Optimizing meta-slots for nonblocking elastic optical switching networks

Elastic optical network is a promising technology for building flexible and wideband communication systems. This technology features the frequency slot unit (FSU) concept, which defines the bandwidth unit in the frequency domain. The utilization of a specified number of consecutive FSUs allows the bandwidth to be flexibly assigned to a data stream. For a successful elastic optical network operation, the use of nonblocking optical switching networks is indispensable. This paper focuses on two previously proposed W-S-W switching network architectures, namely, WSW1 and WSW2. With regard to WSW1, a previous study elucidated that the hardware complexity, which is evaluated by the number of FSUs, decreases by employing the meta-slot scheme. A meta-slot is a frequency range containing one or more FSUs. Although its effectiveness depends on the sizes of meta-slot classes, the previous study did not present how to optimize the meta-slot class sizes. Moreover, the employment of meta-slots was not considered for WSW2 in the previous study. This paper investigates the optimization of meta-slot class sizes and demonstrates that such optimization is modeled as the shortest path problem. For WSW1, the meta-slot scheme optimized by the shortest path model is compared with the previously reported nonblocking conditions. The result confirms the superiority of the optimized meta-slot scheme. For WSW2, the assignment of meta-slots among S-switches is also essential. The paper models the assignment of meta-slots as a bin-packing problem. Thus, the near-optimal assignment can be obtained by a known bin-packing heuristic. For WSW2, the number of S-switches is evaluated for the optimized meta-slot scheme and the previously known nonblocking conditions. The result confirms that the meta-slot scheme is advantageous for WSW2 as well as for WSW1.