Virtual Wavelength Path Research Articles

Converged Optical Network and Data Center Virtual Infrastructure Planning

This paper presents a detailed study of planning virtual infrastructures (VIs) over a physical infrastructure comprising integrated optical network and data center resources with the aim of enabling sharing of physical resources among several virtual operators and services. Through the planning process, the VI topology and virtual resources are identified and mapped to the physical resources. Our study assumes a practical VI demand model without any in advance global knowledge of the VI requests that are handled sequentially. Through detailed integer linear program modeling, two objective functions - one that minimizes the overall power consumption of the infrastructure and one that minimizes the wavelength utilization - are compared. Both are evaluated for the virtual wavelength path and wavelength path optical network architectures. The first objective results in power consumption savings and the two optical network architectures provide similar performances. However, the trend changes for higher load values, due to the inefficient wavelength utilization that the first objective leads to. Finally, we compare the virtual infrastructures created by the two objectives through online traffic provisioning simulations. The objective minimizing wavelength utilization results in VIs suffering higher request blocking compared to the VIs created by the objective minimizing the overall power consumption.

All optical wavelength converter and its application in optical network

All optical network (AON) is a hot topic in recent studies of optical fiber communications. Key techniques in AON include optical switching/routing, optical cross connection (OXC), all optical wavelength conversion (AOWC), all optical buffering, etc. Optical switching/routing is in fact wavelength switching/routing. OXC and wavelength conversion (WC) are introduced into cross nodes so that a virtual wavelength path is established. With WC, communication route is formed only if there is unused wavelength in an individual segment link. The rate wavelength usage is thus greatly increased. The blocking rate of network can be reduced by adding WCs, especially for huge capacity multiple nodes ones. Therefore, WC has attracted much attention in basic research of optical communication and is used in some experimental networks. This dissertation studies all optic wavelength conversion and its application, with the contributions in the following five aspects.

A novel model on dynamic resource allocation in optical networks

A novel model on dynamic resource allocation in the WDM optical networks is proposed, basing on the integrated considerations of the impacts of transmission impairments and service classification on dynamic resource allocation in the optical layer. In this model, the priorities of optical connection requests are mapped into different thresholds of transmission impairments, and a uniform method which is adopted to evaluate the virtual wavelength path (VWP) candidates is defined. The Advanced Preferred Wavelength Sets Algorithm (A-PWS) and the heuristic Dynamic Min-Cost & Optical Virtual Wavelength Path Algorithm (DMC-OVWP) are presented addressing the routing and wavelength assignment (RWA) problem based on dynamic traffic and multi priorities in wavelength-routed optical networks. For a received optical connection request, DMC-OVWP is employed to calculate a list of the VWP candidates, and an appropriate VWP which matches the request’s priority is picked up to establish the lightpath by analyzing the transmission qualities of the VWP candidates.

On the joint link dimensioning and routing metric assignment problem for reliable WDM networks

In this paper, we tackle the joint link dimensioning and routing metric assignment problem for reliable wavelength division multiplexing (WDM) networks. This design problem consists to find the number of wavelength channels on each link and the routing metrics (considering shortest-path routing) that ensure the routing of all virtual wavelength paths (VWPs) and the successful rerouting of the reliable VWPs for all failure scenarios of interest to the network planner. A mixed integer mathematical programming model is proposed for the problem. The model is adapted for the single link failure scenarios. Since the problem is NP -hard, we propose a tabu search algorithm to obtain good approximate solutions for real-size instances of the problem. Finally, a lower bound is proposed and numerical results are presented and analyzed.

An efficient algorithm for virtual-wavelength-path routing minimizing average number of hops

We present a novel heuristic algorithm for routing and wavelength assignment in virtual-wavelength-path (VWP) routed wavelength-division multiplexed optical networks. We are the first to take up the approach of both minimizing the network cost, as well as maximizing the resource utilization. Our algorithm not only minimizes the number of wavelengths required for supporting the given traffic demand on any given topology, but also aims to minimize the mean hop length of all the lightpaths which in turn maximizes the resource utilization. The algorithm initially assigns the minimum hop path to each route and then performs efficient rerouting to reduce the number of wavelengths required while also trying to minimize the average hop length. To further reduce the network cost, we also propose a wavelength assignment procedure for VWP routed networks which minimizes the number of wavelength converters required. Our algorithm has been tested on various topologies for different types of traffic demands and has been found to give solutions much better than previous standards for this problem.

Virtual Wavelength Path Algorithm for Design of WDM Cross-connect Network under Non-Poisson Traffic

Semilightpath algorithm to establish simultaneous wavelength routing and wavelength assignment (RAW) in WDM cross-connect has been considered to quantify blocking probability, the benefit of wavelength conversion, conversion gain and fairness in regular and irregular WDM network topologies. The distinct superiority of the present algorithm over other RAW algorithms has been established from the performance results obtained through detailed network simulation.

Wavelength Conversion in WDM Optical Networks: Strategies and Algorithms for Limiting the Number of Converters in the Optical Cross-Connects

This paper considers the problem of wavelength conversion in optical networks using wavelength division multiplexing technique. In the previous literature, two main wavelength routing and assignment strategies have been introduced: wavelength path (WP) and virtual wavelength path (VWP), depending on whether the signal stays on the same wavelength or is converted to another during its travel throughout the network. While the former method does not require any wavelength conversion, the latter needs wavelength conversion in each optical node and, in particular, a wavelength converter per each signal handled by the node itself. From the previous literature emerged that the VWP leads to optical cross-connect (OXC) with lower dimensions compared to the ones required by the WP scheme, and that the difference between the WP and VWP schemes increases as the number of wavelengths carried by each fiber increases. In this paper a new strategy is introduced, named partial virtual wavelength path (PVWP), with the related wavelength routing and assignment algorithm, which makes limited use of wavelength conversion compared to the VWP scheme, and allows the same advantages of VWP to be attained with lower OXC dimensions. The paper reports a comparative analysis among the different strategies, considering both the cases of a network without failures and a network with the possibility of failure restoration. The main result is that the proposed PVWP strategy allows the same advantages of the VWP scheme with a strongly reduced number of wavelength converters (around 5% of the number required by VWP scheme). This figure does not vary appreciably if failure restoration is considered. The new strategy can be adopted by using an opportune OXC architecture, as illustrated in the paper, which allow a limited number of converters to be shared among all the channels as a common pool.

Strategies and Algorithms for Routing both Unicast and Multicast Paths in WDM Networks

This paper introduces the concept of the multicast optical path in WDM networks, and treats the strategies and the algorithms, which allow the routing of plural multicast paths together with unicast paths. This analysis was motivated by the possibility of exploit the optical layer facilities in the transport network, to carry distributive services, such as video channels (e.g. CATV), without the need of dedicated transmission networks. The strategies and algorithms reported in this paper arise from a generalisation of those ones, which have been previously reported in literature. They are wavelength path (WP: which does not make use of wavelength conversion), virtual wavelength path (VWP: which make full use of wavelength conversion), and partial virtual wavelength path (PVWP: making a parsimonious use of wavelength conversion). The analysis shows the characteristics and performance of those strategies and algorithms considering, as a figure of merit, either the number of wavelengths or the system scale (dimensions of the optical nodes), and compare one to each other in order to point out advantages and disadvantages. The main result is that multicast optical paths can favourably be accommodated in a WDM network, and the strategy we propose, making a parsimonious use of wavelength conversion, allows the lowest system scale to be obtained with a very low number of wavelength converters.

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.

Impact of transmission performance on path routing in all-optical transport networks

The impact of transmission related issues on the routing strategies for transparent all-optical wavelength division multiplexed (WDM) transport networks is analyzed in this paper. Three different categories of routing algorithms are analyzed: algorithms based on the wavelength path (WP) strategy, based on the virtual wavelength path (VWP) strategy and requiring only a limited number of wavelength converters in the network partial virtual wavelength path (PVWP). It results that the PVWP allows a saving in network devices with respect to the WP similar those permitted by the VWP also attaining transmission performances near those attained by the WP that are quite better that those attained by the VWP.

Code division multiplexing lightwave networks based upon optical code conversion

Lightwave networks realized through code division multiple access techniques are extensively studied to determine their ultimate capabilities. Here, these concepts are extended to network implementation by introducing an optical code division multiplexing (OCDM) multihop strategy using optical coding. It is shown that this approach is effective in scaling up existing wavelength division multiplexing (WDM) networks without a significant drain of the wavelength resources. The concept of a virtual optical code path (VOCP) is introduced within the transport layer of the network. It is demonstrated that this is a potential solution to wavelength path (WP) allocation problems which may plague WDM based transport networks of the future. Crucial to the VOCP concept is optical code conversion. The interplay between this added functionality and the optical cross-connect is highlighted; the optical cross-connect serves to establish VOCP/VWP (virtual wavelength path) in the hybrid transport layer. An example of optical code conversion is introduced. It is based on coherent OCDM principles in which bipolar phase-shift keyed (PSK) optical pulse sequences are used as the signature codes. Error-free code conversion using a four-chip optical encoder/decoder is successfully performed at 1.24 Gbit/s. The results show the feasibility of high bit rate OCDM transmission with optical code conversion.

Multicasting in Optical Transport Networks

The introduction of multicasting in optical transport networks is analysed and discussed. Three different optical path realization techniques, involving the multicasting function, are examined: the Multicast Wavelength Path (MWP), the Multicast Virtual Wavelength Path (MVWP) and the Partial Multicast Virtual Wavelength Path (PVWP). A performance evaluation model is reported and results of the performance analysis are discussed. In addition several optical cross-connect architectures, allowing multicasting to be achieved, are investigated and compared. Three different types of optical switches are considered: space division, delivery and coupling, and wavelength switches. Crucial aspects as the modularity, the complexity, the costs and some transmission aspects are taken into account in the analysis.

Virtual wavelength path cross-connect based on optoelectronic wavelength conversion

This paper describes the system design and performance of a virtual wavelength path cross-connect (VWP-XC); we demonstrate its function of wavelength conversion, cross-connection, and transportation. We realize a feasible wavelength conversion technique using an optical receiver and a tunable DBR laser. Frequency stability of a 100 GHz-spaced wavelength-converted signal is confirmed by a multiwavelength simultaneous monitoring circuit (MSMC) to be within 100 MHz. VWP cross-connection and error free transportation over 160 km and four 120 km spans (480 km with 3 repeaters) is confirmed in a five-node VWP network.

100-GHz-spaced 8-channel frequency control of DBR lasers for virtual wavelength path cross-connect system

The authors propose a simultaneous frequency control scheme for multiple DBR lasers in a virtual wavelength path (VWP) cross-connect system. The frequencies of eight DBR lasers are switched and held to the 100 GHz-spaced grid anchored at 193100 GHz, and stabilized to within 100 MHz for 12 h.

Optical path cross-connect system scale evaluation using path accommodation design for restricted wavelength multiplexing

The optical path (OP) technology, which employs both wavelength-division multiplexing and wavelength routing, will be the key to enhanced network integrity and an ubiquitous broadband integrated services digital network (B-ISDN) in the future. To construct the OP network, path accommodation design that can solve simultaneously the problems of path routing and wavelength assignment must be established. Since optical wavelengths are scarce resources, even with state-of-the-art technologies, the available number of wavelengths that can be multiplexed into a fiber is restricted to a relatively small number. This entails space division multiplexing with multiple fibers in the link in order to accommodate the large number of paths within a link. This paper proposes novel OP accommodation design algorithms that can heuristically establish wavelength paths (WPs) or virtual wavelength paths (VWPs) in the network, where each link is composed of multiple fibers. These algorithms minimize the average number of fibers (in other words, cross-connect ports) handled at the WP/VWP cross-connect nodes and enable us to obtain the required OP cross-connect (OPXC) system scale at each node in WP/VWP networks. Algorithms that consider failure restoration are also proposed. Some WP/VWP accommodation designs over a polygrid network are simulated using the proposed algorithms. The difference between the WP and VWP schemes in terms of the required OPXC system scale with and without considering failure restoration is quantitatively evaluated for the first time.

Optical path cross-connect node architectures for photonic transport network

This paper explores the optical path cross-connect (OPXC) node architectures that are essential components of the optical path network. Optical path technologies will play a key role in the development of the platform on which the future bandwidth abundant B-ISDN should be created. This paper highlights the wavelength path (WP) and the virtual wavelength path (VWP) technologies, both of which can greatly enhance the path layer capability and the efficiency of network failure restoration. The OPXC, which handles optical paths, is constructed with an optical switching network. Various WDM-based switching networks, which are aimed at LAN applications, have been reported. On the other hand, few WDM-based switching networks for OPXC systems, which are applicable to the nationwide transport network, have been proposed. In this paper, we elucidate the functional conditions required to construct OPXC nodes for WP and VWP global networks. Next, we assess switching network architectures for their applicability to the transport network. It is shown that the OPXC architecture based on DC-switches (delivery and coupling switches) is superior to the other OPXC architectures in terms of optical losses, modularity, and upgradability. Finally, detailed evaluations of the DC-switch-based OPXC node are presented that confirm its feasibility.

Optical path cross-connect system architecture suitable for large scale expansion

This paper proposes, for WPs (wavelength paths) and VWPs (virtual wavelength paths), a new OPXC (optical path cross-connect) architecture suitable for constructing large scale OPXC systems. The architecture is based on the multimodule concept and uses main modules and junction modules. The proposed OPXC is shown to provide triple the throughput of the conventional OPXC (delivery and coupling switch based) assuming state-of-the-art commercially available devices. It allows traffic demand increases to be supported with less OPXC switch hardware compared to the conventional OPXC architecture. The proposed architecture also keeps the advantages of the conventional architecture: a high level of expandability with regard to incoming/outgoing links and upgradability from a WP network to a VWP network. Thus the proposed OPXC architecture is highly flexible and allows minimum investment to encourage introduction while gracefully supporting future system scale expansion with incremental growth matching the traffic demand.

Photonic transport networks based on optical paths

AbstractThis paper explores the technologies that will enable a further leap forward in transport network evolution. First, requirements of the future transport network are elucidated. Existing network cost is evaluated and the viable means to reduce transport network cost are identified. It is demonstrated that optical path technologies such as WP (wavelength path) and VWP (virtual wavelength path) will play a key role in this. They enhance not only transmission capacity but also cross‐connect node throughput cost‐effectively by capitalizing on the wavelength routeing scheme. Optical path realization technologies focusing on optical path cross‐connect systems are examined. Requirements for the optical path cross‐connect system are then elucidated, and a new cross‐connect system architecture is evaluated. The architecture exploits PLC (planar lightwave circuit) and other commercially available technologies suitable for large‐scale production. The evaluations include cross‐connect node upgradability, modular growth capability, total node cost, optical loss and switching power consumption. It is proved that the architecture has significant advantages over existing switch architectures. The optical path technologies provided in this paper will pave the way for a new transport network paradigm, a ubiquitous, bandwidth‐abundant and affordable broadband ISDN.

Number of wavelengths required for constructing large‐scale optical path networks

AbstractPhotonic networks that exploit the abundant optical bandwidth capability are needed to realize a truly effective B‐ISDN. We have proposed two optical path schemes, the wavelength path (WP) scheme and the virtual wavelength path (VWP) scheme, wherein wave length division multiplexing/frequency division multiplexing (WDM/FDM) technologies are employed in the path layer of the transport networks. Although wave lengths are precious resources in photonic networks, the number of wavelengths required for any network has never been evaluated because of the NP‐completeness of the wavelength assignment problem. In this paper, we propose heuristic optical path accommodation design algorithms that can minimize the wavelength requirements in the network. We also evaluate the wavelength requirements for large‐scale and irregularly structured physical network topologies utilizing the proposed algorithms. Accordingly, we elucidate, for the first time, that the wavelength requirements for the WP and VWP schemes are almost the same regardless of physical network topologies and path demand distribution patterns.

Number of wavelengths required for constructing optical path network considering restoration

AbstractOptical networks that support high‐speed, low‐cost communication services are required. an optical path is proposed that utilizes wavelength multiplexing technology at the path layer of transport network layers. Optical path schemes, wavelength path (WP)/virtual wavelength path (VWP) that can realize optical path networks are also proposed. Although wavelengths are a resource in optical networks, the number of wavelengths required to construct an optical path network has not been evaluated.This paper describes a method of network protection using the optical path technique that enhances network reliability and proposes a method for establishing a restoration path that restores failed active paths in both WP and VWP schemes. Proposed herein is an optical path accommodation design to establish WPs or VWPs in a physical network considering the proposed restoration method. Furthermore, optical path networks are constructed by establishing WPs or VWPs on a physical network that has a regular structure and the number of wavelengths required in the network are evaluated. This evaluation makes it clear that the VWP scheme requires fewer wavelengths than the WP scheme.