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

Enhancing performance of conventional computer networks employing selected SDN principles

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThis research is related to computer networks. In this thesis, three main issues are addressed which affect the performance of any computer network: congestion, efficient resources utilization and link failure. Those issues are related to each other in many situations. Many approaches have been suggested to deal with those issues as well as many solutions were applied. Despite all the improvements of the technology and the proposed solutions, those issues continue to be a burden on the system’s performance. This effect is related to the increase of the Quality of Service (QoS) requirements in modern networks. The basic idea of this research is evolving the intelligence of a conventional computer network when dealing with those issues by adding some features of the Software Defined Networking (SDN). This adoption upgrades the conventional computer network system to be more dynamic and higher self-organizing when dealing with those issues. This idea is applied on a system represented by a computer network that uses the Open Shortest Path First (OSPF) routing protocol. The first improvement deals with the distribution of Internet Protocol (IP) routed flows. The second improvement deals with tunnel establishment that serves Multi-Protocol Label Switching (MPLS) routed flows and the third improvement deals with bandwidth reservation when applying network restoration represented by Fast Re-route (FRR) mechanism to sooth the effect of link failure in OSPF/MPLS routed network. This idea is also applied on another system that uses the Enhanced Interior Gateway Routing Protocol (EIGRP) to improve the performance of its routing algorithm. Adopting the SDN notion is achieved by adding an intelligent controller to the system and creating a dialog of messages between the controller and the conventional routers. This requires upgrading the routers to respond to the new modified system.Our proposed approaches are presented with simulations of different configurations which produce fine results

УСОВЕРШЕНСТВОВАННАЯ МОДЕЛЬ БЫСТРОЙ ПЕРЕМАРШРУТИЗАЦИИ С РЕАЛИЗАЦИЕЙ СХЕМЫ ЗАЩИТЫ ПУТИ И ПРОПУСКНОЙ СПОСОБНОСТИ В ПРОГРАММНО-КОНФИГУРИРУЕМЫХ СЕТЯХ

Предметом дослідження в статті є процеси швидкої перемаршрутизації з реалізацією схеми захисту шляху та пропускної здатності. Мета роботи – вдосконалення моделі швидкої перемаршрутизації з реалізацією схеми захисту шляху та пропускної здатності, яка може бути використана для програмно-конфігурованих мереж. У статті вирішуються наступні завдання: вдосконалення та дослідження математичної моделі швидкої перемаршрутизації з реалізацією схеми захисту шляху та пропускної здатності. Використовуються такі методи: теорія графів, теорія масового обслуговування та методи математичного програмування. Отримано наступні результати: вдосконалено та досліджено математичну модель швидкої перемаршрутизації, яка завдяки введенню додаткових умов дозволяє реалізувати схему захисту шляху 1:n та пропускну здатність у програмно-конфігурованих мережах. Висновки: В рамках запропонованої моделі швидкої перемаршрутизації з реалізацією схеми захисту шляху та пропускної здатності було вирішено завдання розрахунку множини основних і резервних шляхів, що не перетинаються, яке зводилося до розв’язання оптимізаційної задачі цілочисельного лінійного програмування. Перевагою вдосконаленої моделі є можливість реалізації схем захисту 1:1, 1:2,…, 1:n без введення додаткової множини керуючих (маршрутних) змінних, що сприяє зменшенню розмірності оптимізаційної задачі, що розв’язується, та обчислювальної складності її практичної реалізації. Критерій оптимальності маршрутних рішень сприяє формуванню основних і резервних шляхів, що не перетинаються, з максимально високою пропускною здатністю. У цьому випадку шлях з найвищою пропускною здатністю буде відповідати основному шляху, тоді як решта шляхів будуть використовуватися як резервні в порядку зменшення їх пропускної здатності. Загальна кількість обчислених шляхів, що не перетинаються, залежить від обраної схеми надмірності.The subject matter of the article is the fast rerouting processes with the implementation of the protection scheme of the path and its bandwidth. The goal of the work is to improve the performance-based Fast ReRoute model with the protection scheme of the path and its bandwidth, which can be used for Software-Defined Networks. The following tasks are solved in the article: improvement and research of the Fast ReRoute model with the protection scheme of the path and its bandwidth. The following methods are used: graph theory, queuing theory, and mathematical programming methods. The following results were obtained: Fast ReRoute model was improved and investigated. That allows implementing the 1:n protection scheme of the path and its bandwidth in Software-Defined Networks. Conclusions: Within the framework of the proposed Fast ReRoute model with the schemes of the path protection and its bandwidth, the problem of calculating the set of primary and backup disjoint paths was solved. The proposed mathematical model, using the introduction of additional conditions, allowed us to reduce the solution of the technological problem of fast rerouting to the solution of the optimization problem of mixed integer linear programming. The advantage of the improved model is the possibility of implementing protection schemes 1:1, 1:2, ..., 1:n without introducing an additional set of control (routing) variables. This helps to reduce the dimension of the optimization problem to be solved and the computational complexity of its implementation. The optimality criterion of routing solutions contributes to the formation of primary and backup disjoint paths with the maximum bandwidth. In this case, the path with the highest bandwidth will correspond to the primary path, while the remaining paths will be used as a backup, in order to reduce their bandwidth. The total number of calculated disjoint paths depends on the selected redundancy scheme.Предметом исследования в статье являются процессы быстрой перемаршрутизации с реализацией схемы защиты пути и пропускной способности. Цель работы – усовершенствование модели быстрой перемаршрутизации с реализацией схемы защиты пути и пропускной способности, которая может быть использована для программно-конфигурируемых сетей. В статье решаются следующие задачи: усовершенствование и исследование математической модели быстрой перемаршрутизации с реализацией схемы защиты пути и пропускной способности. Используются следующие методы: теория графов, теория массового обслуживания и методы математического программирования. Получены следующие результаты: усовершенствована и исследована математическая модель быстрой перемаршрутизации, которая благодаря введению дополнительных условий позволяет реализовать схему защиты пути 1:n и пропускной способности в программно-конфигурируемых сетях. Выводы: В рамках предложенной модели быстрой перемаршрутизации с реализацией схемы защиты пути и пропускной способности была решена задача расчета множества основных и резервных непересекающихся путей, которая сводилась к решению оптимизационной задачи целочисленного линейного программирования. Преимуществом усовершенствованной модели является возможность реализации схем защиты 1:1, 1:2, ..., 1:n без введения дополнительного множества управляющих (маршрутных) переменных, что способствует уменьшению размерности решаемой оптимизационной задачи и вычислительной сложности ее практической реализации. Критерий оптимальности маршрутных решений способствует формированию основных и резервных непересекающихся путей с максимальной пропускной способностью. В этом случае путь с наивысшей пропускной способностью будет соответствовать основному пути, тогда как остальные пути будут использоваться как резервные, в порядке уменьшения их пропускной способности. Общее количество рассчитанных непересекающихся путей зависит от выбранной схемы резервирования

Stateful Data Plane Abstractions for Software-Defined Networks and Their Applications

RESUMÉ Le Software-Defined Networking (SDN) permet la programmation du réseau. Malheureusement, la technologie SDN actuelle limite la programmabilité uniquement au plan de contrôle. Les opérateurs ne peuvent pas programmer des algorithmes du plan de données tels que l’équilibrage de charge, le contrôle de congestion, la détection de pannes, etc. Ces fonctions sont implémentées à l’aide d’hardware dédié, car elles doivent fonctionner au taux de ligne, c’est-à-dire 10-100 Gbit/s sur 10-100 ports. Dans ce travail, nous présentons deux abstractions de plan de données pour le traitement de paquets à états (stateful), OpenState et OPP. OpenState est une extension d’OpenFlow qui permet la définition des règles de flux en tant que machines à états finis. OPP est une abstraction plus flexible qui généralise OpenState en ajoutant des capacités de calcul, permettant la programmation d’algorithmes de plan de données plus avancés. OpenState et OPP sont à la fois disponibles pour les implémentations d’haute performance en utilisant des composants de commutateurs hardware courants. Cependant, les deux abstractions sont basées sur un choix de design problématique : l’utilisation d’une boucle de rétroaction dans le pipeline de traitement des paquets. Cette boucle, si elle n’est pas correctement contrôlée, peut nuire à la cohérence des opérations d’état. Les approches de verrouillage de la mémoire peuvent être utilisées pour éviter les incohérences, au détriment du débit. Nous présentons des résultats de simulations sur des traces de trafic réelles, montrant que les boucles de rétroaction de plusieurs cycles d’horloge peuvent être supportées avec peu ou pas de dégradation des performances, même avec les charges de travail des plus défavorables. Pour mieux prouver les avantages d’un plan de données programmables, nous présentons deux nouvelles applications : Spider et FDPA. Spider permet de détecter et de réagir aux pannes de réseau aux échelles temporelles du plan de données (i.e., micro/nanosecondes), également dans le cas de pannes à distance. En utilisant OpenState, Spider fournit des fonctionnalités équivalentes aux protocoles de plans de contrôle anciens tels que BFD et MPLS Fast Reroute, mais sans nécessiter un plan de contrôle.---------- ABSTRACT Software-Defined Networking (SDN) enables programmability in the network. Unfortunately, current SDN limits programmability only to the control plane. Operators cannot program data plane algorithms such as load balancing, congestion control, failure detection, etc. These capabilities are usually baked in the switch via dedicated hardware, as they need to run at line rate, i.e. 10-100 Gbit/s on 10-100 ports. In this work, we present two data plane abstractions for stateful packet processing, namely OpenState and OPP. These abstractions allow operators to program data plane tasks that involve stateful processing. OpenState is an extension to OpenFlow that permits the definition of forwarding rules as finite state machines. OPP is a more flexible abstraction that generalizes OpenState by adding computational capabilities, opening for the programming of more advanced data plane algorithms. Both OpenState and OPP are amenable for highperformance hardware implementations by using commodity hardware switch components. However, both abstractions are based on a problematic design choice: to use a feedback-loop in the processing pipeline. This loop, if not adequately controlled, can represent a harm for the consistency of the state operations. Memory locking approaches can be used to prevent inconsistencies, at the expense of throughput. We present simulation results on real traffic traces showing that feedback-loops of several clock cycles can be supported with little or no performance degradation, even with near-worst case traffic workloads. To further prove the benefits of a stateful programmable data plane, we present two novel applications: Spider and FDPA. Spider permits to detect and react to network failures at data plane timescales, i.e. micro/nanoseconds, also in the case of distant failures. By using OpenState, Spider provides functionalities equivalent to legacy control plane protocols such as BFD and MPLS Fast Reroute, but without the need of a control plane. That is, both detection and rerouting happen entirely in the data plane. FDPA allows a switch to enforce approximate fair bandwidth sharing among many TCP-like senders. Most of the mechanisms to solve this problem are based on complex scheduling algorithms, whose feasibility becomes very expensive with today’s line rate requirements. FDPA, which is based on OPP, trades scheduling complexity with per-user state. FDPA works by dynamically assigning users to few (3-4) priority queues, where the priority is chosen based on the sending rate history of a user

Traffic Re-engineering: Extending Resource Pooling Through the Application of Re-feedback

Parallelism pervades the Internet, yet efficiently pooling this increasing path diversity has remained elusive. With no holistic solution for resource pooling, each layer of the Internet architecture attempts to balance traffic according to its own needs, potentially at the expense of others. From the edges, traffic is implicitly pooled over multiple paths by retrieving content from different sources. Within the network, traffic is explicitly balanced across multiple links through the use of traffic engineering. This work explores how the current architecture can be realigned to facilitate resource pooling at both network and transport layers, where tension between stakeholders is strongest. The central theme of this thesis is that traffic engineering can be performed more efficiently, flexibly and robustly through the use of re-feedback. A cross-layer architecture is proposed for sharing the responsibility for resource pooling across both hosts and network. Building on this framework, two novel forms of traffic management are evaluated. Efficient pooling of traffic across paths is achieved through the development of an in-network congestion balancer, which can function in the absence of multipath transport. Network and transport mechanisms are then designed and implemented to facilitate path fail-over, greatly improving resilience without requiring receiver side cooperation. These contributions are framed by a longitudinal measurement study which provides evidence for many of the design choices taken. A methodology for scalably recovering flow metrics from passive traces is developed which in turn is systematically applied to over five years of interdomain traffic data. The resulting findings challenge traditional assumptions on the preponderance of congestion control on resource sharing, with over half of all traffic being constrained by limits other than network capacity. All of the above represent concerted attempts to rethink and reassert traffic engineering in an Internet where competing solutions for resource pooling proliferate. By delegating responsibilities currently overloading the routing architecture towards hosts and re-engineering traffic management around the core strengths of the network, the proposed architectural changes allow the tussle surrounding resource pooling to be drawn out without compromising the scalability and evolvability of the Internet

Addressing climate vulnerability : promoting the participatory rights of indigenous peoples and women through Finnish foreign policy

Julkaistu versi

Wind Energy in Colombia: A Framework for Market Entry

The purpose of this report is to provide decision makers in Colombia (and by extension other countries or regions), who are considering the deployment or consolidation of wind power, with a set of options to promote its use. The options presented are the result of an analysis of the Colombian market; this analysis included simulations and modeling of the country’s power sector, and extensive consultations with operators, managers, and agents. More information on the analysis and simulations is presented in the appendixes. Wind was chosen to exemplify the range of renewable energy alternatives available to complement traditional power sector technologies on the basis of its technical maturity, its relatively low cost compared to other options, the country’s experience, and its wind power potential.wind energy, Colombia

Investigation of the Challenger Accident

The work of the Presidential Commission on the Space Shuttle Challenger Accident (hereafter referred to as the Rogers Commission) and the work of the National Aeronautics and Space Administration in investigating the causes of the accident were reviewed. In addition to reviewing the five volumes of the Rogers Commission, the entire direct on-line Rogers Commission data base, which included full-text and document retrieval capability was also reviewed. The findings and recommendations contained also include materials submitted for the record, staff investigations, interviews, and trips

The power inversion adaptive array

After the brief review on adaptive array processing, three fairly separate topics on the power inversion adaptive array are treated in this thesis. The first topic is the behaviour of a narrowband array using the stochastic gradient descent algorithm, with the environment assumed to rotate at constant velocity in the sine domain. Conditions for steady state weight deviations and output power deterioration from optimal values due to the nonstationary environment are derived and are then used to determine the maximum scan rate of a radar side-lobe canceller. The second topic is the jamming rejection capability of a broadband array using tapped delay line processing. The results obtained are used for designing the tap spacing and number of taps of the delay lines as well as assessing, in terms of the number of variable weights, the relative advantage of the alternative broadband processing method using several narrowband array processors. The frequency distortions at various directions introduced by rejecting the jammers are also studied qualitatively. The third topic is the convergence behaviour of the broadband array when the stochastic gradient descent algorithm is employed. Comparison with the alternative broadband processing method is again given. A simple transformation pre-processor, independent of the external environment and capable of improving the convergence behaviour of using tapped delay line processing, is also derived