Yongmin Qi

Two novel multigranularity optical cross-connect architectures for hierarchical optical networks

Two novel multi-granularity optical cross-connect (MG-OXC) architectures for dense wavelength division multiplexing (DWDM) networks are proposed to realize transparent waveband switching, and hence to reduce the switching and transmission costs. The performances of the two architectures are studied and compared in detail. The functionality of the proposed interconnecting architecture is investigated for a 10-Gb/s WDM system.

Performance analysis of various multi-granularity switching architectures and an on-line RWA algorithm

Waveband switching (WBS) is proposed as a promising technique to reduce the number of switching ports, which could translate to the switching fabric size and cost of the nodes in the dense wavelength division multiplexing (DWDM) network. We propose a routing and wavelength/waveband (RWA) heuristic algorithm, called Maximize the Number of Waveband Route (MNWR) for the dynamic arriving traffic demands in the multi-granularity WBS optical network. We study the performance of various MG-OXC architectures including the serial three-stage MG-OXC and the interconnecting three-stage MG-OXC proposed by our group employing the on-line MNWR algorithm. Simulation results indicate that the interconnecting three-stage MG-OXC outperforms the serial three-stage architecture in terms of blocking performance for dynamic requests.

Evaluation and experiment of a configuration algorithm for three-stage multi-granularity optical cross-connects

From element automatic control view, we propose a configuration algorithm for three-level cross-connects in data plane to handle with bypass, grooming and local add/drop traffic of fiber-level, band-level and wavelength-level by a abstract bipartite graph of MG-OXC and bandwidth utilization spectra graph. The configuration algorithm is evaluated by computer simulation as well as validated by experiment on our flexible Multi-functional Optical Switching Testbed (MOST).

Performance simulation for a novel joint multicasting optical cross-connect based on both space and frequency splitters

The emerging broadband real-time streams applications require the supporting networks to provide multicasting communication at optical layer. The multicasting capable optical cross-connect (MC-OXCs) is the necessary device to implement multicasting at optical layer. The functional building blocks for MC-OXC are light splitters, which can be space splitters or multiwavelength converters (frequency splitters). The space splitter has no wavelength conversion ability, while the frequency splitter has limited fanout, decreased optical signal-to-noise ratio and also is expensive. We proposed a tradeoff architecture called joint multicasting capable optical cross-connect (jMC-OXC) integrating both space splitters and frequency splitters in our previous work. This paper further studies the network performance in terms of member blocking ratio for the jMC-OXC architecture. Three simulation schemes are designed and the results show that the network performance of the jMC-OXCs with limited frequency splitters can obtain a close performance to that with full frequency splitters.

Architecture and performance of a bidirectional OXC based on reversible optical switches with reduced complexity

By exploiting the symmetry of bidirectional wavelength-connections in WDM networks, we propose an N×N bidirectional OXC using one N/2×N/2 reversible optical switch to reduce the complexity of the OXCs. The feasibility is demonstrated at 10 Gb/s. Introduction As the wavelength-count and fiber-count increase rapidly in wavelength-division multiplexed (WDM) networks, high-port-count optical switch matrix is needed. Generally a large switch matrix can be built by smaller available constituent switches as exemplified by the well-known Benes and Clos architectures. WDM networks are wavelength routed and, generally, show bidirectional symmetry in end-toend wavelength connections [1]. By exploiting this symmetry, the complexity of the switch matrix and optical cross-connect (OXC) can be reduced [1-4]. In this paper, such a bidirectional OXC is denoted as BOXC, while a conventional unidirectional OXC is referred to as UOXC. A class of BOXCs based on tuneable fiber Bragg gratings, arrayed-waveguide gratings (AWGs), and three or multi-port optical circulators (OCs) were reported in [2-4]. However, the number of wavelengths that can be supported by them is rather limited, e.g., much less than 160. Simmons et al [1] reported another class of BOXC which achieved N×N cross-connects by using N/2×N/2 switches. However, the optical switches have to be bidirectional crossconnected, in which each mirror is designed to reflect two light beams, as opposed to a single light beam. As a result, the mirrors would be enlarged in area and collimators be doubled in number. In this paper, we propose and demonstrate a novel BOXC by using reversible optical switches (ROSs) together with OCs. This architecture reduces the complexity and implementation cost as compared to other existing approaches, since it uses some conventional optical switches as ROSs. The feasibility and performance are evaluated experimentally for a prototype at 10 Gb/s. Proposed BOXC Architecture The reversibility in optics allows a light ray be reflected and traverse back exactly through the incoming path [5]. The optical mechanical switches [6] and Micro Electromechanical System (MEMS) [7] optical switches work on the basis of light ray principle, and are reversible in optical path. As a result, they would work bidirectionally, i.e., a pair of reverse lights goes in the same path. Therefore, they can be used to construct a BOXC.

Design of ring networks based on parallel multi-granularity hierarchical OADMs

We study the optimization issues of ring networks employing novel parallel multi-granularity hierarchical OADMs. In particular, we attempt to minimize the number of control elements for the off-line case. We present an integer linear programming formulation to obtain the lower bound in optimization, and propose an efficient heuristic algorithm called Global Bandwidth Resource Assignment (GBRA) that is suitable for the design of large-scale OADM networks.

Optimization design of three-stage multigranularity optical cross-connects

We study the design issues of a node in multi-granularity all-optic network based on a proposed dynamic multigranularity including coarse granularity (i.e., fiber and band) and fine granularity (i.e., wavelength) traffic model. An optimization design plan is proposed by analyzing the associated parameters of MG-OXC architecture in detail and optimizing the configuration of them. The proposed optimization design rules can significantly reduce the node complexity and improve the blocking performance of arriving requests, which lead to smaller device size and lower cost in all-optical networks.

Design, implementation, and application of a flexible multifunctional optical switching testbed (MOST)

To solve the scalability and flexibility issue in current optical network testbeds, a Multi-functional Optical Switching Testbed (MOST) has been built. Benefiting from design of modular hardware and layered software, network experiments of scalability and complicated node architecture can be made based on it. The hardware and software structure of the MOST system is explicitly analyzed in the article and demonstrations of a 12-node ASON and shared wavelength conversion ASON on MOST are also reported.

Implementation of Physical Transmission Impairments Constraint Optical Multicasting in Translucent WDM Mesh Networks

A translucent multicasting scheme based on sparsely placed signal re-generable translucent multicasting capable optical cross connect (tMC-OXC) nodes is proposed to provide signal-quality guaranteed multicasting services. We propose a tMC-OXC architecture capable of transparent unicasting and electronic multicasting. The electronic multicasting devices are also used to regenerate the impaired signals. A regeneration weight based MC-OXC nodes placement strategy is designed to construct the translucent network. We propose two multicasting tree construction algorithms to evaluate the performance of the proposed translucent network, where the selected MC-OXC nodes serve as core nodes (we call them hub nodes). Our study shows that no more than 30% nodes need to be equipped with electronic multicasting and electronic 3R regeneration capability, having more than 30% nodes with regeneration capability only slightly enhances the network performance.