Mathematical formulation of provisioning of connections with advance reservation in metro WDM ring networks using reconfigurable OADMs (ROADMs) with tuning constraint

Optical add/drop multiplexers (OADMs) can significantly reduce the cost of metro optical wavelength-division multiplexing (WDM) ring networks by allowing traffic to bypass intermediate nodes without expensive opto-electro-opto (O-E-O) conversion. Some traditional OADMs, called fixed OADMs (FOADMs), can only add/drop traffic on a specific wavelength. Reconfigurable Optical Add/Drop Multiplexers (ROADMs) are emerging, which can add/drop traffic onto/from different wavelengths at different time. ROADMs provide desirable flexibility, enable fast provisioning of dynamic traffic, and save capital expenditure (CapEx) and operational expenditure (OpEx). In order to be cost-effective, some ROADMs employ architectures that tune the ROADM continuously from one wavelength to another, crossing through all the wavelengths in-between, which may cause interference to the connections, if any, on those wavelengths being crossed. In order to prevent existing connections from being interrupted, a constraint needs to be imposed that ROADMs cannot cross working wavelengths when tuning. In this study, the design and the benefits of metro optical WDM network architectures using ROADMs and the impact of this tuning constraint on the performance of the network are investigated. Mathematical formulation of the problem of provisioning of connections with advance reservation, in which the arrival time and departure time of all the connections are known in advance, is presented, and results for a small network are shown.     

Access and metro networks based on WDM technologies

This paper describes the technical issues of access and metro networks based on wavelength division multiplexing (WDM) technologies, some solutions, and an experimental demonstration. A WDM star access network with colorless optical network units (ONUs) is proposed. For realizing the colorless ONU, two approaches are introduced; optical carrier supply and spectrum slicing. In addition, a WDM metro ring network with scalable optical add/drop multiplexers (OADMs), namely the tapped-type OADM, is proposed to effectively accommodate the large amount of traffic issued from access networks. Prototypes are constructed and used to verify the feasibility of the proposed WDM technologies.     

Stackable ROADMs for minimizing lightpath interference during upgrade of in-service WDM networks

Bidirectional stackable ROADMs (BS-ROADMs) with 3-port optical add/drop multiplexers (OADMs) have been presented for minimizing the lightpath interference during reconfiguration of the ROADMs. The BS-ROADM is constructed by connecting some modules with different wavelengths, and it is reconfigured by adding new modules required in it. The reconfigurations of the BS-ROADMs are done for upgrading the in-service networks to support newly appeared traffic demand. The experimental results presented in this paper clarify that the BS-ROADM can multiplex and demultiplex the wavelengths successfully without limiting the pass-through wavelengths, providing the wavelength transparent networks. The reconfiguration of an in-service BS-ROADM can be made without influencing any lightpath in the network, and this type of BS-ROADMs is used for premium users. However, while adding a new module in comparatively low-cost BS-ROADMs in-service, the transmission break of some lightpaths might be taken place. The investigated transmission break time was limited within recovery time specified in the service level agreement for best-effort transmission, which has strong cost-effectiveness rather than high QoS. This upgradability of the BS-ROADMs adds more flexibility in coarse wavelength division multiplexing networks in terms of scalability and reconfigurability.     

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.     

Field Trial of 640-Gbit/s-Throughput, Granularity-Flexible Optical Network Using Packet-Selective ROADM Prototype

Reconfigurable optical add/drop multiplexers (ROADMs) are able to provide flexible wavelength path provisioning in wavelength division multiplexing (WDM) networks. However, the capability of conventional ROADMs is limited to handling wavelength paths, and it does not support fine granularity in add/drop multiplexing of packets. Recently, we have proposed and demonstrated a packet-selective ROADM that combines an acoustooptic wavelength-tunable filter (AOTF) and an optical packet ADM (PADM) using optical code label processing. It provides more efficient utilization of wavelengths than conventional ROADMs. However, the bit rate of the demonstration was limited up to 10 Gbit/s. In this paper, we newly develop a label-selectivity-enhanced optical en/decoder, which allows the optical label recognition with 40-Gbit/s nonreturn-to-zero (NRZ) data packets, and a wide pass-band AOTF for 40-Gbit/s signals. Furthermore, we develop 640-Gbit/s throughput, packet-selective ROADM prototype, and demonstrate a field trial of granularity-flexible 3-node optical network over 173 km. error-free packet ADMs (error rate of under 10^-12) for all 16-wavelength channels at all nodes are obtained.     

A Taxonomical Consideration of Optical Add/Drop Multiplexers

The use of optical add/drop multiplexers (OADMs) is considered as a possible way to save the number of transponders required at a network node by optically bypassing wavelengths that do not need to be dropped. There are many different flavors of OADMs offered by vendors. In this paper, we give a taxonomy of OADMs from the perspectives of both technology considerations and possible implications on network performance. The purpose of the taxonomy is to serve as a frame work for cost and performance studies on dense wavelength division multiplexing (DWDM) optical transmission systems.     

Design and Performance Evaluation of Traffic Grooming Algorithms in WDM Multi-Ring Networks

In this paper, we propose novel traffic grooming algorithms to reduce the cost of the entire system in WDM multi-ring networks. In order to achieve this goal, it is important to construct a virtual topology and groom the traffic in these networks. We consider four kinds of virtual topologies of WDM multi-ring networks according to the way in which traffic is transmitted among rings. Accordingly, we design four kinds of traffic grooming (TG) algorithms depending on the considered virtual topologies: mixed (MTG), partially mixed (PMTG), separate (STG), and independent (ITG) traffic grooming algorithms. Each algorithm consists of a separation, a connection-ring construction, and a grooming procedure. In the separation procedure, all traffic connections are classified into intra and inter-connections. The connection-ring construction procedure makes full connection-rings from traffic connections. The grooming procedure groups connection-rings onto a wavelength in order to reduce the number of SONET add/drop multiplexers (SADMs) and wavelengths and to improve the utilization of network resources. To analyze the performance of each algorithm, a circular multi-ring architecture with uniform traffic is considered. The simulation results show that ITG and PMTG are more efficient in terms of wavelengths. STG and PMTG require a smaller number of SADMs.     

Sliding scheduled lightpath provisioning by mixed partition coloring in WDM optical networks

In WDM optical networks, lightpath provisioning for static, incremental and dynamic traffic model has been widely investigated. However, Internet connectivity services are increasingly showing a new kind of traffic type in the context of optical networks, i.e., sliding scheduled traffic, which does not have a rigid deadline and allows flexible sliding within a large time window. This new traffic type offers opportunity of more efficiently utilizing network resources to accommodate more traffic, and poses new challenges of exploiting the flexibility of scheduling time. In this paper, we formulate the static sliding scheduled lightpath demand (SSLD) provisioning problem as a mixed partition coloring model in which routing and wavelength assignment are conducted simultaneously in compliance with the allowed time window of each request. Then, we propose a novel one-step heuristic algorithm named as maximum conflict degree first conflict reducing (MCDF-CR) to solve the SSLD provisioning problem based on mixed partition coloring model. Simulation results show that our approach can improve wavelengths utilization compared to previous heuristics.     

Performance analysis of multicast routing and wavelength assignment protocol with dynamic traffic grooming in WDM networks

The need for on‐demand provisioning of wavelength‐routed channels with service‐differentiated offerings within the transport layer has become more essential because of the recent emergence of high bit rate Internet protocol (IP) network applications. Diverse optical transport network architectures have been proposed to achieve the above requirements. This approach is determined by fundamental advances in wavelength division multiplexing (WDM) technologies. Because of the availability of ultra long‐reach transport and all‐optical switching, the deployment of all‐optical networks has been made possible. The concurrent transmission of multiple streams of data with the assistance of special properties of fiber optics is called WDM. The WDM network provides the capability of transferring huge amounts of data at high speeds by the users over large distances. There are several network applications that require the support of QoS multicast, such as multimedia conferencing systems, video‐on‐demand systems, real‐time control systems, etc. In a WDM network, the route decision and wavelength assignment of lightpath connections are based mainly on the routing and wavelength assignment (RWA). The multicast RWA's task is to maximize the number of multicast groups admitted or minimize the call‐blocking probability. The dynamic traffic‐grooming problem in wavelength‐routed networks is generally a two‐layered routing problem in which traffic connections are routed over lightpaths in the virtual topology layer and lightpaths are routed over physical links in the physical topology layer. In this paper, a multicast RWA protocol for capacity improvement in WDM networks is designed. In the wavelength assignment technique, paths from the source node to each of the destination nodes and the potential paths are divided into fragments by the junction nodes and these junction nodes have the wavelength conversion capability. By using the concept of fragmentation and grouping, the proposed scheme can be generally applied for the wavelength assignment of multicast in WDM networks. An optimized dynamic traffic grooming algorithm is also developed to address the traffic grooming problem in mesh networks in the multicast scenario for maximizing the resource utilization and minimizing the blocking probability. Copyright © 2011 John Wiley & Sons, Ltd.     

Resource Planning for Dynamic Traffic Grooming in WDM Optical Networks

Dynamic traffic grooming in wavelength division multiplexing (WDM) optical networks refers to consolidating dynamically arriving subwavelength connections onto lightpaths. Most studies on dynamic traffic grooming focused on designing effective algorithms to achieve better performance (typically blocking probability) with given resources such as wavelengths and transponders. In this paper, we study the reverse problem: given the blocking requirement in dynamic traffic grooming, how to determine the resources needed to meet this requirement. We call it resource planning for dynamic traffic grooming. It is raised in a situation that after the initial deployment of optical networks, service providers often need to upgrade resources to accommodate increasing traffic demands. We formulate it as an ILP problem, and developed heuristics to solve this problem for large networks. Numerical results show that the heuristics can achieve good performance, and network resources increase slowly when requiring lower client call blocking probability.     

Architectures and Performance of Optical Packet Switching over WDM

Packet switching over wavelength division multiplexing (WDM) channels is considered with the aim to investigate algorithms for wavelength assignment and to define feasible switch architectures, in the presence of connectionless or connection-oriented transfer modes. In particular, as regards the connection-oriented scenario, mapping of virtual connections onto wavelengths operated by network nodes is considered and procedures are proposed to achieve statistical multiplexing efficiency by dynamic wavelength re-assignment. Switch architectures to support dynamic wavelength encoding and the related performance evaluation are presented and discussed in the paper, evidencing the benefits of packet switching over WDM.     

Multiclass scheduling algorithms for the DAVID metro network

The data and voice integration over dense wavelength-division-multiplexing (DAVID) project proposes a metro network architecture based on several wavelength-division-multiplexing (WDM) rings interconnected via a bufferless optical switch called Hub. The Hub provides a programmable interconnection among rings on the basis of the outcome of a scheduling algorithm. Nodes connected to rings groom traffic from Internet protocol routers and Ethernet switches and share ring resources. In this paper, we address the problem of designing efficient centralized scheduling algorithms for supporting multiclass traffic services in the DAVID metro network. Two traffic classes are considered: a best-effort class, and a high-priority class with bandwidth guarantees. We define the multiclass scheduling problem at the Hub considering two different node architectures: a simpler one that relies on a complete separation between transmission and reception resources (i.e., WDM channels) and a more complex one in which nodes fully share transmission and reception channels using an erasure stage to drop received packets, thereby allowing wavelength reuse. We propose both optimum and heuristic solutions, and evaluate their performance by simulation, showing that heuristic solutions exhibit a behavior very close to the optimum solution.     

Design of WDM PON With Tunable Lasers: The Upstream Scenario

Tunable lasers are potential upstream optical light generators for wavelength-division-multiplexing (WDM) passive optical network (PON), which is a promising solution for next-generation broad-band optical access. The wavelength provisioning flexibility of tunable lasers can increase the admissible traffic in the network as compared to wavelength-specific lasers. Generally, the broader the lasers' tuning ranges, the more the traffic can be admitted to the network. However, broad tuning range requires sophisticated technology, and probably high cost. To achieve the optimal tradeoff between the admissible traffic and the cost, we investigate the relationship between lasers' tuning ranges and the network's admissible traffic and then design WDM PON by selecting lasers with proper tuning ranges for the upstream data transmission. Specifically, we focus on addressing two issues under three scenarios. The two issues are: how to admit the largest traffic by properly selecting lasers, and how to admit given upstream traffic using lasers with tuning ranges as narrow as possible. The three scenarios are: full-range tunable and wavelength-specific lasers are available, limited-range tunable lasers are available, and the exact number of lasers with specific tuning ranges are given.      

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     

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.     

基于AWG的OADM结构设计

光分插复用器（OADM）是实现波长上下话路、灵活配置网络资源的关键网元设备之一，因为阵列波导光栅（AWG）在成本和综合性能方面具有很大的优越性而使其成为目前最适于作为WDM复用器与解复用器以及构成OADM的关键器件，文章详细研究了基于AWG构建OADM的不同结构组成，主要研究了环回和折叠型两种结构，并给出了易于实现集成的平板形结构设计的不同方案。     

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.      

On service provisioning using light-trails in WDM optical networks with waveband switching

As the number of wavelengths in a single optical fiber increases, so does the number of ports needed for wavelength switching in optical cross-connects (OXCs), which may significantly increase the cost and difficulty associated with controlling large OXCs. Waveband switching (WBS) treats several wavelengths as a bundle that is switched through a single port if they share the same switch route, so that the number of ports needed can be reduced. On the other hand, light-trails in wavelength division multiplexing (WDM) optical networks allow intermediate nodes on established optical paths to access the data paths whereas light-paths only allow two end nodes to access the data paths. Therefore, light-trails offer significantly better flexibility for service provisioning and traffic grooming. In this article, we study service provisioning using light-trails in WDM optical networks with the WBS capability under a static traffic model. For comparison, integer linear programs are formulated for establishing light-trails with and without WBS. Numerical studies show that in certain cases, service provisioning with WBS in light-trail networks can reduce the number of ports needed while providing a more flexible sub-wavelength service provisioning capability. However, contrary to intuition, in most cases applying the WBS technique requires more ports in OXCs in light-trail networks. This study provides insights into the network design problem that applies the WBS technology to light-trail based optical networks.     

Design-dimensioning model for transparent WDM packet-switchedirregular networks

A detailed analytical traffic model for all-optical wavelength division multiplexing (WDM) photonic packet-switched networks is presented and the requirements for buffer size and link dimensions are analyzed. This paper shows that due to the topology, packets may generate traffic bottlenecks produced by a tendency of the routing scheme to send packets with different destinations through preferred paths. This effect increases the traffic load and, hence, the probability of blocking at the output links of specific routers in the network and, therefore, a large buffer depth or an increment in the number of fibers per link is required. Three router architectures are analyzed and it is shown that WDM all-optical router architectures with shared contention resolution resources are the best candidates to reduce hardware volume and cost of all-optical networks. It is shown that routers with a bank of completely shared wavelength converters (WCs) require a fraction of WCs compared to router architectures that use a WC per wavelength. This fraction depends on the location of the router, the network topology, and the traffic load in the network. However, in general terms, about 50% to 90% of WCs can be saved by architectures with shared wavelength-conversion resources. Also, it is shown that limited wavelength conversion degrees d=8 and d=10 in packet-switching routers with 16 and 32 wavelengths give the same probability of packet loss performance as full wavelength conversion