2987131
Interface-Based Rate Analysis of Embedded Systems
Interface-based design is now considered to be one of the keys to tackling the increasing complexity of modern embedded systems. The central idea is that different components comprising such systems can be developed independently and a system designer can connect them together only if their interfaces match, without knowing the details of their internals. We use the concept of rate interfaces for compositional (correct-by-construction) design of embedded systems whose components communicate through data streams. Using the associated rate interface algebra, two components can be connected together if the output rate of one component is "compatible" with the input rate of the other component. We formalize this notion of compatibility and show that such an algebra is non-trivial because it has to accurately model the burstiness in the arrival rates of such data streams and the variability in their processing requirements. We discuss how rate interfaces simplify compositional design and at the same time help in functional and performance verification which would be difficult to address otherwise. Finally, we illustrate these advantages through a realistic case study involving a component-based design of a multiprocessor architecture running a picture-in-picture application
16964204
Workload characterization and cost-quality tradeoffs in MPEG-4 decoding on resource-constrained devices
There has been a lot of interest in the embedded systems community on architectures and design methods that are targeted towards multimedia applications. This trend is pri marily motivated by the proliferation of resource and power-constrained portable devices (such as mobile phones and PDAs), a major portion of whose workload is made up of multimedia applications. In this paper, we investigate the tradeoffs between video quality and the processor cycle requirements in such resource-constrained devices, in the particular context of MPEG-4 decoding using an open source codec called XviD. The XviD codec implements a number of powerful coding tools from MPEG-4, which are organized as profiles and levels. Given the specification of an architecture on which an XviD decoder is implemented, the work presented here would guide a multimedia applications developer in selecting appropriate profiles and levels for the corresponding encoder application. While the selection of such profiles has so far been primarily influenced by the network bandwidth in the case of video streaming, our work stresses the importance of additionally taking into account the architecture of the device running the decoder application. Although the relevance of this observation is increasingly being realized, sufficient work has not yet been done to provide guidelines on how to systematically make such selections. This work attempts to address this shortcoming.
7717376
Enriching speech recognition with automatic detection of sentence boundaries and disfluencies
Effective human and automatic processing of speech requires recovery of more than just the words. It also involves recovering phenomena such as sentence boundaries, filler words, and disfluencies, referred to as structural metadata. We describe a metadata detection system that combines information from different types of textual knowledge sources with information from a prosodic classifier. We investigate maximum entropy and conditional random field models, as well as the predominant hidden Markov model (HMM) approach, and find that discriminative models generally outperform generative models. We report system performance on both broadcast news and conversational telephone speech tasks, illustrating significant performance differences across tasks and as a function of recognizer performance. The results represent the state of the art, as assessed in the NIST RT-04F evaluation
5965790
On scalable and locality-aware web document sharing
We propose a scalable Web document sharing infrastructure model called Browsers-Aware Proxy Server. In this design, a proxy server connecting to a group of networked clients maintains an index file of data objects of all clients' browser caches. If a user request misses in its local browser cache and the proxy cache, the browsers-aware proxy server will search the index file attempting to find it in another client's browser cache before sending the request to an upper level proxy or the Web server. If such a request does hit in a remote client, this client will directly forward the data object to the requesting client; or the proxy server fetches the data object from this client and then forwards it to the requesting client. The contributions of this caching model are twofold. First, we show that the amount of sharable data in browser caches is significant and can be utilized for document sharing among clients to improve Web caching performance and scalability. Second, the browsers-aware model can effectively and further improve Web prefetching performance. The browsers-aware model and its supported prefetching technique build a strong locality-aware Internet environment to make Web accesses fast with low communication costs. Conducting trace-driven simulations, we show the effectiveness of the browsers-aware model, and its unique advantages to facilitate prefetching.
1073181
Keeping Secrets within a Family: Rediscovering Parnas
David Parnas wrote several papers in the 1970’s and 1980’s that are now considered classics. The concepts he advocated such as information hiding and use of abstract interfaces are generally accepted as the appropriate way to design nontrivial software systems. However, not all of what he proposed has been fully appreciated and assimilated into our practices. Many of his simple, elegant ideas have been lost amongst the hype surrounding the technologies and methods that have arisen in the past two decades. This paper examines Parnas’s ideas, especially his emphasis on program families, and proposes that college-level computing science and software engineering curricula should renew their attention to these very important principles and techniques and present them in the context of contemporary software development.
19595078
Analysis of Prioritized Crossbar Multiprocessor Systems
Abstract This paper analyzes the performance of crossbar multiprocessor systems under the assumption that processors are organized in a priority hierarchy. A basic model is derived for estimating the probability of acceptance of a memory request for each individual processor with a different priority. Improvements are made by using an adjusted memory request rate. Analytical results are validated by comparison with simulation data for configurations up to 64 X 64 with request rate ⩽ 1. Finally, it is shown that the effective memory bandwidth can be calculated accurately from acceptance probabilities of individual processors.
16602968
Performance prediction of J2EE applications using messaging protocols
Predicting the performance of component-based applications is difficult due to the complexity of the underlying component technology. This problem is exacerbated when a messaging protocol is introduced to create a loosely coupled software architecture. Messaging uses asynchronous communication, and must address quality of service issues such as message persistence and flow control. In this paper, we present an approach to predicting the performance of Java 2 Enterprise Edition (J2EE) applications using messaging services. The prediction is done during application design, without access to the application implementation. This is achieved by modeling the interactions among J2EE and messaging components using queuing network models, calibrating the performance model with architecture attributes associated with these components, and populating the model parameters using a lightweight, application-independent benchmark. Benchmarking avoids the need for prototype testing in order to obtain the value of model parameters, and thus reduces the performance prediction effort. A case study is carried out to predict the performance of a J2EE application with asynchronous communication. Analysis of the resulting predictions shows the error is within 15%.