Multi-layer versus single-layer optical cross-connect architectures for waveband switching

Waveband Switching (WBS) in conjunction with Multi-Granular Optical Cross-connect (MG-OXC) architectures can reduce the cost and complexity of switching nodes. In this paper, we study two MG-OXC architectures: the Single-Layer and the Multi-Layer MG-OXCs, and compare their performances with both off-line (static) and on-line (dynamic) traffic. In the off-line case, we develop feasible near-optimal Integer Linear Programming models (called Off-ILP models) for each of the MG-OXC architectures that aim to reduce the size of the MG-OXC, and compare them with the Balanced Path routing with Heavy-Traffic first waveband assignment (BPHT) heuristic developed for the Multi-Layer MG-OXCs in [4]. The two architectures are then compared in terms of the number of wavelength hops (WH) and MG-OXC ports required to satisfy a given set of traffic demands. In the on-line case, we develop an on-line ILP model called On-ILP, which aims to minimize the number of used ports for each of the MG-OXC architectures, given a fixed number of wavelengths on each link. We also propose a novel efficient heuristic algorithm, called Maximum Overlap Ratio (MOR) to satisfy new requests and compare it with the On-ILP, First-Fit, and Random-Fit algorithms. We compare the two architectures in terms of the blocking probability, weighted (request) acceptance ratio, which serves as an indication of the revenue generated by satisfying the requests. We also study the impact of waveband size in the off-line and on-line cases. Our results indicate that using WBS with either Single-Layer or Multi-Layer MG-OXCs can reduce the number of ports (hence the size and cost) of the switching nodes compared to using ordinary OXCs (without waveband switching). In particular, in the off-line case, using Single-Layer MG-OXCs provides a greater reduction in size than Multi-Layer MG-OXCs, while in the on-line case, using the Multi-Layer MG-OXC is better.