An efficient heuristic waveband assignment algorithm for hierarchical optical path networks utilizing wavelength convertors Zhi-shu Shen n , Hiroshi Hasegawa, Ken-ichi Sato Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan article info Available online 7 August 2012 Keywords: Hierarchical optical path network Wavelength convertor Cost bound abstract We propose a hierarchical optical path network design algorithm that allows for wavelength conversion. The algorithm sequentially solves a set of sub-problems that result from decomposing the original design problem. A novel efficient heuristic is developed to solve the waveband assignment sub-problem that is the bottleneck among the sub-problems. Numerical experiments prove that, by employing wavelength con- version, hierarchical optical path networks will be more cost effective than the single layer optical path network even in the small traffic demand area, where cost-effective- ness cannot be realized without using wavelength conversion, as well as in the relatively large traffic demand area. & 2012 Elsevier B.V. All rights reserved. 1. Introduction The development of WDM (Wavelength Division Multi- plexing) technologies enables us to expand the transmis- sion capacity of optical fibers. The rapid deployment of broadband access including ADSL and FTTH in the world is driving the exponential increase seen in internet traffic. Backbone networks are mostly based on point-to-point WDM transmission systems and electrical forwarding and routing systems. [1]. As a result, O–E–O (Optical–Electri- cal–Optical) conversion is needed at every node. However, with the growth of the traffic volume, electrical routing and O–E–O conversion will become bottlenecks that hinder the construction of large scale cost-effective networks. In order to cope with this, single layer optical path networks that utilize wavelength routing made possible with reconfigurable optical add/drop multiplexers (ROADMs) [1,2] have recently been extensively intro- duced [3]. The penetration of new broadband services (such as high-definition or ultrahigh-definition TV [4] and e-Science [5]) will create further traffic expansion in the near future. The scale of optical switches currently used in OXCs/ROADMs for single layer optical path networks [6] will then need to be substantially expanded. Hierarchical optical path networks that utilize wavebands, a bundle of multiple wavelength paths, have recently been investi- gated as an important technology to solve this problem [6–15]. In contrast to elastic optical path networks [16], which focus on the maximum utilization of spectral resources in fibers, the main goal of studies on hierarch- ical optical path networks is to reduce node cost. Which technology will be suitable depends on the situation. For example, for metro networks with bundles of fiber cables, fiber cost will be relatively low and the reduction of node cost is essential. Moreover, with the recent development of a WaveBand Cross-Connect (BXC) proto- type [17] which is constructed with WaveBand Selective Switches (WBSSs) monolithically integrated on a PLC chip, a substantial reduction in node size and cost can be expected. However, from the viewpoint of hierarchical optical path networks, even the routing and wavelength assignment (RWA) problem for the single layer optical path networks is known to be an NP-complete task [18]. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/osn Optical Switching and Networking 1573-4277/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.osn.2012.07.003 n Corresponding author. Tel.: þ81 52 789 2792; fax: þ81 52 789 3641. E-mail address: z_shen@echo.nuee.nagoya-u.ac.jp (Z.-s. Shen). Optical Switching and Networking 10 (2013) 54–61