Efficient routing and wavelength assignment for multicast in WDMnetworks

The next generation multimedia applications such as video conferencing and HDTV have raised tremendous challenges on the network design, both in bandwidth and service. As wavelength-division-multiplexing (WDM) networks have emerged as a promising candidate for future networks with large bandwidth, supporting efficient multicast in WDM networks becomes eminent. Different from the IP layer, the cost of multicast at the WDM layer involves not only bandwidth (wavelength) cost, but also wavelength conversion cost and light splitting cost. It is well known that the optimal multicast problem in WDM networks is NP-hard. In this paper, we develop an efficient approximation algorithm consisting of two separate but integrated steps: multicast routing and wavelength assignment. We prove that the problem of optimal wavelength assignment on a multicast tree is not NP-hard; in fact, an optimal wavelength assignment algorithm with complexity of O(NW) is presented. Simulation results have revealed that the optimal wavelength assignment beats greedy algorithms by a large margin in networks using many wavelengths on each link such as dense wavelength-division-multiplexing (DWDM) networks. Our proposed heuristic multicast routing algorithm takes into account both the cost of using wavelength on links and the cost of wavelength conversion. The resulting multicast tree is derived from the optimal lightpaths used for unicast     

Architectures and technologies for high-speed optical data networks

Current optical networks are migrating to wavelength division multiplexing (WDM)-based fiber transport between traditional electronic multiplexers/demultiplexers, routers, and switches. Passive optical add-drop WDM networks have emerged but an optical data network that makes full use of the technologies of dynamic optical routing and switching exists only in experimental test-beds. This paper discusses architecture and technology issues for the design of high performance optical data networks with two classes of technologies, WDM and time division multiplexing (TDM). The WDM network architecture presented stresses WDM aware Internet protocol (IP), taking full advantage of optical reconfiguration, optical protection and restoration, traffic grooming to minimize electronics costs, and optical flow-switching for large transactions. Special attention is paid to the access network where innovative approaches to architecture may have a significant cost benefit. In the more distant future, ultrahigh-speed optical TDM networks, operating at single stream data rates of 100 Gb/s, may offer unique advantages over WDM networks. These advantages may include the ability to provide integrated services to high-end users, multiple quality-of-service (QoS) levels, and truly flexible bandwidth-on-demand. The paper gives an overview of an ultrahigh-speed TDM network architecture and describes recent key technology developments such as high-speed sources, switches, buffers, and rate converters     

一种稀疏分光配置约束下的WDM网络多播RWA算法

在波长路由WDM网络中,波长路由和波长分配是RWA算法提高光网络阻塞性能的两个重要阶段和关键技术。文章针对现有的稀疏分光配置约束下的光网络多播RWA算法复杂度高、代价高的问题,提出了一种新的稀疏分光器配置的RWA多播算法。该算法摒弃传统RWA算法在波长路由阶段就考虑稀疏分光约束能力的惯性思维,论文首次提出在波长分配阶段,才通过多播长转换器实现满足稀疏分光约束条件的分光能力传递。仿真结果表明,所提算法在平均代价和所需波长数目方面都获得了较优的性能。     

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.     

Multicast connection capacity of WDM switching networks with limited wavelength conversion

Currently, many bandwidth-intensive applications require multicast services for efficiency purposes. In particular, as wavelength division multiplexing (WDM) technique emerges as a promising solution to meet the rapidly growing demands on bandwidth in present communication networks, supporting multicast at the WDM layer becomes an important yet challenging issue. In this paper, we introduce a systematic approach to analyzing the multicast connection capacity of WDM switching networks with limited wavelength conversion. We focus on the practical all-optical limited wavelength conversion with a small conversion degree d (e.g., d=2 or 3), where an incoming wavelength can be switched to one of the d outgoing wavelengths. We then compare the multicast performance of the network with limited wavelength conversion to that of no wavelength conversion and full wavelength conversion. Our results demonstrate that limited wavelength conversion with small conversion degrees provides a considerable fraction of the performance improvement obtained by full wavelength conversion over no wavelength conversion. We also present an economical multistage switching architecture for limited wavelength conversion. Our results indicate that the multistage switching architecture along with limited wavelength conversion of small degrees is a cost-effective design for WDM multicast switching networks.     

Virtual Source Based Multicast Routing in WDM Optical Networks

Wavelength-division multiplexed (WDM) networks using wavelength-routing are considered to be potential candidates for the next generation wide-area backbone networks. Multicasting is the ability to transmit information from a single source node to multiple destination nodes and is becoming an important requirement in high-speed networks. As WDM technology matures and multicast applications become increasingly popular, supporting multicast routing at the WDM layer becomes an important and yet a challenging topic. This paper concerns with the problem of optical multicast routing in WDM networks. A few nodes in the network may have wavelength conversion and/or splitting capabilities. In this paper, a new multicast tree construction algorithm is proposed. This algorithm is based on a concept called virtual source. A virtual source is a node having both the splitting and wavelength conversion capabilities. By exploiting the presence of virtual source nodes, the proposed algorithm achieves improved performance. To further improve the performance, the algorithm assigns priorities to nodes based on their capabilities. The effectiveness of the proposed algorithm is verified through extensive simulation experiments.     

Multicast with a new switching structure in optical networks

The emergence of new services demands for a multicast function in optical networks. At the same time, wavelength converters are introduced to increase the efficiency of wavelength usage. It is because of the high cost and complex architecture of optical multicast and wavelength conversion technology, that a new switch structure is introduced, in which optical splitters and wavelength converters are shared per-node. In order to accommodate this architecture, a multicast routing and wavelength assignment algorithm in a splitter–converter-sharing optical network and a changing link weight policy to balance network traffic are proposed. By extending RSVP-TE (Resource ReSerVation Protocol-Traffic Engineering) and OSPF-TE (Open Shortest Path First-Traffic Engineering), an optical multicast mechanism is provided, and message type, signaling flow, and finite state machine model are given. Simulations of NSFNET show that, when the number of splitters and converters are 50% and 12.5% of the full equipment respectively, the performance is close to the ideal case. Using a changing link weight policy can improve performance greatly, when there are enough splitters and converters.     

Virtual-node-based multicast routing and wavelength assignment in sparse-splitting optical networks

This paper investigates several problems associated with optical multicast routing and wavelength assignment in sparse-splitting optical networks for interactive real-time media distribution. Unfortunately, the constrained multicast routing with optimized wavelength assignment leads to NP-complete condition. Thus, in this paper, a virtual-node-based multicast routing algorithm is first proposed to satisfy the requirements of interactive real-time multicasting as well as the constraints from underlying optical networks. For the constructed multicast tree, we then associate an effective wavelength assignment algorithm. The experimental results show that the proposed algorithm combination performs well in terms of (1) the wavelength channel cost, (2) the maximum variation of inter-destination node delays, (3) the signal quality, and (4) the number of wavelength conversions.     

一种新型的动态路由和波长分配算法

本文讨论了WDM光网中，在动态业务流量和有限范围波长变换情况下的动态路由和波长分配（RWA）问题，基于Moone-Dijkstra算法，考虑到动态波长变换的可能和限制，提出了一种新型的、可实现动态最小代价路由和最佳虚波长通道的综合启发式算法（DMC－OVMP）。该算法对路由子问题和波长分配子问题既相互独立，又相互结合，优化了RWA，保证了网络信息传输的安全性。对中国教育和科研计算机网（CERNET）基于本算法进行了计算机仿真，实现了低的网络阻塞率。     

On the design of multi-wavelength copy interconnects with reduced complexity

A multi-wavelength copy interconnect is a switching network capable of replicating a signal arriving at the input on a specific wavelength to one or more outputs possibly on different wavelengths. Such an interconnect can be useful in building optical multicast switches for wavelength division multiplexing (WDM) networks. In this article, we investigate, for the first time, the problem of designing copy networks that can simultaneously multicast input signals to a set of outputs while changing the wavelength of the replica according to the required routing pattern. We propose a novel multi-wavelength crossbar (MWX) switch that can switch an input signal on a specific wavelength to two different output wavelengths. The proposed MWX is used as a building block to construct two classes of multi-log_2N copy networks, namely, baseline and Bene? interconnects. The design space of the proposed interconnect classes is characterized and their hardware complexity is analyzed. We show that the proposed interconnects are transparent to existing multicast routing algorithms, and present simple routing algorithms for routing of multicast requests over the proposed designs. Comparisons with existing designs confirm that the proposed interconnects require a smaller number of space switches and wavelength conversion processes as compared to most conventional copy networks. In particular, for a large number of wavelengths and for any number of fibers the proposed design requires 50% less switching elements as compared to best available designs.     

WDM网状网络中一种动态多播自适应业务疏导算法

光多播业务需要消耗大量的WDM光网络带宽资源,业务疏导是光多播网络降低业务请求阻塞率和提高带宽资源利用率的有效方法。提出了一种新型光多播疏导节点结构,研究了疏导端口优先的多播业务疏导算法(TGPFA)和新建光树优先的多播业务疏导算法(TCLFA),进而提出了一种能够适应网络资源变化的动态多播业务疏导算法(ADMGA)。结果表明,在网络资源有限的情况下,ADMGA算法能取得较低的请求阻塞率和带宽阻塞率,获得较好的网络性能。     

一种WDM全光IP路由器的结构设计与分析

为突破“电子瓶颈”的限制，Internet向波分复用(WDM)全光网络演进已是必然的趋势．在光Internet中，光路由器是最为关键的设备之一．文章提出了一种光路由器实现的结构，该结构是以光突发标记交抉为核心，不需经过多次的O／E／O转换，即可实现边缘到边缘的全光域数据传输和处理．文章还对该结构具体实现中的关键问题：光突发数据的格式和装配、报头的提取和识别、路由及光标记交换和拥塞等进行了详细的分析研究，提出了可行的解决办法．最后设计了一个实验系统，并给出了相应的实验结果．     

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.     

Demonstration of an all-optical simultaneous wavelengthconverting/space-switching cross-point device

An integrated device consisting of two cascaded 2×2 crosspoint switches has been utilized to demonstrate a highly functional integrated routing and wavelength converting switch architecture at a data rate of 2.488 Gb/s. This aliens simultaneous space switching and wavelength conversion of optical signals in wavelength-division multiplexed (WDM) networks. Eye diagrams and bit-error-rate (BER) curves are displayed for wavelength conversion and simultaneous routing of a separate signal     

Routing, wavelength and time-slot-assignment algorithms for wavelength-routed optical WDM/TDM networks

This paper studies the connection-assignment problem for a time-division-multiplexed (TDM) wavelength-routed (WR) optical wavelength-division-multiplexing (WDM) network. In a conventional WR network, an entire wavelength is assigned to a given connection (or session). This can lead to lower channel utilization when individual sessions do not need the entire channel bandwidth. This paper considers a TDM-based approach to reduce this inefficiency, where multiple connections are multiplexed onto each wavelength channel. The resultant network is a TDM-based WR network (TWRN), where the wavelength bandwidth is partitioned into fixed-length time slots organized as a fixed-length frame. Provisioning a connection in such a network involves determining a time-slot assignment, in addition to the route and wavelength. This problem is defined as the routing, wavelength, and time-slot-assignment (RWTA) problem. In this paper, we present a family of RWTA algorithms and study the resulting blocking performance. For routing, we use the existing shortest path routing algorithm with a new link cost function called least resistance weight (LRW) function, which incorporates wavelength-utilization information. For wavelength assignment, we employ the existing least loaded (LL) wavelength selection; and for time-slot allocation, we present the LL time-slot (LLT) algorithm with different variations. Simulation-based analyses are used to compare the proposed TDM architecture to traditional WR networks, both with and without wavelength conversion. The objective is to compare the benefits of TDM and wavelength conversion, relative to WR networks, towards improving performance. The results show that the use of TDM provides substantial gains, especially for multifiber networks.     

Avoidance of multicast incapable branching nodes for multicast routing in WDM networks

In this article we study the multicast routing problem in all-optical WDM networks under the spare light splitting constraint. To implement a multicast session, several light-trees may have to be used due to the limited fanouts of network nodes. Although many multicast routing algorithms have been proposed in order to reduce the total number of wavelength channels used (total cost) for a multicast session, the maximum number of wavelengths required in one fiber link (link stress) and the end-to-end delay are two parameters which are not always taken into consideration. It is known that the shortest path tree (SPT) results in the optimal end-to-end delay, but it can not be employed directly for multicast routing in sparse light splitting WDM networks. Hence, we propose a novel wavelength routing algorithm which tries to avoid the multicast incapable branching nodes (MIBs, branching nodes without splitting capability) in the shortest-path-based multicast tree to diminish the link stress. Good parts of the shortest-path-tree are retained by the algorithm to reduce the end-to-end delay. The algorithm consists of tree steps: (1) a DijkstraPro algorithm with priority assignment and node adoption is introduced to produce a SPT with up to 38% fewer MIB nodes in the NSF topology and 46% fewer MIB nodes in the USA Longhaul topology, (2) critical articulation and deepest branch heuristics are used to process the MIB nodes, (3) a distance-based light-tree reconnection algorithm is proposed to create the multicast light-trees. Extensive simulations demonstrate the algorithm’s efficiency in terms of link stress and end-to-end delay.     

Historical data learning based dynamic LSP routing for overlay IP/MPLS over WDM networks

Overlay IP/MPLS over WDM network is a promising network architecture starting to gain wide deployments recently. A desirable feature of such a network is to achieve efficient routing with limited information exchanges between the IP/MPLS and the WDM layers. This paper studies dynamic label switched path (LSP) routing in the overlay IP/MPLS over WDM networks. To enhance network performance while maintaining its simplicity, we propose to learn from the historical data of lightpath setup costs maintained by the IP-layer integrated service provider (ISP) when making routing decisions. Using a novel historical data learning scheme for logical link cost estimation, we develop a new dynamic LSP routing method named Existing Link First (ELF) algorithm. Simulation results show that the proposed algorithm significantly outperforms the existing ones under different traffic loads, with either limited or unlimited numbers of optical ports. Effects of the number of candidate routes, add/drop ratio and the amount of historical data are also evaluated.     

Wavelength-exchanging cross connects (WEX)-a new class of photonic cross-connect architectures

All-optical wavelength division multiplexing (WDM) networks are expected to realize the potential of optical technologies to implement different networking functionalities in the optical domain. A key component in WDM networks is the optical switch that provides the basic functionality of connecting input ports to output ports. Existing WDM switches make use of space switches and wavelength converters (WCs) to realize switching. However, this not only increases the size and the complexity of the switch but also bears heavily on the cost. In this paper, the authors propose a new class of photonic switch architectures called wavelength-exchanging cross connect (WEX) that provides several advantages over existing switches by enabling a single-step space switching and wavelength conversion and thus eliminating the need for a separate conversion stage. This greatly enhances the switch architecture by reducing its size and complexity. The new class of cross-connect architectures is based on the proposed concept of a wavelength-exchange optical crossbar (WOC). The WOC concept is realized using the simultaneous exchange between two optical signals. The proposed WEX architecture is highly scalable. To establish scalability, the authors present a systematic method of developing instances of the switch architectures of an arbitrary large size.     

一种WDM疏导网络动态组播路由算法

对无波长变换能力的波分复用（WDM）疏导网络中的组播路由和波长分配（MRWA）问题进行了研究，提出了动态组播流量疏导算法（DMTGA）。这种算法根据当前网络资源使用情况，结合流量疏导和负载均衡，对链路权重进行动态配置，构建满足组播业务请求带宽需求的组播树。在不同的网络负载下对算法进行仿真，对比分析了DMTGA对业务请求接入率、平均网络资源利用率和全网负载分布的影响。     

New algorithms for multicast routing and wavelength assignment in multi-hop optical WDM networks

We study the problem of multicast routing and wavelength assignment (MC-RWA) in multi-hop optical WDM networks with respect to several target functions. Specially, we first study the MC-RWA problem under the target of minimize maximum hops, an efficient MC-RWA algorithm was proposed for that case. But for the objective of minimizing the total number of wavelength conversions, problem turns out to be NP-hard, we proposed a new approximation MC-RWA algorithm based on group Steiner tree. At last, combining the two objectives, a bi-factor approximation algorithm was introduced to minimize the both targets in the system simultaneously.