Uniform waveband assignment in optical mesh networks

The cost of an optical network in wavelength division multiplexing (WDM) networks can be reduced using optical reconfigurable optical add/drop multiplexers (ROADMs), which allow traffic to pass through without the need for an expensive optical-electro-optical (O-E-O) conversion. Waveband switching (WBS) is another technique to reduce the network cost by grouping consecutive wavelengths and switching them together using a single port per waveband. WBS has attracted the attention of researchers for its efficiency in reducing switching complexity and therefore cost in WDM optical networks. In this paper, we consider the problem of switching wavelengths as non-overlapping uniform wavebands, per link, for mesh networks using the minimum number of wavebands. Given a fixed band size b _s , we give integer linear programming formulations and present a heuristic solution to minimize the number of ROADMs (number of wavebands) in mesh networks that support a given traffic pattern. We show that the number of ROADMs (or number of ports in band-switching cross-connects) can be reduced significantly in mesh networks with WBS compared to wavelength switching using either the ILP or the heuristic algorithm. We also examine the performance of our band assignment algorithms under dynamic traffic.     

静态波带交换中的一种波带粒度取值算法

波带交换可以有效地减少波长交换的交换端口数量,本文研究节点间业务量已知时静态波带交换中的波带粒度取值算法,提出了基于k均值聚类的波带粒度取值算法。算法将业务量相近的业务分为一组,一组内的业务用相同粒度的波带装载,以提高波带的利用率。研究表明,在没有业务疏导的环境下,与其他方法相比,算法使用的波带数量和波带内的空闲波长数量都比较少。本文还研究了静态疏导环境下不同波带粒度取值算法的性能,提出了多波带粒度下的业务装载策略。对于大粒度的波带,使用向下装载,而对于小粒度的波带,使用向上装载,意在减少波带的使用数量的同时提高波带利用率。仿真结果表明,使用静态业务疏导后,本文算法与其他方法相比,依然可以有效地减少波带数量,提高波带利用率。与基于组播路由的静态波带疏导算法相结合,使波带利用率可以达到98%以上。     

Mixed-line-rate optical network design with wavebanding

To cope with ever increasing and more heterogeneous traffic demands, today’s optical backbone networks are expected to support mixed line rates (MLR) over different wavelength channels. MLR networks can be designed to provide flexible rate assignments to low-bit-rate services and high-bit-rate services in a cost-effective manner. But with increasing number of wavelengths in the network, aggregating wavelengths into wavebands can further reduce the network cost.In this study, we incorporate the idea of waveband switching in MLR network design. Wavebanding or grouping of optical paths reduces the optical switch size at the optical cross-connects (OXCs). When several lightpaths share several common links, they can be grouped together and routed as a single waveband. For optical bypass at a transit node, only two optical ports are required for each waveband, hence reducing the port cost. It can be a challenge for an MLR network to waveband wavelengths of different line rates that have different transmission reaches. In our design, we present a suitable switching architecture and propose an efficient and cost-effective approach for wavebanding in an MLR network. The design problem is formulated as a mixed integer linear program (MILP) where the objective is to minimize transponder cost and port cost. A heuristic algorithm for wavebanding in MLR networks is provided. To further optimize our solution, we also present a Simulated Annealing algorithm for wavebanding. Our results show a significant improvement in cost savings compared to single-line-rate (SLR) networks with wavebanding and an MLR network employing only wavelength switching.     

Dynamic Waveband Switching in WDM Mesh Networks Based on a Generic Auxiliary Graph Model

Waveband switching (WBS) is a promising technique to reduce the switching and transmission costs in the optical domain of a wavelength-division multiplexing (WDM) network. This paper considers the problem of provisioning dynamic traffic using WBS in a WDM mesh network. The network of interest is a homogeneous WBS network, where each node has the functionality of WBS. The problem is called the dynamic WBS problem, which involves searching waveband-routes or wavelength-routes for the dynamically arriving traffic requests. The objective is to minimize the total switching and transmission costs in the optical domain. To solve the dynamic WBS problem, an auxiliary graph model capturing the network state is proposed. Based on the auxiliary graph, two heuristic on-line WBS algorithms with different waveband grouping policies are proposed, namely the wavelength-first WBS algorithm based on the auxiliary graph (WFAUG) and the waveband-first WBS algorithm based on the auxiliary graph (BFAUG). Simulation results indicate that WBS is an attractive technique which reduces the overall switching and transmission costs by up to 30% in the network. The results also show that the WFAUG algorithm outperforms the BFAUG algorithm in terms of port savings and cost savings.     

Survivable routing,spectrum and waveband assignment strategy in cloud Optical and Data Center Network

These years, data centers are developing quickly and cloud Optical and Data Center Network (ODCN) has been shown to be the most viable solution for inter-data-center network implementation with less energy consumption and higher transmit rate. At the same time, elastic optical networks and waveband switching can address the problems caused by dramatic increase in network scale. In cloud hierarchical ODCN with flexible spectrum and waveband switching, survivability is an important and complex issue which is needed to be researched. So, we study the survivable routing, spectrum and waveband assignment strategy in cloud hierarchical ODCN, and in this paper, a novel hierarchical shared-protection (HSP) strategy is proposed. We consider spectrum fragmentation, waveband and shared-protection simultaneously. By quantifying the influence of spectrum assignment and the emergence of fragmentation, slots are assigned to the optimal paths. In order to share protection resource or wavebands, a heuristics algorithm named HSPGA is proposed for optimally picking out the two protection paths. Simulation results show that the proposed HSP strategy decreased the amount of employed ports significantly. In addition, the spectrum efficiency is improved.     

Optimized joint cell planning and BS on/off switching for LTE networks

Energy is becoming a main concern nowadays due to the increasing demands on natural energy resources. Base stations (BSs) consume up to 80% of the total energy expenditure in a cellular network. In this paper, we propose and evaluate a green radio network planning approach by jointly optimizing the number of active BSs and the BS on/off switching patterns based on the changing traffic conditions in the network in an effort to reduce the total energy consumption of the BSs. The problem is formulated as an integer optimization problem, which proves to be NP‐complete, and thus it can be efficiently solved for small to medium network sizes. For large network sizes, we propose a heuristic solution with close to optimal performance because the optimal solution becomes computationally complex. Planning is performed based on two approaches: a reactive and a proactive approach. In the proactive approach, planning will be performed starting with the lowest traffic demand until reaching the highest traffic demand, whereas in the reactive approach, the reverse way is considered. Performance results are presented for various case studies and are complemented by testing the proposed approaches using commercial radio network planning tools. Results demonstrate considerable energy savings reaching up to 40% through dynamic adaptation of the number of simultaneously active BSs. Copyright © 2015 John Wiley & Sons, Ltd.     

Cognitive Wireless Mesh Networks with Dynamic Spectrum Access

Wireless Mesh Networks (WMNs) are envisaged to extend Internet access and other networking services in personal, local, campus, and metropolitan areas. Mesh routers (MR) form the connectivity backbone while performing the dual tasks of packet forwarding as well as providing network access to the mesh clients. However, the performance of such networks is limited by traffic congestion, as only limited bandwidth is available for supporting the large number of nodes in close proximity. This problem can be alleviated by the cognitive radio paradigm that aims at devising spectrum sensing and management techniques, thereby allowing radios to intelligently locate and use frequencies other than those in the 2.4 GHz ISM band. These promising technologies are integrated in our proposed Cognitive Mesh NETwork (COMNET) algorithmic framework, thus realizing an intelligent frequency-shifting self-managed mesh network. The contribution of this paper is threefold: (1) A new approach for spectrum sensing is devised without any change to the working of existing de facto mesh protocols. (2) An analytical model is proposed that allows MRs to estimate the power in a given channel and location due to neighboring wireless LAN traffic, thus creating a virtual map in space and frequency domains. (3) These models are used to formulate the task of channel assignment within the mesh network as an optimization problem, which is solved in a decentralized manner. Our analytical models are validated through simulation study, and results reveal the benefits of load sharing by adopting unused frequencies for WMN traffic.     

Joint routing and dimensioning of optical burst switching networks

Existing methods for handling routing and dimensioning in dynamic WDM networks solve the two problems separately. The main drawback of this approach is that a global minimum cost solution cannot be guaranteed. Given that wavelengths are costly resources, determining the minimum network cost is of fundamental importance. We propose an approach which jointly solves the routing and dimensioning problems in optical burst switching (OBS) networks, guaranteeing a target blocking per connection. The method finds the set of routes and the number of wavelengths per network link that minimise the total network cost. To accomplish this, an integer linear programming problem is solved. The proposed method was applied to ring networks, where the optimal solution achieves a reduction in the network cost of 10–40% (for traffic loads <0.4, compared to solving both problems separately). In the case of mesh topologies, to reduce the computational complexity of the method, we applied a variation of it which achieves a local minimum. Even so, a reduction of 5–20% (for traffic loads <0.4) in the network cost was obtained. This ability to lower network cost could make the proposed method the best choice to date for dynamic network operators.     

Channel Assignment for a Metro Hub Under Nonuniform Traffic

We consider a metro wavelength-division- multiplexing (WDM) network in which a metro hub connects multiple local networks to a backbone network. In many practical scenarios, the metro WDM network has nonuniform traffic. A metro hub recently studied in the literature can effectively transport nonuniform traffic via nonuniform channel assignment. To realize this feature, it is necessary to assign wavelength channels within the hub to fulfill the given channel requirements while avoiding wavelength conflict. In this letter, we formulate this wavelength assignment problem and propose an efficient method to solve it.      

Cross-Layer Optimization of Multichannel Multiantenna WMNs

Use of multiple channels can significantly improve the throughput of wireless mesh networks (WMNs). Additionally, recent advances in radio technology have made it possible to realize software-defined radio (SDR), which is capable of switching from one channel to another dynamically. On the other hand, equipping wireless nodes with multiple antennas creates great potential for throughput improvement via interference suppression, spatial multiplexing, and spatial division multiple access techniques. In this paper, we investigate the joint optimization of routing and scheduling in multichannel WMNs, where nodes are equipped with a single SDR and multiple antenna elements. We analyze achievable throughput of these networks under four different multiantenna modes: single user single stream, single user multi stream, multi user single stream, and multi user multi stream, each mode integrates different combinations of multiantenna techniques. We mathematically model scheduling and interference constraints and formulate joint routing and scheduling optimization problem with the objective of maximizing the throughput by minimizing network schedule time such that traffic demands for a set of sessions are satisfied. A column generation-based decomposition approach is proposed to solve the problem. Simulation results are presented to evaluate the impact of number of antennas, number of channels, and number of sessions on the schedule time for the four proposed modes.     

Multi-domain grooming algorithm based on hierarchical integrated multi-granularity auxiliary graph in optical mesh networks

With the size of traffic demands ranges from sub-wavelength-level to wavelength-level, traffic demands need to be aggregated and carried over the network in a cost-effective manner to make sure that the resources are utilized effectively. Therefore, the technique called multi-granularity grooming is proposed to save the cost by reducing the number of switching ports in optical cross-connects. However, the existing multi-granularity grooming algorithms are mostly limited in single-domain optical networks. Since the current optical backbone keeps enlarging and is actually divided to multiple independent domains for achieving the scalability and the confidentiality, it is necessary to study the multi-granularity grooming in multi-domain optical networks. In this paper, we propose a new heuristic algorithm called hierarchical multi-domain multi-granularity grooming (HMMG) based on hierarchical integrated multi-granularity auxiliary graph (H-IMAG) to reduce the total number of optical switching ports. The H-IMAG is composed of the inter-domain virtual topology graph (VTG) and the intra-domain integrated layered auxiliary graph (ILAG), where VTG includes a wavelength virtual topology graph (WVTG) and a waveband virtual topology graph (BVTG), and ILAG includes a wavelength layered auxiliary graph (WLAG) and a waveBand layered auxiliary graph (BLAG). Then, we can groom the sub-wavelength-level demands into lightpaths based on WVTG and WLAG and groom the wavelength-level demands into high-capacity wavebands based on BVTG and BLAG. Simulation results show that performances of H-IMAG can be significantly improved compared with previous algorithm.     

Routing and wavelength assignment with multigranularity traffic in optical networks

We propose a novel switching architecture of multigranularity optical cross-connects (MG-OXCs) for dealing with multigranularity traffic in the optical domain. MG-OXCs can cooperate with the generalized multiprotocol label switching (MPLS) control plane, which provides the advantages of cost reduction, better scalability in physical size, and unified traffic management. Detailed discussions are provided on the characteristics and implementation issues for the switching architecture. Based on the proposed MG-OXCs, two routing and wavelength assignment (RWA) with tunnel allocation algorithms are presented: dynamic tunnel allocation (DTA) and capacity-balanced static tunnel allocation (CB-STA). In the former, we use fixed alternate routing with k-shortest paths to inspect network resources along each alternate path for dynamically setting up lightpaths. For the latter, fiber and waveband tunnels are allocated into networks at the planning stage (or off-line) according to weighted network link-state (W-NLS). We will show that with the proposed algorithms, the RWA problem with tunnel allocation in the optical networks containing MG-OXCs can be solved effectively. Simulation is conducted on networks with different percentages of switching capacity and traffic load. The simulation results show that DTA is outperformed by CB-STA in the same network environment due to a well-disciplined approach for allocating tunnels with CB-STA.. We also find that the mix of the two approaches yields the best performance given the same network environment apparatus.     

Regenerator Placement and Traffic Engineering with Restoration in GMPLS Networks

In this paper, we study regenerator placement and traffic engineering of restorable paths in generalized multiprotocol label switching (GMPLS) networks. Regenerators are necessary in optical networks in order to cope with transmission impairments. We study a network architecture where regenerators are placed only at selected nodes for decreasing cost of regeneration. We propose two heuristic algorithms for optimum placement of these regenerators. Performances of these algorithms in terms of required number of regenerators and computational complexity are evaluated. In this network architecture with sparse regeneration, off-line computation of working and restoration paths is studied for traffic engineering with path rerouting as the restoration scheme. We study two approaches for selecting working and restoration paths from a set of candidate paths and formulate each method as an integer linear programming (ILP) problem. A traffic uncertainty model is developed in order to compare these methods based on their robustness with respect to changing traffic patterns. Traffic engineering methods are compared based on number of additional demands resulting from traffic uncertainties that can be carried over the network. Proposed heuristic regenerator placement algorithms are also evaluated from a traffic engineering point of view.     

Design and Dimensioning of a WDM Mesh Network to Groom Dynamically Varying Traffic

In this paper, we address the traffic grooming problem in WDM mesh networks when the offered traffic is characterized by a set of traffic matrices—a variant of dynamically changing traffic. We justify the need to address this problem in mesh networks and also argue for the validity of our approach to solve this problem. Our primary objective is to design the network in terms of the number of wavelengths and transceivers required to support any offered traffic matrix. We provide a simple and generic framework to minimize the number of transceivers needed in the network. Simulation results have been presented in contrast with a possible approach, to enable comparison with our solution strategy. An ILP formulation of our approach is also presented.     

Topology control for multi-channel multi-radio wireless mesh networks using directional antennas

Directional antennas are widely used technologies for reducing signal interference and increasing spatial reuse. In this paper, we propose a topology control method for multi-channel multi-radio wireless mesh networks that use directional antennas. We are given a set of mesh routers installed in a region and some of them are gateway nodes that are connected to the Internet via wired lines. Each router has a traffic demand (Internet access traffic) generated from the end-users. The problem is how to adjust antenna orientations of radios and assign channels to them to construct a logical network topology, such that the minimum delivery ratio of traffic demands of routers is maximized. We first formulate the problem to an equivalent optimization problem with a clearer measurable metric, which is to minimize the largest interfering traffic of links in the network. We then propose a three-step solution to solve the problem. Firstly, we construct a set of routing trees, with the objective to balance the traffic among tree links. Secondly, we assign the radios of a node to the links it needs to serve, such that the total traffic load of the links that each radio serves is as balanced as possible. Thirdly, we do a fine-grained adjustment of antenna orientations and assign channels to them, such that the transmission area of each antenna will cover all the links it serves and the largest interfering traffic of links is minimized.     

An efficient heuristic waveband assignment algorithm for hierarchical optical path networks utilizing wavelength convertors

We propose a hierarchical optical path network design algorithm that allows for wavelength conversion. The algorithm sequentially solves a set of sub-problems that result from decomposing the original design problem. A novel efficient heuristic is developed to solve the waveband assignment sub-problem that is the bottleneck among the sub-problems. Numerical experiments prove that, by employing wavelength conversion, hierarchical optical path networks will be more cost effective than the single layer optical path network even in the small traffic demand area, where cost-effectiveness cannot be realized without using wavelength conversion, as well as in the relatively large traffic demand area.     

Minimum cost dimensioning of ring optical networks

We consider the problem of traffic grooming of low-rate traffic circuits in WDM rings where circuits are associated with a set of heterogeneous granularities. While networks are no longer limited by transmission bandwidth, the key issue in WDM network design has evolved towards the processing capabilities of electronic switches, routers and multiplexers. Therefore, we focus here on traffic grooming with minimum interconnecting equipment cost. We first formulate the problem as an integer linear programming (ILP) or a mixed integer linear programming (MILP) problem depending on the design specifications: UPSR vs BLSR, fixed vs variable wavelength capacities, non-bifurcated vs bifurcated flows, wavelength continuity vs possible signal regeneration on a different wavelength. Considering the case study of the second SONET ring generation with MSPP like interconnection equipment, we define the cost by a function of the number of transport blades, taking into account that the number of MSPP transport blades makes up a significant portion of the overall network design cost. Using the CPLEX linear programming package, we next compare the optimal solutions of the ILP or MILP programs for different design assumptions, including the classical ring network design scheme with a single hub where the lightpaths directly connect the hub to all other nodes.     

Routing in a linear lightwave network

Dynamic routing of point-to-point connections in a waveband selective linear lightwave network is addressed. Linear lightwave networks are all optical networks in which only linear operations are performed on signals in a waveband selective manner. Special constraints arise because of the linearity in the linear lightwave network. The overall problem of finding a path satisfying all the routing constraints for point-to-point connections is shown to be very complex. Owing to the complexity, the overall routing problem is decomposed into several subproblems. In particular, given a request for a point-to-point connection a waveband is first chosen for the call. Two heuristics, MAXBAND which allocates the most used band to a call and another MINBAND (least used band) are studied. Then, the problem of routing in a given waveband is further divided into smaller subproblems of finding a path in the waveband, checking for feasibility of the path in the chosen waveband and channel allocation (within the waveband). For finding paths in a waveband, K-SP, BLOW-UP and MIN-INT algorithms are proposed. A recursive algorithm checks for feasibility of the path on the waveband. Two channel allocation schemes (within a single waveband) MIN and MAX are presented. Simulations show that using MAXBAND (waveband), MIN-INT (path on waveband) and MIN (channel within waveband) policies resulted in the best performance (least blocking)     

Analysis and application of new quasi-network characteristics of nonuniform mesh in FDTD simulation

The equation of computing the reflection coefficient between two meshes of different sizes is derived. Using the equation, quasi-network characteristics of nonuniform mesh for the finite-difference time-domain technique is found and analyzed. The so-called mesh network (MN) here is a kind of structure composed of the sections of mesh in cascade. The cell sizes of these sections change regularly. By means of choosing the number of mesh sections, length of each section, and cell sizes, some novel network characteristics are obtained, which can be used to match the reflecting wave of nonuniform mesh or improve the transmitted characteristics for a mesh wave to travel along the nonuniform mesh. Formulas for analyzing the MN are given. The characteristics are realized in both one- and three-dimensional cases. The applications and advantages of the MN are shown by computing three different structures, i.e., microstrip-gap capacitor, parallel-coupling filter, and microstrip slot-line transformer.