Performance Comparison of Neighbor Discovery Protocols in Wireless Ad-Hoc Network

In this thesis we consider the problem of neighbor discovery in synchronous single hop wireless ad-hoc networks. The central problem is to establish a broadcasting sequence such that only one transmitter broadcasts at a time while all others listen and every transmitter in the network gets at least one chance to broadcast. We consider the question: how fast we can achieve neighbor discovery with k nodes in the network, each having a unique id assigned from an id space much larger than k in radio communication models with and without collision detection. We take the simulation route to answer this question. We implemented one randomized and two deterministic algorithms for neighbor discovery and compared their performance in terms of number of rounds required as a function of the number of nodes in the network and the size of the space from which ids are chosen. Our simulation results show that the randomized algorithm is most efficient and is easiest to implement. The deterministic algorithm for the no collision detection model has round complexity comparable to the size of the id space and is orders of magnitude less efficient than the randomized algorithm. The deterministic algorithm for the collision detection model is slower than the randomized algorithm by a factor of log(n), where n is the size of the id space. Our analysis would be useful for choosing optimal algorithms for field applications depending on the radio communication model and network topology. It will reveal any large constants or second order terms discarded in the asymptotic analysis of the algorithms, which reduces effectiveness of some algorithms in applications

Data Storage and Dissemination in Pervasive Edge Computing Environments

Nowadays, smart mobile devices generate huge amounts of data in all sorts of gatherings. Much of that data has localized and ephemeral interest, but can be of great use if shared among co-located devices. However, mobile devices often experience poor connectivity, leading to availability issues if application storage and logic are fully delegated to a remote cloud infrastructure. In turn, the edge computing paradigm pushes computations and storage beyond the data center, closer to end-user devices where data is generated and consumed. Hence, enabling the execution of certain components of edge-enabled systems directly and cooperatively on edge devices. This thesis focuses on the design and evaluation of resilient and efficient data storage and dissemination solutions for pervasive edge computing environments, operating with or without access to the network infrastructure. In line with this dichotomy, our goal can be divided into two specific scenarios. The first one is related to the absence of network infrastructure and the provision of a transient data storage and dissemination system for networks of co-located mobile devices. The second one relates with the existence of network infrastructure access and the corresponding edge computing capabilities. First, the thesis presents time-aware reactive storage (TARS), a reactive data storage and dissemination model with intrinsic time-awareness, that exploits synergies between the storage substrate and the publish/subscribe paradigm, and allows queries within a specific time scope. Next, it describes in more detail: i) Thyme, a data storage and dis- semination system for wireless edge environments, implementing TARS; ii) Parsley, a flexible and resilient group-based distributed hash table with preemptive peer relocation and a dynamic data sharding mechanism; and iii) Thyme GardenBed, a framework for data storage and dissemination across multi-region edge networks, that makes use of both device-to-device and edge interactions. The developed solutions present low overheads, while providing adequate response times for interactive usage and low energy consumption, proving to be practical in a variety of situations. They also display good load balancing and fault tolerance properties.Resumo Hoje em dia, os dispositivos móveis inteligentes geram grandes quantidades de dados em todos os tipos de aglomerações de pessoas. Muitos desses dados têm interesse loca- lizado e efêmero, mas podem ser de grande utilidade se partilhados entre dispositivos co-localizados. No entanto, os dispositivos móveis muitas vezes experienciam fraca co- nectividade, levando a problemas de disponibilidade se o armazenamento e a lógica das aplicações forem totalmente delegados numa infraestrutura remota na nuvem. Por sua vez, o paradigma de computação na periferia da rede leva as computações e o armazena- mento para além dos centros de dados, para mais perto dos dispositivos dos utilizadores finais onde os dados são gerados e consumidos. Assim, permitindo a execução de certos componentes de sistemas direta e cooperativamente em dispositivos na periferia da rede. Esta tese foca-se no desenho e avaliação de soluções resilientes e eficientes para arma- zenamento e disseminação de dados em ambientes pervasivos de computação na periferia da rede, operando com ou sem acesso à infraestrutura de rede. Em linha com esta dico- tomia, o nosso objetivo pode ser dividido em dois cenários específicos. O primeiro está relacionado com a ausência de infraestrutura de rede e o fornecimento de um sistema efêmero de armazenamento e disseminação de dados para redes de dispositivos móveis co-localizados. O segundo diz respeito à existência de acesso à infraestrutura de rede e aos recursos de computação na periferia da rede correspondentes. Primeiramente, a tese apresenta armazenamento reativo ciente do tempo (ARCT), um modelo reativo de armazenamento e disseminação de dados com percepção intrínseca do tempo, que explora sinergias entre o substrato de armazenamento e o paradigma pu- blicação/subscrição, e permite consultas num escopo de tempo específico. De seguida, descreve em mais detalhe: i) Thyme, um sistema de armazenamento e disseminação de dados para ambientes sem fios na periferia da rede, que implementa ARCT; ii) Pars- ley, uma tabela de dispersão distribuída flexível e resiliente baseada em grupos, com realocação preventiva de nós e um mecanismo de particionamento dinâmico de dados; e iii) Thyme GardenBed, um sistema para armazenamento e disseminação de dados em redes multi-regionais na periferia da rede, que faz uso de interações entre dispositivos e com a periferia da rede. As soluções desenvolvidas apresentam baixos custos, proporcionando tempos de res- posta adequados para uso interativo e baixo consumo de energia, demonstrando serem práticas nas mais diversas situações. Estas soluções também exibem boas propriedades de balanceamento de carga e tolerância a faltas

Efficient tree-based content-based routing schemes

This thesis is about routing and forwarding for inherently multicast communication such as the communication typical of information-centric networks. The notion of Information-Centric Networking (ICN) is an evolution of the Internet from the current host-centric architecture to a new architecture in which communication is based on “named information”. The ambitious goal of ICN is to effectively support the exchange and use of information in an ever more connected world, with billions of devices, many of which are mobile, producing and consuming large amounts of data. ICN is intended to support scalable content distribution, mobility, and security, for such applications as video on demand and networks of sensors or the so-called Internet of Things. Many ICN architectures have emerged in the past decade, and the ICN community has made significant progress in terms of infrastructure, test-bed deployments, and application case studies. And yet, despite the impressive research effort, the fundamental problems of routing and forwarding remain open. In particular, none of the proposed architectures has developed truly scalable name-based routing schemes and efficient name-based forwarding algorithms. This is not surprising, since the problem of routing based on names, in its most general formulation, is known to be fundamentally difficult. In general, one would want to support application-defined names (as opposed to network-defined addresses) with a compact routing scheme (small routing tables) that uses optimal paths and minimizes congestion, and that admits to a fast forwarding algorithm. Furthermore, one would want to construct this routing scheme with a decentralized and incremental protocol for administrative autonomy and efficient dynamic updates. However, there are clear theoretical limits that simply make it impossible to achieve all these goals. In this thesis we explore the design space of routing and forwarding in an information-centric network. Our purpose is to develop routing schemes and forwarding algorithms that combine many desirable properties. We consider two forms of addressing, one tied to network locations, and one based on more expressive content descriptors. We then consider trees as basic routing structures, and with those we develop routing schemes that are intended to minimize path lengths and congestion, separately or together. For one of these schemes based on expressive content descriptors, we also develop a fast forwarding algorithm specialized for massively parallel architectures such as GPUs. In summary, this thesis presents two efficient and scalable routing algorithms for two different types of networks, plus one scalable forwarding algorithm. We summarize each individual contribution below: Low-congestion geographic routing for wireless networks. We develop a low-congestion, multicast routing scheme designed specifically for wireless networks. The scheme supports geographical multicast routing, meaning routing to a set of nodes addressed by their physical position. The scheme builds a geometric minimum spanning tree connecting the source to all the destinations. Then, for each edge in this tree, the scheme routes a message through a random intermediate node, chosen independently of the set of multicast requests. The intermediate node is chosen in the vicinity of the corresponding edge such that congestion is reduced without stretching routes by more than a constant factor. Multi-tree scheme for content-based routing in ICN. We develop a tree-based routing scheme designed for large-scale wired networks such as the Internet. The scheme supports two forms of addresses: application-defined content descriptors, and network-defined locators. We first show that the scheme is effective in terms of stretch and congestion on the current AS-level Internet graph even with only a few spanning trees. Then we show that our content descriptors, which consist of sets of tags and that are more expressive than the name prefixes used in mainstream ICN, aggregate well in practice under our scheme. We also explain in detail how to use descriptors and locators, together with unique content identifiers, to support the efficient transmission and sharing of information through scalable and loop-free routes. Tag-based forwarding (partial matching) algorithm on GPUs. To accompany our ICN routing scheme, we develop a fast forwarding algorithm that matches incoming packets against forwarding tables with tens of millions of entries. To achieve high performance, we develop a practical solution for the partial matching problem that lies at the heart of this forwarding scheme. This solution amounts to a massively parallel algorithm specifically designed for a hybrid CPU/GPU architecture

Dinamičko formiranje distribuiranog mikro okruženja u računarstvu u oblaku

This thesis presents research in the field of distributed systems. We present the dynamic organization of geodistributed edge nodes into micro data-centers forming micro clouds to cover any arbitrary area and expand capacity, availability, and reliability. A cloud organization is used as an influence with adaptations for a different environment with a clear separation of concerns, and native applications model that can leverage the newly formed system. With the separation of concerns setup, edge-native applications model, and a unified node organization, we are moving towards the idea of edge computing as a service, like any other utility in cloud computing. We also give formal models for all protocols used for the creation of such a system.U sklopu disertacije izvršeno je istraživanje u oblasti distribuiranih sistema. Predstavili smo dinamičku organizaciju geo-distribuiranih čvorova u mikro centre za obradu podataka koji formiraju mikro okruženja računarstva u oblaku kako bi pokrili bilo koje proizvoljno područje i proširili kapacitet, dostupnost i pouzdanost. Koristili smo organizaciju računarstva u oblaku kao inspiraciju, sa adaptacijama za drugačije okruženje sa jasnom podelom nadležnosti, i modelom aplikacija koji može da iskoristi novoformirani sistem. Jasna podela nadležnosti, model aplikacija i dinamička organizacijom čvorova, čine da se predstavljeni model ponude kao i bilo koji drugi uslužni servis. Takođe dajemo formalne modele za sve protokole koji se koriste za stvaranje takvog sistema

Telekomunikacja i Techniki Informacyjne, 2014, nr 1-2

kwartalni

An adaptive physiology-aware communication framework for distributed medical cyber physical systems

For emergency medical cyber-physical systems, enhancing the safety and effectiveness of patient care, especially in remote rural areas, is essential. While the doctor to patient ratio in the United States is 30 to 10,000 in large metropolitan areas, it is only 5 to 10,000 in most rural areas; and the highest death rates are often found in the most rural counties. Use of telecommunication technologies can enhance effectiveness and safety of emergency ambulance transport of patients from rural areas to a regional center hospital. It enables remote monitoring of patients by the physician experts at the tertiary center. There are critical times during transport when physician experts can provide vital assistance to the ambulance Emergency Medical Technicians (EMT) to associate best treatments. However, the communication along the roads in rural areas can range irregularly from 4G to low speed 2G links, including some parts of routes with cellular network communication breakage. This unreliable and limited communication bandwidth together with the produced mass of clinical data and the many information exchanges pose a major challenge in real-time supervision of patients. In this study, we define the notion of distributed emergency care, and propose a novel adaptive physiology-aware communication framework which is aware of the patient condition, the underlying network bandwidth, and the criticality of clinical data in the context of the specific diseases. Using the concept of distributed medical CPS models, we study the semantics relation of communication Quality of Service (QoS) with clinical messages, criticality of clinical data, and an ambulance's undertaken route all in a disease-aware manner. Our proposed communication framework is aimed to enhance remote monitoring of acute patients during ambulance transport from a rural hospital to a regional center hospital. We evaluate the components of our framework through various experimentation phases including simulation, instrumentation, real-world profiling, and validation

A distributed, compact routing protocol for the Internet

The Internet has grown in size at rapid rates since BGP records began, and continues to do so. This has raised concerns about the scalability of the current BGP routing system, as the routing state at each router in a shortest-path routing protocol will grow at a supra-linearly rate as the network grows. The concerns are that the memory capacity of routers will not be able to keep up with demands, and that the growth of the Internet will become ever more cramped as more and more of the world seeks the benefits of being connected. Compact routing schemes, where the routing state grows only sub-linearly relative to the growth of the network, could solve this problem and ensure that router memory would not be a bottleneck to Internet growth. These schemes trade away shortest-path routing for scalable memory state, by allowing some paths to have a certain amount of bounded “stretch”. The most promising such scheme is Cowen Routing, which can provide scalable, compact routing state for Internet routing, while still providing shortest-path routing to nearly all other nodes, with only slightly stretched paths to a very small subset of the network. Currently, there is no fully distributed form of Cowen Routing that would be practical for the Internet. This dissertation describes a fully distributed and compact protocol for Cowen routing, using the k-core graph decomposition. Previous compact routing work showed the k-core graph decomposition is useful for Cowen Routing on the Internet, but no distributed form existed. This dissertation gives a distributed k-core algorithm optimised to be efficient on dynamic graphs, along with with proofs of its correctness. The performance and efficiency of this distributed k-core algorithm is evaluated on large, Internet AS graphs, with excellent results. This dissertation then goes on to describe a fully distributed and compact Cowen Routing protocol. This protocol being comprised of a landmark selection process for Cowen Routing using the k-core algorithm, with mechanisms to ensure compact state at all times, including at bootstrap; a local cluster routing process, with mechanisms for policy application and control of cluster sizes, ensuring again that state can remain compact at all times; and a landmark routing process is described with a prioritisation mechanism for announcements that ensures compact state at all times

Notes on Theory of Distributed Systems

Notes for the Yale course CPSC 465/565 Theory of Distributed Systems