Optical Switching and Networking 3 (2006) 11–23 www.elsevier.com/locate/osn Virtual topology reconfiguration on optical WDM networks considering traffic grooming Ilker Akgun ∗ , Feza Buzluca Computer Engineering Department, Istanbul Technical University, 34469 Istanbul, Turkey Received 14 June 2005; received in revised form 1 November 2005; accepted 9 November 2005 Available online 27 December 2005 Abstract This paper investigates the virtual topology reconfiguration (VTR) problem of optical WDM networks by taking the traffic grooming factor into consideration. Firstly, by applying a common “divide and conquer” approach, the problem is categorized and handled as two independent sub-problems, triggering policy and the proper algorithm. Secondly, the VTR problem considering traffic grooming is formulated with new variables and constraints by a mixed-integer linear program (MILP). In order to handle the tradeoff between the advantages and disadvantages of VTR, both network resource utilization and network disruption are examined and quantified in terms of measurable parameters. A new multi-objective VTR algorithm called integrated reconfiguration (IR) algorithm is proposed to provide better overall VTR performance. Different from previous studies this newly proposed VTR algorithm combines three main factors (traffic load, traffic grooming ratio and route length of lightpaths) into one single objective and considers them all when reconfiguring. The results of simulations indicate that proposed VTR policy, periodic VTR triggering policy with IR algorithm, achieves performance improvements for overall VTR performance. c  2005 Elsevier B.V. All rights reserved. Keywords: Optical WDM networks; Virtual topology reconfiguration; Traffic grooming 1. Introduction The growth of Internet traffic increases the demand for data transmission capacity dramatically. Wavelength Division Multiplexing (WDM) is a promising technique that is expected to fulfill this capacity need. Lightpath (LP) is the basic mechanism of communication in a wavelength routed network. “A lightpath is an all- optical communication channel between two nodes in the network and may span more than one fiber link” [1–3]. Virtual topology (VT) is a set of lightpaths and lightpaths are a set of physical links that sets up physical ∗ Corresponding author. E-mail addresses: akguni@itu.edu.tr (I. Akgun), buzluca@itu.edu.tr (F. Buzluca). topology (PT). Independence between VT and PT is an important characteristic of WDM networks. Due to configurable components of a WDM network VT can be reconfigured dynamically according to variable traffic conditions. A single optical fiber strand has the potential bandwidth of 50 THz or higher. By using WDM, this bandwidth can be divided into multiple non-overlapping frequency or wavelength channels. However, there still exists a large bandwidth gap between a wavelength channel’s transmission speed (e.g., OC-48, OC-192 or OC-768) and the bandwidth requirement of a typical connection request (e.g., STS-1, OC-3, OC-12 or up to full wavelength channel capacity) for backbone applications. In order to use network resources 1573-4277/$ - see front matter c  2005 Elsevier B.V. All rights reserved. doi:10.1016/j.osn.2005.11.001