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.     

Blocking Analysis of Dynamic Traffic Grooming in Mesh WDM Optical Networks

Traffic grooming in wavelength division multiplexing (WDM) optical networks routes and consolidates sub-wavelength connections onto lightpaths, to improve network utilization and reduce cost. It can be classified into static or dynamic, depending on whether the connections are given in advance or randomly arrive/depart. In this paper, an analytical model is developed for dynamic traffic grooming, allowing heterogeneous data rates for sub-wavelength connections, arbitrary alternate routing in both logical and physical topologies, and arbitrary wavelength conversion. The accuracy of the model has been verified by numerical results from simulation.     

A path inflation control strategy for dynamic traffic grooming in IP/MPLS over WDM network

The use of alternate routes for traffic grooming in IP/MPLS over wavelength-division multiplexing (WDM) networks may lead to the propagation of congestion from one link to others in the IP/MPLS layer. This can be tackled by using the path inflation control (PIC) strategy proposed here for operating an IP/MPLS over WDM network in the overlay model. This supports dynamic traffic grooming with less blocking than other strategies. Network resource usage is also efficient as new lightpaths are set up for a new label switched path (LSP) request only when indicated by the congestion conditions.     

Analysis of multi-hop traffic grooming in WDM mesh networks

Traffic grooming is an essential functionality of WDM optical networks to provision multi-granularity subwavelength connections. Depending on the number of lightpaths allowed in a connection route, traffic grooming can be classified as single-hop traffic grooming (SH-TG) and multi-hop traffic grooming (MH-TG). MH-TG is more general and resource-efficient than SH-TG, because it allows connections from different source-destination pairs to share the bandwidth of a lightpath. In this paper, we propose a MH-TG algorithm, namely the fixed-order multi-hop (FOMH) grooming algorithm, based on the fixed-alternate routing approach. We introduce the grooming node selection (GNS) problem in MH-TG and propose three grooming policies, namely exhaustive sequential (ES), limited-hop sequential (LHS) and load sharing (LS) policies, to address the GNS problem. These policies represent different trade-offs among blocking probability, computational complexity and transceiver requirements. Given that the analysis of MH-TG is a relatively unexplored area, we propose an analytical model to evaluate the blocking performance of MH-TG using FOMH and the LS grooming policy. To address the multi-layered routing and multi-rate connection characteristics of traffic grooming, we introduce a novel multi-level decomposition approach in our analytical model which decomposes traffic at four different levels, namely alternate path, connection route, lightpath and link levels. The model also addresses various factors that affect connection blocking probability. These factors include wavelength continuity constraint, channel continuity constraint and route dependence. The Erlang fixed-point approximation method is used to solve the analytical model. Numerical results show that analytical results match well with simulation results. We also evaluate the effect of the grooming policies, the number of virtual hops (lightpaths) within a connection route and the number of alternate paths on the performance of the grooming algorithm.     

Traffic grooming in WDM optical network with grooming resources at Max Connectivity nodes

In this paper, we propose Max Connectivity grooming in WDM mesh networks under static lightpath connection requests. The grooming and wavelength conversion resources are placed at the nodes having maximum connections. We propose a heuristic genetic algorithm (GA) model to solve grooming, routing and wavelength assignment. The GA algorithm has been used to optimize the cost of grooming and wavelength conversion resources. The blocking probability has been investigated under different lightpath connections. The performance of Max Connectivity grooming has been compared with other grooming policies. Our results indicate the improvement of resource utilization with minimum blocking probability.     

一种WDM网状网中基于共享保护的业务量疏导算法

在WDM网络中业务的带宽需求远低于一个波长所提供的带宽,业务量疏导可以聚集低速业务到大容量的光路中从而有效地利用波长带宽资源.目前大多数业务量疏导的研究限于环形网,考虑对WDM网状网中低速业务可靠疏导的文献更少.该文综合考虑WDM网状网生存性及业务量疏导,提出了基于波长分层图的共享保护业务量疏导算法(SPTG-LG,Shared Protection Traffic Grooming algorithm ba,sed on wavelength Layered-Graph),并对算法进行了仿真和分析.     

A Link Bundled Auxiliary Graph Model for Constrained Dynamic Traffic Grooming in WDM Mesh Networks

This paper addresses the two-layer dynamic traffic grooming problem in wavelength-division-multiplexed (WDM) mesh optical networks subject to resource constraints and the generalized wavelength continuity (GWC) constraint. The GWC constraint is a relaxed wavelength continuity constraint which incorporates various kinds of wavelength conversion capabilities that exist in optical networks. As an improvement over the existing layered auxiliary graph (layered-AG) approach which represents each wavelength separately in the auxiliary graph, we introduce a largely simplified link bundled auxiliary graph (LBAG) model and propose the SAG-LB method to find paths and assign wavelengths for new lightpaths subject to the GWC constraint. We propose the constrained integrated grooming algorithm (CIGA) based on the LBAG model. A grooming policy influences the resource utilization by determining the weight function of the auxiliary graph. We propose the least resource path first (LR) grooming policy, which is an improvement over the existing grooming policies in the literature, by integrating the wavelength and transceiver metrics together. Simulation results show that the LBAG model achieves a comparable blocking performance with the layered-AG approach while using a significantly less amount of running time. We also present the worst case time complexity analysis of the CIGA grooming algorithm and evaluate the performance of the LR grooming policy by simulation.     

Comparison of SDH/SONET-WDM multi-layer networks with static and dynamic optical plane

SDH/SONET-WDM multi-layer networks are a very attractive solution to cope with the increasing dynamics and capacities in today’s core networks. In SDH/SONET multi-layer networks, client layer SDH/SONET connections are groomed to wavelength channels and transported using end-to-end lightpaths. Also, intermediate grooming can yield to a more efficient utilization of network resources.In this paper, two principal SDH/SONET-WDM multi-layer network architectures are investigated covering the dynamics either only in the electrical layer or in both layers, respectively. In order to show benefits and drawbacks for the introduction of dynamics in the optical plane of today’s backbone networks, we present a detailed performance evaluation based on simulation studies and compare both architectures for different total network capacities and grooming strategies. We also systematically analyze the traffic composition which until now has only rarely been investigated. We show that changes in the traffic pattern can be covered by a dynamic optical plane. Further, we figure out the timescale for switching operations in the optical layer which is at least two orders of magnitude below the connection’s interarrival rate.     

WDM光网络的多优先级业务疏导机制

IP over WDM网络中,业务疏导能有效提高波长带宽利用率.然而,单一化的业务疏导机制难以满足不同业务的QoS要求,也很难做到经济合理地使用光路.提出了一种支持多优先级业务的疏导机制,该机制根据光路传输的时延和丢包特性来选择恰当的疏导路径,同时,该机制结合了抢占和流量分割技术,能有效地实现流量分割和多路抢占,降低了业务的阻塞概率.仿真结果显示,该疏导机制在保证业务QoS的同时,降低了高优先级业务的阻塞概率;在业务负载低时,能有效减少抢占.     

WDM网络中动态流量的资源效率疏导策略

为了解决波分复用(WDM)网状网络中的动态流量疏导问题,基于收发器节约辅助图模型,提出了一种资源效率疏导策略.它同时考虑收发器和波长链路两种网络资源的有效利用,根据当前的网络状态动态改变疏导策略,使网络不会由于某一种资源的缺乏而导致阻塞所有流量,避免了另一种资源因富余而造成的浪费,从而两种资源都能得到充分利用.在辅助图模型中,根据两种资源的可用数目比值,对各条边设置不同的权值函数,可轻易地实现该策略.仿真结果证明,不管是收发器资源受限还是波长资源受限,该策略都能取得较好的性能,降低了网络的阻塞率.     

Grooming of Arbitrary Traffic in Optical WDM Mesh Networks Using a Genetic Algorithm

In this paper, a genetic algorithm is proposed for grooming of arbitrary traffic in optical mesh networks. Traffic streams are routed in the wavelength division multiplexing (WDM) grooming networks that comprise both fiber links and established lightpaths. Chromosomes are split into multiple versions when multiple shortest routes are found. The selection strategy is based on a comparison between chromosomes. A variety of cost functions are proposed for the routing algorithm and two comparison methods are considered in the selection procedure. Computer simulations are performed with randomly generated traffic patterns. The results show that the algorithm is effective for traffic grooming (TG) problems, and also for routing and wavelength assignment problems.     

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.     

Quality-of-Service Based Protection in MPLS Control WDM Mesh Networks

Intelligent methods for automatic protection and restoration are critical in optical transport mesh networks. This paper discusses the problem of quality-of-service (QoS)-based protection in terms of the protection-switching time and availability for end-to-end lightpaths in a WDM mesh network. We analyze the backup lightpath-sharing problem in such networks and study the correlation of the working lightpaths and the impact of the correlation on the sharing of the backup lightpaths. We present a multi-protocol-label-switching (MPLS) control-based fully distributed algorithm to solve the protection problem. The proposed algorithm includes intelligent and automatic procedures to set up, take down, activate, restore, and manage backup lightpaths. It greatly reduces the required resources for protection by allowing the sharing of network resources by multiple backup lightpaths. At the same time, it guarantees, if possible, to satisfy the availability requirement even with resource sharing by taking the correlation of working lightpaths into consideration. A simple analysis of the proposed algorithm in terms of computation time and message complexity indicates that the implementation of the algorithm is practical. The illustrative studies that compare the performance of 1:1, unlimited sharing, and QoS-based backup sharing algorithms indicate that QoS-based sharing achieves comparable performance as unlimited sharing, which is much better than the 1:1 backup scheme in terms of connection blocking probability, average number of connections in the network for a given offered load, and network resource utilization.     

Hierarchical routing and traffic grooming in IP/MPLS-based ASON/GMPLS multi-domain networks

Routing, connection setup, and path computation are well-known problems in multi-domain networks, which have been largely analyzed in pure IP (packet) networks. In circuit-switched optical multi-domain networks, there remain, however, a number of routing and path computation challenges. Traffic grooming means combining a number of low-speed traffic streams so that the high capacity of each lightpath may be used as efficiently as possible, as path computation implements the core of the grooming function, it is obvious that solutions for the traffic grooming problem in optical multi-domain networks are still not sufficiently investigated. In this study we propose a methodology to address the problems of routing, connection setup, and traffic grooming in optical multi-domain networks, which adapts a two-level hierarchical routing scheme and full-mesh topology abstraction algorithm to improve routing scalability and lower inter-domain blocking probabilities; additionally our proposed methodology adapts a scheme for traffic grooming in DWDM multi-domain networks to improve the resources usage. To test our proposed methodology we propose a detailed IP/MPLS-based ASON/GMPLS multi-domain multilayer test framework.     

Traffic grooming in mesh WDM optical networks - performance analysis

Traffic grooming is an important task in interworking between the wavelength-division multiplexing (WDM) optical network that supplies "pipes" at the wavelength granularity, and the attached client networks that usually require connections of subwavelength granularity. The focus of this paper is to conduct performance analysis of grooming dynamic client traffic in WDM optical networks with a mesh topology. This paper first briefly introduces the traffic grooming problem in WDM optical networks and the issues related to performance analysis. It then develops two link blocking models, an exact model based on the stochastic knapsack problem and an approximation model based on an approximate continuous time Markov chain (CTMC). The end-to-end performance analysis is conducted using the reduced load approximation. The result obtained from analysis is shown to be accurate compared with the numerical result obtained from simulation.     

Traffic grooming,routing, and wavelength assignment in an optical WDM mesh networks based on clique partitioning

In wavelength routed optical networks, the number of wavelength channels is limited due to several constraints and each wavelength as well as each lightpath support traffic in the Gbps range. On the other hand, the traffic requested by an individual connection is still in the Mbps range. Therefore, to utilize the network resources (such as bandwidth and transceivers) effectively, several low-speed traffic streams have to be efficiently groomed or multiplexed into one or more high-speed lightpaths. The grooming problem of a static demand is considered as an optimization problem. In this work, we have investigated the traffic grooming problem with the objective of maximizing the network throughput for wavelength-routed mesh networks and map this problem to the clique partitioning problem. We have proposed an algorithm to handle general multi-hop static traffic grooming based on the clique partitioning concept. The efficiency of our approach has been established through extensive simulation on different sets of traffic demands with different bandwidth granularities for different network topologies and compared the approach with existing algorithms.     

Comprehensive performance modeling and analysis of multicasting in optical networks

Multicasting is becoming increasingly important in today's networks. In optical networks, optical splitters facilitate the multicasting of optical signals. By eliminating the transmission of redundant traffic over certain links, multicasting can improve network performance. However, in a wavelength-division multiplexed (WDM) optical network, the lack of wavelength conversion necessitates the establishment of a single multicast circuit (light-tree) on a single wavelength. On the other hand, establishing several unicast connections (lightpaths) to satisfy a multicast request, while requiring more capacity, is less constrained in terms of wavelength assignment. The objective of the paper is to evaluate the tradeoff between capacity and wavelength continuity in the context of optical multicasting. To this end, we develop accurate analytical models with moderate complexity for computing the blocking probability of multicast requests realized using light-trees, lightpaths, and combinations of light-trees and lightpaths. Numerical results indicate that a suitable combination of light-trees and lightpaths performs best when no wavelength conversion is present.     

Post‐Disaster least loaded lightpath routing in elastic optical networks

Disaster events directly affect the physical topology of core networks and may lead to simultaneous failure of multiple lightpaths leading to massive service outages for network operators. To recover from such a failure scenario, the existing routing algorithms running on network nodes (routers or switches) typically attempt to reestablish the connections over new routes with shortest distances and hop count approach. However, this approach may result in congestion on some links, while other links may have the unutilized capacity. Hence, intelligent lightpath computing techniques are required to efficiently route network traffic over the new routes by considering traffic load of each link in addition to distance and hop count to minimize network congestion. In this paper, we have proposed a capacity‐constrained maximally spatial disjoint lightpath algorithm to tackle the provisioning and restoration of disrupted lightpaths in a postdisaster scenario in the context of elastic optical networking. This algorithm computes an alternate least loaded lightpath for disrupted primary lightpath using capacity‐constrained shortest lightpath. Alternate lightpath selection is based on a criteria parameter for a lightpath to be least loaded and constrained by either the length or the spatial distance between primary and alternate lightpaths. The spatial distance between lightpaths enables to reestablish the disrupted connection request away from disaster proximity. The performance of the proposed algorithm is evaluated through simulation for several parameters like blocking probability, network utilization, connection success rates, and minimum spatial distance.     

Label Preference Schemes for Lightpath Provisioning and Restoration in Distributed GMPLS Networks

In wavelength-routed networks based on a GMPLS control plane, the resource reservation protocol with traffic engineering extensions (RSVP-TE) allows to establish end-to-end lightpaths. The resource reservation can be blocked due to lack of available resources (forward blocking) or due to resource contentions (backward blocking). In wavelength-routed networks, the backward blocking is the predominant blocking contribution, when traffic load is low or highly-dynamic and when lightpath restoration takes place. To reduce the backward blocking, the paper proposes two label preference (LP) schemes compliant with RSVP-TE message exchanges. LP schemes provide the destination node with a label identifying the preferred wavelength to reserve. The preferred label is computed in a distributed way during the forward signaling phase, with the objective of assigning disjoint wavelengths to reservation attempts that may contend the resources. Simulation results demonstrate that, compared to other schemes, LP schemes are effective in reducing the backward blocking during both lightpath provisioning and restoration, without negatively impacting the forward blocking.     

Worst-case analysis of dynamic wavelength allocation in opticalnetworks

This paper proposes algorithms for allocating wavelengths to connections (lightpaths) in optical wavelength division multiplexed networks, predominantly for ring topologies. A worst-case model is considered, where no blocking of lightpaths is allowed, and there are no assumptions made on the traffic arrival and holding times. The traffic is characterized only by its load L, which is the maximum number of lightpaths that can be present on any link, assuming no blocking. A dynamic traffic model is considered where requests to set up lightpaths arrive over time and, must be accommodated without rerouting existing lightpaths, and lightpaths may be terminated over time as well. For networks without wavelength conversion, we show that at least 0.5Llog ₂N wavelengths are required by any dynamic algorithm for rings of N nodes and present an algorithm that uses at most Llog₂ N+L wavelengths for rings and 2(L-1)log₂N for trees. We also study the worst-case behavior of the well-known first-fit algorithm, and show that it requires at most 2.52Llog₂N+5L wavelengths (small variants of these constants are proven as well). When limited wavelength conversion is allowed, we first show how to use expanders to insure no blocking in arbitrary topologies. Then, we present conversion patterns for rings with conversion degree d=2, which require Llog₂L+4L or 2Llog₂log₂L+4L wavelengths, thereby eliminating the dependence (that exists without wavelength conversion) between the number of wavelengths and N. We also consider different traffic models where lightpath setup requests arrive over time, but once set up, lightpaths are never taken down. For this model, the number of wavelengths needed is shown to be only max{0,L-d}+L for a conversion degree of d