Delivering Consistent Network Performance in Multi-tenant Data Centers

Data centers are growing rapidly in size and have recently begun acquiring a new role as cloud hosting platforms, allowing outside developers to deploy their own applications on large scales. As a result, today\u27s data centers are multi-tenant environments that host an increasingly diverse set of applications, many of which have very demanding networking requirements. This has prompted research into new data center architectures that offer increased capacity by using topologies that introduce multiple paths between servers. To achieve consistent network performance in these networks, traffic must be effectively load balanced among the available paths. In addition, some form of system-wide traffic regulation is necessary to provide performance guarantees to tenants. To address these issues, this thesis introduces several software-based mechanisms that were inspired by techniques used to regulate traffic in the interconnects of scalable Internet routers. In particular, we borrow two key concepts that serve as the basis for our approach. First, we investigate packet-level routing techniques that are similar to those used to balance load effectively in routers. This work is novel in the data center context because most existing approaches route traffic at the level of flows to prevent their packets from arriving out-of-order. We show that routing at the packet-level allows for far more efficient use of the network\u27s resources and we provide a novel resequencing scheme to deal with out-of-order arrivals. Secondly, we introduce distributed scheduling as a means to engineer traffic in data centers. In routers, distributed scheduling controls the rates between ports on different line cards enabling traffic to move efficiently through the interconnect. We apply the same basic idea to schedule rates between servers in the data center. We show that scheduling can prevent congestion from occurring and can be used as a flexible mechanism to support network performance guarantees for tenants. In contrast to previous work, which relied on centralized controllers to schedule traffic, our approach is fully distributed and we provide a novel distributed algorithm to control rates. In addition, we introduce an optimization problem called backlog scheduling to study scheduling strategies that facilitate more efficient application execution

Sliver: A BPEL Workflow Process Execution Engine for Mobile Devices

The Business Process Execution Language (BPEL) has become the dominant means for expressing traditional business processes as workflows. The widespread deployment of mobile devices like PDAs and mobile phones has created a vast computational and communication resource for these workflows to exploit. However, BPEL so far has been deployed only on relatively heavyweight server platforms such as Apache Tomcat, leaving the potential created by these lower-end devices untapped. This paper presents Sliver, a BPEL workflow process execution engine that supports a wide variety of devices ranging from mobile phones to desktop PCs. We discuss the design decisions that allow Sliver to operate within the limited resources of a mobile phone or PDA. We also evaluate the performance of a prototype implementation of Sliver

Supporting Collaborative Behavior in MANETs using Workflows

Groupware activities provide a powerful representation for many collaborative tasks. Today, the technologies that support typical groupware applications often assume a stable wired network infrastructure. The potential for collaboration in scenarios that lack this fixed infrastructure remains largely untapped. Such scenarios include activities on construction sites, wilderness exploration, disaster recovery, and rapid intervention teams. Communication in these scenarios can be supported using wireless ad hoc networks, an emerging technology whose full potential is yet to be understood and realized. In this paper, we consider the fundamental technical issues that need to be addressed in order to introduce groupware concepts into mobile ad hoc networks. Starting with a simple workflow model, we examine the process of allocating its actions to physically-mobile agents in a manner that accommodates transient communication and runtime errors

MobiWork: Mobile Workflow for MANETs

The workflow model is well suited for scenarios where many entities work collaboratively towards a common goal, and is used widely today to model complex business processes. However, the fundamental workflow model is very powerful and can be applied to a wider variety of application domains. This paper represents an initial investigation into the possibility of using workflows to model collaboration in an ad hoc mobile environment. Moving to a mobile setting introduces many challenges as the mobility of the participants in a workflow imposes constraints on allocation of workflow tasks, coordination among participants, and marshaling of results. We present an algorithm that heuristically allocates tasks to participants based on their capabilities and mobility and discuss the architecture and implementation of MobiWork, our prototype system that allocates and executes workflows in an ad hoc mobile environment. An evaluation of the performance of our heuristic algorithm is also presented

Performance-Engineered Network Overlays for High Quality Interaction in Virtual Worlds

Overlay hosting systems such as PlanetLab, and cloud computing environments such as Amazon’s EC2, provide shared infrastructures within which new applications can be developed and deployed on a global scale. This paper ex-plores how systems of this sort can be used to enable ad-vanced network services and sophisticated applications that use those services to enhance performance and provide a high quality user experience. Specifically, we investigate how advanced overlay hosting environments can be used to provide network services that enable scalable virtual world applications and other large-scale distributed applications requiring consistent, real-time performance. We propose a novel network architecture called Forest built around per-session tree-structured communication channels that we call comtrees. Comtrees are provisioned and support both unicast and multicast packet delivery. The multicast mechanism is designed to be highly scalable and light-weight enough to support the rapid changes to multicast subscriptions needed for efficient support of state updates within virtual worlds. We evaluate performance using a combination of analysis and experimental measurement of a partial system prototype that supports fully functional distributed game sessions. Our results provide the data needed to enable accurate projections of performance for a variety of session and system configurations

Supercharged PlanetLab Platform Architecture

This report describes the Supercharged Planetlab Platform (SPP), a system designed as a prototype of an internet-scale overlay hosting platform. Overlay networks have become an important vehicle for delivering Internet applications. Overlay network nodes are typically implemented using general purpose servers or clusters. The SPP offers a more integrated architecture, combining general-purpose servers with high performance Network Processor (NP) subsystems. SPP nodes have recently been deployed as part of the Global Environment for Network Innovation (GENI) and are available for use by research users

Continuous learning approach towards the professional development school in practice

The paper aims at designing a developmental model which could evaluate and support the reform in the Netherlands, called professional development school (PDS). PDS refers to collaboration between school and educational institution wherein the professional development of teachers is supported by specific conditions (Holmes Group, 1990 in Bergen, 2006). The higher education reform aims at implementing a better quality of education for primary school teachers. Two higher education institutions and five primary schools participate in this project. Document analysis, literature study and semi-structured interviews were carried out in order to design the model of PDS. There were 12 participants in the interview, namely, representatives from educational institutions, primary school coaches, primary school directors, students and PDS project leaders. There were 5 developmental models designed representing 4 significant perspectives in PDS. The results of the research indicate that the most helpful model to capture the development of PDS is a learning organisation model based on the comprehensive learning organisation theory (Watkins & Marsick, 1993; Watkins, Yang & Marsick, 2004). However, the design and application of the developmental learning organisation model is a challenging and creative task. Thus, the paper describes the concept of PDS and its application in practice simultaneously presenting different perspectives and models how to capture the development of PDS. Finally, it concludes with the discussion.(DIPF/Orig.

Sliver: A BPEL Workflow Process Execution Engine for Mobile Devices

Abstract. The Business Process Execution Language (BPEL) has become the dominant means for expressing traditional business processes as workflows. The widespread deployment of mobile devices like PDAs and mobile phones has created a vast computational and communication resource for these workflows to exploit. However, BPEL so far has been deployed only on relatively heavyweight server platforms such as Apache Tomcat, leaving the potential created by these lower-end devices untapped. This paper presents Sliver, a BPEL workflow process execution engine that supports a wide variety of devices ranging from mobile phones to desktop PCs. We discuss the design decisions that allow Sliver to operate within the limited resources of a mobile phone or PDA. We also evaluate the performance of a prototype implementation of Sliver.