Cloud-edge hybrid applications

Many modern applications are designed to provide interactions among users, including multi- user games, social networks and collaborative tools. Users expect application response time to be in the order of milliseconds, to foster interaction and interactivity. The design of these applications typically adopts a client-server model, where all interac- tions are mediated by a centralized component. This approach introduces availability and fault- tolerance issues, which can be mitigated by replicating the server component, and even relying on geo-replicated solutions in cloud computing infrastructures. Even in this case, the client-server communication model leads to unnecessary latency penalties for geographically close clients and high operational costs for the application provider. This dissertation proposes a cloud-edge hybrid model with secure and ecient propagation and consistency mechanisms. This model combines client-side replication and client-to-client propagation for providing low latency and minimizing the dependency on the server infras- tructure, fostering availability and fault tolerance. To realize this model, this works makes the following key contributions. First, the cloud-edge hybrid model is materialized by a system design where clients maintain replicas of the data and synchronize in a peer-to-peer fashion, and servers are used to assist clients’ operation. We study how to bring most of the application logic to the client-side, us- ing the centralized service primarily for durability, access control, discovery, and overcoming internetwork limitations. Second, we dene protocols for weakly consistent data replication, including a novel CRDT model (∆-CRDTs). We provide a study on partial replication, exploring the challenges and fundamental limitations in providing causal consistency, and the diculty in supporting client- side replicas due to their ephemeral nature. Third, we study how client misbehaviour can impact the guarantees of causal consistency. We propose new secure weak consistency models for insecure settings, and algorithms to enforce such consistency models. The experimental evaluation of our contributions have shown their specic benets and limitations compared with the state-of-the-art. In general, the cloud-edge hybrid model leads to faster application response times, lower client-to-client latency, higher system scalability as fewer clients need to connect to servers at the same time, the possibility to work oine or disconnected from the server, and reduced server bandwidth usage. In summary, we propose a hybrid of cloud-and-edge which provides lower user-to-user la- tency, availability under server disconnections, and improved server scalability – while being ecient, reliable, and secure.Muitas aplicações modernas são criadas para fornecer interações entre utilizadores, incluindo jogos multiutilizador, redes sociais e ferramentas colaborativas. Os utilizadores esperam que o tempo de resposta nas aplicações seja da ordem de milissegundos, promovendo a interação e interatividade. A arquitetura dessas aplicações normalmente adota um modelo cliente-servidor, onde todas as interações são mediadas por um componente centralizado. Essa abordagem apresenta problemas de disponibilidade e tolerância a falhas, que podem ser mitigadas com replicação no componente do servidor, até com a utilização de soluções replicadas geogracamente em infraestruturas de computação na nuvem. Mesmo neste caso, o modelo de comunicação cliente-servidor leva a penalidades de latência desnecessárias para clientes geogracamente próximos e altos custos operacionais para o provedor das aplicações. Esta dissertação propõe um modelo híbrido cloud-edge com mecanismos seguros e ecientes de propagação e consistência. Esse modelo combina replicação do lado do cliente e propagação de cliente para cliente para fornecer baixa latência e minimizar a dependência na infraestrutura do servidor, promovendo a disponibilidade e tolerância a falhas. Para realizar este modelo, este trabalho faz as seguintes contribuições principais. Primeiro, o modelo híbrido cloud-edge é materializado por uma arquitetura do sistema em que os clientes mantêm réplicas dos dados e sincronizam de maneira ponto a ponto e onde os servidores são usados para auxiliar na operação dos clientes. Estudamos como trazer a maior parte da lógica das aplicações para o lado do cliente, usando o serviço centralizado principalmente para durabilidade, controlo de acesso, descoberta e superação das limitações inter-rede. Em segundo lugar, denimos protocolos para replicação de dados fracamente consistentes, incluindo um novo modelo de CRDTs (∆-CRDTs). Fornecemos um estudo sobre replicação parcial, explorando os desaos e limitações fundamentais em fornecer consistência causal e a diculdade em suportar réplicas do lado do cliente devido à sua natureza efémera. Terceiro, estudamos como o mau comportamento da parte do cliente pode afetar as garantias da consistência causal. Propomos novos modelos seguros de consistência fraca para congurações inseguras e algoritmos para impor tais modelos de consistência. A avaliação experimental das nossas contribuições mostrou os benefícios e limitações em comparação com o estado da arte. Em geral, o modelo híbrido cloud-edge leva a tempos de resposta nas aplicações mais rápidos, a uma menor latência de cliente para cliente e à possibilidade de trabalhar oine ou desconectado do servidor. Adicionalmente, obtemos uma maior escalabilidade do sistema, visto que menos clientes precisam de estar conectados aos servidores ao mesmo tempo e devido à redução na utilização da largura de banda no servidor. Em resumo, propomos um modelo híbrido entre a orla (edge) e a nuvem (cloud) que fornece menor latência entre utilizadores, disponibilidade durante desconexões do servidor e uma melhor escalabilidade do servidor – ao mesmo tempo que é eciente, conável e seguro

Media Processing in Video Conferences for Cooperating Over the Top and Operator Based Networks

Telecom operators have dominated the communication industry for a long time by providing services with guaranteed quality of service. Such services are provided by the operator at the cost of maintaining a high grade network. With the introduction of broadband and internet, many over the top (OTT) services have emerged. These services use the underlying operator networks as a mere bit pipe while all service intelligence resides in the application running on the client device. Introduction of OTT services has seen a good response from general users who are no longer bound to services provided by the network operator. This in turn has caused operators and telecom companies to loose the ownership of their customers. This thesis takes media processing in video conferencing as a case study to compare the two competing domains of operator networks and OTT networks. Both domains offer video conferencing to end users, but they follow different architectures. The study shows that OTT services can perform much better if they utilize support of the underlying network. This will also bring the user base back to the network operator. The proposal is to turn the competition into cooperation between both parties. Assessments are done from both technical as well as business perspectives to assert that such cooperative agreements are possible and should be experimented in real life

Network coding meets multimedia: a review

While every network node only relays messages in a traditional communication system, the recent network coding (NC) paradigm proposes to implement simple in-network processing with packet combinations in the nodes. NC extends the concept of "encoding" a message beyond source coding (for compression) and channel coding (for protection against errors and losses). It has been shown to increase network throughput compared to traditional networks implementation, to reduce delay and to provide robustness to transmission errors and network dynamics. These features are so appealing for multimedia applications that they have spurred a large research effort towards the development of multimedia-specific NC techniques. This paper reviews the recent work in NC for multimedia applications and focuses on the techniques that fill the gap between NC theory and practical applications. It outlines the benefits of NC and presents the open challenges in this area. The paper initially focuses on multimedia-specific aspects of network coding, in particular delay, in-network error control, and mediaspecific error control. These aspects permit to handle varying network conditions as well as client heterogeneity, which are critical to the design and deployment of multimedia systems. After introducing these general concepts, the paper reviews in detail two applications that lend themselves naturally to NC via the cooperation and broadcast models, namely peer-to-peer multimedia streaming and wireless networkin

Decentralization of multimedia content in a heterogeneous environment

The aim of this study has been the decentralization of multimedia content in a heterogeneous environment. The environment consisted of the research networks connecting the European Organization for Nuclear Research and the Finnish University and Research Network. The European Organization for Nuclear Research produces multimedia content which can be used as studying material all over the world. The Web University pilot in the European Organization for Nuclear Research has been developing a multimedia content delivery service for years. Delivering the multimedia content requires plenty of capacity from the network infrastructure. Different content of the material can have different demands for the network. In a heterogeneous environment, like the Internet, fulfilling all the demands can be a problem. Several methods exist to improve the situation. Decentralization of the content is one of the most popular solutions. Mirroring and caching are the main methods for decentralization. Recently developed content delivery networks are using both of these techniques to satisfy the demands of the content. The practical application consisted of measurements of the network connection between the multimedia server in the European Organization for Nuclear Research and the Finnish University and Research Network, planning and building a decentralization system for the multimedia content. After the measurements, it became clear that there is n o need for decentralization of the multimedia content for users that are able to utilise the Finnish University and Research Network. There could be double today's usage, and still there would be no problems with the capacity. However, the European Organization for Nuclear Research routes all traffic that comes from outside research networks through a gateway in the USA. This affects every connection that is made from Finland: users are not able to use the international connection offered by the Finnish University and Research Network. For these users I designed and built a simple, modular and portable decentralization system

Scalable reliable on-demand media streaming protocols

This thesis considers the problem of delivering streaming media, on-demand, to potentially large numbers of concurrent clients. The problem has motivated the development in prior work of scalable protocols based on multicast or broadcast. However, previous protocols do not allow clients to efficiently: 1) recover from packet loss; 2) share bandwidth fairly with competing flows; or 3) maximize the playback quality at the client for any given client reception rate characteristics. In this work, new protocols, namely Reliable Periodic Broadcast (RPB) and Reliable Bandwidth Skimming (RBS), are developed that efficiently recover from packet loss and achieve close to the best possible server bandwidth scalability for a given set of client characteristics. To share bandwidth fairly with competing traffic such as TCP, these protocols can employ the Vegas Multicast Rate Control (VMRC) protocol proposed in this work. The VMRC protocol exhibits TCP Vegas-like behavior. In comparison to prior rate control protocols, VMRC provides less oscillatory reception rates to clients, and operates without inducing packet loss when the bottleneck link is lightly loaded. The VMRC protocol incorporates a new technique for dynamically adjusting the TCP Vegas threshold parameters based on measured characteristics of the network. This technique implements fair sharing of network resources with other types of competing flows, including widely deployed versions of TCP such as TCP Reno. This fair sharing is not possible with the previously defined static Vegas threshold parameters. The RPB protocol is extended to efficiently support quality adaptation. The Optimized Heterogeneous Periodic Broadcast (HPB) is designed to support a range of client reception rates and efficiently support static quality adaptation by allowing clients to work-ahead before beginning playback to receive a media file of the desired quality. A dynamic quality adaptation technique is developed and evaluated which allows clients to achieve more uniform playback quality given time-varying client reception rates

Ordering, timeliness and reliability for publish/subscribe systems over WAN

In the last few years, the increasing use of the Internet and geo-political, sociological and financial changes induced by globalization, are paving the way for a connected world where the information is always available at the right place and the right time. As such, applications previously deployed for ``closed'' environmets, are now federating into geographically distributed systems connected through a Wide Area Network (WAN). By this evolution, in the near future no system will be isolated: every system will be composed by interconnected systems, i.e., it will be a System of Systems (SoS). Example of SoS are the Large-scale Complex Critical Infrastructure (LCCIs), such as power grids, transport infrastructures (airports and seaports), financial infrastructures, next generation intelligence platforms, to cite a few. In these systems, multiple sources of information generate a high volume of events that need to be delivered to all intended destinations by respecting several Quality of Service (QoS) constraints imposed by the critical nature of LCCIs. As such, particular attention is devoted to the middleware solution used to disseminate information in the SoS. Due to its inherently scalability provided by space, time and synchronization decoupling properties, the publish/subscribe paradigm is becoming attractive for the implementation of a middleware service for LCCIs. However, scalability is not the only requirement exhibited by SoS. Several services need to control a broader set of QoS requirements, such as timeliness, ordering and reliability. Unfortunately, current middleware solutions do not address QoS constraints required by SoS. Current publish/subscribe middleware solutions for the WAN environment offer only a best effort event dissemination, with no additional control on QoS. Just a few implementations try to address some isolated QoS policy, making them not suitable for a SoS scenario. The contribution of this thesis is to devise a QoS layer that can be posed on top of a generic publish/subscribe middleware that enriches its service by addressing: (i) ordering, (ii) reliability and (iii) timeliness in event dissemination in SoS over WAN. Specifically, we first analyze several real case studies, by highlighting their QoS requirements in terms of ordering, reliability and timeliness, and compare these requirements with both current research prototypes and commercial systems. Then, we fill the gap by proposing novel algorithms to address those requirements. The proposed protocols can also be combined together in order to provide the QoS level required by the particular application. In this way, QoS issues do not need to be addressed at application level, so as to leave applications to implement just their native functionalities

Ordering, timeliness and reliability for publish/subscribe systems over WAN

In the last few years, the increasing use of the Internet and geo-political, sociological and financial changes induced by globalization, are paving the way for a connected world where the information is always available at the right place and the right time. As such, applications previously deployed for ``closed'' environmets, are now federating into geographically distributed systems connected through a Wide Area Network (WAN). By this evolution, in the near future no system will be isolated: every system will be composed by interconnected systems, i.e., it will be a System of Systems (SoS). Example of SoS are the Large-scale Complex Critical Infrastructure (LCCIs), such as power grids, transport infrastructures (airports and seaports), financial infrastructures, next generation intelligence platforms, to cite a few. In these systems, multiple sources of information generate a high volume of events that need to be delivered to all intended destinations by respecting several Quality of Service (QoS) constraints imposed by the critical nature of LCCIs. As such, particular attention is devoted to the middleware solution used to disseminate information in the SoS. Due to its inherently scalability provided by space, time and synchronization decoupling properties, the publish/subscribe paradigm is becoming attractive for the implementation of a middleware service for LCCIs. However, scalability is not the only requirement exhibited by SoS. Several services need to control a broader set of QoS requirements, such as timeliness, ordering and reliability. Unfortunately, current middleware solutions do not address QoS constraints required by SoS. Current publish/subscribe middleware solutions for the WAN environment offer only a best effort event dissemination, with no additional control on QoS. Just a few implementations try to address some isolated QoS policy, making them not suitable for a SoS scenario. The contribution of this thesis is to devise a QoS layer that can be posed on top of a generic publish/subscribe middleware that enriches its service by addressing: (i) ordering, (ii) reliability and (iii) timeliness in event dissemination in SoS over WAN. Specifically, we first analyze several real case studies, by highlighting their QoS requirements in terms of ordering, reliability and timeliness, and compare these requirements with both current research prototypes and commercial systems. Then, we fill the gap by proposing novel algorithms to address those requirements. The proposed protocols can also be combined together in order to provide the QoS level required by the particular application. In this way, QoS issues do not need to be addressed at application level, so as to leave applications to implement just their native functionalities

MediaSync: Handbook on Multimedia Synchronization

This book provides an approachable overview of the most recent advances in the fascinating field of media synchronization (mediasync), gathering contributions from the most representative and influential experts. Understanding the challenges of this field in the current multi-sensory, multi-device, and multi-protocol world is not an easy task. The book revisits the foundations of mediasync, including theoretical frameworks and models, highlights ongoing research efforts, like hybrid broadband broadcast (HBB) delivery and users' perception modeling (i.e., Quality of Experience or QoE), and paves the way for the future (e.g., towards the deployment of multi-sensory and ultra-realistic experiences). Although many advances around mediasync have been devised and deployed, this area of research is getting renewed attention to overcome remaining challenges in the next-generation (heterogeneous and ubiquitous) media ecosystem. Given the significant advances in this research area, its current relevance and the multiple disciplines it involves, the availability of a reference book on mediasync becomes necessary. This book fills the gap in this context. In particular, it addresses key aspects and reviews the most relevant contributions within the mediasync research space, from different perspectives. Mediasync: Handbook on Multimedia Synchronization is the perfect companion for scholars and practitioners that want to acquire strong knowledge about this research area, and also approach the challenges behind ensuring the best mediated experiences, by providing the adequate synchronization between the media elements that constitute these experiences