Boris Koldehofe

Mobile fog: a programming model for large-scale applications on the internet of things

The ubiquitous deployment of mobile and sensor devices is creating a new environment, namely the Internet of Things(IoT), that enables a wide range of future Internet applications. In this work, we present Mobile Fog, a high level programming model for the future Internet applications that are geospatially distributed, large-scale, and latency-sensitive. We analyze use cases for the programming model with camera network and connected vehicle applications to show the efficacy of Mobile Fog. We also evaluate application performance through simulation.

Complex Event Processing

Complex Event Processing (CEP) has evolved into the paradigm of choice for the development of monitoring and reactive applications. It also has a strong impact on future information systems and the way we subscribe to and consume information. Besides being a highly active research field, CEP already plays an important role in many application areas like logistics, energy management, finance, or manufacturing processes. Its importance for information systems is expected to grow further with the increasing number of decentralized information sources, such as blogs, and with the deployment of tagging and sensing technology as well as its integration in real-world objects. CEP addresses two crucial prerequisites to build highly scalable and dynamic systems. First, it decouples providers and receivers of information. Neither the providers need knowledge about the set of relevant receivers, nor do receivers need to know the set of relevant data or event sources. Second, CEP-systems do not only mediate information in form of events between providers and consumers, but support the detection of relationships among events, for instance, temporal relations that can be specified by definition of correlation rules (often called Event Patterns). Through aggregation and composition new complex events can be generated and used subsequently to derive more abstract events. CEP provides a natural decoupling between basic events with a strong relationship to the semantics of the underlying technology (e. g. sensor readings) and complex events closer to the semantics of the application. Therefore, it enables information systems to perform independent reconfigurations at the technical and application level. Furthermore, the stepwise correlation of events can help to reduce the message load and thus contributes towards a highly scalable information system. Business applications are increasingly interconnected and can impose a massive event load to be processed by current CEP systems. Moreover, the importance of sensing devices in applications is expected to grow. In the future, the Internet of Things may comprise billions of sensing devices. CEP will be a tool to derive understandable information on the basis of a large number of events. In this context it is important to support the distribution of event correlation in the presence of highly dynamic systems and support mechanisms for self-organization. Guaranteeing non-functional properties, such as, reliability, availability, performance, and security pose major challenges on the technical infrastructure, while expressiveness of event languages, event derivation and usability are challenges to make CEP accessible to a broader user community. This special issue intends to provide an insight on the applications and principles as well as the evolution of CEP. Moreover, we believe the selected articles from International and German researchers illustrate current trends and challenges in designing powerful, scalable as well as secure event processing systems. The group of Sharma Chakravarthy has a long experience in the field of Complex Event Processing and has designed one of the early and very influential event correlation languages, called Snoop. The work by Chakravarthy et al. gives a historical view on the development as well as the roots of Complex Event Processing. Furthermore, the authors point out important applications and challenges that go hand-in-hand with the development of CEP Systems. Distributed event-based systems are the key to increase the scalability of today’s information systems. Jacobsen et al. present the PADRES system which addresses the design of adaptive event-based systems. In their approach they show how content-based publish/subscribe systems can be extended to account also for composition of complex events as well as enable uniform query mechanisms for events in the future and the past. While in the past many efforts have focused on the design of efficient and expressive event-based systems, it is often hard to estimate the performance of eventbased systems in combination with QoS requirements of applications. The work by Kounev and Sachs bridges this gap by reviewing and proposing performance models that fit Distributed Event-Based Systems particularly well. Although the benefits of distributed event-based systems are often highlighted by researchers, so far most industrial solutions still rely on centralized event processing technology. Pletat et al. identify in their article one obstacle in deploying distributed event processing

Evaluating the educational impact of visualization

The educational impact of visualization depends not only on how well students learn when they use it, but also on how widely it is used by instructors. Instructors believe that visualization helps students learn. The integration of visualization techniques in classroom instruction, however, has fallen far short of its potential. This paper considers this disconnect, identifying its cause in a failure to understand the needs of a key member in the hierarchy of stakeholders, namely the instructor. We describe these needs and offer guidelines for both the effective deployment of visualizations and the evaluation of instructor satisfaction. We then consider different forms of evaluation and the impact of student learning styles on learner outcomes.

MigCEP: operator migration for mobility driven distributed complex event processing

A recent trend in communication networks --- sometimes referred to as fog computing --- offers to execute computational tasks close to the access points of the networks. This enables real-time applications, like mobile Complex Event Processing (CEP), to significantly reduce end-to-end latencies and bandwidth usage. Most work studying the placement of operators in such an environment completely disregards the migration costs. However, the mobility of users requires frequent migration of operators, together with possibly large state information, to meet latency restrictions and save bandwidth in the infrastructure. This paper presents a placement and migration method for providers of infrastructures that incorporate cloud and fog resources. It ensures application-defined end-to-end latency restrictions and reduces the network utilization by planning the migration ahead of time. Furthermore, we present how the application knowledge of the CEP system can be used to improve current live migration techniques for Virtual Machines to reduce the required bandwidth during the migration. Our evaluations show that we safe up to 49% of the network utilization with perfect knowledge about a users mobility pattern and up to 27% of the network utilization when considering the uncertainty of those patterns.

Securing Broker-Less Publish/Subscribe Systems Using Identity-Based Encryption

The provisioning of basic security mechanisms such as authentication and confidentiality is highly challenging in a content-based publish/subscribe system. Authentication of publishers and subscribers is difficult to achieve due to the loose coupling of publishers and subscribers. Likewise, confidentiality of events and subscriptions conflicts with content-based routing. This paper presents a novel approach to provide confidentiality and authentication in a broker-less content-based publish/subscribe system. The authentication of publishers and subscribers as well as confidentiality of events is ensured, by adapting the pairing-based cryptography mechanisms, to the needs of a publish/subscribe system. Furthermore, an algorithm to cluster subscribers according to their subscriptions preserves a weak notion of subscription confidentiality. In addition to our previous work , this paper contributes 1) use of searchable encryption to enable efficient routing of encrypted events, 2) multicredential routing a new event dissemination strategy to strengthen the weak subscription confidentiality, and 3) thorough analysis of different attacks on subscription confidentiality. The overall approach provides fine-grained key management and the cost for encryption, decryption, and routing is in the order of subscribed attributes. Moreover, the evaluations show that providing security is affordable w.r.t. 1) throughput of the proposed cryptographic primitives, and 2) delays incurred during the construction of the publish/subscribe overlay and the event dissemination.

Cordies: expressive event correlation in distributed systems

Complex Event Processing (CEP) is the method of choice for the observation of system states and situations by means of events. A number of systems have been introduced that provide CEP in selected environments. Some are restricted to centralised systems, or to systems with synchronous communication, or to a limited space of event relations that are defined in advance. Many modern systems, though, are inherently distributed and asynchronous, and require a more powerful CEP. We present Cordies, a distributed system for the detection of correlated events that is designed for the operation in large-scale, heterogeneous networks and adapts dynamically to changing network conditions. With its expressive language to describe event relations, it is suitable for environments where neither the event space nor the situations of interest are predefined but are constantly adapted. In addition, Cordies supports Quality-of-Service (QoS) for communication in distributed event correlation detection.

Meeting subscriber-defined QoS constraints in publish/subscribe systems

Current distributed publish/subscribe systems consider all participants to have similar QoS requirements and contribute equally to the systems resources. However, in many real‐world applications, the message delay tolerance of individual participants may differ widely. Disseminating messages according to individual delay requirements not only allows for the satisfaction of user‐specific needs, but also significantly improves the utilization of the resources that participants contribute to a publish/subscribe system. In this article, we propose a peer‐to‐peer‐based approach to satisfy the individual delay requirements of subscribers in the presence of bandwidth constraints. Our approach allows subscribers to dynamically adjust the granularity of their subscriptions according to their bandwidth constraints and delay requirements. Subscribers maintain the overlay in a decentralized manner, exclusively establishing connections that satisfy their individual delay requirements, and that provide messages exactly meeting their subscription granularity. The evaluations show that for many practical workloads, the proposed publish/subscribe system can scale up to a large number of subscribers and performs robustly in a very dynamic setting. Copyright

The power of software-defined networking: line-rate content-based routing using OpenFlow

A lot of research effort has been invested to support efficient content-based routing. Nevertheless, practitioners often fall back to far less expressive communication paradigms like multicast groups. The benefits of content-based routing in minimizing bandwidth consumption are often rendered useless by simpler communication paradigms that rely on line-rate processing of data packets at the switches of the network providers. Contrary content-based routing protocols face the inherent overhead in matching the content of events against subscriptions leading to far lower throughput rates and higher end-to-end delays. However, recent trends in networking such as software defined networking in combination with network virtualization have tremendous potential to change the picture. In our opinion this will significantly increase acceptance of sophisticated middleware like content-based routing in the future. To support our claims we outline in this paper a reference architecture that may be used to build middleware for Future Internet applications. Furthermore, we provide a solution for realizing content-based routing at line-rate relying on this reference architecture and illustrate research problems that need to be addressed.

Distributed spectral cluster management: a method for building dynamic publish/subscribe systems

In recent years peer-to-peer (P2P) networking has gained high popularity for large-scale content distribution. Prominent systems expect a large user base with rather diversified demands. Yet it is highly challenging to achieve scalability without sacrificing the expressiveness of queries in such systems. This paper proposes distributed spectral cluster management, an approach which adapts the techniques from spectral graph theory to work in distributed settings. The proposed approach is applied to content-based publish/subscribe to i) significantly reduce the cost for event dissemination by clustering subscribers exploiting the similarity of events, ii) preserve the expressiveness of the subscription language, and iii) perform robustly in the presence of workload variations. The evaluations analyze the accuracy of the proposed distributed spectral mechanisms and show their effectiveness to significantly reduce the efforts to disseminate events under many practical workloads.

MCEP: A Mobility-Aware Complex Event Processing System

With the proliferation of mobile devices and sensors, complex event proceesing (CEP) is becoming increasingly important to scalably detect situations in real time. Current CEP systems are not capable of dealing efficiently with highly dynamic mobile consumers whose interests change with their location. We introduce the distributed mobile CEP (MCEP) system which automatically adapts the processing of events according to a consumers location. MCEP significantly reduces latency, network utilization, and processing overhead by providing on-demand and opportunistic adaptation algorithms to dynamically assign event streams and computing resources to operators of the MCEP system.