On Architecture and Limitation of Optical Multiprotocol Label Switching (MPLS) Networks Using Optical-Orthogonal-Code (OOC)/Wavelength Label

To accommodate the explosive packet-based data traffic in WDM networks, intelligent optical routing and switching are required in optical transport networks. Optical multiprotocol label switching networks emerged to meet this demand. In this paper, different schemes for implementing an OMPLS network are introduced. An optical MPLS network using OOC/wavelengths as labels is proposed. Based on an all-optical code converter, the architecture of the optical core router is demonstrated. The fundamental limits on scalability of the proposed core router, namely the label capacity, and the blocking probability of the label switched path setup are investigated, and closed-form solutions are derived.     

未来光因特网中的光交换方式及其发展趋势

Internet的业务流量正以每六个月翻一番的速度快速增长,未来网络中,数据业务超过话音业务只是时间问题,因此,基于电路交换的电信网升级到支持基于分组交换的数据业务是不可避免的,但是对因特网来说,由于光逻辑与光存储等器件不成熟,发展全光分组交换,技术上异常困难。另一方面,近来新提出的光突发交换,技术上相对简单,性能特点优异,因而成为更理想的选择,本文介绍了全光分组交换和光突发交换的研究现状,比较了两者的优缺点,最后指出改进光突发交换性能的两种方式。     

Regenerator Placement and Traffic Engineering with Restoration in GMPLS Networks

In this paper, we study regenerator placement and traffic engineering of restorable paths in generalized multiprotocol label switching (GMPLS) networks. Regenerators are necessary in optical networks in order to cope with transmission impairments. We study a network architecture where regenerators are placed only at selected nodes for decreasing cost of regeneration. We propose two heuristic algorithms for optimum placement of these regenerators. Performances of these algorithms in terms of required number of regenerators and computational complexity are evaluated. In this network architecture with sparse regeneration, off-line computation of working and restoration paths is studied for traffic engineering with path rerouting as the restoration scheme. We study two approaches for selecting working and restoration paths from a set of candidate paths and formulate each method as an integer linear programming (ILP) problem. A traffic uncertainty model is developed in order to compare these methods based on their robustness with respect to changing traffic patterns. Traffic engineering methods are compared based on number of additional demands resulting from traffic uncertainties that can be carried over the network. Proposed heuristic regenerator placement algorithms are also evaluated from a traffic engineering point of view.     

Resource management in an integrated optical network

We propose a novel integrated optical network switching architecture. The proposal offers an approach to signaling for the purpose of transport on an all-optical network of optical and nonoptical legacy network traffic. In order to provide effective end-to-end control and efficient transport services, new signaling and control techniques are required. Standard organizations such as Optical Interworking Forum (OIF) and Internet Engineering Task Force have developed interface methods between client and transport networks, as well as signaling processes for resource allocation. We propose a network controller, which implements interfaces for such integration in the intermediate future, as well as provides a feasible path for the long-term objective of all optical networking. Performance and capacity issues for these systems introduce new dimensions to the existing set of networking problems, since optical paths can now be set up in real-time. There are two main contributions in this paper: (1) functional composition of a network controller, which translates legacy signaling to optical connection signaling and path establishment and (2) determining when to issue an optical connection request based on the current network conditions such as link utilization, so that the integrated optical network can operate efficiently. Analytical approximations, as well as simulation results for call blocking performance are also presented.     

全光网中光码流性能的整体监控

波分复用(WDM)多粒度交换可重构全光网是当前光通信网发展的方向,该文构造了一种实际试验网,提出了一种 眼图法对网中数字光信号进行全面监控的方法,并在自建WDM多粒度交换可重构全光网试验床上进行了演示,结果显示在网络重构等各种条件下均可对网中各波长通道数字信号的信噪比、定时抖动、功率、误码率等进行实时监测控制,该方法对光信号的协议和速率透明且能对各种光性能劣化进行鉴别。     

Overspill routing in optical networks: a true hybrid optical network design

To efficiently support the highly dynamic traffic patterns of the current Internet in large-scale switches, we propose a new hybrid optical network design: Overspill Routing In Optical Networks (ORION). By taking advantage of the reduced (electronic) processing requirements of all-optical wavelength switching, the electronic bottleneck is relieved. At the same time, ORION achieves a level of statistical multiplexing comparable to the more traditional point to point WDM solutions, circumventing the bandwidth inefficiencies of all-optical wavelength switched networks, caused by dynamic traffic patterns. The result is a true hybrid optical network design, forming a bridge between these two switching concepts. In this paper the generic concept of ORION is described. An example node design, based on current advanced optical technologies, is described in detail. The ORION concept is also evaluated, comparing it with its two composing technologies, optical wavelength switching and point to point WDM, as well as a third, more trivial, hybrid one, through several case studies.     

全光时延线的实现和应用

从光时延线的原理、结构和性能等方面对全光时延线的实现方法进行了详述,并认为基于波长转换和光纤色散的全光可调时延线将在全光网络中具有重要作用;之后,对光时延线在OTDM、光学测量和光交换中的应用进行了介绍,最后总结了全光时延线需要改进的几个方面。     

An introduction to optical burst switching

Optical burst switching is a promising solution for all-optical WDM networks. It combines the benefits of optical packet switching and wavelength routing while taking into account the limitations of the current all-optical technology. In OBS, the user data is collected at the edge of the network, sorted based on a destination address, and grouped into variable sized bursts. Prior to transmitting a burst, a control packet is created and immediately sent toward the destination in order to set up a bufferless optical path for its corresponding burst. After an offset delay time, the data burst itself is transmitted without waiting for a positive acknowledgment from the destination node. The OBS framework has been widely studied in the past few years because it achieves high traffic throughput and high resource utilization. However, despite the OBS trademarks such as dynamic connection setup or strong separation between data and control, there are many differences in the published OBS architectures. In this article we summarize in a systematic way the main OBS design parameters and the solutions that have been proposed in the open literature.     

Path selection methods with multiple constraints in service-guaranteed WDM networks

We propose a new approach to constraint-based path selection for dynamic routing and wavelength allocation in optical networks based on WDM. Our approach considers service-specific path quality attributes, such as physical layer impairments, reliability, policy, and traffic conditions, and uses a flooding-based transfer of path information messages from source to destination to find multiple feasible paths. It is fully decentralized, as it uses local network state information. To better understand how multiple constraints impact the efficiency of wavelength routing, and consequently provision the service guarantees, we specifically focus on electronic regenerators that, while being widely considered as the basic building blocks for optical switching nodes, are likely to impose conflicting constraints on routing. For example, electronic regenerators extend the optical reach and could perform wavelength shifting, but also induce impairments, such as delays and operational costs. The question for constraint-based routing is how to account for these conflicting effects. To validate the network modeling, a wide range of networking scenarios are simulated, such as ring, mesh and interconnections of all-optical networks with electronic gateways. For all these scenarios, our approach is shown to efficiently accommodate multiple, conflicting routing metrics related to different services and network architectures.     

Routing algorithm using the flooding mechanism in a hybrid optical-CDMA and WDM all-optical network

This study describes specific characteristics of optical technology and the requirements they place on routing and path selection. Moreover, a concept for an all-optical circuit-switched network is presented that utilizes near future WDM and optical-CDMA technologies. Mainly this study emphasizes on devising a routing algorithm for all-optical networks that use these technologies and taking into consideration the optical technology attributes. The assumption that parallel channels traversing the same path have the same metric (cost) is no longer valid. The algorithm adopts a flooding mechanism to compute metrics corresponding to every possible path between source and destination nodes based on link impairments and switch characteristics. From amongst computed costs, a selection is taken minimizing the cost by using Viterbi algorithm. This way, codes and wavelengths are assigned based on the characteristics of each link for each possible route, thus optimizing the network's performance.     

Architecture of an all-optical circuit-switched multistageinterconnection network

An architecture of an all-optical multistage interconnection network is proposed. The network supports a circuit-switching model of communication and can provide parallel optical paths among input and output ports. It uses an address-based routing algorithm for path setup which, due to its decentralized nature, makes this network suitable for designing high-speed switching systems. These switches are commonly used in telephony and multiprocessor systems. The proposed architecture uses bistable optical devices, such as interference filters, as essential components of its switching modules. Since these devices can be easily fabricated, the implementation of this architecture is feasible. Various design issues related to optical clock generation, its distribution, data synchronization, and intensity restoration are also discussed     

Dynamic Waveband Switching in WDM Mesh Networks Based on a Generic Auxiliary Graph Model

Waveband switching (WBS) is a promising technique to reduce the switching and transmission costs in the optical domain of a wavelength-division multiplexing (WDM) network. This paper considers the problem of provisioning dynamic traffic using WBS in a WDM mesh network. The network of interest is a homogeneous WBS network, where each node has the functionality of WBS. The problem is called the dynamic WBS problem, which involves searching waveband-routes or wavelength-routes for the dynamically arriving traffic requests. The objective is to minimize the total switching and transmission costs in the optical domain. To solve the dynamic WBS problem, an auxiliary graph model capturing the network state is proposed. Based on the auxiliary graph, two heuristic on-line WBS algorithms with different waveband grouping policies are proposed, namely the wavelength-first WBS algorithm based on the auxiliary graph (WFAUG) and the waveband-first WBS algorithm based on the auxiliary graph (BFAUG). Simulation results indicate that WBS is an attractive technique which reduces the overall switching and transmission costs by up to 30% in the network. The results also show that the WFAUG algorithm outperforms the BFAUG algorithm in terms of port savings and cost savings.     

Edge‐Node Deployed Routing Strategies for Load Balancing in Optical Burst Switched Networks

Optical burst switching is a promising switching paradigm for the next IP‐over‐optical network backbones. However, its burst loss performance is greatly affected by burst contention. Several methods have been proposed to address this problem, some of them requiring the network to be flooded by frequent state dissemination signaling messages. In this work, we present a traffic engineering approach for path selection with the objective of minimizing contention using only topological information. The main idea is to balance the traffic across the network to reduce congestion without incurring link state dissemination protocol penalties. We propose and evaluate two path selection strategies that clearly outperform shortest path routing. The proposed path selection strategies can be used in combination with other contention resolution methods to achieve higher levels of performance and support the network reaching stability when it is pushed under stringent working conditions. Results show that the network connectivity is an important parameter to consider.     

Traffic engineering in multigranularity heterogeneous optical WDM mesh networks through dynamic traffic grooming

In this article we investigate the problem of efficiently provisioning connections of different bandwidth granularities in a heterogeneous WDM mesh network through dynamic traffic grooming schemes under traffic engineering principles. Due to the huge amount of traffic a WDM backbone network can support and the large geographic area it can cover, constructing and upgrading such an optical WDM network can be costly. Hence, it is extremely important for network operators to apply traffic engineering strategies to cost-effectively support different bandwidth granularity services using only the appropriate amount of network resources. This requires an optical WDM network to have multigranularity switching capability, and such a network tends to be a multivendor heterogeneous network. However, WDM network heterogeneity increases the difficulty and challenge of efficient traffic provisioning. In this article we present different TE issues that need to be carefully considered in such an optical WDM network, and propose possible solutions and extensions for the generalized multiprotocol label switching optical network control plane. We extend an existing generic graph model to perform efficient traffic grooming and achieve different TE objectives through simple shortest path computation algorithms. We show that our approach is very practical and very suitable for traffic engineering in a heterogeneous multigranularity optical WDM mesh network.     

Enhanced Optimal and Heuristic Solutions of the Routing Problem in Light-Trail Networks

Light-trail is an efficient and feasible technology for IP transport over all-optical networks. The proposition of light-trails for all-optical networks has demonstrated a number of advantages over other paradigms such as Wavelength Routing (WR), Optical Burst Switching (OBS) and Optical Packet Switching (OPS). This article tackles the routing problem of light-trails with the solution objective of minimizing the number of needed light-trails to accommodate an offered traffic matrix. We present two enhancements to the Integer Linear Programming (ILP) formulation of the routing problem. We also propose a computationally efficient routing heuristic for use with static and incremental traffic models. The heuristic is based on routing flows one-by-one. This is done by assigning a set of attributes to each flow and to each network path. The flow attributes are used to determine the order in which flows are presented to the routing algorithm. The path attributes are used to determine which path is selected to route the flow at hand. The efficiency of the proposed heuristic is confirmed using example problems of different network topologies.     

An Optical Network Architecture With Distributed Switching Inside Node Clusters Features Improved Loss, Efficiency, and Cost

The novel core network architecture presented in this paper realizes distributed all-optical switching of payload by partitioning the network into a number of geographically limited domains, where two-way reservations are effective. Thus, inside each domain, loss is eliminated, while traffic from many nodes can be aggregated into single bursts, improving efficiency. Clustered nodes contribute contiguous optical slots, which are marshaled into composite optical frames destined for other clusters, under the guidance of a reservation-based control protocol. The lossless aggregation of traffic from several core nodes allows the use of cost-effective bufferless all-optical transport among the domains with electrical buffers employed at the periphery of the system. The end result is a triple improvement in loss probabilities, efficiency, and cost. This is achieved by exploiting three features of the architecture: the distributed switching functionality (as in early LANs when centralized switching was expensive), localized reservations (avoiding the intolerable delays of end-to-end reservations), and a reduced number of source-destination pairs (by means of node clustering into reservation domains)     

光码分多址全光网络实现方案

本文提出一种利用时域编码的光码分多址(OCDMA)技术构造全光通信网络的实现方案.给出了OCDMA全光接入网,OCDMA光交叉连接、光交换、光上下路、光复用的具体实现方法,给出了OCDMA全光网络体系结构.     

All-optical four-fiber bidirectional line-switched ring

An all-optical four-fiber bidirectional line-switched ring (O-4F/BLSR) architecture is proposed. This new physical layer networking protocol uses wavelengths as tributaries and an optical supervisory channel to carry overhead information. Optical channels can be added and dropped from the ring, and virtual wavelength paths can be provisioned. Both node and link failures of a network can be protected through a two layer protection scheme. Protection switching within the optical multiplex section layer (OMS) restores failure caused by loss of optical continuity in a way similar to the SONET 4F/BLSR line switching. Protection switching within the optical channel layer restores single channel failure using 1:N protection. Test results show that the O-4F/BLSR can restore traffic in less than 50 ms. A self-healing, bandwidth efficient, and scalable all-optical transport network evolving from this O-4F/BLSR architecture is possible     

Performance evaluation of a new technique for IP support in a WDMoptical network: optical composite burst switching (OCBS)

The optical composite burst switching (OCBS) technique is proposed to be implemented in an all-optical backbone network to support Internet protocol (LP) traffic. The OCBS is based on two main features. First, several IP packets are assembled in a single macropacket, called burst. Second, the burst contention in an optical switch is handled by means of two techniques, the wavelength dimension and the burst-dropping (BD) technique. Different from traditional optical burst switching, where an entire burst is discarded when all of the output wavelengths are engaged at the arrival instant of the burst, a switch adopting the BD technique discards only the initial part of a burst finding all of the engaged output wavelengths while forwarding the final part of the burst, beginning at the instant in which one wavelength becomes free. The OCBS allows an increase in the switch throughput in terms of number of accepted IP packets because a burst contains a given number of IP packets. We introduce the analytical model that allows us to evaluate the effectiveness of the technique and, in particular, the obtained saving; furthermore, a sensitivity analysis of the saving, with respect to both the optical burst switch parameters and the traffic load, is carried out     

Design and experimental demonstration of a variable-length optical packet routing system with unified contention resolution

This paper presents theoretical design, network simulation, implementation, and experimental studies of optical packet routing systems supporting variable-length packets. The optical packet switching network exploits unified contention resolution in core routers in three optical domains (wavelength, time, and space) and in edge routers by traffic shaping. The optical router controller and lookup table, implemented in a field-programmable gate array (FPGA), effectively incorporates the contention resolution scheme with pipelined arbitration of asynchronously arriving variable-length packets. In addition, real-time performance monitoring based on the strong correlation between the bit-error rates of the optical label and those of the data payload indicates its application in optical time-to-live detection for loop mitigations. Successful systems integration resulted in experimental demonstration of the all-optical packet switching system with contention resolution for variable-size packets.