Clock Hierarchies: An Abstraction for Grouping and controlling Media Systems

Synchronization plays an important role in multimedia systems at various levels of abstraction. In this paper, we propose a set of powerful abstractions for controlling and synchronizing continuous media streams in distributed environments. The proposed abstractions are based on a very general computation model, which allows media streams to be processed (i.e. produced, consumed or transformed) by arbitrarily structured networks of linked components. Further, compound components can be composed of existing ones to provide higher levels of abstractions. The clock abstraction is provided to control individual media streams, i.e. streams can be started, paused or scaled by issuing the appropriate clock operations. Clock hierarchies are used to hierarchically group related streams, where each clock in the hierarchy identifies and controls a certain (sub)group of streams. Control and synchronization requirements can be expressed in a uniform manner by associating group members with control or sync attributes. An important property of the concept of clock hierarchies is that it can be combined in a natural way with component nesting

P4CEP: Towards In-Network Complex Event Processing

In-network computing using programmable networking hardware is a strong trend in networking that promises to reduce latency and consumption of server resources through offloading to network elements (programmable switches and smart NICs). In particular, the data plane programming language P4 together with powerful P4 networking hardware has spawned projects offloading services into the network, e.g., consensus services or caching services. In this paper, we present a novel case for in-network computing, namely, Complex Event Processing (CEP). CEP processes streams of basic events, e.g., stemming from networked sensors, into meaningful complex events. Traditionally, CEP processing has been performed on servers or overlay networks. However, we argue in this paper that CEP is a good candidate for in-network computing along the communication path avoiding detouring streams to distant servers to minimize communication latency while also exploiting processing capabilities of novel networking hardware. We show that it is feasible to express CEP operations in P4 and also present a tool to compile CEP operations, formulated in our P4CEP rule specification language, to P4 code. Moreover, we identify challenges and problems that we have encountered to show future research directions for implementing full-fledged in-network CEP systems.Comment: 6 pages. Author's versio

gSPICE: Model-Based Event Shedding in Complex Event Processing

Overload situations, in the presence of resource limitations, in complex event processing (CEP) systems are typically handled using load shedding to maintain a given latency bound. However, load shedding might negatively impact the quality of results (QoR). To minimize the shedding impact on QoR, CEP researchers propose shedding approaches that drop events/internal state with the lowest importances/utilities. In both black-box and white-box shedding approaches, different features are used to predict these utilities. In this work, we propose a novel black-box shedding approach that uses a new set of features to drop events from the input event stream to maintain a given latency bound. Our approach uses a probabilistic model to predict these event utilities. Moreover, our approach uses Zobrist hashing and well-known machine learning models, e.g., decision trees and random forests, to handle the predicted event utilities. Through extensive evaluations on several synthetic and two real-world datasets and a representative set of CEP queries, we show that, in the majority of cases, our load shedding approach outperforms state-of-the-art black-box load shedding approaches, w.r.t. QoR