Abstract
Optical Network-on-Chip (ONoC) is emerging as a key on-chip communication architecture for multiprocessor systems. While multicast communication commonly exists in various parallel applications for Chip Multi-Processors (CMPs), most existing studies for multicast in an ONoC only consider the optimization of one multicast. This limits the practical applications because real systems often have to handle multiple multicasts requested from various applications. In this paper, we investigate the wavelength assignment strategies for multiple multicasts based on path-based routing in an ONoC, with the objective of reducing the number of wavelengths required. We first propose an intra-multicast wavelength assignment strategy including two different wavelength assignment methods, Multicast with Single Wavelength (MSW) and Multicast with Multiple Wavelengths (MMW), which are two configurations by assigning a single wavelength or multiple wavelengths to the same multicast, respectively. Then, two modified conflict graphs are proposed to evaluate the wavelength requirements of MSW and MMW. By analyzing the distribution of different multicasts, we further design a Layer-based Wavelength Assignment algorithm for Multiple Multicasts (LWAMM) to implement the inter-multicast wavelength assignment. The key idea is to allocate non-overlapping paths to the same layer (a detailed explanation will be given in Section IV) that is logically duplicated from the given ONoC, and assign the same wavelength to the paths in the same layer. Since the number of wavelengths is equal to the number of layers, it can be reduced by allocating all paths to as few layers as possible. Finally, simulation results verify our theoretical results, and show that LWAMM can reduce the average number of wavelengths used by 11.31%, 15.1%, and 17.7%, respectively, when the multicast ratios are 30%, 50%, and 90%, compared to other path-based schemes.