Error-Correcting Codes for Networks, Storage and Computation

The advent of the information age has bestowed upon us three challenges related to the way we deal with data. Firstly, there is an unprecedented demand for transmitting data at high rates. Secondly, the massive amounts of data being collected from various sources needs to be stored across time. Thirdly, there is a need to process the data collected and perform computations on it in order to extract meaningful information out of it. The interconnected nature of modern systems designed to perform these tasks has unraveled new difficulties when it comes to ensuring their resilience against sources of performance degradation. In the context of network communication and distributed data storage, system-level noise and adversarial errors have to be combated with efficient error correction schemes. In the case of distributed computation, the heterogeneous nature of computing clusters can potentially diminish the speedups promised by parallel algorithms, calling for schemes that mitigate the effect of slow machines and communication delay. This thesis addresses the problem of designing efficient fault tolerance schemes for the three scenarios just described. In the network communication setting, a family of multiple-source multicast networks that employ linear network coding is considered for which capacity-achieving distributed error-correcting codes, based on classical algebraic constructions, are designed. The codes require no coordination between the source nodes and are end to end: except for the source nodes and the destination node, the operation of the network remains unchanged. In the context of data storage, balanced error-correcting codes are constructed so that the encoding effort required is balanced out across the storage nodes. In particular, it is shown that for a fixed row weight, any cyclic Reed-Solomon code possesses a generator matrix in which the number of nonzeros is the same across the columns. In the balanced and sparsest case, where each row of the generator matrix is a minimum distance codeword, the maximal encoding time over the storage nodes is minimized, a property that is appealing in write-intensive settings. Analogous constructions are presented for a locally recoverable code construction due to Tamo and Barg. Lastly, the problem of mitigating stragglers in a distributed computation setup is addressed, where a function of some dataset is computed in parallel. Using Reed-Solomon coding techniques, a scheme is proposed that allows for the recovery of the function under consideration from the minimum number of machines possible. The only assumption made on the function is that it is additively separable, which renders the scheme useful in distributed gradient descent implementations. Furthermore, a theoretical model for the run time of the scheme is presented. When the return time of the machines is modeled probabilistically, the model can be used to optimally pick the scheme's parameters so that the expected computation time is minimized. The recovery is performed using an algorithm that runs in quadratic time and linear space, a notable improvement compared to state-of-the-art schemes. The unifying theme of the three scenarios is the construction of error-correcting codes whose encoding functions adhere to certain constraints. It is shown that in many cases, these constraints can be satisfied by classical constructions. As a result, the schemes presented are deterministic, operate over small finite fields and can be decoded using efficient algorithms.</p

Medium Access Control and Network Coding for Wireless Information Flows

This dissertation addresses the intertwined problems of medium access control (MAC) and network coding in ad hoc wireless networks. The emerging wireless network applications introduce new challenges that go beyond the classical understanding of wireline networks based on layered architecture and cooperation. Wireless networks involve strong interactions between MAC and network layers that need to be jointly specified in a cross-layer design framework with cooperative and non-cooperative users. For multi-hop wireless networks, we first rediscover the value of scheduled access at MAC layer through a detailed foray into the questions of throughput and energy consumption. We propose a distributed time-division mechanism to activate dynamic transmitter-receiver assignments and eliminate interference at non-intended receivers for throughput and energy-efficient resource allocation based on stable operation with arbitrary single-receiver MAC protocols. In addition to full cooperation, we consider competitive operation of selfish users with individual performance objectives of throughput, energy and delay. We follow a game-theoretic approach to evaluate the non-cooperative equilibrium strategies at MAC layer and discuss the coupling with physical layer through power and rate control. As a cross-layer extension to multi-hop operation, we analyze the non-cooperative operation of joint MAC and routing, and introduce cooperation stimulation mechanisms for packet forwarding. We also study the impact of malicious transmitters through a game formulation of denial of service attacks in random access and power-controlled MAC. As a new networking paradigm, network coding extends routing by allowing intermediate transmitters to code over the received packets. We introduce the adaptation of network coding to wireless environment in conjunction with MAC. We address new research problems that arise when network coding is cast in a cross-layer optimization framework with stable operation. We specify the maximum throughput and stability regions, and show the necessity of joint design of MAC and network coding for throughput and energy-efficient operation of cooperative or competitive users. Finally, we discuss the benefits of network coding for throughput stability in single-hop multicast communication over erasure channels. Deterministic and random coding schemes are introduced to optimize the stable throughput properties. The results extend our understanding of fundamental communication limits and trade-offs in wireless networks

On applying network coding to wireless ad hoc networks : A study of robustness, efficiency and cross-layer synergy

Ph.DDOCTOR OF PHILOSOPH

Networks, Communication, and Computing Vol. 2

Networks, communications, and computing have become ubiquitous and inseparable parts of everyday life. This book is based on a Special Issue of the Algorithms journal, and it is devoted to the exploration of the many-faceted relationship of networks, communications, and computing. The included papers explore the current state-of-the-art research in these areas, with a particular interest in the interactions among the fields

LIPIcs, Volume 261, ICALP 2023, Complete Volume

LIPIcs, Volume 261, ICALP 2023, Complete Volum

Distributed optimization algorithms for multihop wireless networks

Recent technological advances in low-cost computing and communication hardware design have led to the feasibility of large-scale deployments of wireless ad hoc and sensor networks. Due to their wireless and decentralized nature, multihop wireless networks are attractive for a variety of applications. However, these properties also pose significant challenges to their developers and therefore require new types of algorithms. In cases where traditional wired networks usually rely on some kind of centralized entity, in multihop wireless networks nodes have to cooperate in a distributed and self-organizing manner. Additional side constraints, such as energy consumption, have to be taken into account as well. This thesis addresses practical problems from the domain of multihop wireless networks and investigates the application of mathematically justified distributed algorithms for solving them. Algorithms that are based on a mathematical model of an underlying optimization problem support a clear understanding of the assumptions and restrictions that are necessary in order to apply the algorithm to the problem at hand. Yet, the algorithms proposed in this thesis are simple enough to be formulated as a set of rules for each node to cooperate with other nodes in the network in computing optimal or approximate solutions. Nodes communicate with their neighbors by sending messages via wireless transmissions. Neither the size nor the number of messages grows rapidly with the size of the network. The thesis represents a step towards a unified understanding of the application of distributed optimization algorithms to problems from the domain of multihop wireless networks. The problems considered serve as examples for related problems and demonstrate the design methodology of obtaining distributed algorithms from mathematical optimization methods

Combining SOA and BPM Technologies for Cross-System Process Automation

This paper summarizes the results of an industry case study that introduced a cross-system business process automation solution based on a combination of SOA and BPM standard technologies (i.e., BPMN, BPEL, WSDL). Besides discussing major weaknesses of the existing, custom-built, solution and comparing them against experiences with the developed prototype, the paper presents a course of action for transforming the current solution into the proposed solution. This includes a general approach, consisting of four distinct steps, as well as specific action items that are to be performed for every step. The discussion also covers language and tool support and challenges arising from the transformation

Auto-configuration of Critical Network Infrastructure

Until the turn of the millennia, many electricity, water and gas supply plant operators used analogue serial cabling to communicate between highly customised systems to control and manage their plants. Since then, cost reductions and increased flexibility have become possible through the use of COTS (Commodity-Off-The- Shelf) equipment. These have radically changed communication between critical infrastructure devices, but have also introduced risks to the domain; one example being the major incident at a German steel mill in 2014 [14]. Donna F. Dodson, Chief of CyberSecurity at NIST has stated that “There’s an increase in free tools available focusing on industrial control systems. And greater hacker interest.” A common strategy to mitigate these risks is the extensive use of firewalls. Firewalls are not as simple as they appear. Efficient and reliable firewall security requires expertise in arcane, vendor-dependent configuration languages [15] and even then, configuration errors are common [97, 128, 129]. It is easy to complain about short-term thinking in firewall designers, but, at a deeper level the problem is that current approaches conflate multiple concerns: i.e., they incorporate network, protocol and hardware dependent details into security policy, in an unsystematised manner. In this thesis we tackle this problem. We begin by building a mathematically rigorous foundation for the design of security policies that separates divergent concerns. The formal foundations allow security administrators to reason about their network security; for instance to (i) show that certain types of traffic flows are impossible; and (ii) compare their security to industry best practices to check it complies and so on. In particular, we design our policy framework with Supervisory Control And Data Acquisition (SCADA) networks in mind; these networks control the distributed assets of many critical infrastructure plants. In doing so, we consider the requirements of a security policy specification that are general in nature as well as specific to a SCADA network context. An example requirement is verifiability: a property that increases transparency in the framework and provides security administrators assurance of expected security outcome. Lack of verifiability in current firewall configuration platforms contribute to the broken-by-design networks found in practice. Moreover, we apply design principles derived from real SCADA case studies [97] and industry best-practices [21,117], to develop simple policy specification features that are easy to administer correctly. We demonstrate the use of these specification features through a prototype implementation that creates secure-by-design networks. In enabling security by design, we (i) prevent policy emergence: i.e., implicit definition of policy as a result of many small decisions with complex interactions; and (ii) support rigorous verification: from policy consistency and best-practice compliance checks to pre-deployment verification, we only allow deploying policies that deliver the expected security outcome; and (iii) protect proactively: security can’t be purely reactive, placing pre-verified security controls prior to a cyber attack can prevent significant, expensive damage to system infrastructure.Thesis (Ph.D.) -- University of Adelaide, School of Mathematical Sciences, 201