Sumeer Bhola

SMash: secure component model for cross-domain mashups on unmodified browsers

Mashup applications mix and merge content (data and code) from multiple content providers in a users browser, to provide high-value web applications that can rival the user experience provided by desktop applications. Current browser security models were not designed to support such applications and they are therefore implemented with insecure workarounds. In this paper, we present a secure component model, where components are provided by different trust domains, and can interact using a communication abstraction that allows ease of specification of a security policy. We have developed an implementation of this model that works currently in all major browsers, and addresses challenges of communication integrity and frame-phishing. An evaluation of the performance of our implementation shows that this approach is not just feasible but also practical.

Congestion control in a reliable scalable message-oriented middleware

This paper presents congestion control mechanisms for reliable and scalable message-oriented middleware following the publish/subscribe communication model. We identify the key requirements of congestion control in this environment, how it differs from congestion control for the Internet, and propose a combination of two congestion control mechanisms, (1) driven by a publisher hosting broker (PDCC), (2) driven by a subscriber hosting broker (SDCC). SDCC decouples the notion of a receive window and a NACK window, and is used by subscriber hosting brokers in recovery mode. PDCC implements a scalable and low latency feedback loop between a publisher hosting broker and all subscriber hosting brokers, which is used to adjust the rate of publishing new messages, to allow brokers in recovery to eventually catch up, and other brokers to keep up. We present a detailed experimental evaluation of our implementation of these mechanisms in the Gryphon system by injecting network failures and link congestion.

Scalably supporting durable subscriptions in a publish/subscribe system

We describe algorithms to scalably support durable subscriptions in a publish-subscribe system. Durable subscriptions are guaranteed exactly-once message delivery, despite periods of disconnection from the system. Our algorithms persistently log each message only once in the system, and can support administratively specified ’early-release’ policies that reclaim persistent storage in the presence of misbehaving durable subscribers. To efficiently recover messages missed by a disconnected durable subscriber, without refiltering messages published while the subscriber was disconnected, we persistently log filtering information in a manner optimized for the read/write pattern of durable subscriptions. Consolidation of data-structures across all subscribers that are done with catching up (after a disconnection), helps the system support a larger number of subscribers. We experimentally demonstrate the low-latency and scalability properties of our implementation, both in the presence and absence of failures.

Utility-aware Resource Allocation in an Event Processing System

Event processing systems link event producers and consumers in a flexible manner, by supporting multiple communication patterns and powerful message transformations. Such systems support both loosely coupled communication patterns, such as one-to-one or one-to-many and tightly coupled (request-response) patterns. An important concern in these systems is the allocation of resources used to support event processing. These include traditional constrained resources such as CPU and network, as well as an increasing reliance on storage resources. For instance, transactional and reliable producers require events to be logged to stable storage. In this paper we consider the problem of utility driven allocation of these resources, taking into account resource capacity. In contrast to previous work, we (1) develop a unified utility model to deal with throughput requirements of one-way flows and latency requirements of request-response flows, (2) differentiate between classes of consumers for one-to-many flows and subject these classes to consumer admission control, (3) compute system optimization constraints using both resource bandwidth and latency and (4) develop a control architecture that combines periodic optimization with continuous rate control, both of which are utility aware. We describe an experimental evaluation of our approach on a prototype event processing server.

Pulsar: a resource-control architecture for time-critical service-oriented applications

The complexity of real-time systems is growing extremely rapidly, as they move from isolated devices to multilevel networked systems. Traditional methodologies for developing and managing these systems are not scaling to meet the requirements of a new generation of distributed applications. While developers of complex real-time applications are looking to service-oriented architecture to address their needs for ease of development and flexibility of integration, current software infrastructures for service-oriented applications do not address the issue of predictable latency for the applications they host. In this paper, we present Pulsar, a resource-control architecture for managing the end-to-end latency of a set of distributed, time-critical applications. The primary entity of Pulsar is called a controller, which regulates an aspect of resource allocation or scheduling policy. Controllers utilize policy configurations, which may include latency targets to be achieved or resource allocations to be honored, and interact with resource allocators and schedulers (e.g., thread schedulers, memory allocators, or bandwidth reservation mechanisms) to effect local policy. Controllers also provide feedback on how well they are executing a policy. Pulsar includes an application model which captures resource-sensitive behavior and requirements and is independent of high-level programming models and application programming interfaces.

Utility Optimization for Event-Driven Distributed Infrastructures

Event-driven distributed infrastructures are becoming increasingly important for information dissemination and application integration. We examine the problem of optimal resource allocation for such an infrastructure composed of an overlay of nodes. Resources, like CPU and network bandwidth, are consumed by both message flows and message consumers; therefore, we consider both rate control for flows and admission control for consumers. This makes the optimization problem difficult because the objective function is nonconcave and the constraint set is nonconvex. We present LRGP (Lagrangian Rates, Greedy Populations), a scalable and efficient distributed algorithm to maximize the total system utility. The key insight of our solution involves partitioning the optimization problem into two types of subproblems: a greedy allocation for consumer admission control and a Lagrangian allocation to compute the flow rates, and linking the subproblems in a manner that allows tradeoffs between consumer admission and flow rates while satisfying the nonconvex constraints. LRGP allows an autonomic approach to system management where nodes collaboratively optimize aggregate system performance. We evaluate the quality of results and convergence characteristics under various workloads.

Villa: an event based middleware for real-time collaboration on the Internet

It is becoming increasingly clear that the next generation of Internet applications will involve the efficient exchange of real-time information. The current Internet technology does not provide sufficient support for such applications. Instead, the current protocols and engines on the Internet are designed for static information browsing. A primary goal of this research project is to study the requirements of Internet applications requiring extensive real-time information exchange and to develop a framework and the required middleware which can be used to write such scalable collaborative applications over the Internet. This paper describes the architecture and the implementation of such a system called Villa. Villa is based on an asynchronous event-based toolkit and is designed to build scalable collaborative applications over the Internet.

Middleware support for scalable services

Services targeted to the home environment must deal with software and hardware heterogeneity of client and server machines. Distributed object based middleware is attractive for building distributed services in such heterogeneous environments for a number of reasons. In particular, distributed objects can hide the complexities that arise from distribution and heterogeneity in the underlying system. To deal with the scale of home based applications and to reduce the effects of high latencies in such environments, we have been exploring efficient implementations of distributed object systems that exploit caching and replication of service state. In this paper, we explore issues related to object state caching and communication for distributed object systems.

Subscription propagation and content-based routing with delivery guarantees

Subscription propagation enables efficient content-based routing in publish/subscribe systems and is a challenging problem when it is required to support reliable delivery in networks with redundant routes. We have designed a generic model and a highly-asynchronous algorithm accomplishing these goals. Existing algorithms can be interpreted as different encodings and optimizations of the generic algorithm and hence their correctness can be derived from the generic algorithm.