A general approach for all-to-all routing in multihop WDM optical networks

WDM optical networks provide unprecedented high speed and reliability for message transfer among the nodes. All-to-all routing is a fundamental routing problem in such networks and has been well studied on single hop WDM networks. However, the number of wavelengths to realize all-to-all routing on the single hop model typically is very large. One way to reduce the number of wavelengths is to use k-hop routing, in which each routing path consists of k segments and each segment is assigned a different wavelength, where k usually is a small constant. Because of the complexity of design and analysis for such a routing problem, only few papers discussed and proposed all-to-all routing by k/spl ges/2 hops. However, the proposed algorithms are usually exceeding complicated even for ring topologies. Often, an ad hoc approach is employed to deal with each individual topology. In this paper we propose a generic method for all-to-all routing in multi-hop WDM networks, which aims to minimize the number of wavelengths. We illustrate the approach for several optical networks of commonly used topology, including lines, rings, tori, meshes, and complete binary trees. For each case an upper bound on the number of wavelengths is obtained. The results show that this approach produces clear routing paths, requires less wavelengths, and can easily incorporate load balancing. For simple topologies such as lines and rings, this approach easily produces the same bounds on the number of wavelengths that were hard-obtained previously. Moreover, this general approach provides a unified routing algorithm for any d-dimensional torus, which seems impossible to obtain by the previous approach.     

Optimal WDM schedules for optical star networks

We consider single-hop wavelength-division multiplexed networks in which the transmitters take a nonzero amount of time, called tuning latency, to tune from one wavelength to another. For such networks, we show that, under certain conditions on the traffic matrix, there exist polynomial-time algorithms that produce the optimal schedule. Further, the tuning latency is masked in the length of the optimal schedule. Using Chernoff-Hoeffding bounds, we show that the condition on the traffic matrix is satisfied with high probability when the wavelength reuse factor is large, i.e., the number of nodes is large compared to the number of wavelengths. Simulation results show the dramatic improvement in the performance of the network using our algorithm as compared with other heuristics     

Packet scheduling in broadcast WDM networks with arbitrarytransceiver tuning latencies

We consider the problem of scheduling packet transmissions in a broadcast, single-hop wavelength-division multiplexing (WDM) network, with tunability provided only at one end. Our objective is to design schedules of minimum length to satisfy a set of traffic requirements given in the form of a demand matrix. We address a fairly general version of the problem as we allow arbitrary traffic demands and arbitrary transmitter tuning latencies. The contribution of our work is twofold, First we define a special class of schedules which permit an intuitive formulation of the scheduling problem. Based on this formulation we present algorithms which construct schedules of length equal to the lower bound provided that the traffic requirements satisfy certain optimality conditions. We also develop heuristics which, in the general case, give schedules of length equal or very close to the lower bound. Secondly, we identify two distinct regions of network operation. The first region is such that the schedule length is determined by the tuning requirements of transmitters; when the network operates within the second region however, the length of the schedule is determined by the traffic demands, not the tuning latency. The point at which the network switches between the two regions is identified in terms of system parameters such as the number of nodes and channels and the tuning latency. Accordingly, we show that it is possible to appropriately dimension the network to minimize the effects of even large values of the tuning latency     

Lightpath restoration in WDM optical networks

Optical networks employing wavelength-division multiplexing and wavelength routing are potential candidates for future wide area networks. Because these networks are prone to component failures and carry a large volume of traffic, maintaining a high level of service availability is an important issue. This article discusses providing tolerance capability to the optical layer in WDM-based transport networks. It presents a survey on restoration schemes available in the literature, explains the operation of these schemes, and discusses their performance.     

WDM Ethernet passive optical networks

WDM EPONs not only allow for cautious pay-as-you-grow upgrades of single-channel TDM EPONs but also avoid linearly increasing polling cycle times for an increasing number of ONUS. In this article, we first provide a comprehensive overview of the state of the art of TDM EPONs and recently reported dynamic bandwidth allocation algorithms, including decentralized scheduling schemes. After reviewing previous work on WDM EPONs, we address the requirements of WDM upgraded EPONs and make recommendations on an evolutionary WDM upgrade at the architecture, protocol, and dynamic bandwidth allocation algorithm levels, taking backward compatibility with MPCP and future-proofness against arbitrary WDM ONU structures into account. We describe and compare online and offline scheduling paradigms for WDM EPONs. Our simulation results indicate that online scheduling can achieve lower delays, especially at high loads. We outline areas of future research on WDM EPONs.     

WDM网络波带交换算法分析

主要介绍了WDM光网络中的波带交换(Waveband Switching)问题的基本概念、技术特点.并分析了研究波带交换问题与波长路由问题(RWA)的不同之处,总结了波带交换算法常用的分析和研究方法.     

WDM光网络中的业务量疏导

波分复用（WDM）技术在主干传送网中巳广泛应用，WDM光网络的研究进展也非常迅速，光网络中的业务量疏导定义为复用、解复用和交换低速率业务流到大容量的光路中的行为。介绍了WDM光网络的业务量疏导的重要性，研究方法及其最新研究进展情况。     

Mini-slot TDM WDM optical networks

In recent years, optical transport networks have evolved from interconnected SONET/WDM ring networks to mesh-based optical WDM networks. Time-slot wavelength switching is to aggregate the lower rate traffic at the time-slot level into a wavelength in order to improve bandwidth utilization. With the advancement of fiber-optics technologies, continual increase of fiber bandwidth and number of wavelengths in each fiber, it is possible to divide a wavelength in a fiber into time-slots, and further divide a time-slot into mini-slots so that the fiber bandwidth can be more efficiently utilized. This article proposes a router architecture with an electronic system controller to support optical data transfer at the mini-slot(s) of a time-slot in a wavelength for each hop of a route. The proposed router architecture performs optical circuit switching and does not use any wavelength converter. Each node in the mini-slot TDM WDM optical network consists of the proposed router architecture. Three different network topologies are used to demonstrate the effectiveness and behavior of this type of network in terms of blocking probability and throughput.     

Optimal nonuniform wavebanding in WDM mesh networks

Grouping together a set of consecutive wavelengths in a WDM network and switching them together as a single waveband could achieve savings in switching costs of an optical cross-connect. This technique is known as waveband switching. While previous work has focused on either uniform band sizes or nonuniform band sizes considering a single node or ring networks, in this paper we focus on optimizing the number of wavebands and their sizes for mesh topologies. We formulate a problem of optimizing the number of wavebands in a mesh network for a given set of lightpaths. The objective of the band minimization problem is to minimize the number of nonuniform wavebands in the network while satisfying the traffic requests. We formulate an integer linear program and propose efficient heuristics. Simulation results are presented to demonstrate the effectiveness of the proposed approaches under static traffic case. Our results show that the number of switching elements can be reduced by a large amount using waveband switching compared to wavelength switching. We also apply the proposed waveband strategy to the dynamic stochastic traffic case and evaluate the network performance in terms of blocking probability through numerical simulations.     

Control architecture in optical burst-switched WDM networks

Optical burst switching (OBS) is a promising solution for building terabit optical routers and realizing IP over WDM. In this paper, we describe the basic concept of OBS and present a general architecture of optical core routers and electronic edge routers in the OBS network. The key design issues related to the OBS are also discussed, namely, burst assembly (burstification), channel scheduling, burst offset-time management, and some dimensioning rules. A nonperiodic time-interval burst assembly mechanism is described. A class of data channel scheduling algorithms with void filling is proposed for optical routers using a fiber delay line buffer. The LAUC-VF (latest available unused channel with void filling) channel scheduling algorithm is studied in detail. Initial results on the burst traffic characteristics and on the performance of optical routers in the OBS network with self-similar traffic as inputs are reported in the paper.     

Tree-shared multicast in optical burst-switched WDM networks

In this paper, we propose a new multicast scheme called tree-shared multicasting (TS-MCAST) in optical burst-switched wavelength-division-multiplexing networks, taking into consideration overheads due to control packets and guard bands (GBs) associated with data bursts. In TS-MCAST, multicast traffic belonging to multiple multicast sessions from the same source-edge node to possibly different destination-edge nodes can be multiplexed together in a data burst, which is delivered via a shared multicast tree. To support TS-MCAST, we propose three tree-sharing strategies based on equal coverage, super coverage, and overlapping coverage, and present a simple shared multicast tree-construction algorithm. For performance comparison, we consider two other multicast schemes: separate multicasting (S-MCAST) and multiple unicasting (M-UCAST). We show that TS-MCAST outperforms S-MCAST and M-UCAST in terms of bandwidth consumed and processing load (i.e., number of control packets) incurred for a given amount of multicast traffic under the same unicast traffic load with static multicast sessions and membership.     

Provisioning algorithms for WDM optical networks

This paper concerns connection provisioning for optical networks employing wavelength division multiplexing. A heuristic algorithm is developed and numerically studied for routing and wavelength assignment of a set of static connection requests. The algorithm runs much faster than the optimum solution of this problem. An adaptation of the algorithm is proposed to design restorable networks which can handle a specified set of failures. The proposed algorithm is based on taking all failures into consideration simultaneously, and performs better than developing independent designs for each failure     

Design protection for WDM optical networks

With wavelength division multiplexing (WDM) networks the failure of a single link or component may cause the simultaneous failure of several optical channels, potentially making impossible restoration by rerouting directly in higher layers directly using the optical network (SDH, ATM, internal protocol (IP)). To address this, we introduce the concept of design protection, which aims at making such failure propagations impossible. We present the disjoint alternate path (DAP) algorithm which places optical channels in order to maximize design protection. We show the result on various network examples     

Efficient scheduling of transmissions in optical broadcast networks

All-optical networks (AONs) with a broadcast-star based physical topology offer the possibility of transmission scheduling to resolve channel and receiver conflicts. This paper considers the problem of scheduling packet transmissions in a wavelength-division multiplexed (WDM) optical network with tunable transmitters and fixed-tuned receivers. The scheduling problem is complicated by tuning latency, a limited number of channels, and arbitrary traffic demands. We first analyze scheduling all-to-all packet transmissions and obtain a new lower bound for the schedule length. The lower bound is achieved by an algorithm proposed by Pieris and Sasaki (1994). We then extend the analysis to the case of arbitrary traffic demands and obtain lower bounds for the schedule length. Two constructions for scheduling algorithms are provided through list scheduling and multigraphs. The upper bounds so obtained not only provide performance guarantees with arbitrary demands, but also nearly meet the lower bound in simulations     

Protection interoperability for WDM optical networks

The failure of a single optical link or node in a wavelength division multiplexing (WDM) network may cause the simultaneous failure of several optical channels. In some cases, this simultaneity may make it impossible for the higher level (SONET or IP) to restore service. This occurs when the higher level is not aware of the internal details of network design at the WDM level. We call this phenomenon “failure propagation.” We analyze three types of failure propagation, called “bottleneck,” “connectivity,” and “multiple groups.” Then we present a solution based on the definition of appropriate requirements at network design and a WDM channel placement algorithm, protection interoperability for WDM (PIW). Our method does not require the higher level to be aware of WDM internals, but still avoids the three types of failure propagation mentioned above. We finally show the result on various network examples     

On scheduling all-to-all personalized connection and cost-effectivedesigns in WDM rings

We consider the problem of scheduling all-to-all personalized connections (AAPC) in WDM rings. Scheduling one connection for every source-destination pair in a network of limited connectivity provides a way to reduce routing control and guarantee throughput. For a given number of wavelengths K and a given number of transceivers per node T, we first determine the lower bound (LB) on the schedule length, which depends on both K and T. To achieve the LB, either the network bandwidth, the I/O capacity, or both should be fully utilized. This approach first constructs and then schedules circles, each of which is formed by up to four non-overlapping connections and can fully utilize the bandwidth of one wavelength. The proposed circle construction and scheduling algorithms can achieve the LB if K⩽T相似文献   

Protecting multicast sessions in WDM optical mesh networks

Recent advances in wavelength-division-multiplexing (WDM) technology are expected to facilitate bandwidth-intensive multicast applications. However, a single fiber (bundle) cut on such a network can disrupt the transmission of information to several destination nodes on a "light tree"-based multicast session. Thus, it is imperative to protect multicast sessions e.g., by reserving resources along backup trees. We show that, if a backup tree is directed-link-disjoint to its primary counterpart, then data loss can be prevented in the event of any single link failure. We provide mathematical formulations for efficient routing and wavelength assignment (RWA) of several multicast sessions (including their backup trees for dedicated protection) at a globally optimum cost. We present these formulations for networks equipped with two kinds of multicast-capable switch architectures: one using the opaque (O-E-O) approach and the other using transparent (all-optical) approach. We expand our formulations to accommodate sparse splitting constraints in a network, in which an optical splitter has limited splitting fanout and each node has a limited number of such splitters. We develop a profit-maximizing model that would enable a network operator to be judicious in selecting sessions and simultaneously routing the chosen ones optimally. We illustrate the solutions obtained from solving these optimization problem formulations for a representative-size network.     

Coherent and incoherent crosstalk in WDM optical networks

The impact of coherent and incoherent crosstalk on an optical signal passing through optical cross-connect nodes (OXC's) in wavelength division multiplexing (WDM) optical networks is studied, and the analytical expressions are given. Such crosstalk will be generated when the optical propagation delay differences of optical paths in an OXC do not exceed the coherent time of the lasers. While causing fluctuation of signal power, coherent crosstalk may cause noise or not, depending on the relationship between the optical propagation delay differences and the time duration of one bit of the signal. Incoherent crosstalk may cause very high noise power, because it can be a coherent combination of crosstalk contributions. The statistical impact of all crosstalk contributions on signal is studied by simulation, and the concept of quantile is proposed to relax the crosstalk specification requirement for components. The crosstalk specification requirements are then obtained for components used in WDM optical networks with different scales     

WDM光网络中动态流量的疏导

流量疏导是当今光网络研究中的一个前沿和热点问题,在波分复用(WDM)光网络中使用流量疏导技术能有效降低网络的成本,减少网络节点中业务信息的处理量.文章讨论了动态流量疏导的意义及其分类,分析了关于在各种网络结构中动态流量疏导的研究近况,最后对今后的发展方向做了一番展望.     

Modeling of in-band crosstalk in WDM optical networks

In this paper, we analyze three different simulation models which allow the impact of in-band crosstalk on the transmission performances of wavelength division multiplexing (WDM) optical networks to be evaluated: an accurate simulation (AS), a Gaussian correlated noise (GCN) model, and a Gaussian white noise (GWN) model. In the AS, an interfering channel is generated at each node and added to the signal after an optical filtering. The final result must be averaged with respect to the message transmitted on the interfering channels and to the phases of the optical carriers. In the GCN the crosstalk term is modeled as a Gaussian correlated noise, whose spectrum coincides with that of the interfering channel. This model can be further simplified if the noise is also assumed uncorrelated (GWN approximation). The results obtained by these simulation models are also compared with those produced by an analytical model allowing to evaluate the in-band crosstalk penalty