Regenerative all-optical wavelength multicast for next generation WDM network and system applications

We experimentally demonstrate regenerative all-optical wavelength multicast by simultaneous multi-wavelength conversion of 10 Gb/s non-return-to-zero signals to four ITU 100 GHz spaced channels with a receiver sensitivity improvement of 1.84 dB and less than 0.14 dB difference among all the multicast channels, using a single commercial monolithically integrated SOA-MZI. The multicast device also exhibited about 22 dB optical signal-to-noise ratio enhancement for all the converted channels compared to the original signal channel without wavelength conversion. Our experiment for the first time revealed the regeneration properties of a SOA-MZI device for WDM wavelength multicast purposes, and proved the excellent performance of a simple scheme for various future network and system applications, such as all-optical wavelength routing and grid networking.     

Monolithically integrated 40-gb/s switchable wavelength converter

An all-optical switchable wavelength-converting module at 40 Gb/s line rate is demonstrated in a fully integrated InP chip. The device combines a semiconductor optical amplifier-based wavelength converter and a fast-tunable multifrequency laser. Sub-nanosecond switching among the eight channels of the integrated laser is shown, and error-free operation of the wavelength conversion process at 40 Gb/s for each wavelength is demonstrated. The applications of fast switching wavelength conversion for optical switching and packet routing are discussed.     

Wavelength switching components for future photonic networks

This article provides a review of integrated laser and semiconductor optical amplifier components that have been configured to provide a variety of all-optical functions such as wavelength conversion, routing, signal regeneration, and add-drop multiplexing. The components have been devised so that they can be reliably and simply used within a multiwavelength network. The article introduces the components by outlining the current leading techniques for wavelength conversion using SOAs, namely by way of cross-gain modulation, cross-phase modulation, and four-wave mixing. The integrated SOA distributed feedback laser is then shown to provide excellent regeneration properties, not only overcoming fiber dispersion limitations but also polarization mode dispersion. Finally, the devices are shown to make possible a regenerative wavelength switching node where routing is achieved using a tunable laser to provide regenerative wavelength conversion followed by an arrayed waveguide router. This switch shows promise for use in future photonic packet switching architectures     

On-line integrated routing in dynamic multifiber IP/WDM networks

This paper focuses on dynamic integrated routing in multifiber Internet protocol/wavelength-division multiplexing (IP/WDM) networks, which can be implemented through either one-step routing (OSR) or two-step routing (TSR) approach. Based on an extended layered-graph, two resource assignment strategies, termed channel-level balance (CLB) and link-level balance (LLB), are proposed to balance the traffic in the network at different levels. To further improve the performance, a parameter K is introduced to make a dynamic tradeoff between the logical-layer links and the optical-layer links. Simulation studies are carried out for various topologies. The results show that LLB is better than CLB in most cases, and LLB combined with OSR has the optimal performance. Also, we find that the routing approach and the resource assignment strategy individually play different roles with different values of r/sub l/ that is introduced to indicate the resource richness of the network. As a multifiber network is functionally equivalent to a single-fiber network with limited wavelength conversion, we investigate the effects of wavelength conversion by studying the multifiber IP/WDM networks. The analysis shows that, when the granularity of each connection request is much smaller than the wavelength granularity, wavelength conversion may increase the request blocking probability in the network.     

An architecture for a wavelength-interchanging cross-connectutilizing parametric wavelength converters

This paper proposes an architecture for a wavelength-interchanging cross-connect (WIXC) that can be used as a switching node of strictly transparent and scalable networks with all-optical routing and all-optical wavelength conversion capabilities. This architecture utilizes all-optical parametric wavelength converters based on difference-frequency-generation (DFG) or four-wave mixing (FWM), although this work focuses only on the implementation using difference-frequency-generation wavelength converters. The proposed WIXC architecture exploits the unique wavelength mapping properties of parametric wavelength converters: mirror image mapping and simultaneous multichannel wavelength conversion. The derivation of this architecture involves application of a space/wavelength transformation to the classical Benes switch fabric. The connection setup for the resulting architecture follows the well established looping algorithm, and the architecture is scalable in both the ports and the wavelengths. The scaling occurs in an orderly fashion, which allows modular upgrades of WIXC's for cost-effective evolution of the networks. The unique properties of the parametric wavelength converter including transparent and multichannel conversion capabilities result in a WIXC architecture that requires fewer wavelength converters while maintaining scalability and transparency     

Operation of WDM networks with different wavelength conversioncapabilities

We study the impact of wavelength conversion capability on wavelength routing WDM networks with fixed shortest-path routing. We propose a method for implementing wavelength routing in a WDM network with partial wavelength conversion capability. Simulation results show that such partial wavelength conversion networks provide a performance in between that of wavelength continuous networks and those with full conversion capability. In addition, it can be seen that only limited wavelength conversion capability is enough to provide a performance close to that of a network with full conversion. Analytical and simulation bounding results for the full and no conversion cases have also been provided     

Routing framework for all-optical DWDM metro and long-haul transport networks with sparse wavelength conversion capabilities

In this paper, we propose a novel routing framework for all-optical dense wavelength-division-multiplexing transport networks with sparse wavelength conversion capabilities. The routing framework includes an integer linear programming formulation to handle the static lightpath establishment problem and a novel open shortest path first protocol extension that advertises the availability of wavelength usage and wavelength conversion resources. Our routing framework addresses the limitations of the extensions presented in the literature because it also includes: 1) an efficient flooding protocol that is suitable for the dynamic nature of these networks and 2) an efficient route and wavelength computation engine that minimizes connection costs without hindering the blocking probability.     

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     

Fixed-alternate routing and wavelength conversion inwavelength-routed optical networks

Consider an optical network which employs wavelength-routing crossconnects that enable the establishment of wavelength-division-multiplexed (WDM) connections between node pairs. In such a network, when there is no wavelength conversion, a connection is constrained to be on the same wavelength channel along its route. Alternate routing can improve the blocking performance of such a network by providing multiple possible paths between node pairs. Wavelength conversion can also improve the blocking performance of such a network by allowing a connection to use different wavelengths along its route. This work proposes an approximate analytical model that incorporates alternate routing and sparse wavelength conversion. We perform simulation studies of the relationships between alternate routing and wavelength conversion on three representative network topologies. We demonstrate that alternate routing generally provides significant benefits, and that it is important to design alternate routes between node pairs in an optimized fashion to exploit the connectivity of the network topology. The empirical results also indicate that fixed-alternate routing with a small number of alternate routes asymptotically approaches adaptive routing in blocking performance     

多波长全光环网路由寻径和波长分配算法

文章讨论多波长全光网(包括有光波转换功能和无光波转换功能)中路由寻径和波长分配问题,通过数学分析和建模方法对其进行分析,并与现有综合线性规划算法比较,给出分析结果。文中得出的结论对多波长全光环网的设计和优化有一定参考价值。     

On Multicast Routing for Wavelength-Routed WDM Networks with Dynamic Membership

Future broadband networks must support integrated services and offer flexible bandwidth usage. In our previous work in [1], we explored the optical link control (OLC) layer on the top of optical layer that enables the possibility of bandwidth on-demand (BoD) 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 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 join 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 low as possible. The same algorithm can be applied to other wavelength routing architectures with redefinition of electronic copy cost. The effectiveness of the proposed wavelength router architecture as well as the dynamic multicast algorithm is evaluated by simulation.     

Effects of wavelength routing and selection algorithms onwavelength conversion gain in WDM optical networks

Wavelength-division multiplexing (WDM) technology is emerging as the transmission and switching mechanism for future optical mesh networks. In these networks it is desired that a wavelength can be routed without electrical conversions. Two technologies are possible for this purpose: wavelength selective cross-connects (WSXC) and wavelength interchanging cross-connects (WIXC), which involve wavelength conversion. It is believed that wavelength converters may improve the blocking performance, but there is a mix of results in the literature on the amount of this performance enhancement. We use two metrics to quantify the wavelength conversion gain: the reduction in blocking probability and the increase in maximum utilization, compared to a network without converters. We study the effects of wavelength routing and selection algorithms on these measures for mesh networks. We use the overflow model to analyze the blocking probability for wavelength-selective (WS) mesh networks using the first-fit wavelength assignment algorithm. We propose a dynamic routing and wavelength selection algorithm, the least-loaded routing (LLR) algorithm, which jointly selects the least-loaded route-wavelength pair. In networks both with and without wavelength converters the LLR algorithm achieves much better blocking performance compared to the fixed shortest path routing algorithm. The LLR produces larger wavelength conversion gains; however, these large gains are not realized in sufficiently wide utilization regions and are diminished with the increased number of fibers     

Dynamic routing and wavelength assignment in the presence of wavelength conversion for all-optical networks

Blocking probability has been one of the key performance indexes in the design of wavelength-routed all-optical WDM networks. Existing research has demonstrated that an effective Routing and Wavelength Assignment (RWA) algorithm and wavelength conversion are two primary vehicles for improving the blocking performance. However, these two issues have largely been investigated separately; in particular the existing RWA algorithms have seldom considered the presence of wavelength conversion. In this paper, we firstly demonstrate that the existing dynamic RWA algorithms do not work well in the presence of wavelength conversion as they usually only take into account the current traffic, and do not explicitly consider the route lengths. We then propose a weighted least-congestion routing and first-fit wavelength assignment (WLCR-FF) algorithm that considers both the current traffic load and the route lengths jointly. We further introduce an analytical model that can evaluate the blocking performance for WLCR algorithm. We carry out extensive numerical studies over typical topologies including ring, mesh-torus, and the 14-node NSFNET; and compare the performance of WLCR-FF with a wide variety of existing routing algorithms including static routing, fixed-alternate routing and least-loaded routing. The results conclusively demonstrate that the proposed WLCR-FF algorithm can achieve much better blocking performance in the presence of sparse or/and full wavelength conversion.     

A Node-Level Blocking Probability Analysis for WRONs

This work presents the blocking performance of a single node with (full or limited) wavelength conversion in wavelength routed optical networks (WRON) based on the theory of probability. A blocking probability model is proposed. Particularly, we pay more attention to investigate wavelength routing node performance improvement by using the more feasible case of limited wavelength conversion. Based on our analytical model, we calculate the blocking probability for a single wavelength routing node and then make a simulation to validate it. It is shown that a node with low conversion degrees having a small number of fiber link ports and a large number of wavelengths per link is a more realistic choice.     

波分复用波长路由节点的阻塞特性分析

利用概率统计理论的方法，从节点层次上定量分析了节点规模、复用波长数目以及波长转换对波分复用(WDM)波长路由网络中波长路由节点的影响。提出了基于概率统计的节点阻塞模型。数值结果突出表明波长转换能力越强的全光节点，其性能越优。为了提高网络资源的使用效率并增强全光网络的灵活性，必须实现全光网络中的虚波长路由波长转换器。通过数值计算找到了阻塞性能和代价的折中，研究中发现配置较低波长转换能力波长转换器的波长路由节点将会具备更强的性价比优势，当前在构建光通信系统时使用弱波长转换能力的光节点更可行。     

Segment shared protection in WDM networks with partial wavelength conversion

In this paper, we propose a novel approach of survivable routing for segment shared protection (SSP) in mesh wavelength division multiplexing networks with partial wavelength conversion capability, with which spare capacity is allocated dynamically for a given working lightpath. The survivable routing process is formulated into a shortest path searching problem on the transferred graph of cycles (TGC) and wavelength graph of paths (WGP).     

Wavelength converter placement under different RWA algorithms in wavelength-routed all-optical networks

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 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 the fixed-alternate routing (FAR) algorithm and least-loaded routing (LLR) algorithm. Under the FAR algorithm, we propose a heuristic algorithm called minimum blocking probability first for wavelength converter placement. Under the LLR algorithm, we propose another heuristic algorithm called weighted maximum segment length. The objective of the converter placement algorithms 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 compared with full wavelength conversion under the same RWA algorithm.     

A novel dynamic survivable routing in WDM optical networks with/without sparse wavelength conversion

In this paper, we study the dynamic survivable routing problem, both in optical networks without wavelength conversion and in optical networks with sparse wavelength conversion, and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and genetic algorithms (GA). By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously report cycles (that are formed by two disjoint-link routes) into the routing tables, our new hybrid algorithm can promptly determine the first population of cycles for a new request based on the routing table of its source node, without the time consuming process associated with current GA-based lightpath protection schemes. We further improve the performance of our algorithm by introducing a more advanced fitness function that is suitable for both the above networks. Extensive simulation studies on the ns-2 network simulator show that our hybrid algorithm achieves a significantly lower blocking probability than the conventional survivable routing algorithms for all the cases we studied.     

OPERA: an optical packet experimental routing architecture withlabel swapping capability

This paper describes experimental and simulation results of the optical packet experimental routing architecture (OPERA) project. The OPERA network is based on a novel optical network interface router design that is optically regenerative and supports optical Internet protocol related functions including label swapping, packet routing and forwarding operations and wavelength reuse. Routing is based on subcarrier multiplexed header addressing, packet-rate wavelength conversion, and arrayed waveguide router technology. The routers are cascadable and use a unique double stage wavelength converter that supports header regeneration/replacement and maintains the payload extinction ratio. This approach overcomes dispersion limitations normally encountered using double sideband subcarrier multiplexing across a network. A discrete time simulation of the physical transport in an 8-hop network is reported. Multihop routing is experimentally demonstrated between two all-optical nodes and three input-output (I-O) ports of a waveguide grating array router. Packet-rate subcarrier header processing and wavelength conversion between six wavelengths is shown with high signal-to-noise ratio (SNR) of recovered payload and headers at each hop     

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。