A collaborative Web browsing session may take place over a network, allowing the presenter on a first computer to direct the audio and visual components of a browser on one or more second computers. The second computer is instructed to log into a control site that downloads an active control, such as an applet, to the second computer. The present invention allows a collaborative Web browsing session ('session'), as created by the presenter and witnessed by one or more users on second computers, to be recorded and archived by the control site. When a user of a computer is connected to the control site through a communication network such as the World Wide Web, that user may log into the control site and request to view an archived session. The session will then be replayed by the control site on the user's computer, directing the audio and visual components of the browser on the user's computer as if the user was attending the live session. The recorded session replays the events of the live session in real time such that the playback experience contains the same audio and visual events that took place when the session was originally being recorded.

System and method for record and playback of collaborative web browsing session

We consider the problem of fair resource allocation in a system containing different resource types, where each user may have different demands for each resource. To address this problem, we propose Dominant Resource Fairness (DRF), a generalization of max-min fairness to multiple resource types. We show that DRF, unlike other possible policies, satisfies several highly desirable properties. First, DRF incentivizes users to share resources, by ensuring that no user is better off if resources are equally partitioned among them. Second, DRF is strategy-proof, as a user cannot increase her allocation by lying about her requirements. Third, DRF is envy-free, as no user would want to trade her allocation with that of another user. Finally, DRF allocations are Pareto efficient, as it is not possible to improve the allocation of a user without decreasing the allocation of another user. We have implemented DRF in the Mesos cluster resource manager, and show that it leads to better throughput and fairness than the slot-based fair sharing schemes in current cluster schedulers.

https://static.usenix.org/event/nsdi11/tech/full_papers/Ghodsi.pdf

Dominant resource fairness: fair allocation of multiple resource types

View-oriented group communication is an important and widely used building block for many distributed applications. Much current research has been dedicated to specifying the semantics and services of view-oriented group communication systems (GCSs). However, the guarantees of different GCSs are formulated using varying terminologies and modeling techniques, and the specifications vary in their rigor. This makes it difficult to analyze and compare the different systems. This survey provides a comprehensive set of clear and rigorous specifications, which may be combined to represent the guarantees of most existing GCSs. In the light of these specifications, over 30 published GCS specifications are surveyed. Thus, the specifications serve as a unifying framework for the classification, analysis, and comparison of group communication systems. The survey also discusses over a dozen different applications of group communication systems, shedding light on the usefulness of the presented specifications. This survey is aimed at both system builders and theoretical researchers. The specification framework presented in this article will help builders of group communication systems understand and specify their service semantics; the extensive survey will allow them to compare their service to others. Application builders will find a guide here to the services provided by a large variety of GCSs, which could help them choose the GCS appropriate for their needs. The formal framework may provide a basis for interesting theoretical work, for example, analyzing relative strengths of different properties and the costs of implementing them.

/pdf/group-communication-specifications-a-comprehensive-study-3qr5fuqw6l.pdf

Group communication specifications: a comprehensive study

This paper focuses on the problem of providing efficient run-time support to multimedia applications in a real-time system, where two types of tasks can coexist simultaneously: multimedia soft real-time tasks and hard real-time tasks. Hard tasks are guaranteed based on worst case execution times and minimum interarrival times, whereas multimedia and soft tasks are served based on mean parameters. The paper describes a server-based mechanism for scheduling soft and multimedia tasks without jeopardizing the a priori guarantee of hard real-time activities. The performance of the proposed method is compared with that of similar service mechanisms through extensive simulation experiments and several multimedia applications have been implemented on the HARTIK kernel.

/pdf/integrating-multimedia-applications-in-hard-real-time-4yc0jax79v.pdf

Integrating multimedia applications in hard real-time systems

Tools to understand complex system behaviour are essential for many performance analysis and debugging tasks, yet there are many open research problems in their development. Magpie is a toolchain for automatically extracting a system's workload under realistic operating conditions. Using low-overhead instrumentation, we monitor the system to record fine-grained events generated by kernel, middleware and application components. The Magpie request extraction tool uses an application-specific event schema to correlate these events, and hence precisely capture the control flow and resource consumption of each and every request. By removing scheduling artefacts, whilst preserving causal dependencies, we obtain canonical request descriptions from which we can construct concise workload models suitable for performance prediction and change detection. In this paper we describe and evaluate the capability of Magpie to accurately extract requests and construct representative models of system behaviour.

/pdf/using-magpie-for-request-extraction-and-workload-modelling-1gfx849p4j.pdf

Using magpie for request extraction and workload modelling

We propose and analyze a proportional share resource allocation algorithm for realizing real-time performance in time-shared operating systems. Processes are assigned a weight which determines a share (percentage) of the resource they are to receive. The resource is then allocated in discrete-sized time quanta in such a manner that each process makes progress at a precise, uniform rate. Proportional share allocation algorithms are of interest because: they provide a natural means of seamlessly integrating real and non-real-time processing; they are easy to implement; they provide a simple and effective means of precisely controlling the real-time performance of a process; and they provide a natural means of policing so that processes that use more of a resource than they request have no ill-effect on well-behaved processes. We analyze our algorithm in the context of an idealized system in which a resource is assumed to be granted in arbitrarily small intervals of time and show that our algorithm guarantees that the difference between the service time that a process should receive and the service time it actually receives is optimally bounded by the size of a time quantum. In addition, the algorithm provides support for dynamic operations, such as processes joining or leaving the competition, and for both fractional and non-uniform time quanta. As a proof of concept we have implemented a prototype of a CPU scheduler under FreeBSD. The experimental results shows that our implementation performs within the theoretical bounds and hence supports real-time execution in a general purpose operating system.

A proportional share resource allocation algorithm for real-time, time-shared systems

XTV is a distributed system for sharing X Window applications synchronously among a group of remotely located users at workstations running X and interconnected by the Internet. The major components of the system are designed and implemented in such a way that make them reusable in other collaborative systems and applications. A description is presented of the fine technical details and knowledge required to understand and replicate the work which went into developing XTV. The following concepts are discussed: interception, distribution and translation of traffic between X clients and display servers; regulation of access to tools using a token passing mechanism and reverse-translation of server traffic; and accommodation of systems with different architectures which may have different byte orders for integer representation. >

XTV: a framework for sharing X Window clients in remote synchronous collaboration

Now that cellular networks are being called upon to support real-time interactive multimedia traffic such as video teleconferencing, these networks must be able to provide their users with quality-of-service (QoS) guarantees. Although the QoS provisioning problem arises in wireline networks as well, mobility of hosts, scarcity of bandwidth, and channel fading make QoS provisioning a challenging task in wireless networks. It has been noticed that multimedia applications can tolerate and gracefully adapt to transient fluctuations in the QoS that they receive from the network. The management of such adaptive multimedia applications is becoming a new research area in wireless networks. As it turns out, the additional flexibility afforded by the ability of multimedia applications to tolerate and adapt to transient changes in the QoS parameters can be exploited by protocol designers to significantly improve the overall performance of wireless systems. The main contribution of this paper is to propose a novel, rate-based, borrowing scheme for QoS provisioning in high-speed cellular networks carrying multimedia traffic. Our scheme attempts to allocate the desired bandwidth to every multimedia connection originating in a cell or being handed off to the cell. The novelty of our scheme is that, in case of insufficient bandwidth, in order not to deny service to requesting connections (new or hand-off), bandwidth will be borrowed, on a temporary basis, from existing connections. Our borrowing scheme guarantees that no connection gives up more than its fair share of bandwidth, in the sense that the amount of bandwidth borrowed from a connection is proportional to its tolerance to bandwidth loss. Importantly, our scheme ensures that the borrowed bandwidth is promptly returned to the degraded connections. Extensive simulation results show that our rate-based QoS provisioning scheme outperforms the best previously known schemes in terms of call dropping probability, call blocking probability, and bandwidth utilization.

/pdf/rate-based-borrowing-scheme-for-qos-provisioning-in-4pq3olm6p4.pdf

Rate-based borrowing scheme for QoS provisioning in multimedia wireless networks

We describe a new framework for resource allocation that unifies the well-known proportional share and reservation policies. By exploiting the duality between these policies, we provide a level of integration for scheduling batch, interactive, and real time applications not achieved before. To each client we associate a weight that represents the rate at which the client has to pay for the resource, and a share that represents the fraction of the resource that the client should receive. These two parameters are interdependent. A fixed rate corresponds to a proportional share allocation, while a fixed share corresponds to a reservation. Furthermore, once one parameter is fixed the other one results automatically: if a client asks for a fixed share then the competition for the resource determines the rate at which it has to pay, while if the rate is fixed, the competition determines the service time the client should receive. To implement this framework we have developed a new proportional share algorithm, called Earliest Eligible Virtual Deadline First, that achieves optimal accuracy, i.e., the difference between the service time that a client should receive in an ideal system, and the service time it has actually received in the real system is bounded by the size of a time quantum. This tight bound makes it possible to provide support for highly predictable, real-time services. As a proof of concept we have implemented a prototype of a CPU scheduler under the FreeBSD operating system. The experimental results show that our scheduler achieves the goal of providing integrated support for batch and real-time applications. Moreover, the accuracy of our implementation was within 10% of the theoretical bounds.

/pdf/on-the-duality-between-resource-reservation-and-proportional-55mgr8dzvi.pdf

On the Duality between Resource Reservation and Proportional Share Resource Allocation

Many distance learning systems claim to be interactive, but few can offer two-way video, on-the-fly interaction and application sharing. To address these limitations, our research group built the Interactive Remote Instruction (IRI) system, which links sites over a high-speed intranet, allowing students at geographically dispersed satellite campuses and community colleges to take a class together. Access from home PCs through a Windows NT port is planned but not yet available. IRI improves on the Old Dominion University's Teletechnet system in five areas: video resolution, asymmetrical video presence, interaction, teacher support and computer simulations.

Hussein Abdel-Wahab

Papers

A proportional share resource allocation algorithm for real-time, time-shared systems

XTV: a framework for sharing X Window clients in remote synchronous collaboration

Rate-based borrowing scheme for QoS provisioning in multimedia wireless networks

On the Duality between Resource Reservation and Proportional Share Resource Allocation

Interactive distance learning over intranets