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.     

Effective wavelength assignment algorithms for optimizing designcosts in SONET/WDM rings

In high-speed wavelength-division-multiplexed synchronous optical network (SONET) ring networks, the terminal equipment costs associated with electronic multiplexing can be predominantly high. Placing a wavelength add-drop multiplexer (WADM) at each network node allows certain wavelengths to optically bypass the node without being electronically terminated. This approach can effectively reduce the total equipment cost if connections and channels are appropriately assigned in traffic grooming. In this paper, we present a series of wavelength optimization and wavelength assignment algorithms with the objective to optimize the number of required SONET add-drop multiplexers and yet minimizes the number of wavelengths in both unidirectional and bidirectional rings under an arbitrary grooming factor. In our analysis, we have considered both uniform and general nonuniform all-to-all network traffic. As a simple model for realistic traffic patterns, a special case of nonuniform traffic, distance-dependent traffic, is analyzed in detail. Significant ADM savings are observed for different traffic scenarios using our proposed algorithms     

Performance of WDM ring and bus networks in the presence ofhomodyne crosstalk

This paper examines the effects of coherent and incoherent homodyne crosstalk in wavelength division multiplexed (WDM) ring and bus networks using reconfigurable optical add-drop multiplexers (OADM's). It is widely understood that incoherent homodyne crosstalk causes power penalties at the receivers in these networks. We show that coherent homodyne crosstalk causes a range of possible received powers, and that coherent and incoherent crosstalk together lead to a range of possible power penalties. A Monte Carlo simulation is used to examine the probability distribution of power penalties due to homodyne crosstalk under various conditions. We find that increasing the switch and multiplexer crosstalk within each OADM, and increasing the number of WDM channels, all produce increased probabilities of large power penalties. However, the number of nodes through which a signal is transmitted does not affect the power penalty distribution     

A heuristic solution to SONET ADM minimization for static traffic grooming in WDM uni-directional ring networks

In recent years, minimization of add-drop multiplexers (ADMs) in wavelength division multiplexing (WDM) optical networks has gained lots of attention in both the research and commercial areas. This motivates the research presented in this paper. A heuristic algorithm is formulated for static traffic grooming in WDM uni-directional ring networks with an eye to minimize the number of required ADMs. The distinguished feature of the proposed heuristic is that it pairs up the calls of a given static traffic to approach the solution. The proposed heuristic is compared with the previous approach with same network configuration and traffic matrix to establish its effectiveness.     

Quantifying the benefit of wavelength add-drop in WDM rings withdistance-independent and dependent traffic

One drawback to deploying wavelength division multiplexed (WDM) synchronous optical network (SONET) rings is the potentially large amount of equipment necessary for their deployment. Wavelength add-drop multiplexers potentially reduce the amount of required SONET terminal equipment by allowing individual wavelengths to optically bypass a node rather than being electronically terminated. We have quantified the maximum terminal-equipment savings attainable using wavelength add-drop for rings carrying uniform traffic and rings carrying distance-dependent traffic. The analysis makes use of both an enumerative methodology, and a “super-node” approximation technique that is applicable to arbitrary ring size and internode demand. In both the uniform and distance-dependent traffic scenarios, maximum terminal-equipment savings are shown to rapidly increase, over the region of interest, with both network size and internode demand. The value of wavelength add-drop is accordingly expected to grow rapidly in rings interconnecting numerous high-capacity nodes     

Wavelength-interleaved OADMs incorporating optimized multiple phase-shifted FBGs for fiber-radio systems

We demonstrate that a single fiber Bragg grating (FBG)-based optical add-drop multiplexer can be used to improve the optical spectral efficiency in a mm-wave WDM-fiber wireless network. The technique employs wavelength interleaving in conjunction with optical single-sideband modulation, together with a single multiphase-shifted fiber Bragg grating. Wavelength optical add-drop features are also demonstrated using the grating, and our results show the performance of the novel grating in terms of channel isolation and add-drop functionality. We perform simulations to optimize placement of the phase shifts when an apodization profile is applied to the grating, in an attempt to minimize in-band and out-of-band transmission-amplitude ripples. Experiments are performed using cascade configurations both with the apodized gratings with optimal phase-shift positions and with the original unoptimized gratings. The experimental results demonstrate how these novel gratings can be used in fiber-radio networks incorporating multiple optical add-drop multiplexers.     

Dynamic traffic grooming algorithms for reconfigurable SONET over WDM networks

The emergence of wavelength-division multiplexing (WDM) technology provides the capability for increasing the bandwidth of synchronous optical network (SONET) rings by grooming low-speed traffic streams onto different high-speed wavelength channels. Since the cost of SONET add-drop multiplexers (SADM) at each node dominates the total cost of these networks, how to assign the wavelength, groom the traffic, and bypass the traffic through the intermediate nodes has received a lot of attention from researchers recently. Moreover, the traffic pattern of the optical network changes from time to time. How to develop dynamic reconfiguration algorithms for traffic grooming is an important issue. In this paper, two cases (best fit and full fit) for handling reconfigurable SONET over WDM networks are proposed. For each approach, an integer linear programming model and heuristic algorithms (TS-1 and TS-2, based on the tabu search method) are given. The results demonstrate that the TS-1 algorithm can yield better solutions but has a greater running time than the greedy algorithm for the best fit case. For the full fit case, the tabu search heuristic yields competitive results compared with an earlier simulated annealing based method and it is more stable for the dynamic case.     

AWG-based metro WDM networking

A plethora of metropolitan area wavelength-division multiplexing networks have been proposed and examined in recent years with the aim to alleviate the bandwidth bottleneck between increasingly higher-speed local/access networks and high-speed backbone networks. Many of the considered metropolitan area networks use the arrayed waveguide grating as an optical building block. As we review in this article, in ring, interconnected ring, and meshed metro WDM networks, the AWG is typically used to realize wavelength multiplexers, demultiplexers, or optical add-drop multiplexers without capitalizing on spatial wavelength reuse. By using the AWG as a wavelength router, highly efficient star metro WDM networks can be realized due to extensive spatial wavelength reuse. We give an overview of star metro WDM networks that are able to meet modular upgradability, transparency, flexibility, efficiency, reliability, and protection requirements of future metro networks. AWG-based star networks also enable an evolution path of ring networks toward highly efficient and fault-tolerant hybrid star-ring metro network solutions.     

An effective and comprehensive approach for traffic grooming andwavelength assignment in SONET/WDM rings

In high-speed SONET rings with point-to-point WDM links, the cost of SONET add-drop multiplexers (S-ADMs) can be dominantly high. However, by grooming traffic (i.e., multiplexing lower-rate streams) appropriately and using wavelength ADMs (WADMs), the number of S-ADMs can be dramatically reduced. In this paper, we propose optimal or near-optimal algorithms for traffic grooming and wavelength assignment to reduce both the number of wavelengths and the number of S-ADMs. The algorithms proposed are generic in that they can be applied to both unidirectional and bidirectional rings having an arbitrary number of nodes under both uniform and nonuniform (i.e., arbitrary) traffic with an arbitrary grooming factor. Some lower bounds on the number of wavelengths and S-ADMs required for a given traffic pattern are derived, and used to determine the optimality of the proposed algorithms. Our study shows that using the proposed algorithms, these lower bounds can he closely approached in most cases or even achieved in some cases. In addition, even when using a minimum number of wavelengths, the savings in S-ADMs due to traffic grooming (and the use of WADMs) are significant, especially for large networks     

Design of grooming architectures for optical WDM mesh networks: limited grooming with electronic wavelength conversion

In this article, we consider the problem of traffic grooming in optical wavelength division multiplexed (WDM) mesh networks under static traffic conditions. The objective of this work is to minimize the network cost and in particular, the electronic port costs incurred for meeting a given performance objective. In earlier work, we have shown the benefits of limited grooming switch architectures, where only a subset of wavelengths in a network are equipped with expensive SONET Add Drop Multiplexers (SADM) that provide the grooming functionality. In this work, we also consider the wavelength conversion capability of such groomers. This can be achieved using a digital cross-connect (DCS) in the grooming switch to switch low-speed connections between the SADMs (and hence, between wavelengths). The grooming switch thus avoids the need for expensive optical wavelength converters. Based on these observations, we propose a limited conversion-based grooming architecture for optical WDM mesh networks. The local ports at every node in this architecture can be one of three types: an add-drop port, a grooming port that allows wavelength conversion or a grooming port that does not allow wavelength conversion. The problem studied is: given a static traffic model, where should the different ports be placed in a network? We formulate this as an optimization problem using an Integer Linear Programing (ILP) and present numerical results for the same. We also present a heuristic-based approach to solve the problem for larger networks.     

Reconfigurable multichannel optical add-drop multiplexersincorporating eight-port optical circulators and fiber Bragg gratings

We propose and demonstrate two new strictly nonblocking reconfigurable multichannel optical add-drop multiplexers (RM-OADMs) using optical circulators and fiber Bragg gratings. By effectively using eight-port optical circulators, the new structures significantly reduce component count and insertion loss, and achieve good crosstalk performance. One of the new RM-OADMs potentially achieves the lowest insertion loss among existing RM-OADMs     

Bidirectional grating wavelength shifter with a broad-rangetunability by using a beam of uniform strength

Bidirectional chirp-free tuning in Bragg reflection wavelength by as much as 12.52 mm has been achieved based on the principle of a beam of uniform strength. The experimental results are in good agreement with the theoretical analysis. The tuning device is simple in configuration, low cost, and easy to operate, which can be used in numerous applications, such as tunable fiber grating lasers and reconfigurable wavelength add-drop multiplexers, etc     

Quantifying the benefit of configurability in circuit-switched WDMring networks with limited ports per node

In a reconfigurable network, lightpath connections can be dynamically changed to reflect changes in traffic conditions. This paper characterizes the gain in traffic capacity that a reconfigurable wavelength division multiplexed (WDM) network offers over a fixed topology network where lightpath connections are fixed and cannot be changed. We define the gain as the ratio of the maximum offered loads that the two systems can support for a given blocking probability. We develop a system model to approximate the blocking probability for both the fixed and reconfigurable systems. This model is different from previous models developed to analyze the blocking probability in WDM networks in that it accounts for a port limitation at the nodes. We validate our model via simulation and find that it agrees strongly with simulation results. We study high-bandwidth calls, where each call requires an entire wavelength and find that reconfigurability offers a substantial performance improvement, particularly when the number of available wavelengths significantly exceeds the number of ports per node. In this case, in a ring with N nodes, the gain approaches a factor of N/2 over a fixed topology unidirectional ring, and N/4 over a fixed topology bidirectional ring. Hence, a reconfigurable unidirectional (bidirectional) ring can support N/2(N/4) times the load of a fixed topology unidirectional (bidirectional) ring. We also show that for a given traffic load, a configurable system requires far fewer ports per node than a fixed topology system. These port savings can potentially result in a significant reduction in overall system costs     

Improved approaches for cost-effective traffic grooming in WDM ringnetworks: ILP formulations and single-hop and multihop connections

Traffic grooming is the term used to describe how different traffic streams are packed into higher speed streams. In a synchronous optical network-wavelength division multiplexing (SONET-WDM) ring network, each wavelength can carry several lower-rate traffic streams in time division (TDM) fashion. The traffic demand, which is an integer multiple of the timeslot capacity, between any two nodes is established on several TDM virtual connections. A virtual connection needs to be added and dropped only at the two end nodes of the connection; as a result, the electronic add-drop multiplexers (ADMs) at intermediate nodes (if there are any) will electronically bypass this timeslot. Instead of having an ADM on every wavelength at every node, it may be possible to have some nodes on some wavelength where no add-drop is needed on any timeslot; thus, the total number of ADMs in the network (and, hence, the network cost) can be reduced. Under the static traffic pattern, the savings can be maximized by carefully packing the virtual connections into wavelengths. In this work, we allow arbitrary (nonuniform) traffic and we present a formal mathematical definition of the problem, which turns out to be an integer linear program (ILP). Then, we propose a simulated-annealing-based heuristic algorithm for the case where all the traffic is carried on directly connected virtual connections (referred to as the single-hop case). Next, we study the case where a hub node is used to bridge traffic from different wavelengths (referred to as the multihop case). We find the following main results. The simulated-annealing-based approach has been found to achieve the best results, so far, in most cases, relative to other comparable approaches proposed in the literature. In general, a multihop approach can achieve better equipment savings when the traffic-grooming ratio is large, but it consumes more bandwidth     

Routing and wavelength assignment in all-optical networks

Considers routing connections in a reconfigurable optical network using WDM. Each connection between a pair of nodes in the network is assigned a path through the network and a wavelength on that path, such that connections whose paths share a common link in the network are assigned different wavelengths. The authors derive an upper bound on the carried traffic of connections (or equivalently, a lower bound on the blocking probability) for any routing and wavelength assignment (RWA) algorithm in such a network. The bound scales with the number of wavelengths and is achieved asymptotically (when a large number of wavelengths is available) by a fixed RWA algorithm. The bound can be used as a metric against which the performance of different RWA algorithms can be compared for networks of moderate size. The authors illustrate this by comparing the performance of a simple shortest-path RWA (SP-RWA) algorithm via simulation relative to the bound. They also derive a similar bound for optical networks using dynamic wavelength converters, which are equivalent to circuit-switched telephone networks, and compare the two cases. Finally, they quantify the amount of wavelength reuse achievable in large networks using the SP-RWA via simulation as a function of the number of wavelengths, number of edges, and number of nodes for randomly constructed networks as well as de Bruijn networks. They also quantify the difference in wavelength reuse between two different optical node architectures     

Architectures and technologies for high-speed optical data networks

Current optical networks are migrating to wavelength division multiplexing (WDM)-based fiber transport between traditional electronic multiplexers/demultiplexers, routers, and switches. Passive optical add-drop WDM networks have emerged but an optical data network that makes full use of the technologies of dynamic optical routing and switching exists only in experimental test-beds. This paper discusses architecture and technology issues for the design of high performance optical data networks with two classes of technologies, WDM and time division multiplexing (TDM). The WDM network architecture presented stresses WDM aware Internet protocol (IP), taking full advantage of optical reconfiguration, optical protection and restoration, traffic grooming to minimize electronics costs, and optical flow-switching for large transactions. Special attention is paid to the access network where innovative approaches to architecture may have a significant cost benefit. In the more distant future, ultrahigh-speed optical TDM networks, operating at single stream data rates of 100 Gb/s, may offer unique advantages over WDM networks. These advantages may include the ability to provide integrated services to high-end users, multiple quality-of-service (QoS) levels, and truly flexible bandwidth-on-demand. The paper gives an overview of an ultrahigh-speed TDM network architecture and describes recent key technology developments such as high-speed sources, switches, buffers, and rate converters     

Study of the performance of a transparent and reconfigurablemetropolitan area network

The transport performance of an optically transparent regional-size ring network testbed with circumference of 280 km, based on metro-area optimized optical layer components and fiber, is demonstrated under dynamic traffic conditions. For the longest transmission path, excellent transmission performance is achieved using cost-effective directly modulated signals. Network reconfigurability is achieved using add-drop modules that are commercially available as of this writing. We show that the dynamic nature of the network does not affect the system performance. In particular, we show that electronic gain control of erbium-doped amplifiers is capable of managing switching transients in amplified metro-scale networks     

Cross-Layer Design of ASE-Noise-Limited Island-Based Translucent Optical Networks

This paper considers the design and dimensioning of translucent optical networks based on the concept of optical transparent islands. In systems with dispersion compensation, amplified spontaneous emission (ASE) noise becomes a dominant physical-layer impairment in constraining the maximal transparent reach limit of a lightpath. Taking this dominant impairment into account, an efficient transparent island division algorithm is proposed to divide a large transport network into a few optical transparent islands and to minimize the total number of opaque island-border nodes. Optimization models for translucent network dimensioning are presented to maximize served traffic demand given certain network capacity and to minimize the required wavelength capacity given a certain traffic demand matrix. Simulation studies show that the proposed transparent island division approach and network-dimensioning optimization models require only 25% opaque nodes to overcome the constraint of transparent reach limit and achieve performance as good as that of a more expensive 100% opaque network.      

Optimal routing and wavelength assignment to minimize the number of SONET ADMs in WDM rings

In this study, we consider the routing and wavelength assignment problem on SONET over WDM ring networks. Our problem is the minimum ADM (add-drop multiplexer) cost problem of minimizing the number of ADM equipment instead of the minimum wavelength problem. To deal with the complexity of the problem, we create a new mathematical formulation and suggest an efficient solution method based on the branch-and-price method. We exploit the structure of the ring network to develop an efficient algorithm and show the efficiency using computer simulations.     

A comparison of the homodyne crosstalk characteristics of opticaladd-drop multiplexers

We compare the homodyne crosstalk characteristics of a number of different optical add-drop multiplexer (OADM) structures, in the context of wavelength-division multiplexed (WDM) ring or bus network links. Nine fixed-wavelength and rive reconfigurable OADM structures are examined. For the fixed-wavelength structures, we find considerable variation in the levels of incoherent crosstalk, and generally low coherent crosstalk levels. For the reconfigurable structures, incoherent crosstalk levels are quite similar, but the coherent crosstalk levels differ considerably. The range of homodyne crosstalk-induced power penalties is calculated for all structures, and the probability distribution is found for each reconfigurable OADM. The effects of the number of OADMs in the link and the number of wavelength channels in the network are also studied. We find that the best choice of OADM depends on the application