Recursive Loop-Free Alternates for full protection against transient link failures

In this paper, we propose a routing technique, “recursive Loop-Free Alternates (rLFAs)”, to alleviate packet loss due to transient link failures. The technique consists of a backup path calculation with corresponding re-routing scheme based on the Loop-Free Condition (LFC) as defined in the basic specification for IP Fast Re-Route (IPFRR). Under this routing strategy, nodes calculate backup paths by modifying the weights of links in the primary shortest path tree. If a failure occurs, the detecting node determines the number of recursions, which indicates the number of times packets must be forwarded along the alternate next hops to bypass the failed link. This technique guarantees full repair coverage for single link failures. We evaluate the performance of our proposed technique through simulations and show that the incurred overheads, the stretch of its pre-computed alternate paths, and the failure-state Maximum Link Utilisation (MLU) are minimal

Resilient routing in the internet

Although it is widely known that the Internet is not prone to random failures, unplanned failures due to attacks can be very damaging. This prevents many organisations from deploying beneficial operations through the Internet. In general, the data is delivered from a source to a destination via a series of routers (i.e routing path). These routers employ routing protocols to compute best paths based on routing information they possess. However, when a failure occurs, the routers must re-construct their routing tables, which may take several seconds to complete. Evidently, most losses occur during this period. IP Fast Re-Route (IPFRR), Multi-Topology (MT) routing, and overlays are examples of solutions proposed to handle network failures. These techniques alleviate the packet losses to different extents, yet none have provided optimal solutions. This thesis focuses on identifying the fundamental routing problem due to convergence process. It describes the mechanisms of each existing technique as well as its pros and cons. Furthermore, it presents new techniques for fast re-routing as follows. Enhanced Loop-Free Alternates (E-LFAs) increase the repair coverage of the existing techniques, Loop-Free Alternates (LFAs). In addition, two techniques namely, Full Fast Failure Recovery (F3R) and fast re-route using Alternate Next Hop Counters (ANHC), offer full protection against any single link failures. Nevertheless, the former technique requires significantly higher computational overheads and incurs longer backup routes. Both techniques are proved to be complete and correct while ANHC neither requires any major modifications to the traditional routing paradigm nor incurs significant overheads. Furthermore, in the presence of failures, ANHC does not jeopardise other operable parts of the network. As emerging applications require higher reliability, multiple failures scenarios cannot be ignored. Most existing fast re-route techniques are able to handle only single or dual failures cases. This thesis provides an insight on a novel approach known as Packet Re-cycling (PR), which is capable of handling any number of failures in an oriented network. That is, packets can be forwarded successfully as long as a path between a source and a destination is available. Since the Internet-based services and applications continue to advance, improving the network resilience will be a challenging research topic for the decades to come

Study of fault-tolerant software technology

Presented is an overview of the current state of the art of fault-tolerant software and an analysis of quantitative techniques and models developed to assess its impact. It examines research efforts as well as experience gained from commercial application of these techniques. The paper also addresses the computer architecture and design implications on hardware, operating systems and programming languages (including Ada) of using fault-tolerant software in real-time aerospace applications. It concludes that fault-tolerant software has progressed beyond the pure research state. The paper also finds that, although not perfectly matched, newer architectural and language capabilities provide many of the notations and functions needed to effectively and efficiently implement software fault-tolerance

Equal cost multipath routing in IP networks

IP verkkojen palveluntarjoajat ja loppukäyttäjät vaativat yhä tehokkaampia ja parempilaatuisia palveluita, mikä vaatii tuotekehittäjiä tarjoamaan hienostuneempia liikennesuunnittelumenetelmiä verkon optimointia ja hallintaa varten. IS-IS ja OSPF ovat standardiratkaisut hoitamaan reititystä pienissä ja keskisuurissa pakettiverkoissa. Monipolkureititys on melko helppo ja yleispätevä tapa parantaa kuorman balansointia ja nopeaa suojausta tällaisissa yhden polun reititykseen keskittyvissä verkoissa. Tämä diplomityö kirjoitettiin aikana, jolloin monipolkureititys toteutettiin Tellabs-nimisen yrityksen 8600-sarjan reitittimiin. Tärkeimpiä kohtia monipolkureitityksen käyttöönotossa ovat lyhyimmän polun algoritmin muokkaukseen ja reititystaulun toimintaan liittyvät muutokset ohjaustasolla sekä kuormanbalansointialgoritmin toteutus reitittimen edelleenkuljetustasolla. Diplomityön tulokset sekä olemassa oleva kirjallisuus osoittavat, että kuormanbalansointialgoritmilla on suurin vaikutus yhtä hyvien polkujen liikenteen jakautumiseen ja että oikean algoritmin valinta on ratkaisevan tärkeää. Hajakoodaukseen perustuvat algoritmit, jotka pitävät suurimman osan liikennevuoista samalla polulla, ovat dominoivia ratkaisuja nykyisin. Tämän algoritmityypin etuna on helppo toteutettavuus ja kohtuullisen hyvä suorituskyky. Liikenne on jakautunut tasaisesti, kunhan liikennevuoiden lukumäärä on riittävän suuri. Monipolkureititys tarjoaa yksinkertaisen ratkaisun, jota on helppo konfiguroida ja ylläpitää. Suorituskyky on parempi kuin yksipolkureititykseen perustuvat ratkaisut ja se haastaa monimutkaisemmat MPLS ratkaisut. Ainoa huolehdittava asia on linkkien painojen asettaminen sillä tavalla, että riittävästi kuormantasauspolkuja syntyy.Increasing efficiency and quality demands of services from IP network service providers and end users drive developers to offer more and more sophisticated traffic engineering methods for network optimization and control. Intermediate System to Intermediate System and Open Shortest Path First are the standard routing solutions for intra-domain networks. An easy upgrade utilizes Equal Cost Multipath (ECMP) that is one of the most general solutions for IP traffic engineering to increase load balancing and fast protection performance of single path interior gateway protocols. This thesis was written during the implementation process of the ECMP feature of Tellabs 8600 series routers. The most important parts in adoption of ECMP are changes to shortest path first algorithm and routing table modification in the control plane and implementation of load balancing algorithm to the forwarding plane of router. The results of the thesis and existing literature prove, that the load balancing algorithm has the largest affect on traffic distribution of equal cost paths and the selection of the correct algorithm is crucial. Hash-based algorithms, that keep the traffic flows in the same path, are the dominating solutions currently. They provide simple implementation and moderate performance. Traffic is distributed evenly, when the number of flows is large enough. ECMP provides a simple solution that is easy to configure and maintain. It outperforms single path solutions and competes with more complex MPLS solutions. The only thing to take care of is the adjustment of link weights of the network in order to create enough load balancing paths

Resilient and Scalable Forwarding for Software-Defined Networks with P4-Programmable Switches

Traditional networking devices support only fixed features and limited configurability. Network softwarization leverages programmable software and hardware platforms to remove those limitations. In this context the concept of programmable data planes allows directly to program the packet processing pipeline of networking devices and create custom control plane algorithms. This flexibility enables the design of novel networking mechanisms where the status quo struggles to meet high demands of next-generation networks like 5G, Internet of Things, cloud computing, and industry 4.0. P4 is the most popular technology to implement programmable data planes. However, programmable data planes, and in particular, the P4 technology, emerged only recently. Thus, P4 support for some well-established networking concepts is still lacking and several issues remain unsolved due to the different characteristics of programmable data planes in comparison to traditional networking. The research of this thesis focuses on two open issues of programmable data planes. First, it develops resilient and efficient forwarding mechanisms for the P4 data plane as there are no satisfying state of the art best practices yet. Second, it enables BIER in high-performance P4 data planes. BIER is a novel, scalable, and efficient transport mechanism for IP multicast traffic which has only very limited support of high-performance forwarding platforms yet. The main results of this thesis are published as 8 peer-reviewed and one post-publication peer-reviewed publication. The results cover the development of suitable resilience mechanisms for P4 data planes, the development and implementation of resilient BIER forwarding in P4, and the extensive evaluations of all developed and implemented mechanisms. Furthermore, the results contain a comprehensive P4 literature study. Two more peer-reviewed papers contain additional content that is not directly related to the main results. They implement congestion avoidance mechanisms in P4 and develop a scheduling concept to find cost-optimized load schedules based on day-ahead forecasts

Advanced engineering - Supporting research and technology

Telemetry simulations, radar equipment and experiments, and related supporting research for Deep Space Networ

The safety of industrially-based controllers incorporating software

This thesis is concerned with the safety of industrial controllers which incorporate software. Software safety is compared with software reliability as a means of discussing the special concerns of safety. Definitions are given for the terms hazard, risk, danger and safe. A relationship between these terms has been attempted and the philosophy of safety is discussed. A formal definition of software safety is given. The factors influencing the development of software are examined. The subjectivity of safety is discussed in the context of safety measurement being a conjoint measurement. Methods of assessing the risk resulting from the use of software are described along with a discussion on the impracticability of using state transition diagrams to isolate catastrophic failure conditions. Categories of danger are discussed and three categories are advanced. The structuring of the software for safety is discussed and the principle of using safety modules and integrity locks is proposed. In discussing the reasons for errors remaining present in the software after testing two methods of measurement are suggested; Plexus and Fallibility Index. The need to declare variables is discussed. An experiment involving 119 volunteers was conducted to examine the influence of the length of variable names'on the correct usage. It was found that variables with a character length of 7 have a better probability of correct interpretation than others. The methods of assessing safety are discussed and the measurements proposed were applied to a commercially available product in the form of a Software Safety Audit. It is concluded that some aspects of the safety of controllers incorporating software can be quantified and that further research is needed