades because there is no signal regeneration, thus increasing Bit-Error-Rate (BER) of the signal. However, users would not accept a light-path with a high BER. Even it is not acceptable if the establishment of a light-path causes the BER of other existing light-paths to become unacceptably high. Therefore, considering physical layer impairments, the quality of a light-path must be checked during the light-path setup in the second category. In this article, the operations of dynamic RWA techniques proposed in transparent networks for the second category are reviewed in detail. These techniques are called Quality of Transmission Aware (QoT-aware) RWA and are grouped in two groups: integrated QoT and RWA, and QoT after Pure RWA. Each group can be further divided into direct modelling and indirect modelling sub-groups. A comprehensive discussion is also provided to compare dynamic QoT-aware RWA techniques based on different network and physical layer parameters.

A Linearized Statistical XPM Model for Accurate Q-factor Computation

Non-linear physical layer impairments make the mathematical programming formulation of off-line impairment-aware (IA) Routing and Wavelength Assignment (RWA) problem to be non-linear. To alleviate that, this paper presents for the first time a statistical linear model to compute the Cross Phase Modulation (XPM) noise variance. Exhaustive evaluation reveals that the proposed linear model provides an accurate Q-factor estimation. An example of Integer Linear Programming (ILP) formulation integrating the XPM model is also given.

A heuristic algorithm for lightpath scheduling in next-generation WDM optical networks

We study the routing and wavelength assignment (RWA) problem of scheduled lightpath demands (SLDs) in all-optical wavelength division multiplexing networks with no wavelength conversion capability. We consider the deterministic lightpath scheduling problem in which the whole set of lightpath demands is completely known in advance. The objective is to maximize the number of established lightpaths for a given number of wavelengths. Since this problem has been shown to be NP complete, various heuristic algorithms have been developed to solve it suboptimally. In this paper, we propose a novel heuristic RWA algorithm for SLDs based on the bee colony optimization (BCO) metaheuristic. BCO is a newborn swarm intelligence metaheuristic approach recently proposed to solve complex combinatorial optimization problems. We compare the efficiency of the proposed algorithm with three simple greedy algorithms for the same problem. Numerical results obtained by numerous simulations performed on the widely used realistic European Optical Network topology indicate that the proposed algorithm produces better-quality solutions compared to those obtained by greedy algorithms. In addition, we compare the results of the BCO---RWA---SLD algorithm with four other heuristic/metaheuristic algorithms proposed in literature to solve the RWA problem in the case of permanent (static) traffic demands.

Prediction-based routing as RWA in multilayer traffic engineering

Multilayer traffic engineering (MLTE) allows coping with ever-increasing and varying traffic demands in IP-over-Optical multilayer networks. It utilizes cross-layer TE (Traffic Engineering) techniques to provision optical lightpath capacity to the IP/MPLS (Internet Protocol/ Multi-Protocol Label Switching) logical topology on-demand. Such provisioning however causes optical connection arrival rates that pose strong performance requirements to Routing and Wavelength Assignment (RWA) strategies. Collecting up-to-date network information for the RWA with rapidly changing network states can be quite difficult. Exposing optical layer state information to the IP layer in the overlay model, or transforming this optical layer information in a workable representation in an integrated control plane is similarly problematic. Prediction-Based Routing (PBR) has been proposed as a RWA mechanism for optical transport networks; it bases routing not on possibly inaccurate or outdated network state, but instead on previous connections set-up. In this article, we propose to implement PBR as the RWA mechanism in the optical layer of a multilayer network, and use the predictive capabilities of PBR to expose dynamic optical network information into the multilayer traffic engineering algorithm with minimal control plane overhead. Some simulations show the benefits of using the PBR in the optical layer for MLTE purposes.

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.

LC-DLA: A fair congestion-aware Distributed Lightpath Allocation mechanism

One of the main challenges in all-optical WDM networks is the problem of Routing and Wavelength Assignment (RWA). In large-scale networks with heavy traffic load, distributed RWA is more suitable than centralized RWA. One of the distributed algorithms proposed recently is Distributed Lightpath Allocation (DLA) [1]. We use the DLA as our basic algorithm to design a new congestion-aware RWA algorithm, called Least-Congested Distributed Lightpath Allocation (LC-DLA). We consider congestion in the network as a decision point for solving RWA. Selection of the least congested path among available paths from source to destination can improve the blocking probability of the network. Fairness is one of the crucial metrics that network designers should consider. We define a new concept for fairness in RWA. Our performance evaluations show that LC-DLA can provide good blocking and fairness performances in WDM networks.

The effect of Stimulated Raman Scattering (SRS) in Routing and Wavelength Assignment (RWA) in WDM mesh and ring topologies

In this paper, the impact of Stimulated Raman Scattering (SRS) in Routing and Wavelength Assignment (RWA) is performance analyzed in three different setting in the number of hops in routes using fixed shortest path routing in 8-nodes mesh and 8-nodes ring topologies. Performance result shows the impact of SRS is more apparent in 8-nodes ring topology compared to 8-nodes mesh topology when the number of optical channel is 32 for all the setting of the number of hops in routes. Whereas when the number of channels is 16, the impact of SRS is not much different in both topologies. Furthermore, the impact of SRS is more apparent in 4-hops setting compared to 2-hops and 3-hops setting used in the routes. It suggests that in order to support more traffic request by higher optical channel, the acceptable connection due to SRS depletion to be established depends on the number of hops used in routing scheme indirectly depends on different network topology.

Selfish routing and wavelength assignment strategies with advance reservation in inter-domain optical networks

The main challenge in developing large data network in the wide area is in dealing with the scalability of the underlying routing system. Accordingly, in this work we focus on the design of an effective and scalable routing and wavelength assignment (RWA) framework supporting advance reservation services in wavelength-routed WDM networks crossing multiple administrative domains. Our approach is motivated by the observation that traffic in large optical networks spanning several domains is not controlled by a central authority but rather by a large number of independent entities interacting in a distributed manner and aiming at maximizing their own welfare. Due to the selfish strategic behavior of the involved entities, non-cooperative game theory plays an important role in driving our approach. Here the dominant solution concept is the notion of Nash equilibria, which are states of a system in which no participant can gain by deviating unilaterally its strategy. On this concept, we developed a selfish adaptive RWA model supporting advance reservation in large-scale optical wavelength-routed networks and developed a distributed algorithm to compute approximate equilibria in computationally feasible times. We showed how and under which conditions such approach can give rise to a stable state with satisfactory solutions and analyzed its performance and convergence features.

Optimal regenerator assignment and resource allocation strategies for translucent optical networks

Physical layer impairments in wavelength-routed networks limit the maximum distance, a signal can travel in the optical domain, without significant distortion. Therefore, signal regeneration is required at some intermediate nodes for long-haul lightpaths. In translucent WDM networks, sparsely located regenerators at certain nodes can be used to offset the impact of physical layer impairments. The routing and wavelength assignment (RWA) techniques in such translucent networks need to take into consideration the availability of regenerators and the maximum optical reach of the transparent lightpaths (without any regeneration). Although there has been significant research interest in RWA algorithms for translucent networks, much of the research has focused on dynamic RWA techniques. Only a handful of recent papers have considered the static (offline) case, and they typically propose heuristic algorithms to solve this complex design problem for practical networks. In this paper, we propose a generalized integer linear program (ILP) based formulation for static regenerator assignment and RWA in translucent WDM optical networks, with sparse regenerator placement. To the best of our knowledge, such a formulation that optimally allocates resources for a set of lightpaths for translucent networks, given the physical network, the locations of the regenerators, and the maximum optical reach has not been considered before. The proposed formulation is important for two reasons. First, it can serve as a benchmark for evaluating different heuristic approaches that may be developedin the future. Second, we show that using a novel node representation technique, it is possible to drastically reduce the number of integer variables. This means that unlike existing ILP formulations, our approach can actually be used to generate optimal solutions for practical networks, with hundreds of lightpath demands.

Variable neighbourhood search for resolving routing and wavelength assignment problem in optical wavelength-division multiplexing networks

The issue of finding optimal signal routes is one of the main challenges within the framework of optimal networks. This study aims at illustrating the development of a new, mixed-integer mathematical model for solving the static routing and wavelength assignment (RWA) problem in optical wavelength-division multiplexing (WDM) networks and presents the comparison of results obtained by heuristics and CPLEX commercial software. The objective function of the mathematical model is to minimise the blocking probability by maximising the number of successfully connected lightpaths. In this paper two WDM networks with full wavelength conversion nodes were tested. The proposed heuristics are the variable neighbourhood search (VNS) and tabu search (TS). Firstly, the authors compare the results obtained by these two heuristics and CPLEX on a low-complexity WDM network, aiming to determine whether these heuristics may yield results which approximate optimal results. Secondly, having illustrated that the heuristics provide satisfactory results, the authors run these heuristics on a high-complexity WDM network. The results indicate minor differences in blocking probability and show that in majority cases, VNS spends ten times less CPU time as opposed to TS. In conclusion, the authors argue that VNS heuristic is appropriate for resolving this static RWA problem.

A new model for allocating resources to scheduled lightpath demands

Recent research has clearly established that holding-time-aware routing-and-wavelength-assignment (RWA) schemes lead to significant improvements in resource utilization for scheduled traffic. Two different models have been proposed for scheduled traffic in the literature – (i) the fixed window model, where the setup and the teardown times of the scheduled demands are known in advance and (ii) the sliding window model, where a demand can be allocated anytime within a larger time-window. In this paper, we introduce a new model, the segmented sliding window model, where a demand may be decomposed into two or more components and each component can be sent separately. We present an integer linear program (ILP) formulation for resource allocation under the proposed segmented sliding window model and show that both the fixed and the traditional sliding window models can be treated as a special case of our generalized segmented sliding window model. We consider networks both with and without wavelength converters, and include the option of path protection for each lightpath. For larger networks, we also present a heuristic algorithm for allocating resources. Finally, we show through simulations that our approach leads to significantly higher throughput, even compared to the recent holding-time-aware RWA schemes, which have already been shown to outperform holding-time-unaware models.

DWDM 기반 차세대 광 인터넷 망에서 VS기반의 차등화된 멀티캐스트 라우팅 및 파장할당 알고리즘 연구

지난 수 십 년간 통신 기술의 발전과 웹 서비스의 팽창은 인터넷 사용자 수의 폭발적인 증가와 화상회의, 가상 증감 현실, 인터넷 게임 등 실시간 멀티미디어 멀티캐스트 서비스의 급격한 증가를 초래했다. 고밀도 파장분할다중화기술에 기반한 DWDM(Dense-Wavelength Division Multiplexing) 기술은 인터넷 사용자의 증가와 그에 따른 대역폭 요구를 수용하기 위한 방안으로 국가나 글로벌 영역 범위의 차세대 인터넷망 구현을 위한 백본망 기술로 여겨지며, 이러한 DWDM 전달망에서는 멀티캐스트 연결 요구에 대해 최적의 경로를 선택하고 선택된 경로에 효율적으로 파장을 할당하는 멀티캐스트 RWA(Routing and Wavelength Assignment) 문제가 파장 대역폭의 효율적인 활용 측면에서 매우 중요하게 다루어지고 있다. 주어진 파장 수 환경에서 최대한 많은 수의 멀티캐스트 연결을 달성하는 문제는 일반적으로 Non -deterministic Polynomial-time-complete 문제로 여겨지는 데, 본 논문에서는 가상소스를 기반으로 노드의 능력에 따른 차등화로 우선 순위를 적용하여 휴리스틱하게 멀티캐스트 라우팅 경로를 효율적으로 선정하는 DVS-PMIPMR (Differentiated Virtual Source-based Priority Minimum Interference Path Multicast Routing) 알고리즘을 제안한다. 마지막으로 같은 조건에서 더 많은 수의 멀티캐스트 라우팅 패스의 연결이 가능함을 시뮬레이션 및 성능분석 증명한다. Over the past decade, the improvement of communications technologies and the rapid spread of www (World Wide Web) have brought on the exponential growth of users using Internet and real time multimedia multicast services like video conferencing, tele-immersive virtual reality, and Internet games. The dense-wavelength division multiplexing (DWDM) networks have been widely accepted as a promising approach to meet the ever-increasing bandwidth demands of Internet users, especially in next generation Internet backbone networks for nation-wide or global coverage. A major challenge in the next generation Internet backbone networks based on DWDM technologies is the resolution of the multicasting RWA (Routing and Wavelength Assignment) problem; given a set of wavelengths in the DWDM network, we set up light-paths by routing and assigning a wavelength for each connection so that the multicast connections are set-upped as many as possible. Finding such optimal multicast connections has been proven to be Non-deterministic Polynomial-time-complete. In this paper, we suggest a new heuristic multicast routing and wavelength assignment method for multicast sessions called DVS-PMIPMR (Differentiated Virtual Source-based Priority Minimum Interference Path Multicast Routing algorithm). We measured the performance of the proposed algorithm in terms of number of wavelength and wavelength channel. The simulation results demonstrate that DVS-PMIPMR algorithm is superior to previous multicast routing algorithms.

Elastic Bandwidth Allocation in Flexible OFDM-Based Optical Networks

Orthogonal Frequency Division Multiplexing (OFDM) has recently been proposed as a modulation technique for optical networks, because of its good spectral efficiency, flexibility, and tolerance to impairments. We consider the planning problem of an OFDM optical network, where we are given a traffic matrix that includes the requested transmission rates of the connections to be served. Connections are provisioned for their requested rate by elastically allocating spectrum using a variable number of OFDM subcarriers and choosing an appropriate modulation level, taking into account the transmission distance. We introduce the Routing, Modulation Level and Spectrum Allocation (RMLSA) problem, as opposed to the typical Routing and Wavelength Assignment (RWA) problem of traditional WDM networks, prove that is also NP-complete and present various algorithms to solve it. We start by presenting an optimal ILP RMLSA algorithm that minimizes the spectrum used to serve the traffic matrix, and also present a decomposition method that breaks RMLSA into its two substituent subproblems, namely 1) routing and modulation level and 2) spectrum allocation <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({\rm RML}+{\rm SA})$</tex></formula> , and solves them sequentially. We also propose a heuristic algorithm that serves connections one-by-one and use it to solve the planning problem by sequentially serving all the connections in the traffic matrix. In the sequential algorithm, we investigate two policies for defining the order in which connections are considered. We also use a simulated annealing meta-heuristic to obtain even better orderings. We examine the performance of the proposed algorithms through simulation experiments and evaluate the spectrum utilization benefits that can be obtained by utilizing OFDM elastic bandwidth allocation, when compared to a traditional WDM network.

Offline Impairment-Aware RWA and Regenerator Placement in Translucent Optical Networks

In translucent optical networks, the physical layer impairments degrading the optical signal are considered in the network planning. In this paper, we investigate the offline problem of routing and wavelength assignment (RWA) and regenerator placement (RP) in translucent networks, minimizing the lightpath blocking and regenerator equipment cost. We address two variants of the problem, which correspond to two different types of quality of transmission (QoT) estimators, called linear and nonlinear. In a nonlinear QoT, nonlinear impairments like crosstalk or cross-phase modulation, which account for the interferences from neighboring lightpaths in the network are explicitly computed. Then, the QoT estimated for a lightpath depends on the routes of other lightpaths in the network. In the linear QoT, the effects of the nonlinear impairments are overestimated and accumulated to the rest of the impairments in the QoT calculation. As a result, the QoT estimation of a lightpath solely depends on its route. For the linear case, we formulate an optimal integer linear programming model of the problem, to the best of the authors' knowledge, for the first time in the literature. Its simplicity allows us to test it for small- and medium-size networks. Also, we propose two heuristic methods, namely, lightpath segmentation and three-step, and a tight lower bound for the regenerator equipment cost. For the nonlinear QoT case, we propose a new heuristic called iterative RP (IRP). Both the IRP and three-step algorithms are designed to guarantee that no lightpath blocking is produced by signal degradation. This is a relevant difference with respect to earlier proposals. The performance and the scalability of our proposals are then investigated by carrying out extensive tests. Results reveal that the solutions obtained by the heuristic algorithms are optimal or close to optimal, and outperform the earlier proposals in the literature.

A Simple and Speedy Routing with Reduced Resource Information in Large-Capacity Optical WDM Networks

This paper discusses a simple and speedy routing method in large-capacity optical Wavelength Division Multiplexing (WDM) networks. The large-capacity WDM network is necessary to accommodate increasing traffic load in future. In this large-capacity WDM network, each link has many fibers and a huge amount of optical data can be transmitted through these fibers simultaneously. Optical path is configured for transmitting optical data by wavelength reservation including routing and wavelength assignment (RWA). Since traditional RWA methods have to treat much information about available wavelengths in each fiber, it is difficult to resolve RWA problem on time. In other words, the electrical processing becomes the bottleneck in the large-capacity WDM network. Therefore, a simple and speedy RWA method is necessary for the large-capacity WDM network. In this paper, we propose the simple and effective RWA method which considers reduced information as Network Map. The objective is to improve the network performance by using multiple fibers effectively. The complex processing is not suitable for data transmission because the switching operation must be done in very short time for one request. In addition to this, it is not practical to collect detailed network information frequently. The proposed wavelength assignment method assigns wavelength more uniformly than traditional method, and therefore, the proposed routing method can select routes without considering detailed information about each wavelength state. The proposed routing method needs only local information and reduced network information. This paper shows that the proposed routing method can get suitable solution for large-capacity optical WDM networks through computer simulations. The proposed RWA method drastically improves the loss probability against other simple RWA methods. This paper also describes two types of optical switches with tunable or fixed wavelength conversions. The wavelength converters with relatively low technology becomes effective with the proposed RWA method in the large-capacity WDM network. This paper reveals that complex routing methods are not necessary for large-capacity optical WDM networks.

Multi-Granular Optical Switching: A Classified Overview for the Past and Future

The wavelength routed network (WRN) accommodates traffic demands by establishing lightpaths along the corresponding routing paths. The wavelength of each lightpath is switched individually by traditional wavelength optical cross-connects (T-OXCs) to transit the traffic. Due to the traffic explosion and the resulted growth in wavelength number, WRNs face a challenge of the increase in node-size (i.e., the port number of a T-OXC) as well as the associated cost and control complexity. As an alternative solution, waveband switching (WBS) is introduced to group multiple wavelengths together as a band or fiber. Whenever possible, the group of wavelengths requires just a single port at a multi-granular optical cross-connect (MG-OXC). One fundamental problem in WBS networks is the routing and wavelength assignment (RWA). With the major goal of minimizing the port numbers in WBS networks, the optimal RWA problem was shown to be NP-Hard. In the literature, various Integer Linear Programming models are proposed to optimally solve a small-size RWA problem, and many heuristic algorithms are proposed to provide a practical solution for the large-scale RWA problem in WBS networks. In this work, we comprehensively review literature studies on waveband switching networks. The topics covered include architecture, RWA problem solving strategies, and future challenges of wavelength conversion, protection, and lightpath rerouting in WBS networks. We aim at presenting a classified view of WBS networks, based on various aspects including the traffic pattern, node and network architecture, grouping policy, and the band configurations. We investigate factors that affect the goal of port reduction and blocking minimization in WBS networks. In addition, we explore several unique features of waveband switching in protection, wavelength conversion and rerouting, along which we point out multiple open challenges in WBS networks that deserve further studies.