Layer assignment and routing optimization for advanced technologies

As VLSI technology scales to deep sub-micron and beyond, it becomes increasingly challenging to achieve timing closure for VLSI design. Since a complete design flow consists of several phases, such as logic synthesis, placement, and routing, interconnect synthesis plays an important role which includes buffer insertion/sizing and timing-driven routing. Although progress has been achieved by many advanced routing techniques, the following aspects can be exploited sufficiently for further improvement: (1) incremental layer assignment for timing optimization; (2) signal routing with the requirement of regularity; (3) power-efficient optical-electrical interconnect paradigm. Thus, to perform the layer assignment and routing optimization for advanced technologies, an automated routing engine in a global view is essential to benefit the interconnect design while satisfying specific requirements. This dissertation proposes a set of algorithms and methodology on layer assignment and routing optimization for advanced technologies. The research includes two timing-driven incremental layer assignment approaches, synergistic topology generation and routing synthesis for signal groups, and optical-electrical routing design for power efficiency. For incremental layer assignment, most of the conventional approaches target via minimization but neglect the timing issues. Meanwhile, via delays are ignored but should be considered in emerging technology nodes. Then two timing-driven incremental layer assignment frameworks are proposed, where all the nets are solved simultaneously with the integration of via delays: (1) optimization of the total sum of net delays and reduction of slew violations; (2) minimization of critical path timing in selected nets. For on-chip signal routing, the bundled bits in one group may have different pin locations, but they have to be routed in a regular manner by sharing common topologies. Very few previous works target inter-bit regularity via multi-layer topology selection. Furthermore, the routability and wire-length of the signal bits should also be optimized. Then an advanced synergistic routing engine is promoted, which is able to not only control routability and wire-length but also guide each bit routing intelligently for design regularity. For optical-electrical co-design routing, optical interconnect shows its advantage due to the dominance of bandwidth-distance-power properties. The previous works lack a detailed exploration of optical-electrical co-design for on-chip interconnects. During the transmission, signal quality can be affected by various loss sources and Electrical to Optical (EO)/Optical to Electrical (OE) conversion overheads should also be considered. Then a power-efficient routing flow for on-chip signals is presented, where optical connections can collaborate with electrical wires seamlessly. The effectiveness of proposed algorithms and techniques is demonstrated in this dissertation. These approaches are able to achieve the improvements regarding specific metrics and eventually benefit the routing flow.Electrical and Computer Engineerin

Segment Routing: a Comprehensive Survey of Research Activities, Standardization Efforts and Implementation Results

Fixed and mobile telecom operators, enterprise network operators and cloud providers strive to face the challenging demands coming from the evolution of IP networks (e.g. huge bandwidth requirements, integration of billions of devices and millions of services in the cloud). Proposed in the early 2010s, Segment Routing (SR) architecture helps face these challenging demands, and it is currently being adopted and deployed. SR architecture is based on the concept of source routing and has interesting scalability properties, as it dramatically reduces the amount of state information to be configured in the core nodes to support complex services. SR architecture was first implemented with the MPLS dataplane and then, quite recently, with the IPv6 dataplane (SRv6). IPv6 SR architecture (SRv6) has been extended from the simple steering of packets across nodes to a general network programming approach, making it very suitable for use cases such as Service Function Chaining and Network Function Virtualization. In this paper we present a tutorial and a comprehensive survey on SR technology, analyzing standardization efforts, patents, research activities and implementation results. We start with an introduction on the motivations for Segment Routing and an overview of its evolution and standardization. Then, we provide a tutorial on Segment Routing technology, with a focus on the novel SRv6 solution. We discuss the standardization efforts and the patents providing details on the most important documents and mentioning other ongoing activities. We then thoroughly analyze research activities according to a taxonomy. We have identified 8 main categories during our analysis of the current state of play: Monitoring, Traffic Engineering, Failure Recovery, Centrally Controlled Architectures, Path Encoding, Network Programming, Performance Evaluation and Miscellaneous...Comment: SUBMITTED TO IEEE COMMUNICATIONS SURVEYS & TUTORIAL

Optimal Algorithms for Near-Hitless Network Restoration via Diversity Coding

Diversity coding is a network restoration technique which offers near-hitless restoration, while other state-of-the art techniques are significantly slower. Furthermore, the extra spare capacity requirement of diversity coding is competitive with the others. Previously, we developed heuristic algorithms to employ diversity coding structures in networks with arbitrary topology. This paper presents two algorithms to solve the network design problems using diversity coding in an optimal manner. The first technique pre-provisions static traffic whereas the second technique carries out the dynamic provisioning of the traffic on-demand. In both cases, diversity coding results in smaller restoration time, simpler synchronization, and much reduced signaling complexity than the existing techniques in the literature. A Mixed Integer Programming (MIP) formulation and an algorithm based on Integer Linear Programming (ILP) are developed for pre-provisioning and dynamic provisioning, respectively. Simulation results indicate that diversity coding has significantly higher restoration speed than Shared Path Protection (SPP) and p-cycle techniques. It requires more extra capacity than the p-cycle technique and SPP. However, the increase in the total capacity is negligible compared to the increase in the restoration speed.Comment: An old version of this paper is submitted to IEEE Globecom 2012 conferenc

Traffic engineering in dynamic optical networks

Traffic Engineering (TE) refers to all the techniques a Service Provider employs to improve the efficiency and reliability of network operations. In IP over Optical (IPO) networks, traffic coming from upper layers is carried over the logical topology defined by the set of established lightpaths. Within this framework then, TE techniques allow to optimize the configuration of optical resources with respect to an highly dynamic traffic demand. TE can be performed with two main methods: if the demand is known only in terms of an aggregated traffic matrix, the problem of automatically updating the configuration of an optical network to accommodate traffic changes is called Virtual Topology Reconfiguration (VTR). If instead the traffic demand is known in terms of data-level connection requests with sub-wavelength granularity, arriving dynamically from some source node to any destination node, the problem is called Dynamic Traffic Grooming (DTG). In this dissertation new VTR algorithms for load balancing in optical networks based on Local Search (LS) techniques are presented. The main advantage of using LS is the minimization of network disruption, since the reconfiguration involves only a small part of the network. A comparison between the proposed schemes and the optimal solutions found via an ILP solver shows calculation time savings for comparable results of network congestion. A similar load balancing technique has been applied to alleviate congestion in an MPLS network, based on the efficient rerouting of Label-Switched Paths (LSP) from the most congested links to allow a better usage of network resources. Many algorithms have been developed to deal with DTG in IPO networks, where most of the attention is focused on optimizing the physical resources utilization by considering specific constraints on the optical node architecture, while very few attention has been put so far on the Quality of Service (QoS) guarantees for the carried traffic. In this thesis a novel Traffic Engineering scheme is proposed to guarantee QoS from both the viewpoint of service differentiation and transmission quality. Another contribution in this thesis is a formal framework for the definition of dynamic grooming policies in IPO networks. The framework is then specialized for an overlay architecture, where the control plane of the IP and optical level are separated, and no information is shared between the two. A family of grooming policies based on constraints on the number of hops and on the bandwidth sharing degree at the IP level is defined, and its performance analyzed in both regular and irregular topologies. While most of the literature on DTG problem implicitly considers the grooming of low-speed connections onto optical channels using a TDM approach, the proposed grooming policies are evaluated here by considering a realistic traffic model which consider a Dynamic Statistical Multiplexing (DSM) approach, i.e. a single wavelength channel is shared between multiple IP elastic traffic flows

Cross-layer modeling and optimization of next-generation internet networks

Scaling traditional telecommunication networks so that they are able to cope with the volume of future traffic demands and the stringent European Commission (EC) regulations on emissions would entail unaffordable investments. For this very reason, the design of an innovative ultra-high bandwidth power-efficient network architecture is nowadays a bold topic within the research community. So far, the independent evolution of network layers has resulted in isolated, and hence, far-from-optimal contributions, which have eventually led to the issues today's networks are facing such as inefficient energy strategy, limited network scalability and flexibility, reduced network manageability and increased overall network and customer services costs. Consequently, there is currently large consensus among network operators and the research community that cross-layer interaction and coordination is fundamental for the proper architectural design of next-generation Internet networks. This thesis actively contributes to the this goal by addressing the modeling, optimization and performance analysis of a set of potential technologies to be deployed in future cross-layer network architectures. By applying a transversal design approach (i.e., joint consideration of several network layers), we aim for achieving the maximization of the integration of the different network layers involved in each specific problem. To this end, Part I provides a comprehensive evaluation of optical transport networks (OTNs) based on layer 2 (L2) sub-wavelength switching (SWS) technologies, also taking into consideration the impact of physical layer impairments (PLIs) (L0 phenomena). Indeed, the recent and relevant advances in optical technologies have dramatically increased the impact that PLIs have on the optical signal quality, particularly in the context of SWS networks. Then, in Part II of the thesis, we present a set of case studies where it is shown that the application of operations research (OR) methodologies in the desing/planning stage of future cross-layer Internet network architectures leads to the successful joint optimization of key network performance indicators (KPIs) such as cost (i.e., CAPEX/OPEX), resources usage and energy consumption. OR can definitely play an important role by allowing network designers/architects to obtain good near-optimal solutions to real-sized problems within practical running times

Network planning for the future railway communications

Los Sistemas Inteligentes de Transporte están cambiando la forma en que concebimos el futuro de la movilidad. En particular, los ferrocarriles están experimentando un proceso de transformación para modernizar el transporte público y las operaciones ferroviarias. Tecnologías como el 5G, la fibra óptica y la nube han surgido como catalizadores para digitalizar el ferrocarril proporcionando comunicaciones de alta velocidad y baja latencia. Este TFG se centra en la exploración de redes que permitan el control del tren y la transmisión de datos a bordo. El objetivo es planificar la infraestructura de red (dimensionamiento y asignación de recursos) necesaria para las futuras comunicaciones del sistema ferroviario de larga distancia de la Deutsche Bahn en Alemania. En este trabajo, proponemos una arquitectura de red que puede satisfacer los requisitos de rendimiento de las aplicaciones para trenes y pasajeros. Presentamos un método para la colocación de estaciones base 5G a lo largo de las vías del tren para garantizar el rendimiento necesario en el borde de la celda. Por último, presentamos el problema de colocación y asignación de centros de datos. El objetivo es encontrar el número necesario de centros de datos y su ubicación en la red, y asignarlos a cada estación de tren. Realizamos simulaciones en cuatro escenarios diferentes, en los que modificamos parámetros de entrada como la latencia máxima tolerada y el número máximo de centros de datos. Los resultados obtenidos muestran el compromiso entre la latencia alcanzada y el coste de la infraestructura.Els Sistemes Intel·ligents de Transport estan canviant la manera en què concebem el futur de la mobilitat. En particular, els ferrocarrils estan experimentant un procés de transformació per modernitzar el transport públic i les operacions ferroviàries. Tecnologies com el 5G, la fibra òptica i el núvol han sorgit com a catalitzadors per digitalitzar el ferrocarril proporcionant comunicacions d'alta velocitat i baixa latència. Aquest TFG se centra en l'exploració de xarxes que permetin el control dels trens i la transmissió de dades a bord. L'objectiu és planificar la infraestructura de xarxa (dimensionament i assignació de recursos) necessària per a les futures comunicacions del sistema ferroviari de llarga distància de la Deutsche Bahn a Alemanya. En aquest treball, proposem una arquitectura de xarxa que pot satisfer els requisits de rendiment de les aplicacions per a trens i passatgers. Presentem un mètode per a la col·locació d'estacions base 5G al llarg de les vies del tren per garantir el rendiment necessari a la vora de la cel·la. Per últim, presentem el problema de col·locació i assignació de centres de dades. L'objectiu és trobar el nombre necessari de centres de dades i la seva ubicació a la xarxa, i assignar-los a cada estació de tren. Realitzem simulacions en quatre escenaris diferents, on modifiquem paràmetres d'entrada com la latència màxima tolerada i el nombre màxim de centres de dades. Els resultats obtinguts mostren el compromís entre la latència assolida i el cost de la infraestructura.Smart Transportation Systems are changing the way we conceive the future of mobility. In particular, railways are undergoing a transformation process to modernize public transportation and rail operation. Technologies like 5G, optical fiber and the cloud have emerged as catalysts to digitalize the railway by providing high-speed and low-latency communications. This bachelor's thesis focuses on the exploration of networks enabling train control and on-board data communications. The goal is to plan the network infrastructure (dimensioning and resource allocation) needed for the future communications in the train mobility scenario for Deutsche Bahn's long-distance railway system in Germany. In this work, we propose a network architecture that can meet the performance requirements of train and passenger applications. We present an approach for 5G base station placement along the rail tracks to guarantee the necessary throughput at the cell edge. Finally, we introduce the data center placement and assignment problem. The objective is to find the required number of data centers and their location in the network, and to assign them to each train station. We perform simulations in four different scenarios, in which we modify input parameters such as the maximum tolerated latency and the maximum number of data centers. The obtained results show the trade-off between the achieved latency and the infrastructure cost