Terahertz communications are envisioned as a key enabler for 6G networks. The abundant spectrum available in such ultra high frequencies has the potential to increase network capacity to huge data rates. However, they are extremely affected by blockages, to the point of disrupting ongoing communications. In this paper, we elaborate on the relevance of predicting visibility between users and access points (APs) to improve the performance of THz-based networks by minimizing blockages, that is, maximizing network availability, while at the same time keeping a low reconfiguration overhead. We propose a novel approach to address this problem, by combining a neural network (NN) for predicting future user–AP visibility probability, with a probability threshold for AP reselection to avoid unnecessary reconfigurations. Our experimental results demonstrate that current state-of-the-art handover mechanisms based on received signal strength are not adequate for THz communications, since they are ill-suited to handle hard blockages. Our proposed NN-based solution significantly outperforms them, demonstrating the interest of our strategy as a research line.

Global optimization of access point (AP) assignment to user terminals requires efficient monitoring of user behavior, fast decision algorithms, efficient control signaling, and fast AP reassignment mechanisms. In this scenario, software defined networking (SDN) technology may be suitable for network monitoring, signaling, and control. We recently proposed embedding virtual switches in user terminals for direct management by an SDN controller, further contributing to SDN-oriented access network optimization. However, since users may restrict terminal-side traffic monitoring for privacy reasons (a common assumption by previous authors), we infer user traffic classes at the APs. On the other hand, since handovers will be more frequent in dense small-cell networks (e.g., mmWave-based 5G deployments will require dense network topologies with inter-site distances of ~150-200 m), the delay to take assignment decisions should be minimal. To this end, we propose taking fast decisions based exclusively on extremely simple network-side application flow-type predictions based on past user behavior. Using real data we show that a centralized allocation algorithm based on those predictions achieves network utilization levels that approximate those of optimal allocations. We also test a distributed version of this algorithm. Finally, we quantify the elapsed time since a user traffic event takes place until its terminal is assigned an AP, when needed.

Summary Virtual desktop infrastructure (VDI) solutions seek to provide a satisfactory user experience at the client side when accessing remote desktop applications, even from mobile devices with limited capabilities. This paper presents a new approach, improving on previous work by the authors, in which a combination of Virtual Network Computing (VNC) and streaming protocols allowed efficient remote web access to virtualized applications within a cloud architecture. The new approach simplifies virtual machine templates, from which virtual machine instances are deployed, by centralizing software modules, greatly simplifying their management. Our new contribution consists of an integrated solution with specific WebM video encoding modules in charge of application visual output processing, an Hypertext Transfer Protocol (HTTP) streaming server, and a VNC server. The solution can be installed in the hypervisor of the host machines instead of replicating the servers and modules throughout the guest (virtual) machines that run the virtualized applications. Consequently, their implementations are unique and independent of the operating system of the virtual machines. In short, it is not necessary to provide different implementations for different operating systems, which reduces the complexity of virtual machine templates and greatly simplies platform management. To demonstrate our solution, we have modified the Quick Emulator (QEMU)‐Kernel‐based Virtual Machine (KVM) hypervisor source code accordingly. We also present qualitative and quantitative analyses that demonstrate that the new approach is advantageous in terms of software management and quality of experience, compared with our previous work and other well‐known thin clients, contributing to the enhancement of VDI systems. Copyright © 2015 John Wiley & Sons, Ltd.

Software-Defined Networking (SDN) has gained momentum in recent years, in a bid to transform networking ecosystems. It has already been applied to data center networks and wide area networks, such as Google's WAN. A software-defined approach is thus a reasonable candidate architecture for other highly dynamic environments such as future 5G mobile networks. This paper presents a two-level software-defined approach for the future 5G architecture at the network and radio access layer. At each level, a dedicated logical centralised controller and northbound/southbound Application Programming Interfaces are defined. Two cross-layer schemes are also introduced for interaction between controllers.

Optical Packet Switching (OPS) has been proposed as the ultimate solution for Wavelength Division Multiplexing (WDM) core networks, but it has not achieved commercial status due to numerous technological requisites such as packet tunable wavelength conversions, switching times in the order of nanoseconds, and individual wavelength switching. Nevertheless, new OPS paradigms reduce technological complexity by eliminating wavelength conversions and performing joint wavelength switching. Moreover, new interferometric optical devices capable of switching two optical signals in sub-nanosecond times are already commercially available. In this paper, we propose an all-optical switch architecture based on these devices, which switch all wavelengths as a bundle. We also perform a preliminary analysis of this architecture with some simplifications that allow us to set an upper bound on the maximum bit rate attainable in an ideal network (relaxing the need for 3R regeneration and electro-optical conversions).

Authorities recommend the practice of moderate physical activity to improve health and quality of life, but sometimes it is difficult to find the willpower or the motivation to reserve a few minutes to exercise. In this paper we describe a new tool designed to help users to practice sport and record their achievements, which makes the activity more social (finding friends, sharing results, etc.). Furthermore, this tool has been integrated in the "Ubiquitous Oulu", an intelligent city that provides the building blocks to bring it closer to citizens. In this real-life environment we had the opportunity to assess the technical viability of RunWithUs and to identify the main interests of its potential users.

Optical switching fabrics are gaining interest as in multi Terabit switching devices; the advantages over their electronic equivalents are mainly their information density and power consumption. Arrayed Waveguide Gratings (AWGs) are promising optical devices proposed by the academic and industrial community to build optical switching fabrics. Because of their wavelength routing property, AWGs allow wavelength reuse over different ports introducing in-band crosstalk which strongly limits scalability of AWG-based backplanes. However, this effect can be mitigated or even completely avoided by means of proper scheduling algorithms. In this paper, we present several modified scheduling algorithms which limit the effect of coherent crosstalk in AWG-based switching fabrics and achieve good performance in terms of throughput and delay.

Most all-optical switching paradigms assume that different wavelengths are switched independently, which limits scalability. In optical cell switching (OCS), time is divided into time slots of fixed size by time-division multiplexing, and the wavelengths in a time slot are all bundled. Thus, each OCS switch (OCX) has a single switching plane and performs mere time-space switching. In OCS, each OCX requires optical slot synchronizers (OSYNs) at all inputs for the arrival slots to be aligned, so that cells can be simultaneously forwarded. In a recent OCS paradigm -not-aligned OCS-, the OSYNs and the alignment process are no longer required. Cell shifting still takes place inside the OCXs for minimizing the gaps between cells, but it is not necessary to align them to a reference time. Not-aligned OCS has clear advantages over aligned OCS: the total number of fiber delay loops (FDLs) and the hardware cost are reduced, and the number of switching operations is also lower. Moreover, cell arrival time to the switch is not critical, and the network becomes simpler and more flexible. In this paper, we propose a new distributed resource scheduling algorithm for not-aligned OCS networks, which takes connection blocking probability to reasonable values for practical loads.

As wireless mesh networks become more widely deployed, media streaming in such networks poses a pressing research issue because of the increasing importance of multimedia applications. The challenge with wireless mesh networks is the time-varying wireless channel compounded by multi-hop transmission. However, wireless mesh networks also present an opportunity, i.e., the redundancy provided by broadcast wireless media and mesh connectivity. In this paper, we present a joint interchannel and network coding schema to take advantage of this opportunity and to overcome the challenge of wireless mesh networks. We evaluate of the proposed joint coding through both mathematical analysis and computer simulation. The results demonstrate significant benefits in terms of protection against packet losses and bandwidth utilization of the joint coding schema.

Packet switches with optical fabrics can potentially scale to higher capacities. It is also potentially possible to improve their reliability, and reduce both their footprint and power consumption. A well-known alternative for implementing hardwired switches is Arrayed Waveguide Grating (AWG). Ideally, AWG insertion losses do not depend on the number of input-output ports, meaning that scalability is theoretically infinite. However, accurate second-order assessment has demonstrated that in-band crosstalk exponentially increases the power penalty, limiting the realistic useful size of AWG commercial devices to about 10-15 ports (13-18 dB). On the other hand, the in-band crosstalk at AWG outputs depends on the connection pattern set by the scheduling algorithm and this port count limitation is calculated for worst-case scenarios. In this paper, we show that distributed schedulers with predetermined connection patterns can be used to avoid these harmful arrangements. We also show that the probability of worst-case patterns is very low, allowing us to set a more realistic port limit for general centralized schedulers and very small losses. With these results, we calculate more realistic port count limits for both scheduler types.

The parallel hierarchical matching (PHM) algorithm is a distributed maximal size matching scheduler for virtual output-queued switches. In a previous letter, we formulated an upper bound on the maximum number of iterations PHM requires to achieve a maximal size matching in any traffic scenario. In this letter, we follow an analytical approach to find the average number of iterations for PHM to achieve a maximal size matching under diverse traffic models. The estimated number of iterations is O(log2N), as in the case of iSLIP-like algorithms

The deployment of optical packet switching (OPS) in dense wavelength division multiplexing (DWDM) backbone networks is perceived as a medium term promising alternative. Scalability restrictions imply that conventional switching architectures are unfeasible in this large-scale scenario. In a previous paper, the wavelength-distributed knockout architecture was proposed as a cost-effective scaling strategy for OPS switching fabrics. In this paper, this growable architecture is applied to OPS switching fabrics able to emulate output buffering. We also propose an scheduling algorithm which provides optimum performance if knockout packet losses are made negligible. The mathematical analysis to evaluate the knockout packet loss probability of this architecture is obtained, under uniform and non-uniform traffic patterns. To complement the switch dimensioning process, an upper bound assuring 0-knockout packet losses is compared with the exact analytical results.

Input-queued packet switches are more scalable than output-queued ones. However, due to HOL blocking, their throughput is poor. The virtual output queueing (VOQ) switch architecture and several buffer schedulers have been proposed to overcome this problem. Among them, the class of iterative maximal matching algorithms, with the first example being parallel iterative matching (PIM), which uses random selection, and iSLIP that uses round-robin selection, and has become a de facto standard in switching research. iSLIP admit efficient practical implementations, and has several variants with different pointer updating strategies - like FIRM, DRRM and RDSRR - that improve performance. In previous work, we formulated a new scheduler, parallel hierarchical matching (PHM), which compare favorably to iSLIP-like algorithms. PHM can be considered a parallelization of previous high-performance sequential hierarchical matching algorithms, like 2DRR or WWFA. In this paper, we compare their delay performance for same decision response-time, determined from ASIC implementations, and for different traffic models.

iSLIP and parallel hierarchical matching (PHM) are distributed maximal size matching schedulers for input-buffered switches. Previous research has analyzed the hardware cost of those schedulers and their performance after a small number of iterations. In this paper, we formulate an upper bound for the number of iterations required by PHM to converge. Then, we compare the number of iterations required by iSLIP and PHM to achieve a maximal throughput under uniform Bernoulli traffic, by means of simulation. Finally, we obtain the corresponding delay performances, which are similar. The results suggest that PHM has both the advantages of previous hierarchical matching algorithms (low hardware complexity) and iSLIP (low number of iterations).