A next-generation optical regional access network

We describe an optical regional access network which combines electronic IP routing with intelligent networking functionality of the optical WDM layer. The optical WDM layer provides such networking functions as network logical topology reconfiguration, optical flow switching to offload traffic and bypass IP routers, wavelength routing of signals, protection switching and restoration in the optical domain, and flexible network service provisioning by reconfigurable wavelength connectivity. We discuss key enabling technologies for the WDM layer and describe their limitations. The symbiosis of electronic and optical WDM networking functions also allows support for heterogeneous format traffic and will enable efficient gigabit-per-second user access in next-generation Internet networks     

Constrained and Unconstrained overspill routing in optical networks: a detailed performance evaluation

In this article, we present a detailed performance evaluation of a hybrid optical switching (HOS) architecture called Overspill Routing in Optical Networks (ORION). The ORION architecture combines (optical) wavelength and (electronic) packet switching, so as to obtain the individual advantages of both switching paradigms. In particular, ORION exploits the possible idle periods of established lightpaths to transmit packets destined to the next common node, or even directly to their common end-destination. Depending on whether all lightpaths are allowed to simultaneously carry and terminate overspill traffic or overspill is restricted to a sub-set of wavelengths, the architecture limits itself to constrained or un-constrained ORION. To evaluate both cases, we developed an extensive network simulator where the basic features of the ORION architecture were modeled, including suitable edge/core node switches and load-varying sources to simulate overloading traffic conditions. Further, we have assessed various aspects of the ORION architecture including two basic routing/forwarding policies and various buffering schemes. The complete network study shows that ORION can absorb temporal traffic overloads, as intended, provided sufficient buffering is present. We also demonstrate that the restriction of simultaneous packet insertions/extractions, to reduce the necessary interfaces, do not deteriorate performance and thus the use of traffic concentrators assure ORION’s economic viability.     

WDM-based packet networks

We discuss design considerations for wavelength division multiplexing (WDM)-based packet networks. In the near term, such networks are likely to consist of WDM links connected using some form of electronic multiplexing. The focus of this article is on the joint design of the electronic and optical layer with the objective of simplifying the network and reducing the protocol stack. To that end, we discuss the benefits of optical flow switching, network reconfiguration, traffic grooming, and optical layer protection. We also discuss the state of all-optical packet networking with particular focus on local area network technology     

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     

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.     

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。     

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.     

Advances in photonic packet switching: an overview

The current fast-growing Internet traffic is demanding more and more network capacity every day. The concept of wavelength-division multiplexing has provided us an opportunity to multiply network capacity. Current optical switching technologies allow us to rapidly deliver the enormous bandwidth of WDM networks. Photonic packet switching offers high-speed, data rate/format transparency, and configurability, which are some of the important characteristics needed in future networks supporting different forms of data. In this article we present some of the critical issues involved in designing and implementing all-optical packet-switched networks     

An All-Optical Access-Metro Interface for Hybrid WDM/TDM PON Based on OBS

A new all-optical access-metro network interface based on optical burst switching (OBS) is proposed. A hybrid wavelength-division multiplexing/time-division multiplexing (WDM/TDM) access architecture with reflective optical network units (ONUs), an arrayed-waveguide-grating outside plant, and a tunable laser stack at the optical line terminal (OLT) is presented as a solution for the passive optical network. By means of OBS and a dynamic bandwidth allocation (DBA) protocol, which polls the ONUs, the available access bandwidth is managed. All the network intelligence and costly equipment is located at the OLT, where the DBA module is centrally implemented, providing quality of service (QoS). To scale this access network, an optical cross connect (OXC) is then used to attain a large number of ONUs by the same OLT. The hybrid WDM/TDM structure is also extended toward the metropolitan area network (MAN) by introducing the concept of OBS multiplexer (OBS-M). The network element OBS-M bridges the MAN and access networks by offering all-optical cross connection, wavelength conversion, and data signaling. The proposed innovative OBS-M node yields a full optical data network, interfacing access and metro with a geographically distributed access control. The resulting novel access-metro architectures are nonblocking and, with an improved signaling, provide QoS, scalability, and very low latency. Finally, numerical analysis and simulations demonstrate the traffic performance of the proposed access scheme and all-optical access-metro interface and architectures     

Approaches to optical Internet packet switching

Wavelength-division multiplexing is currently being deployed in telecommunications networks in order to satisfy the increased demand for capacity brought about by the explosion in Internet use. The most widely accepted network evolution prediction is via an extension of these initial predominantly point-to-point deployments, with limited system functionalities, into highly interconnected networks supporting circuit-switched paths. While current applications of WDM focus on relatively static usage of individual wavelength channels, optical switching technologies enable fast dynamic allocation of WDM channels. The challenge involves combining the advantages of these relatively coarse-grained WDM techniques with emerging optical switching capabilities to yield a high-throughput optical platform directly underpinning next-generation networks. One alternative longer-term strategy for network evolution employs optical packet switching, providing greater flexibility, functionality, and granularity. This article reviews progress on the definition of optical packet switching and routing networks capable of providing end-to-end optical paths and/or connectionless transport. To date the approaches proposed predominantly use fixed-duration optical packets with lower-bit-rate headers to facilitate processing at the network-node interfaces. Thus, the major advances toward the goal of developing an extensive optical packet-switched layer employing fixed-length packets are summarized, but initial concepts on the support of variable-length IP-like optical packets are also introduced. Particular strategies implementing the crucial optical buffering function at the switching nodes are described, motivated by the network functionalities required within the optical packet layer     

Optical networks with hybrid routing

All-optical switching or wavelength routing has the benefit of optical bypass that can eliminate expensive high-speed electronic processing at intermediate nodes and reduce significantly the cost of high-bandwidth transport. But all-optical switching has the limitations of coarse granularity, lack of multiplexing gain, and scarcity of wavelength resources, which do not mesh well with Internet traffic that has many small and diverse flows and emphasizes the importance of resource sharing. In particular, wavelength routed light paths have difficulty to seamlessly converge with multiprotocol label switching label-switched paths that have arbitrary bandwidth granularity and relatively abundant labels. In this paper, we propose a hybrid wavelength and subwavelength routing scheme that can preserve the benefits of optical bypass for large traffic flows at the same time provide multiplexing gain for small traffic flows. We first study the hybrid routing scheme using static optimization that produces an optimal path set and a partition between wavelength and subwavelength routing. We then present a dynamic heuristic that tracks the static optimization closely. During the process, we proposed a traffic arrival process called incremental arrival with sporadic random termination to more accurately model practical optical network traffic generation process.     

Some principles for designing a wide-area WDM optical network

We explore design principles for next-generation optical wide-area networks, employing wavelength-division multiplexing (WDM) and targeted to nationwide coverage. This optical network exploits wavelength multiplexers and optical switches in routing nodes, so that an arbitrary virtual topology may be embedded on a given physical fiber network. The virtual topology, which is used as a packet-switched network and which consists of a set of all-optical “lightpaths”, is set up to exploit the relative strengths of both optics and electronics-viz. packets of information are carried by the virtual topology “as far as possible” in the optical domain, but packet forwarding from lightpath to lightpath is performed via electronic switching, whenever required. We formulate the virtual topology design problem as an optimization problem with one of two possible objective functions: (1) for a given traffic matrix, minimize the network-wide average packet delay (corresponding to a solution for present traffic demands), or (2) maximize the scale factor by which the traffic matrix can be scaled up (to provide the maximum capacity upgrade for future traffic demands). Since simpler versions of this problem have been shown to be NP-hard, we resort to heuristic approaches. Specifically, we employ an iterative approach which combines “simulated annealing” (to search for a good virtual topology) and “flow deviation” (to optimally route the traffic-and possibly bifurcate its components-on the virtual topology). We do not consider the number of available wavelengths to be a constraint, i.e., we ignore the routing of lightpaths and wavelength assignment for these lightpaths. We illustrate our approaches by employing experimental traffic statistics collected from NSFNET     

All-optical wavelength conversion using a pulse reformatting optical filter

We introduce a general concept for the design of all-optical wavelength converters with pulse reformatting functionality. The novel wavelength converters are based on a single semiconductor optical amplifier followed by an optical filter. A microelectromechanical system-based realization is shown and simultaneous 40 Gb/s wavelength conversion, switching and signal format conversion is demonstrated. The new pulse reformatting optical filter device outperforms current schemes with respect to input-power requirements, input-power dynamic range and signal quality.     

A broad view on overspill routing in optical networks: a real synthesis of packet and circuit switching?

The emerging wavelength switched networks reduce the strain on packet forwarding. Unfortunately, that solution is not really efficient on a bandwidth level, and is not ideally suited for bursty traffic. Packet switched solutions, whether electronic or optical, can use statistical multiplexing to cope with bursty traffic and yield better bandwidth efficiency. We present a novel network concept that can combine these two worlds, withholding their advantages. We introduce this Overspill Routing In Optical Networks (ORION), and discuss several aspects of it: the overall architecture and network concept, node design and implementation, and evaluation at network level as well as node level.     

All-optical wavelength conversion: technologies and applications inDWDM networks

Dense WDM technologies make effective use of the vast fiber bandwidth and offer an added dimension to all-optical networks. Wavelength conversion at key network nodes is emerging as a fundamental functionality that can allow transparent interoperability, contention resolution, wavelength routing, and, in general, better utilization of the network resources under dynamic traffic patterns. We offer an overview of the enabling technologies and extend the treatment to the network application of these converters. Attention is given to semiconductor optical amplifiers and their use in wavelength converters. Converters based on four-wave mixing as well as those based on nonlinear optical loop mirrors are evaluated, paying special attention to signal integrity and architectural as well as performance issues. The use of wavelength converters in wavelength routing networks is explored together with the application of these devices in contention resolution and in the routing wavelength assignment problem. Future directions are outlined at the system as well as network levels     

Advances in the management and control of optical Internet

Given the ever increasing demand for network bandwidth, and the phenomenal advances in optical wavelength division multiplexing (WDM) networking technologies, a major component of the next generation Internet will be an Internet protocol (IP)-based optical WDM network. As IP over WDM networking technologies mature, a number of important architectural, management and control issues have surfaced. These issues need to be addressed before a true next generation optical Internet can emerge. We enumerate some of the key architectural, management and control issues and discuss corresponding approaches and advances made toward addressing these issues. We first review the different IP/WDM networking architectural models and their tradeoffs. We outline and discuss several management and control issues and corresponding approaches related to the configuration, fault, and performance management of IP over dynamic WDM networks. We present an analysis and supporting simulation results demonstrating the potential benefits of dynamic IP over WDM networks. We then discuss the issues related to IP/WDM traffic engineering in more detail, and present the approach taken in the NGI SuperNet Network Control and Management Project funded by DARPA. In particular, we motivate and present an innovative integrated traffic-engineering framework for reconfigurable IP/WDM networks. It builds on the strength of multiprotocol label switching for fine-grain IP load balancing, and on the strength of reconfigurable WDM networking for reducing the IP network's weighted-hop-distance, and for expanding the bottleneck bandwidth     

Optical burst switching for service differentiation in thenext-generation optical Internet

In an effort to eliminate the electronic bottleneck, new optical switches/routers (hardware) are being built for the next-generation optical Internet where IP runs over an all-optical WDM layer. However, important issues yet to be addressed in terms of protocols (software) are how to develop a new paradigm that does not require any buffer at the WDM layer, as in circuit switching, and elimination of any layers between which exist mainly due to historical reasons. At the same time, such a paradigm should also efficiently support bursty traffic with high resource utilization as in packet switching. This article surveys design issues related to a new switching paradigm called optical burst switching, which achieves a balance between circuit and packet switching while avoiding their shortcomings. We describe how OBS can be applied to the next-generation optical Internet, and in particular how offset times and delayed reservation can help avoid the use of buffer, and support quality of service at the WDM layer     

Control architecture in optical burst-switched WDM networks

Optical burst switching (OBS) is a promising solution for building terabit optical routers and realizing IP over WDM. In this paper, we describe the basic concept of OBS and present a general architecture of optical core routers and electronic edge routers in the OBS network. The key design issues related to the OBS are also discussed, namely, burst assembly (burstification), channel scheduling, burst offset-time management, and some dimensioning rules. A nonperiodic time-interval burst assembly mechanism is described. A class of data channel scheduling algorithms with void filling is proposed for optical routers using a fiber delay line buffer. The LAUC-VF (latest available unused channel with void filling) channel scheduling algorithm is studied in detail. Initial results on the burst traffic characteristics and on the performance of optical routers in the OBS network with self-similar traffic as inputs are reported in the paper.     

Analysis of a dynamically wavelength-routed optical burst switchednetwork architecture

The concept of optical burst switching (OBS) aims to allow access to optical bandwidth in dense wavelength division multiplexed (DWDM) networks at fractions of the optical line rate to improve bandwidth utilization efficiency. This paper studies an alternative network architecture combining OBS with dynamic wavelength allocation under fast circuit switching to provide a scalable optical architecture with a guaranteed QoS in the presence of dynamic and bursty traffic loads. In the proposed architecture, all processing and buffering are concentrated at the network edge and bursts are routed over an optical transport core using dynamic wavelength assignment. It is assumed that there are no buffers or wavelength conversion in core nodes and that fast tuneable laser sources are used in the edge routers. This eliminates the forwarding bottleneck of electronic routers in DWDM networks for terabit-per-second throughput and guarantees forwarding with predefined delay at the edge and latency due only to propagation time in the core. The edge burst aggregation mechanisms are evaluated for a range of traffic statistics to identify their impact on the allowable burst lengths, required buffer size and achievable edge delays. Bandwidth utilization and wavelength reuse are introduced as new parameters characterizing the network performance in the case of dynamic wavelength allocation. Based on an analytical model, upper bounds for these parameters are derived to quantify the advantages of wavelength channel reuse, including the influence of the signaling round-trip time required for lightpath reservation. The results allow to quantify the operational gain achievable with fast wavelength switching compared to quasistatic wavelength-routed optical networks and can be applied to the design of future optical network architectures     

A generalized framework for analyzing time-space switched opticalnetworks

The advances in photonic switching have paved the way for realizing all-optical time switched networks. The current technology of wavelength division multiplexing (WDM) offers bandwidth granularity that matches peak electronic transmission speed by dividing the fiber bandwidth into multiple wavelengths. However, the bandwidth of a single wavelength is too large for certain traffic. Time division multiplexing (TDM) allows multiple traffic streams to share the bandwidth of a wavelength efficiently. While introducing wavelength converters and time slot interchangers to improve network blocking performance, it is often of interest to know the incremental benefits offered by every additional stage of switching. As all-optical networks in the future are expected to employ heterogeneous switching architectures, it is necessary to have a generalized network model that allows the study of such networks under a unified framework. A network model, called the trunk switched network (TSN), is proposed to facilitate the modeling and analysis of such networks. An analytical model for evaluating the blocking performance of a class of TSNs is also developed. With the proposed framework, it is shown that a significant performance improvement can be obtained with a time-space switch with no wavelength conversion in multiwavelength TDM switched networks. The framework is also extended to analyze the blocking performance of multicast tree establishment in optical networks. To the best of our knowledge, this is the first work that provides an analytical model for evaluating the blocking performance for tree establishment in an optical network. The analytical model allows a comparison between the performance of various multicast tree construction algorithms and the effects of different switch architectures