December 2012, 19(6): 105–112 www.sciencedirect.com/science/journal/10058885 http://jcupt.xsw.bupt.cn The Journal of China Universities of Posts and Telecommunications Spectral resource defragmentation based on PCE in flexible bandwidth optical networks LIN Qun (,), ZHAO Yong-li, CAO Xu-ping, YU Xiao-song, TANG Ting-ting, ZHANG Jie State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China Abstract The granularity of the flexible bandwidth optical network is the spectral slots, which is much smaller than that of the wavelength switch optical network. For the dynamic clients’ connections setup and tear down processes, it will give rise to fragmentation of spectral resources. It is the decline in the probability of finding sufficient contiguous spectrum for new connections that result in the fragmentation of spectral resource. To be more specific, these spectra may be unavailable and waste. In this case, the severe waste of the spectrum will lead to low efficiency in spectral utilization and will not adapt to large capacity requirements of transmission in the future. Because path computation element (PCE) framework has the characteristics of the central disposal and deployment of the spectrum resource, we construct the spectral resource allocation scenario based on PCE framework in the flexible bandwidth optical network to use spectrum resource effectively. Based on the principle of the generation of the fragmentation, we put forward a spectrum resource defragmentation algorithm to consolidate the available spectrum for clients’ connections. The simulation results indicate that this algorithm is able to reduce fragmentation of network, improve the continuity of spectral resource, reduce the blocking rate of services in the network and improve the spectral efficiency significantly. Keywords flexible bandwidth optical network, PCE framework, spectral fragmentation, spectral resource defragmentation 1 Introduction Exponentially increasing demand for communication capacity is already approaching the limit of single mode fiber capacity in many links around the world. At the same time, dynamically varying traffic demand is requiring an efficient and agile utilization of the optical spectrum. Flexible bandwidth networking emerged recently as a promising paradigm for assigning elastic spectral bandwidth to traffic demands with various modulation formats and spectral efficiencies [1]. The flexible bandwidth optical network supports channels operating at heterogeneous line rates by allocating spectral resources in a flexible and dynamic manner [2]. In the flexible wavelength division multiplexing (FWDM) network, the channel spacing and channel center frequency are not fixed on standard ITU-T Received date: 21-09-2012 Corresponding author: LIN Qun, E-mail: linqun682@gmail.com DOI: 10.1016/S1005-8885(11)60324-5 grids, leading to higher spectral efficiency. Additionally, the spectrum in the FWDM network may be dynamically allocated to support dynamic traffic demands [3]. However, the spectrum resource cannot be overlapped in wireless communications and several services in the same area cannot share the same spectrum resource. Different from this, the same sub-carriers on different fibers can be reused but must be continuous [4–6]. Upon tear down of connections, allocated spectral resources are released for future requests. In a dynamic traffic scenario, this channel setup and tear down processes give rise to fragmentation of spectral resources. The spectral efficiency in the network is compromised due to the fragmentation of the available spectrum into small noncontiguous spectral bands, decreasing the probability of finding sufficient contiguous spectrum for a connection. New arriving requests are then either forced to utilize more spectrum in the network or blocked in spite of sufficient spectrum being available [3].