Optical Core Networks Research Articles

Synthesis of Optical Wavelet Filters

The goal of the next generation of core and access optical networks is not the only the optical time and frequency signal multiplexing, but also the entire data processing performed in the optical domain, without any electrical-to-optical-to-electrical conversion. In a recent paper, we presented innovative planar lightwave circuit devices that perform the discrete wavelet transform and the wavelet packets decomposition of a data signal in the optical domain. The same filtering procedure was used to design optical encoders-decoders that generate-process a set of orthogonal optical code simultaneously. The aim of this letter is to furnish the synthesis guidelines for two-port lattice-form optical wavelet filters, starting from the half-band filters architecture presented by Jinguji et al.

NEW SCHEMES FOR CONNECTION ESTABLISHMENT IN GMPLS ENVIRONMENT FOR WDM NETWORKS

Generalized Multi-Protocol Label Switching (GMPLS) is growing in popularity as a set of protocols for provisioning and managing core optical networks. In this paper, we present new schemes for provisioning lightpaths in WDM optical network. We first propose a path selection scheme required for deploying lightpaths in GMPLS environment. When a request for lightpath arrives at a source LSR, in GMPLS it is required to send request messages from an upstream LSR to the downstream LSR for setting up a lightpath. Therefore it is needed that an appropriate route be selected through the optical network for the requested lightpath. Keeping in mind its signaling characteristics we describe a path selection algorithm that can be built on GMPLS to enhance its performance. We next propose a path setup scheme for setting up the connection using the path selected with our earlier scheme. The lookahead approach of our path set up scheme enables it to work faster than existing GMPLS path setup protocols. We performed extensive simulation and found that the blocking probability of the WDM networks in GMPLS environment is lower when using our schemes than with the existing standard protocols.

Network control and management challenges in opaque networks utilizing transparent optical switches

There is a potential for significant cost, footprint, and power savings by eliminating unnecessary opto-electronic conversions on a signal path in a core optical mesh network. The article addresses and clarifies some fundamental issues surrounding all-optical networking and all-optical switching, and analyzes the trade-offs between transparent and opaque networking. It investigates a number of networking and interface compatibility issues that arise for an opaque network with transparent switches, and presents a number of ways to address these issues.

Framework for dynamic optical virtual private networks (VPNs): architecture and analysis

The authors explore the problem of dynamic virtual private networks (VPNs) over wavelength division multiplexing (WDM) networks to facilitate the guarantee of diverse quality of service (QoS) requirements of different traffic streams, especially those with very stringent delay jitter requirements and with bursty characteristics. Each VPN consists of different traffic streams with various quality sensitivities. The proposed QoS model provides three types of QoS services for various VPNs: static, optical burst switching (OBS) and alternative VPNs. All the three types provide transmission in the optical core networks without any O/E/O conversion. The static type has a set of dedicated or shared lightpaths which have been pre-allocated and the traffic from this VPN has a constant bit rate (CBR). The OBS type need to setup the lightpath using so-called optical burst switching while a traffic stream with variable bit rate (VBR) request, is occurring. The alternative type has to set up a lightpath based on two-way reservation protocols such as tell-and-wait (TAW) for the traffic with unspecified bit rate (UBR) or available bit rate (ABR). The proposed model is suitable for carrying the multimedia applications which have various sensitivities to delay and jitter. By employing dynamic VPNs directly over the WDM layer, one can eliminate the often complex QoS related functions in the upper protocol layers, and thus increase the overall communication efficiency. Furthermore, this could be the first step towards providing fine grained service over optical wide area networks. In addition, basic performance analysis and preliminary results are presented, based on simulation, and the network designer is provided with a quantitative assessment of proportion for different traffic types with different QoS service requirements.

An Evolutionary Design Algorithm for Ring-based SDH optical core networks

This paper presents a ring-based SDH optical core network design problem with multiple constraints. A novel evolutionary algorithm (EA) is developed to successfully find near-optimal solutions for a realistic case study. Compared to a genetic algorithm, this EA is demonstrated to be more efficient and effective by experimental simulation results, and shows promise for tackling ring-based network design problems.

Routing and protection in GMPLS networks: From shortest paths to optimized designs

Shortest path algorithms such as shortest path first (SPF) and constrained shortest path first (CSPF) are widely used in online traffic engineering where connections need to be set up one at a time as connection requests arrive sequentially. We propose an approach, called design-based routing (DBR), whereby optimized paths computed offline are used to guide online path setups. Offline path computation in generalized multiprotocol label switching (GMPLS) networks does not pose a significant challenge since optical core or metro networks typically consist of a few dozen to hundreds of nodes compared to hundreds to more than one thousand nodes in pure data networks. DBR takes advantage of available demand information based on customer prescriptions, traffic projections, and historical measurements to build an approximate traffic demand matrix for path optimization. By means of simulation, we perform comparative evaluations of opaque GMPLS networks under static and dynamic connections with different protection modes. The results indicate that DBR outperforms SPF and CSPF under a wide range of operating conditions and is robust to inaccuracies in the estimation of the traffic demand matrix. We then construct routing schemes with resource management and online measurement. The simulation results indicate that resource management provides an effective way to mitigate greed inherent in CSPF, and online measurement provides an effective way to improve DBR performance when the traffic demand information used in the design of DBR paths is different from the actual traffic demand.

End-to-end contention resolution schemes for an optical packet switching network with enhanced edge routers

This paper investigates contention resolution schemes for optical packet switching networks from an end-to-end perspective, where the combined exploitation of both core routers and edge routers are highlighted. For the optical-core network, we present the architecture of an optical router to achieve contention resolution in wavelength, time, and space domains. Complementing the solution involving only the core router intelligences, we propose performance enhancement schemes at the network edge, including a traffic-shaping function at the ingress edge and a proper dimensioning of the drop port number at the egress edge. Both schemes prove effective in reducing networkwide packet-loss rates. In particular, scalability performance simulations demonstrate that a considerably low packet-loss rate (0.0001% at load 0.6) is achieved in a 16-wavelength network by incorporating the performance enhancement schemes at the edge with the contention resolution schemes in the core. Further, we develop an field-programmable gate-array (FPGA)-based switch controller and integrate it with enabling optical devices to demonstrate the packet-by-packet contention resolution. Proof-of-principle experiments involving the prototype core router achieve an error-free low-latency contention resolution.

Shaping self-similar traffic at access of optical network

The focus of this paper is shaping of self-similar traffic at the access of an optical node. Due to the lack of optical memories, we suggest a combined exploitation of electronic memories in the edge of the optical network by means of shaping and propose two novel shaping algorithms that dynamically shape the incoming traffic so as to meet Quality of Service (QoS) requirements while keeping with the optical core network constraints. The first algorithm follows a deterministic approach and is based on the service curves theory. It dynamically, on an interval basis, adjusts the shaping parameters to the token bucket described self-similar traffic. The second, alternative shaping algorithm follows a stochastic approach. It blindly shapes the traffic using a jumping observation window.

Future WAN architecture driven by services, traffic volume, and technology trends

Wide area networks (WANs) today involve protocol and topological hierarchies. Protocol hierarchy involves Internet protocol (IP), asynchronous transfer mode (ATM), synchronous optical network (SONET), and dense wavelength division multiplexing (DWDM). Self-healing SONET rings provide very fast restoration, and DWDM allows the creation of multiple wavelengths (“virtual fibers”) from a single optical fiber, providing ever-increasing capacity to the SONET layer. Topological hierarchy involves edge nodes and core nodes for IP, ATM, and SONET. It provides traffic aggregation and statistical multiplexing, takes advantage of transport bandwidth and economy of size of packet/cell switches, and allows easier operations. A confluence of factors, however, is driving changes in this network architecture. Explosive growth in traffic volume and emergence of true multiwavelength, multiservice optical networks will make flatter (more heavily meshed) service networks supported by an optical core network more economical in the future. In this paper, we discuss the factors driving this shift in the network architecture, quantify its cost advantage, describe its impact on the requirements for network elements comprising the optical transport network (OTN) and the service network, and discuss new management/control paradigms as well as opportunities for new revenue-generating services resulting from the new architecture.

Next generation networks

The forces for high speed, high capacity data services are driving the next generation network architecture toward a packet network. These next generation networks are basically of two types: wired networks and wireless networks. Changes in network services, technology and regulation are creating a golden era of network innovation. Much is certain in this evolution. For instance, the networks will have a shared, packet-based, optical-core network using dense wavelength division multiplexing (DWDM) optical transport with optical add/drop and multiplexing. Wireless communications is expected to be a major driver for growth in the telecommunications industry over the next decade. It will become a cornerstone of the information society. Future networks (both wireless and wireline) of the type described here will pave the way for an environment in which information will be made more portable, personal and affordable. They will achieve the ultimate goal of communications-communications from anywhere to anywhere-clear as a bell.

Dynamic Routing and Wavelength Assignment in Survivable WDM Networks

Dense wavelength division multiplexing (DWDM) networks are very attractive candidates for next generation optical Internet and intelligent long-haul core networks. In this paper we consider DWDM networks with wavelength routing switches enabling the dynamic establishment of lightpaths between each pair of nodes. The dynamic routing and wavelength assignment (RWA) problem is studied in multifiber networks, assuming both protection strategies: dedicated and shared. We solve the two subproblems of RWA simultaneously, in a combined way using joint methods for the wavelength selection (WS) and wavelength routing (WR) tasks. For the WS problem in contrast to existing strategies we propose a new, network state based selection method, which tries to route the demand on each wavelength, and selects the best one according to different network metrics (such as available channels, wavelengths per fiber and network load). For the WR problem we propose several weight functions for using in routing algorithms (Dijkstra or Suurballe), adapting dynamically to the load of the links and to the length of the path. The combination of different wavelength selection and routing (WS&WR) methods enables wide configuration opportunities of our proposed algorithm allowing good adaptation to any network state. We also propose the extension of the RWA algorithm for dedicated and shared protection and a new method for applying shared protection in dynamic WDM environment. The detailed analysis of the strategies demonstrate that our RWA algorithm provides significantly better performance than previous methods in terms of blocking probability whether with or without protection methods.

Invited: Routing Strategies for Capacity-Efficient and Fast-Restorable Mesh Optical Networks

Wavelength division multiplexed (WDM)-based mesh network infrastructures that route optical connections using intelligent optical cross-connects (OXCs) are emerging as the technology of choice to implement the next generation core optical networks. In these architectures a single OXC is capable of switching tens of terabits of traffic per second. With such data transfer rates at stake, it becomes increasingly challenging for carriers to (1) efficiently and cost-effectively operate and manage their infrastructure, and (2) cope with network failures while guaranteeing prescribed service level agreements (SLAs) to their customers. Proper routing of primary and backup paths is a critical component of the routing and restoration architecture required to meeting these challenges. In this paper we review some of the various strategies and approaches proposed so far to intelligently route connections while at the same time providing guaranteed protection against various types of network failures. We explore the tradeoffs associated with these approaches, and investigate in particular different, sometimes competing aspects, such as cost/capacity required, level of protection (link vs. node failure), restoration time, and complexity of route computation.

Comparison of two optical-core networks

The resource requirements for two optical-core network architectures are compared. One architecture is a highly optimized, multihop mesh of optical switches, in which the number of optical nodes traversed by a light path is bounded. The other is a single-hop composite-star structure. We show in a case study that although the composite star may require a higher fiber-distance value than the optimized mesh structure, it needs many fewer ports and a smaller optical switching fabric to achieve the same throughput. The single-hop network does not require any wavelngth conversion, it eliminates the need for traffic engineering, and is resilient to changes in the spatial distribution of traffic. Results are quantified through simulation.

Design of a cross-border optical core and access networking field trial: first outcomes of the ACTS-PELICAN project

A large advanced optical network was assembled and operated in the field, featuring access, metropolitan, and core optical networks with advanced functionality and technology in all parts of the network. It demonstrates the reliability and viability of photonic technologies, and management functions in a trial representative of a global network infrastructure. The core network is a transparent all-optical meshed network with wavelength crossconnects partly 2R-regenerating, operating at 2.5 and 10 Gb/s, and supporting various protection schemes including 1:N shared OCH protection. The metropolitan network is a ring composed of OADMs supporting OMS protection. The interconnection to the SuperPON access network is made through an ATM switch. The ATM-based SuperPON supports a dynamic medium access control (MAC) protocol. For the first time, a 10 Gb/s wavelength-converted connection was demonstrated in the field in a transparent all-optical managed network. The field trial has demonstrated many points of progress as compared to the previous state of the art: cascadability experiments in a real network with reasonable distances and low compensation, various node functions, interworking of various equipment types, new optical protection, and dynamic MAC protocol. The (transport) TMN/Q3 integrated management system played an important role to achieve the network experiments: it allowed us to provision and reconfigure the end-to-end optical paths very quickly (<3 s) from the centralized management platform. This trial is also the first one representative of an advanced global optical network infrastructure including core, metro, and access networks, supporting end-to-end multimedia services. This article reports the project results before the field deployment which took place in April 2000.

Optical performance monitoring in reconfigurable WDM optical networks using subcarrier multiplexing

Optical performance monitoring (OPM) is an important approach to determine the quality of optical channels within an optical core network without passing data through optoelectronic regeneration at the monitor points. Using this approach, the quality or "health" of signals can be determined at arbitrary points in a network without knowledge of the transport history of the data or the details of the transmission path. We report experimental results on the use of subcarrier multiplexing (SCM) to perform a variety of monitoring functions including chromatic dispersion monitoring, wavelength registration, power monitoring, and signal-to-noise ratio (SNR) monitoring.

IP over optical networks: architectural aspects

The Internet transport infrastructure is moving toward a model of high-speed routers interconnected by intelligent optical core networks. A consensus is emerging in the industry on utilizing an IP-centric control plane within optical networks to support dynamic provisioning and restoration of lightpaths. At the same time, there are divergent views on how IP routers must interact with optical core networks to achieve end-to-end connectivity. This article describes the architectural alternatives for interconnecting IP routers over optical networks, considering the routing and signaling issues. Also, the application of IP-based protocols for dynamic provisioning and restoration of lightpaths, as well as the interworking of multivendor optical networks is described.

Free-space micromachined optical switches for optical networking

Fiber-optic switches with high port count have emerged as leading candidates for deployment in future optical transport networks, where restoration and provisioning in the optical layer will become increasingly important. This paper reviews the principle and performance of free-space micromachined optical switches (FS-MOS) featuring free-rotating hinged micromirrors. A single-chip FS-MOS that implements the critical function of bridging-essential for restoration in core optical networks is also proposed and demonstrated. The scalability of FS-MOS devices, and the dependence of their insertion losses on mirror-angle, are estimated theoretically. Simulation results suggest that the FS-MOS approach holds considerable promise for being expandable to the port-count values that will be needed in future core-transport lightwave networks.