646 IEEE COMMUNICATIONS LETTERS, VOL. 9, NO. 7, JULY 2005 Waveband Switching Networks with Limited Wavelength Conversion Xiaojun Cao, Vishal Anand, Jikai Li, and Chunsheng Xin Abstract— We study reconfigurable Multi-Granular Optical Cross-Connects (MG-OXCs) in Waveband Switching networks with limited wavelength conversion and propose a heuristic algorithm to minimize the number of used wavelength converters while reducing the blocking probability. Index Terms—Wavelength Division Multiplexing, wavelength routed networks, multi-granular optical cross-connects, wave- band switching. I. I NTRODUCTION W AVEBAND Switching (WBS) networks have attracted significant attention for their practical importance in reducing the port count, associated control complexity, and cost of photonic Cross-Connects [1]–[3]. The main idea of WBS is to group several wavelengths together as a band, and switch the band using a single port whenever possible (e.g., as long as it carries only bypass or express traffic), and demultiplex the band to switch individual wavelength only when some traffic needs to be added/dropped [4]–[7]. In this work, we consider WBS networks with the Three-Layer Multi- Granular Optical Cross-Connect ( MG-OXC) architecture as shown in Fig. 1. Such an MG-OXC has only a predetermined limited port count at the band cross-connect (BXC) layer and a limited number of wavelength converters at the wavelength cross-connect (WXC) layer. There is a significant amount of research on the bene- fit of wavelength conversion in wavelength-routed networks (WRNs) using ordinary OXCs (see for example, [8]). As wave- length conversion is expensive and can result in degradation of signal quality, much attention in the literature has been paid to research topics on sparse placement of a limited number of wavelength converters or limited-range wavelength converters in WRNs (see for example, [9]). None of the existing works has addressed the blocking performance and efficient usage of limited wavelength conversion in WBS networks. The focus of this research is on the challenging problem of designing WBS algorithm that efficiently allocates wavelength converters and at the same time maximizes the benefit of wavebanding to satisfy new lightpath requests. We show that our proposed algorithm is especially useful in minimizing the number of Manuscript received November 22, 2004. The associate editor coordinating the review of this letter and approving it for publication was Prof. Changcheng Huang. X. Cao is with the Department of Information Technology, Rochester Institute of Technology, Rochester, NY 14623, USA, (email: cao@it.rit.edu). V. Anand is with the Department of Computer Science, SUNY College at Brockport, Brockport, NY 14420 USA (email: vanand@brockport.edu). J. Li is with the Department of Computer Science, The College of New Jersey, Ewing, NJ 08628 USA (email: jli@tcnj.edu). C. Xin is with the Department of Computer Science, Norfolk State University, Norfolk, VA 23504 USA (email: cxin@nsu.edu). Digital Object Identifier 10.1109/LCOMM.2005.07025. Y β Z α Fig. 1. Architecture of a Reconfigurable MG-OXC activated wavelength converters and ports, thus reducing net- work operating costs, while achieving a low request blocking probability. II. MULTI -GRANULAR OPTICAL CROSS-CONNECT ARCHITECTURE WITH WAVELENGTH CONVERSION Fig. 1 shows the MG-OXC architecture we consider in this work. The WXC and BXC layers consist of cross-connect(s) and multiplexer(s)/demultiplexer(s). The WXC layer includes a wavelength cross-connect (WXC) switch that is used to bypass/add/drop lightpaths at this layer, wavelength conver- sion bank, band-to-wavelength (BTW) demultiplexers, and wavelength-to-band (WTB) multiplexers. The BTW demulti- plexers are used to demultiplex bands into wavelengths, while the WTB multiplexers are used to multiplex wavelengths into bands. The wavelength conversion bank is used to convert optical signals from one wavelength to another. At the BXC layer, the waveband cross-connect switch is used to switch wavebands. The BXC layer also includes the fiber-to-band (FTB) demultiplexers and band-to-fiber (BTF) multiplexers. Similarly, fiber cross-connect (FXC) switch is used to switch fibers at the FXC layer. Let α denote the ratio of fibers that can be demultiplexed into bands using FTB ports and β the ratio of bands that can be demultiplexed to wavelengths using BTW ports. As indicated in [2], it is unnecessary to demultiplex all the fibers into bands and bands into wavelengths, and even with limited reconfiguration (i.e., α< 1 or β< 1), intelligent algorithms can considerably reduce the port count required to satisfy dynamic incremental traffic with an acceptable request 1089-7798/05$20.00 c  2005 IEEE