We review our work on an intra-data center (DC) network based on co-deployment of optical packet switching (OPS) and optical circuit switching (OCS), conducted within the framework of a five-year-long national R&D program in Japan (∼March 2016). For the starter, preceding works relevant to optical switching technologies in intra-DC networks are briefly reviewed. Next, we present the architecture of our torus-topology OPS and agile OCS intra-DC network, together with a new flow management concept, where instantaneous optical path on-demand, so-called Express Path is established. Then, our hybrid optoelectronic packet router (HOPR), which handles 100 Gbps (25 Gbps × 4-wavelength) optical packets and its enabling device and sub-system technologies are presented. The HOPR aims at a high energy-efficiency of 0.09 [W/Gbps] and low-latency of 100 ns regime. Next, we provide the contention resolution strategies in the OPS and agile OCS network and present the performance analysis with the simulation results. It is followed by the discussions on the power consumption of intra-DC networks. We compare the power consumption and the throughput of a conventional fat-tree topology with the Ndimensional torus topology. Finally, for further power saving, we propose a new scheme, which shuts off HOPR buffers according to the server operation status.Index Terms-Data center (DC), energy efficiency, network topology, packet switching, switching system, virtual machine (VM).

Hierarchical overlay structure is an alternative solution to integrate the existing and future heterogeneous wireless networks for providing subscribers with better mobile broadband services. Traffic loss performance in such integrated heterogeneous networks is necessary for operator's network dimensioning and planning. This paper investigates the computationally efficient loss performance modeling for multiservice in hierarchical heterogeneous wireless networks. A speed-sensitive call admission control scheme is considered in our model in order to assign overflowed calls to the appropriate tiers. This approach avoids unnecessary and frequent handoff between cells and reduces signaling overheads. An approximation model with guaranteed accuracy and low computational complexity is presented for the loss performance of multiservice traffic. The accuracy of the numerical results is validated by comparing the results from the approximation with the simulations.

The Quasi-Stationary Approximation (QSA) is often applied to systems and networks where traffic can be classified as short-lived and long-lived. In this paper, we consider an integrated service system that serve short-lived non-real-time and long-lived real-time traffic. For such a system, we introduce a new method, called Generalized Quasi-Stationary Approximation (GQSA), that provides a way to trade off computational complexity and accuracy. Numerical results are provided to demonstrate the benefit achieved by GQSA.

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