Performance Evaluation of Optical Path Networks Utilizing Waveband Selective Switch-based Cross-connects Hai-Chau Le 1, 2 , Tien-Ban Nguyen 1 , Hiroshi Hasegawa 2 , Ken-ichi Sato 2 1. Faculty of Telecommunications Posts and Telecommunications Institute of Technology Hanoi, Vietnam 2. Dept. of Electrical Engineering and Computer Science Nagoya University Nagoya, Japan Abstract—We introduce a waveband cross-connect architecture that utilizes small-scale waveband selective switches to make the best use of present optical switch technologies and exploit coarse granular optical routing for large capacity optical path networks. We then propose an appropriate network design algorithm for the coarse granular routing optical path networks utilizing the developed node architecture. Numerical experiments proved that applying the small-scale waveband selective switch-based node architecture offers a significant switch scale reduction. Impact of waveband capacity selection on the overall switch scale reduction also investigated. I. INTRODUCTION Recent advances in optical transmission technologies and related node technologies have significantly increased backbone and metro network capacities. Wavelength path routing using reconfigurable optical add/drop multiplexers (ROADMs) and optical cross-connects (OXCs) has been introduced and a large-scale deployment of single-layer optical path networks utilizing ROADMs/OXCs is being conducted in Japan and North America [1]. The expected future Internet traffic growth dominated by the penetration of new video- centric broadband services including ultra-High Definition/3D- TV and e-Science will trigger an explosive increase in the necessary switch scale of OXCs/ROADMs [1-2]. The need for bandwidth-abundant and cost-effective networks that can support the ever-increasing traffic is becoming more and more critical. An attractive approach to cost-effectively enhancing optical switch capacity is the introduction of multi-granular optical path networks along with hierarchical optical cross- connects (HOXCs), which are capable of switching optical signals at different granularities: wavelength paths and waveband paths (bundles of multiple wavelengths) [1–10]. In multi-granular optical path networks, wavelength paths are grouped into waveband paths and transferred through intermediate nodes. Wavelengths inside a waveband path are simultaneously switched as one entity. Figure 1 illustrates basic principles of multi-granular optical path networks. Typical hierarchical optical cross-connect architectures include two independently functional switching parts: a waveband cross-connect (WBXC) for switching coarse granular optical paths, waveband paths, and a wavelength cross-connect (WXC) to provide finer granular routing of wavelength paths [3-5]. Optical path routing capability of an HOXC depends on the node architecture applied [4]. The efficiency of multi-granular optical path networks, indicated by the obtained cost and port count reductions, has been verified [5-10]. It has been shown that introduction of coarse granular routing (waveband path routing) can help reducing greatly the required optical port count and thus, can decrease the entire switch scale needed, especially for the large traffic demand area [6-8]. On the other hand, the key operation to increase fiber utilization and to enhance the effectiveness of the coarse granular routing is the introduction of intermediate grooming; which includes unbundling waveband paths and merging at intermediate nodes [6, 9]. However, limiting the grooming capability is crucial in cutting down total switch scale of a hierarchical optical cross-connect [8]. Fortunately, the work given in [9] also demonstrates that end-to-end waveband scheme (waveband switching only) offers almost the same network cost reduction as that efficiently combines waveband switching and wavelength grooming at intermediate nodes when the given traffic demands become greater. In other words, impact of grooming wavelength paths is negligible for large traffic area. Based on that, this paper focuses on end-to-end waveband switching to realize very large capacity optical networks. Figure 1. Multi-granular optical path routing principles The effectiveness of multi-granular optical path networks in terms of optical switch port count ratio, the ratio of total optical switch port count of a multi-granular optical path network to that of the corresponding single layer optical path network, has been investigated in [9, 10] (see Figure 2). It demonstrates that over the wide area wherein the ratio is less than 1, the multi- granular optical path network can reduce the total optical port count. The cost efficiency of the multi-granular optical path The 2012 International Conference on Advanced Technologies for Communications (ATC 2012) 978-1-4673-4352-7/12/$31.00 ©2012 IEEE 323