In this paper, we investigate the wavelength assignment issue in wavelength-routed all-optical WDM networks with Sparse-Partial Wavelength Conversion. Traditionally, wavelength assignment is only designed for the purpose of decreasing the blocking probability. In Sparse-Partial Wavelength Conversion, wavelength assignment can be used to decrease the number of wavelength converters if keeping the same level of blocking probability. We propose three different wavelength assignment algorithms, namely Segment-First First Fit (SFFF), Path-First First-Fit (PFFF), and Minimum Converter Allocation (MCA). Our results show that MCA is the best one among the three, and it can achieve very close performance to Sparse Wavelength Conversion by using a very small number of wavelength converters. The performance of PFFF is very close to MCA, and it is very simple to be implemented.
Wavelength conversion has been shown as one of the key techniques that can improve the blocking performance in a wavelength-routed all-optical network. Given that wavelength converters nowadays are still very expensive, how to make effective use of the limited number of wavelength converters becomes an important issue. In this paper, we propose a novel sparse-partial wavelength conversion (SPWC) architecture with the inherent flexibility that can facilitate network carriers to migrate the optical backbone to support wavelength conversion. We demonstrate that this architecture can significantly save the number of wavelength converters while still achieving excellent blocking performance. We further investigate the wavelength converter placement problem. Simulation results indicate that, with appropriate wavelength assignment and wavelength converter placement scheme, the performance of the wavelength-routed all-optical network with only 1-5% of wavelength conversion capability is very close to that of the networks with full-complete wavelength conversion capability.
Blocking has been the key performance index in the design of an all-optical network. Existing research demonstrates that an effective routing and wavelength assignment (RWA) strategy and a proper wavelength converter placement algorithm are the two primary vehicles for improving the blocking performance. However, these two issues have largely been investigated separately in that the existing RWA algorithms have seldom considered the presence of wavelength conversion, while the wavelength converter placement algorithms have largely assumed that a static routing and random wavelength assignment algorithm is employed. In this paper we present some strong evidences that these two issues need to be considered jointly, and call for the re-examination of both RWA and wavelength converter placement.
This article is divided into two parts. First we demonstrate that the conventional RWA algorithms do not work well in the presence of wavelength conversion since they usually only take into consideration the distribution of available wavelengths, and do not explicitly consider the lengths of routes. Through extensive simulation over a variety of topologies, we demonstrate that a weighted least-congestion routing and first-fit wavelength assignment (WLCR-FF) RWA algorithm can achieve much better blocking performance than static routing, fixed-alternate routing, or least-loaded routing algorithms in the environment of sparse or full wavelength conversion.
Secondly, using simulation we show that a heuristic-based converter placement algorithm called Weighted Maximum Segment Length (WMSL) algorithm proposed for a simple dynamic RWA (i.e., the least-loaded routing algorithm) under sparse wavelength conversion, not only outperforms existing wavelength converter placement algorithms by a large margin, but also can achieve almost the same performance as that of full wavelength conversion using the same RWA algorithm.
We have recently witnessed a phenomenal growth in the development and deployment of wireless services, evident from the proliferation of the cellular data services and the emerging wireless multimedia applications. This opens up a new avenue for research, and calls for the re-examination of some of the fundamental issues in wireless cellular networks. With the cell size being systematically reduced into micro-cell and pico-cell systems, in order to increase the overall network capacity, one of the key challenges is the design of effective call admission control (CAC) policies, which have to guarantee potentially different quality of service (QoS) requirements from diverse traffic types while at the same time maintaining high utilization of the scarce wireless bandwidth. The objectives of this article are to review the key issues involved in the design of call admission control policies based on some of the recent proposals, and to discuss the challenges associated to offer effective support for multi-services
This paper presents a formal study on channelized bandwidth resource provisioning for multi-rate and multi-session video broadcast in a broadband wireless network with heterogeneous users. The formulation is generic in that it considers both inter-session and intra-session wireless resource allocation. It also takes into account the most fundamental issues associated with video transmission including encoding complexity, transport overhead, non-linear relationship between the receiver perceived video quality and the delivered bandwidth, and intra- and inter-session fairness. In addition, we derive an optimal allocation scheme to manage the scarce wireless resources.
Sparse wavelength conversion and appropriate routing and wavelength assignment (RWA) algorithms are the two key factors in improving the blocking performance in wavelength-routed all-optical networks. It has been shown that the optimal placement of a limited number of wavelength converters in an arbitrary mesh network is an NP complete problem. There have been various heuristic algorithms proposed in the literature, in which most of them assume that a static routing and random wavelength assignment RWA algorithm is employed. However, the existing work shows that fixed-alternate routing and dynamic routing RWA algorithms can achieve much better blocking performance. Our study in this paper further demonstrates that the wavelength converter placement and RWA algorithms are closely related in the sense that a well designed wavelength converter placement mechanism for a particular RWA algorithm might not work well with a different RWA algorithm. Therefore, the wavelength converter placement and the RWA have to be considered jointly. The objective of this paper is to investigate the wavelength converter placement problem under fixed-alternate routing algorithm and least-loaded routing algorithm. Under the fixed-alternate routing algorithm, we propose a heuristic algorithm called Minimum Blocking Probability First (MBPF) algorithm for wavelength converter placement. Under the least-loaded routing algorithm, we propose a heuristic converter placement algorithm called Weighted Maximum Segment Length (WMSL) algorithm. The objective of the converter placement algorithm is to minimize the overall blocking probability. Extensive simulation studies have been carried out over three typical mesh networks, including the 14-node NSFNET, 19-node EON and 38-node CTNET. We observe that the proposed algorithms not only outperform existing wavelength converter placement algorithms by a large margin, but they also can achieve almost the same performance comparing with full wavelength conversion under the same RWA algorithm.
This paper addresses the problem of wavelength assignment and wavelength routing in a wide-area optical network, where Wavelength Division Multiplexing (WDM) technology has emerged as the transmission and switching choice. One of the major design issues in this network is the assignment of the limited number of wavelengths among network stations so that higher aggregate capacity can be achieved. The problem of wavelength assignment and routing is proved to be NP-hard problem. The present literature on this topic is a large repertoire of heuristics that produce good solutions in a reasonable amount of time. These heuristic, however, have restricted applicability in a practical environment because they have a number of fundamental problems including high time complexity, lack of scalability with respect to optimal solutions. In this paper, we propose genetic based algorithm with an objective to simultaneously meet the goals of height performance and fast running time. In addition, we propose to apply the Greedy Random Adaptive Search Procedure (GRASP) to solve the wavelength assignment problem. We demonstrate that our proposed algorithms can achieve lower blocking probability while taking considerably less running time when compared to one of the best known heuristic wavelength assignment algorithms proposed by Zhang and Acampora, in which close to optimal solution can be obtained.
Future broadband networks must support integrated services and offer flexible bandwidth usage. In our previous work, we explore the optical link control layer on the top of optical layer that enables the possibility of bandwidth on-demand service directly over wavelength division multiplexed (WDM) networks. Today, more and more applications and services such as video-conferencing software and Virtual LAN service require multicast support over the underlying networks. Currently, it is difficult to provide wavelength multicast over the optical switches without optical/electronic conversions although the conversion takes extra cost. In this paper, based on the proposed wavelength router architecture (equipped with ATM switches to offer O/E and E/O conversions when necessary), a dynamic multicast routing algorithm is proposed to furnish multicast services over WDM networks. The goal is to joint a new group member into the multicast tree so that the cost, including the link cost and the optical/electronic conversion cost, is kept as less as possible. The effectiveness of the proposed wavelength router architecture as well as the dynamic multicast algorithm is evaluated by simulation.
In this paper, we study the problem of employing virtual private network (VPN) over wavelength division multiplexing networks to facilitate the guarantee of diverse quality of service requirements of different VPNs. A wavelength routed backbone network is considered. A VPN is specified by the desired logical topology and an a priori traffic matrix.
KEYWORDS: Receivers, Transmitters, Wavelength division multiplexing, Stars, Local area networks, Control systems, Process control, Data transmission, Channel projecting optics, Optical components
Extensive research and considerable progress in the dense optical wavelength division multiplexing (WDM) technology has made it the most likely candidate for implementation in next-generation high performance switches, LANs and MANs. The first key challenge is the continuous development of cost-effective optical components in order to realize practical networks. The next main challenge is to design an effective channel access protocol that will: (a) take full advantage of the existing and emerging optical technologies, (b) fairly and successfully coordinate transmissions between the networks nodes, and (c) efficiently manage the enormous fiber bandwidth. There have been many access protocols proposed for WDM networks including quite a few proposals that require many more channels than the number of nodes. The practical device characteristics impose an upper limit on the number of available WDM channels. Our focus in this paper is on systems with many nodes and small number of channels. We study the use of in-band signaling mechanism compared to the separate control channel (out-band signaling) approach. Signaling is used to achieve coordination between source and destination with respect the communication channel. The objective of this paper is to understand the key trade-offs in the protocol design for such networks through close examinations of the two approaches. Our intent is not to claim the superiority of either approach, rather to stimulate further studies on such systems.
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