WDM格型光网络中的动态组播共享保护算法

该文针对WDM格型网络中单链路失效的情况,提出了一种保护动态组播业务的基于路径的优化共享保护(PB-OSPM)算法。该算法在基于最优路径对的共享不相交路径(OPP-SDP)算法的基础上,通过引入保护波长使用情况矩阵和波长预留矩阵记录预留波长资源的使用情况,允许不发生冲突的不同组播的保护路径间共享预留波长资源。研究采用欧洲光网络(EON)的拓扑对PB-OSPM算法和OPP-SDP算法在增性网络负载情况下的网络冗余度和同波长资源配置和网络负载情况下动态网络负载的网络连接阻塞率做了仿真。结果表明,相同条件下,PB-OSPM算法比OPP-SDP算法有更低的连接阻塞率。组播业务间波长资源的共享是提高波长资源利用率的有效方法。     

WDM网络动态组播业务共享保护算法

该文研究了WDM网络中动态组播业务的保护.为提高网络资源的利用率,降低连接请求阻塞率,和单播业务的共享保护方案类似,组播连接之间也可以共享保护波长.本文提出了一种动态组播业务共享保护算法,并对算法的性能进行了仿真,同时和组播业务专有保护算法进行了比较.仿真结果表明,共享保护算法比专有保护算法使用了更少的波长资源,具有更低的连接阻塞率.     

WDM网络动态组播业务管道失效保护

在光网络的建设中,为降低建设成本,多条链路往往经过同一条管道。在很多情况下,光纤链路的失效是由管道故障引起的,需要为网络的管道故障提供保护。该文研究了动态组播业务的单管道故障保护,给出了两种专有保护算法(SDP-DP和SDS-DP)和一种保护波长共享保护算法(SDS-SDP),并对各算法的连接阻塞率进行了仿真分析。仿真表明,在大部分情况下,由于SDS-SDP共享了连接请求之间的保护波长,SDS-SDP算法的连接阻塞率最低;而在低网络负载的情况下,SDP-DP算法有最低的连接阻塞率。     

WDM光网络中一种优先共享通路保护算法

为了提高波分复用光网络的可靠性,常采用分段共享通路保护算法,该方法通常要求保护通路要均匀分段并且应满足共享风险链路组约束,网络业务的阻塞率也就比较高,因此提出了用优先共享通路保护算法来降低业务阻塞率。通过计算机仿真进行了理论分析和实验验证,取得了两种保护算法下的业务阻塞率和资源预留比的数据。结果表明,优先共享保护通路算法能够有效地融合分段共享通路保护算法的优点,同时在业务的阻塞率和资源预留比方面优于分段共享保护通路算法。     

WDM光网络保护中一种新的波长预留方法

研究了WDM网状网中双链路失效的保护设计问题,在双链路失效保护时采用"裁剪相继最短路"算法计算工作通路和保护通路,而预留波长时利用波长预留矩阵预留资源,并进行仿真实验.实验结果表明,基于BRM的波长预留方法与已有的两步计算法相比大大减少预留资源.     

基于贪婪算法的WDM网络组播路由算法的研究

文章首先用贪婪算法找出在现有网络结构中完成任务所需的波长数较少的波长集,然后依据其上每条链路的权值,用最短路径算法生成一棵组播树,使其跳数和阻塞率较低,以保证网络能够在使用较少波长资源的情况下,快速、有效地传送数据.     

网状WDM网中多播业务的共享保护设计

研究网状波分复用(WDM)光网络中动态多播业务的保护方案,提出一种共享保护和重配置(SPR)算法.该算法根据网络状态动态调整链路代价,为每个多播业务请求建立最小代价工作树,并为光树上互不重叠的工作段提供链路分离的保护段.当网络中发生链路失效时,进行业务段保护切换和局部资源重配置.仿真表明,该算法可以合理共享波长资源、平衡网络负载,有效保护WDM网中任意单链路失效,并在多链路失效情况下大大提高业务恢复能力.     

网状WDM网中双链路失效的共享路径保护设计

该文研究了WDM网状网中双链路失效问题,在假定所有链路共享风险链路组(Share Risk Link Group, SRLG)分离的条件下,提出了一种动态共享路径保护(Dynamic Shared-Path Protection,DSPP)算法。DSPP能根据网络状态动态调整链路代价,为每条业务请求选择一条最小代价的工作路由和两条最小代价且SRLG分离的保护路由。仿真表明,DSPP不仅能完全保护双链路失效,并且能在资源利用率、阻塞率和保护切换时间之间进行性能折衷。     

弹性光网络双重故障下的自适应保护级别算法

为了降低弹性光网络中双链路故障保护下的业务及带宽阻塞率、均衡带宽资源分配,提出了一种双重故障下的自适应保护级别算法。该算法综合考虑传输距离、调制格式等因素,根据链路频谱资源使用状态动态地更新链路惩罚系数,选取最佳路径进行传输,同时根据请求类型及网络空闲资源状态自适应地选择保护方法,为业务提供最大限度的保护。仿真结果表明,在双链路故障下,算法在阻塞率方面取得了较好的性能,同时均衡了网络中各链路上的资源使用。     

双链路故障时的共享路径保护

在波长路由光网络中,网络的存活性已经受到越来越多的重视.对单链路故障时的保护已经不能满足某些关键性业务对网络存活性的要求,因而研究了双链路故障时的共享路径保护技术.在动态业务下,将共享路径保护问题归结为整数线性规划.在节点无波长转换能力的情况下,分别提出了为当前业务计算最优路径和固定路径两种策略下的整数线性规划.数值结果表明,相对于专用保护,双链路故障时的共享路径保护能够节约30%左右的波长链路资源.     

Achieving resource reduction for protecting multicast sessions in WDM mesh networks

The advances in wavelength division multiplexing (WDM) technology are expected to facilitate bandwidth-intensive multicast application by establishing a light-tree, which regards the source node as the root, and involves all the destination nodes. The light-tree is sensitive to failures, e.g., a single fiber cut may disrupt the transmission of information to several destination nodes. Thus, it is imperative to protect multicast sessions. In this work, we investigate the problem of protecting dynamic multicast sessions in mesh WDM networks against single link failures. Our objectives are to minimize the usage of network resources in terms of wavelength links for provisioning survivable multicast session, and to reduce the multicast session blocking probability. We propose two efficient multicast session protecting algorithms, called Optimal Path Pair based Removing Residual Links (OPP-RRL) and Source Leaf Path based Avoiding Residual Links (SLP-ARL), which try to reduce the usage of network resource by removing or avoiding residual links in the topology consisting of light-tree and its backup paths. To evaluate the proposed algorithms, we apply Integer Linear Programming (ILP) to generate an optimal solution. We also compare the proposed algorithms with existing algorithms through simulation. Simulation results indicate that the two proposed algorithms have better performance than other existing algorithms in terms of wavelength links required and network blocking probability. Furthermore, the solutions generated by the two proposed algorithms are quite close to the solutions generated by ILP in terms of the number of wavelength links required, when the network size is small.     

Dynamic Multicast Session Provisioning in WDM Optical Networks with Sparse Splitting Capability

In this work, we study dynamic provisioning of multicast sessions in a wavelength-routed sparse splitting capable WDM network with an arbitrary mesh topology where the network consists of nodes with full, partial, or no wavelength conversion capabilities and a node can be a tap-and-continue (TaC) node or a splitting and delivery (SaD) node. The objectives are to minimize the network resources in terms of wavelength-links used by each session and to reduce the multicast session blocking probability. The problem is to route the multicast session from each source to the members of every multicast session, and to assign an appropriate wavelength to each link used by the session. We propose an efficient online algorithm for dynamic multicast session provisioning. To evaluate the proposed algorithm, we apply the integer linear programming (ILP) optimization tool on a per multicast session basis to solve off-line the optimal routing and wavelength assignment given a multicast session and the current network topology as well as its residual network resource information. We formulate the per session multicast routing and wavelength assignment problem as an ILP. With this ILP formulation, the multicast session blocking probability or success probability can then be estimated based on solving a series of ILPs off-line. We have evaluated the effectiveness of the proposed online algorithm via simulation in terms of session blocking probability and network resources used by a session. Simulation results indicate that our proposed computationally efficient online algorithm performs well even when a fraction of the nodes are SaD nodes.     

A Novel Shared Segment Protection Algorithm for Multicast Sessions in Mesh WDM Networks

This paper investigates the problem of protecting multicast sessions in mesh wavelength‐division multiplexing (WDM) networks against single link failures, for example, a fiber cut in optical networks. First, we study the two characteristics of multicast sessions in mesh WDM networks with sparse light splitter configuration. Traditionally, a multicast tree does not contain any circles, and the first characteristic is that a multicast tree has better performance if it contains some circles. Note that a multicast tree has several branches. If a path is added between the leave nodes on different branches, the segment between them on the multicast tree is protected. Based the two characteristics, the survivable multicast sessions routing problem is formulated into an Integer Linear Programming (ILP). Then, a heuristic algorithm, named the adaptive shared segment protection (ASSP) algorithm, is proposed for multicast sessions. The ASSP algorithm need not previously identify the segments for a multicast tree. The segments are determined during the algorithm process. Comparisons are made between the ASSP and two other reported schemes, link disjoint trees (LDT) and shared disjoint paths (SDP), in terms of blocking probability and resource cost on CERNET and USNET topologies. Simulations show that the ASSP algorithm has better performance than other existing schemes.     

On Finding the Multicast Protection Tree Considering SRLG in WDM Optical Networks

In this letter, a new sharing mechanism, SRLG sharing, is proposed, which allows the links of the same shared risk link group (SRLG) in a primary light tree to share protections in WDM optical networks. In previous studies, how to share spare resources with SRLG constraints has not been studied in multicast optical networks. In this letter, considering SRLG sharing, we propose a novel algorithm –multicast with SRLG sharing (MSS)– to establish a protection light tree. Finally, the algorithm MSS and the algorithm multicast with no SRLG sharing (MNSS) are compared through a simulation to show that our new sharing scheme of SRLG sharing is more efficient than that of no SRLG sharing in terms of spare resource utilization and blocking probability.     

Routing Mechanisms Employing Adaptive Weight Functions for Shortest Path Routing in Optical WDM Networks

Optical dense wavelength division multiplexed (DWDM) networks are an attractive candidate for the next generation Internet and beyond. In this paper, we consider routing and wavelength assignment in a wide area wavelength routed backbone network that employs circuit-switching. When a session request is received by the network, the routing and wavelength assignment (RWA) task is to establish a lightpath between the source and destination. That is, determine a suitable path and assign a set of wavelengths for the links on this path. We consider a link state protocol approach and use Dijkstras shortest path algorithm, suitably modified for DWDM networks, for computing the shortest paths. In [1] we proposed WDM aware weight functions that included factors such as available wavelengths per link, total wavelengths per link. In this paper, we present new weight functions that exploit the strong correlation between blocking probability and number of hops involved in connection setup to increase the performance of the network. We also consider alternate path routing that computes the alternate paths based on WDM aware weight functions. The impact of the weight functions on the blocking probability and delay is studied through discrete event simulation. The system parameters varied include number of network nodes, wavelengths, degree of wavelength conversion, and load. The results show that the weight function that incorporates both hop count and available wavelength provides the best performance in terms of blocking probability.     

Reducing vulnerability of shared-path protection subject to double-link failures in WDM mesh networks

Shared-path protection (SPP) is a capacity- efficient mechanism to provide 100% single-link failure protection in WDM mesh networks. After the first link failure, however, if reconfiguration is unavailable, a second link failure may lead to tremendous service interruption. Vulnerability of a link is the percentage of links that are vulnerable to the arbitrary second link failure after the link failed and network vulnerability is defined as the average vulnerability of links in the network. In this article, we present three policies that can reduce network vulnerability by reducing backup sharing in shared-path protection. The first policy tries to restrict the times of sharing a wavelength-link by connections. The second policy tries to avoid backup sharing on highly vulnerable links. The third policy tries to avoid backup sharing on highly vulnerable wavelength-links. Algorithms to implement these policies based on a similar framework are presented. Numerical results suggest that there is a trade-off between capacity efficiency and network vulnerability in all the three policies. The third policy can deliver a better performance in terms of blocking probability and network vulnerability.

适用于波长交换光网络（WSON）的波长旋转图模型设计

将网络虚拓扑链路及关联波长均匀分布到旋转球体的表面,建立了新型的波长交换光网络(WSON)的波长旋转图模型,并基于旋转图模型提出了路由波长分配(RWA)新策略及算法.仿真结果表明,每条链路的总波长数分别为4和8时,新策略算法的阻塞率平均降低5.03%和9.71%,资源利用率平均提高3.3%和1.54%.该模型用于解决具有波长转换能力的RWA问题效果明显.     

Blocking in Wavelength-Routed Optical Networks With Heterogeneous Traffic

In this paper, we present a new analytical model that can give an accurate estimation of the blocking probabilities in wavelength-routed optical networks with heterogeneous traffic. By heterogeneous, we mean that each session offered to the network has its own traffic intensity and burstiness. In such cases, the blocking probability of a session is determined by the busy-wavelength distributions of the links seen at the arrival points of its calls. Thus, we first present two single-link models to estimate the arrival-point busy-wavelength distribution of a link with heterogeneous traffic: the full-population (FP) model and the reduced-population (RP) model. Both models are based on the BPP/M/W/W model, where the first two moments of an arbitrary session are matched by those of a birth–death process whose arrival rate linearly varies with the average number of busy wavelengths occupied by its own calls. We show that different sessions have different arrival-point busy-wavelength distributions depending on the burstiness of their traffic, i.e., a bursty session observes the link more congested than a smooth session. Next, we provide two extensions of the single-link models, the FP-full-load link-correlation model and the RP-reduced-load link-correlation model, to estimate the blocking probabilities of optical networks with heterogeneous traffic and sparse wavelength conversion. Both models employ the existing link-correlation models to take into account the occupied-wavelength-index correlation between two adjacent links. By comparing the results from the models with simulation results, we demonstrate that both models well approximate the blocking probabilities of individual sessions, as well as the network-wide blocking probability, for a wide range of traffic intensity, burstiness, and heterogeneity.     

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.