全光网络中感知信号损伤的RWA算法

在全光网络中，信号沿着光通路在非理想介质中传输时，会引起质量恶化。当达到一定程度时。该光通路不可用。物理层的传输损伤引起连接阻塞。为了提供高质量的连接，路由和波长分配算法需要考虑信号质量。光信噪比和极化模式色散被认为是主要的限制因素。有两种感知损伤的RWA算法：最优路径算法，最先符合算法。     

波长路由网络选路时的光信号质量限制研究

光网络中,路由与波长分配(RWA)算法是最优化网络性能的核心问题之一,传统的RWA算法都假设光网络的物理层状态是理想的,即不存在光信号传输损伤的问题.通过对这个缺陷的分析,将光信号的传输损伤问题充分考虑到路由与波长分配算法中,从算法的角度来实现对光信号的传输保护,这样做不仅能有效防止业务的物理损伤阻塞,还能极大地提高光网络的性能.     

ASON中基于传输损伤的RWA算法研究

路由和波长分配(RWA)算法是ASON中的一个关键问题.由于信号传输过程中存在传输损伤,这将会影响到不同连接请求的公平性.对现有算法进行研究,提出了一种改进算法,在保证公平性的同时,尽量降低网络的阻塞率.仿真表明该算法能有效的降低阻塞,提高资源利用率.     

基于多物理层损伤限制的光网络RWA算法研究

在透明光网络中,如何在选路过程中自适应地规避物理层损伤进而实现高质量的传输服务是亟待解决的问题.提出了一种面向多物理损伤约束的RWA算法,改进原有损伤感知RWA算法考虑物理损伤单一不够全面的问题,尝试将多个物理损伤作为路径选择的多个约束条件,从而可以选择损伤最小的光路来完成光连接的请求,从而满足未来高传输质量的需求.     

WDM光网络的光路传输质量估计算法

在波长路由WDM光网中,信号在路由与波长分配算法(RWA)选定的光路上传输．传输过程中引入的各种串扰和噪声使信号的传输质量受到损伤,信号质量不断下降,目的结点无法正确有效地接收光信号。通过定义合理的结点和传输链路模型．提出了一种考虑线性传输损伤的比特错误率估算方法．在光路建立之前预先估计WDM网络中将要建立光路的传输质量,以此作为网络优化设计过程中RWA算法选路的依据。通过网络仿真和实验验证了算法的正确性。     

WDM网络分布式物理损伤感知RWA算法

随着传输速率的不断升级,在透明传送过程中,各种损伤的积累会对光信号的质量造成严重影响,因而不能保证高QoS(服务质量)地传输信号.文章提出一种物理损伤感知的分布式RWA(波长路由分配)算法,将物理层传输质量评估分布在中继段路由和波长信道中,分别由损伤感知路由、波长通道传输质量排序和按优先级分配3部分构成.仿真实例证明了...     

光网络中支持区分业务的损伤感知QoS机制

光网络中物理层损伤会造成明显的信号质量下降。为了保证QoS(服务质量),必须在RWA(路由和波长分配)算法中考虑这些损伤及其引起的变化。文章提出了一种损伤感知的差异化路由与波长算法,并针对规则Mesh网络与Cernet网络进行了数值仿真,结果表明,在满足QoS要求的情况下优先保证网络中高等级业务的波长分配,能降低高等级业务的阻塞率,并能提高网络总体的资源利用率。     

WDM光网中的一种邻域加权累积的波长分配策略

针对光核心传送网中单纤场景下的路由选择与波长分配（Routing and Wavelength Assignment,RWA）问题,提出了一种邻域加权累积的波长分配策略。在一条路径上为一个连接请求选择波长时,将网络的所有链路归入当前路径的不同邻域中,然后根据与路径之间的距离为不同邻域赋予不同的权重,进而对每个波长在全网中被占用的个数进行加权累积,最后选择累积值最大的可用波长建立连接。仿真结果表明,相对于现有的阻塞率最低的最大使用（Most-Used）波长分配策略,所提策略具有更低的阻塞率。     

多光纤ASON网络动态路由优化算法

本文研究了多光纤波分复用光网络中的动态路由和波长分配问题，提出了基于分层图模型的一种新的多光纤网络的动态路由优化算法，该算法将连接请求的建立转化为在分层图模型中为该请求寻找一条最优路径，这使得设计者可以同时考虑路由和波长分配的问题，从而取得更好的效果。模拟结果显示基于分层图模型的(MFD—RWA：MultiFiber Dynamic：Routing and Wavelength Assignment)算法优于传统的动态最短路径算法。     

波分复用光网络中的波长路由分配策略

路由选择和波长分配是WDM光传输网中非常重要的问题.本文结合交叉连接节点,提出了一种基于最短路径的动态路由选择方案;然后利用这种动态的路由选择策略,以网络的阻塞性能为优化目标分配波长,达到充分利用网络资源的目的.计算机仿真结果表明,无论在单纤或者多纤WDM光传输网络中,利用这种策略的RWA算法优于传统的固定路由和单纯动态路由算法     

A new solution to the K-shortest paths problem and its application in wavelength routed optical networks

In communication networks, traffic carried over long paths suffers from a higher call blocking probability (CBP) than those carried over short paths. This is a well-known fairness problem. Such a problem becomes more serious in wavelength-routed optical networks (WRONs) due to the wavelength continuity constraint. This paper aims to enhance the fairness characteristic in WRONs by the novel classified alternate routing (CAR) approach. As a foundation of this approach, the first K-shortest paths (KSP) between a designated source/destination node pair in a given network should be obtained simultaneously. This has been studied as the KSP problem in the literature. In this paper, a new loopless deviation (LD) algorithm for solving such a loopless KSP problem will be proposed. It outperforms existing solutions in terms of running time in real-life implementations. In order to measure the fairness characteristic, we first classify all connection requests into categories such as 1-hop traffic, 2-hop traffic, etc., according to the number of minimal hop count between the corresponding source/destination node pair. We then quantify the fairness characteristic by the ratio of the average CBP of each traffic category to that of 1-hop traffic such that CBP ratios with a value closer to 1 are preferred. We will show that such a measure criterion is more precise and robust than existing ones in the literature. Finally, numerical experiments will reveal that the CAR approach outperforms existing fairness enhancement methods when considering the comprehensive performance in terms of the balance between the fairness characteristic and the overall CBP feature.     

Dynamic resource allocation algorithm in multi-user cooperative OFDMA systems: considering QoS and fairness constraints

Wireless transmission systems are constrained by several parameters such as the available spectrum bandwidth, mobile battery energy, transmission channel impairments and users’ minimum quality-of-service. In this paper, a new strategy is investigated that aims at improving the allocation of resources in a dual hop OFDMA cooperative network consisting in multi source–destination pairs and multiple decode-and-forward relays. First, the joint optimization of three types of resources: power, sub-channel and relay nodes, is formulated as a problem of subchannel-relay assignment and power allocation, with the objective of minimizing overall transmission power under the bit-error-rate and data rate constraints. However, the optimal solution to the optimization problem is computationally complex to obtain and may be unfair. Assuming knowledge of the instantaneous channel gains for all links in the entire network, an iterative three-step resource allocation algorithm with low complexity is proposed. In order to guarantee the fairness of users, several fairness criteria are also proposed to provide attractive trade-offs between network performance (i.e. overall transmission power, average network lifetime and average outage probability) and fairness to all users. Numerical studies are conducted to evaluate the performance of the proposed algorithm in two practical scenarios. Simulation results show that the proposed allocation algorithm achieves an efficient trade-off between network performance and fairness among users.     

Cost Effective Shared Path Protection for WDM Optical Mesh Networks with Partial Wavelength Conversion

In this paper, we study routing and wavelength assignment of connection requests in survivable WDM optical mesh networks employing shared path protection with partial wavelength conversion while 100% restorability is guaranteed against any single failures. We formulate the problem as a linear integer program under a static traffic model. The objective is to minimize the total cost of wavelength-links and wavelength converters used by working paths and protection paths of all connections. A weight factor is used which is defined as the cost ratio of a wavelength converter and a wavelength-link. Depending on the relative cost of bandwidth and wavelength conversion, the optimization objective allows a proper tradeoff between the two. The proposed algorithm, the shortest-widest-path-first (SWPF) algorithm, uses a modified Dijkstra's algorithm to find a working path and a protection path for each connection request in the wavelength graph transformed from the original network topology. When there are multiple candidate paths that have the same minimum total cost, the path along which the maximum number of converters used at each node is minimized is chosen by the SWPF algorithm. We have evaluated the effectiveness of the proposed algorithm via extensive simulation. The results indicate that the performance of the proposed algorithm is very close to that of the optimal solutions obtained by solving the ILP formulation and outperforms existing heuristic algorithms in terms of total number of converters used and the maximum number of converters required at each node in the network. The proposed algorithm also achieves slightly better performance in terms of total cost of wavelength-links and converters used by all connections. We also investigated shared path protection employing converter sharing. The results show that the technique can reduce not only the total number of converters used in the network but also the maximum number of converters required at each node, especially when a large number of converters are needed in the network. In this study, although the ILP formulation is based on static traffic, the proposed algorithm is also applicable to routing dynamic connection requests.     

Simultaneous effect of connection admission control in distance and bandwidth capacity on WDM network performance

This article presents an algorithm for dynamic-routing and wavelength assignment (D-RWA) in an optical WDM network. The approach is based on a genetic algorithm (GA) and it includes a connection admission control (CAC), to provide a network with simultaneous fairness in distance and bandwidth capacity. The algorithm is evaluated by means of computer simulations using a mesh network with two types of node architectures capable of performing traffic grooming. Combining the two types of nodes, the performance of four network configurations is compared. Assuming that one of the two node types is more costly, two sparse node allocations are suggested to maintain the network cost-effective. The algorithm assigns wavelengths to the ligthpaths, routes the traffic streams, manages the grooming of sub-wavelength tributaries onto full wavelength channels, provides fairness, and minimizes the overall blocking probability of connection requests. Numerical results attest the usefulness of the proposed approach considering several scenarios of distance and bandwidth capacity classes of requests. Simultaneous and isolated simulations of the two fairness schemes are also compared, emphasizing the versatility of the algorithm.     

Considering physical layer impairments in offline RWA

We consider the offline version of the routing and wavelength assignment problem in transparent all-optical networks. In such networks and in the absence of regenerators, the signal quality of a transmission degrades due to physical layer impairments. Certain physical effects cause choices for one lightpath to affect and be affected by the choices made for other lightpaths. This interference among lightpaths is particularly difficult to formulate in an offline algorithm, since in this version of the problem we start without any established connections, and the utilization of lightpaths are the variables of the problem. For this reason the majority of work performed in this field either neglects lightpath interactions or assumes a worst case interference scenario. In this article we present a way to formulate interlightpath interference as additional constraints on RWA and show how to incorporate these constraints in an IA-RWA algorithm that directly accounts for the most important physical layer impairments. The objective of the resulting cross-layer optimization problem is not only to serve the connection requests using the minimum number of wavelengths (network layer objective), but also to select lightpaths that have acceptable quality of transmission performance (physical layer objective).     

Automated adaptive on-line Multi-Layer Traffic Engineering through “tailoring” wavelength-paths in the Fragment Graph

In Multi-Layer networks, where more than one layer is switched, i.e., connections are set up using not only the upper, e.g., IP layer but the underlying wavelength layer as well leads often to suboptimal performance due to long wavelength paths, that do not allow routing the traffic along the shortest path. The role of MLTE (Multi-Layer Traffic Engineering) is to cut (fragment) these long wavelength-paths into parts (fragments) that allow better routing at the upper layer, or to concatenate (defragment) two or more fragments into longer paths when the network load is low and therefore fewer hops are preferred.In this paper we present a new model, the Fragment Graph (FG) and an algorithm for this model that supports Fragmentation and De-Fragmentation of wavelength paths making the network always instantly adapt to changing traffic conditions. We introduce the notion of shadow links to model “λ-path tailoring”. We implicitly assume that the wavelength paths carry such, e.g., IP traffic that can be interrupted for a few milliseconds and that even allows minor packet reordering.To show the superior performance of our approach in various network and traffic conditions we have carried out an intensive simulation study where we compare blocking ratios and path lengths and we analyze the dynamic behavior and fairness of the proposed and of reference methods.     

Impairment aware optimal diverse routing for survivable optical networks

In wavelength-routed optical networks, a lightpath connection can be provisioned only if a path, or a pair of paths in case of path protection is required, can be found which satisfies multiple constraints while simultaneously achieving optimal primary cost. The primary cost can be any metric set by network administrators, and the constraints concerned in optical networks include wavelength continuity constraint, accumulation effect of some transmission impairments in the optical domain, and SRLG-disjoint requirement in survivable networks. In this paper, the impact of these constraints on the optimal path calculation algorithms is studied. Three novel algorithms for solving this problem, which we call “Impairment Aware Optimal Path Pair” problem, are proposed, and their performance is evaluated through extensive simulations. This research has been supported by a National Natural Science Foundation of China (NSFC) grant (90604002, 60472008), and Program for New Century Excellent Talents in University grant (NCET-05-0807).     

一种公平的多优先级WDM光网络波长分配算法

文章研究了波分复用(WDM)光网络中动态业务下的波长分配问题,在无波长转换器的条件下,提出了一种加入了公平性考虑的动态门限算法.该算法在支持多优先级的动态门限法的基础上,通过更新初始优先级减少了不同距离光路连接请求间的阻塞率差别,改善了公平性.计算机仿真结果说明了该算法的有效性.     

A distributed ant-based algorithm for routing and wavelength assignment in an optical burst switching flexible spectrum network with transmission impairments

This work describes a distributed algorithm inspired by ant colony optimisation for a solution to the problem of dynamic routing and wavelength assignment with wavelength continuity constraint in optical burst switched networks. The evaluation was conducted in a wavelength division multiplexed network environment with limited number of wavelength channels and in a flexible spectrum network environment undergoing transmission impairments. The simulations in the flexible spectrum network environment aim to replicate the effects of both linear and nonlinear physical layer impairments. Under these effects, an optical burst control packet could be lost during traversal of the network with no measure in place to notify the network of the loss or to free up optical resource reservations. The optical burst switching acknowledgement protocol has been modified in this work to account for a burst control packet failure by implementing a traversal acknowledgement to cater for its loss. The performance of the distributed ant-based algorithm has been extensively evaluated on several network topologies and compared with that obtained by shortest path routing and ant colony routing and wavelength assignment. The results show that the distributed ant-based algorithm significantly improves the burst transmission success probability in the wavelength division multiplexed network environment and provides a good solution in the flexible spectrum network environment undergoing transmission impairments.     

Dynamic routing of restorable bandwidth-guaranteed tunnels using aggregated network resource usage information

The paper presents new algorithms for dynamic routing of restorable bandwidth-guaranteed paths. We assume that connections are requested one-by-one and there is no prior knowledge of future arrivals. In order to guarantee restorability an alternate link (node) disjoint backup (restoration) path has to be determined, as well as an active path, when the connection is initiated. This joint on-line routing problem is particularly important in optical networks and in MPLS networks for dynamic provisioning of bandwidth-guaranteed or wavelength paths. A simple solution is to find two disjoint paths, but this results in excessive resource usage. Backup path bandwidth usage can be reduced by judicious sharing of backup paths amongst certain active paths while still maintaining restorability. The best sharing performance is achieved if the routing of every path in progress in the network is known to the routing algorithm at the time of a new path setup. We give a new integer programming formulation for this problem. Complete path routing knowledge is a reasonable assumption for a centralized routing algorithm, but is not often desirable, particularly when distributed routing is preferred. We show that a suitably developed algorithm which uses only aggregated information, and not per-path information, is able to perform almost as well as one using complete information. Disseminating this aggregate information is feasible using proposed traffic engineering extensions to routing protocols. We formulate the dynamic restorable bandwidth routing problem in this aggregate information scenario and develop efficient routing algorithms. The performance of our algorithm is close to the complete information bound.