Telecom standards efficiently enable time synchronization mechanisms in multi-node Quantum Networks (QNs) by combining Synchronous Ethernet (SyncE) and Precision Time Protocol (PTP). The architecture explored in this work utilizes SyncE to provide all connected nodes with a stable and precise frequency reference, adjustable in the range from 1 Hz to 125MHz, obtaining sub-nanosecond temporal jitter in the real-time/quantum plane. This reference is complemented with PTP to provide a distributed time reference for synchronization with a microsecond-level temporal allocation capability. In particular, in the control plane, PTP enables time division multiple access (TDMA) for sharing the quantum channel in multi-node quantum networks QNs. It is demonstrated that the proposed architecture achieves nanosecond synchronous transfer in the real-time/quantum plane and allocates microsecond time windows through the control plane. The theoretical model and experimental results validate performing common quantum communications operations with 98% fidelity and 10−2quantum bit error rate (QBER) at an emission rate of 12.5 Mqb/s. The results confirm that SyncE/PTP synchronization is a viable and scalable solution for future multi-node QN infrastructures.

This work describes a novel approach for the reduction of energy consumption in data centres (DCs) that will yield benefits both in terms of running costs and its environmental impact. The method is based on the introduction of collaborative interactions and flexibility clauses in contracts between all the DC ecosystem entities. The included entities are all the actors along the energy production–consumption chain, from the energy provider to the Information Technology customer. The collaborative approach also integrates the interaction between federated DCs. In this paper, we find a detailed description of the architecture that enables interaction between the DC ecosystem parties, which is designed to be progressively deployed, allowing traditional and ‘greened’ services to coexist, and without modification of the existing DC automation and framework systems.

Loss-free schemes are defined to ensure successful packet/burst transmissions in optical packet/burst switching networks. To this end, they rely on a collision-free routing and wavelength assignment (CF-RWA) scheme combined with simple contention resolution mechanisms that guarantee the absence of losses in intermediate links. Here, the CF-RWA problem is studied. In particular, by using graph theory, the problem of finding CF-RWA schemes that minimise the number of wavelengths to serve a given traffic matrix is set. The problem is simplified when it is formulated by using pre-defined sets of non-colliding paths. Within this framework, the problem is shown to be equivalent to finding a given vertex-set colouring of the so-called restriction digraph. Here, two heuristic algorithms are proposed to obtain such vertex-set colourings. One of them provides a suitable CF-RWA without having to solve the minimisation problem. By way of example, the proposed method is applied to the NSFNet and the EON network providing quasi-optimal results.

Contention resolution is a major issue in OBS networks. Several proposals that ensure burst transmissions without losses inside the network have been studied in the literature. Two of these proposals are based on combining a collision-free routing and wavelength assignment scheme with simple contention avoidance/resolution mechanisms. The static approach defines variable offsets and ensures contention avoidance by means of a suitable pre-assignment of offset windows to each communication. The dynamic approach guarantees the successful resolution of all contentions by using a single FDL at each intermediate node. Both proposals are based on giving priority to transmissions coming from the upstream. Hence, when an upstream node misbehaves or changes its transmission traffic pattern, it might delay new burst allocations on downstream nodes, leading to burst losses in the worst case. In this paper we deal with the fairness issue of these proposals. Thus, we introduce simple mechanisms that guarantee the transmission of the committed load for each communication, allowing, at the same time, the dynamic sharing of the spare bandwidth on each wavelength. The proposed mechanisms are analyzed by means of simulation.

This work introduces a new approach to get loss-free burst/packet transmission in optical burst and packet switched networks. To this end, our proposal defines (1) a routing and wavelength assignment (RWA) scheme based on the concept of wavelength tree, and (2) a simple contention resolution mechanism that solves contention using a limited number of fiber delay lines. We show that using the proposed scheme, for a 2-link-connected network with n nodes, there exists communication between any pair of nodes with [n/2] wavelengths. We apply this approach to address the problem of finding (conflict-free) transmission schemes in iterated line digraphs. Such digraphs have proved to be very useful models for dense, easily mutable, and fault tolerant communication networks. Examples of such networks are the well-known De Bruijn and Kautz digraphs and the wrapped butterfly networks. Our study leads us to define a useful tool for obtaining wavelength trees. By way of example, we illustrate the scheme operation for the 2-regular Kautz digraph. Simulation results show a good behavior in terms of transmission delay and resources utilization.

This paper proposes a simple procedure to ensure burst transmission without losses in Optical Burst Switching ring networks. The contention problem is solved by providing a scheme that pre-assigns, to each communication, a given wavelength and an offset window. This approach does not need any additional control information and, since burst contention is avoided, the network capacity and the wavelength utilization are maximized under dynamic traffic assumptions. The study is done by using techniques from graph theory. In particular, the so-called (acyclic) restriction digraphs provide a sharp lower bound for the number of required wavelengths, and support a greedy algorithm for assigning a suitable offset window to each communication. An alternative formulation of the obtained schemes, in terms of matrices, is also discussed. Simulation results of different feasible solutions are provided, showing low transmission delays and quite balanced wavelength utilization.