Ahmet Uyar

Grid services for earthquake science

We describe an information system architecture for the ACES (Asia–Pacific Cooperation for Earthquake Simulation) community. It addresses several key features of the field—simulations at multiple scales that need to be coupled together; real‐time and archival observational data, which needs to be analyzed for patterns and linked to the simulations; a variety of important algorithms including partial differential equation solvers, particle dynamics, signal processing and data analysis; a natural three‐dimensional space (plus time) setting for both visualization and observations; the linkage of field to real‐time events both as an aid to crisis management and to scientific discovery. We also address the need to support education and research for a field whose computational sophistication is rapidly increasing and spans a broad range. The information system assumes that all significant data is defined by an XML layer which could be virtual, but whose existence ensures that all data is object‐based and can be accessed and searched in this form. The various capabilities needed by ACES are defined as grid services, which are conformant with emerging standards and implemented with different levels of fidelity and performance appropriate to the application. Grid Services can be composed in a hierarchical fashion to address complex problems. The real‐time needs of the field are addressed by high‐performance implementation of data transfer and simulation services. Further, the environment is linked to real‐time collaboration to support interactions between scientists in geographically distant locations. Copyright

Service-oriented architecture for a scalable videoconferencing system

The availability of increasing network bandwidth and computing power provides new opportunities for videoconferencing systems over Internet. Multimedia capable devices with broadband Internet connections are spreading rapidly. Even cell phones will have broadband Internet access in the near future. This requires universally accessible and scalable videoconferencing systems that can deliver thousands of concurrent audio and video streams. However, developing videoconferencing systems over Internet is a challenging task, since audio and video communications require high bandwidth and low latency. In addition, the processing of audio and video streams is computing intensive. Therefore, it is particularly difficult to develop scalable systems that support high number of users with various capabilities. Current videoconferencing systems such as IP-Multicast and H.323 can not fully address the problem of scalability and universal accessibility. These systems lack flexible service oriented architecture to support increasingly diverse. We believe that with the advancements in computing power and network bandwidth, more flexible and service oriented systems should be developed. In this paper, we outline a service oriented architecture for videoconferencing, GlobalMMCS, based on a publish/subscribe event brokering network, NaradaBrokering.

Service oriented architecture for VoIP conferencing

Most current Voice/Video over IP (VoIP) systems are either highly centralized or dependent on IP multicast. We propose the Global Multimedia Collaboration System as a scalable, integrated and service-oriented VoIP conferencing system, based on a SOAP-based collaboration framework and advanced messaging oriented middleware. This system can provide media and session services to heterogeneous endpoints including H.323, SIP, Access Grid, and RealPlayer as well as accommodating diverse clients such as cellular phones. We suggest that our approach opens up new opportunities for extending classic VoIP systems by using these new technologies designed for scalable Internet based service-oriented computing. Copyright

Investigating the performance of audio/video service architecture I: single broker

Increasing network bandwidth and computing power provide new opportunities for videoconferencing systems over Internet. The number of homes and small offices with broadband Internet connections are increasing rapidly. Even cell phones have broadband Internet access in the near future. Therefore, it is not inconceivable to imagine that the trend in the increasing usage of videoconferencing systems continue by accelerating. This requires universally accessible and scalable videoconferencing systems that can deliver thousands of concurrent audio and video streams. However, developing videoconferencing systems over Internet is a challenging task, since audio and video distribution requires high bandwidth and low latency. Current videoconferencing systems such as IP-multicast and H.323 can not fully address the problem of scalability and universal accessibility. We propose service oriented architecture for videoconferencing, GlobalMMCS, and use an event brokering middleware, NaradaBrokering, to deliver real-time audio and video streams to high number of users. The performance of the event brokering network is critical to the success of this videoconferencing system. In this paper, we provide comprehensive analysis of a NaradaBrokering broker in the context of audio/video delivery. The results provide guidelines for the deployment of GlobalMMCS in particular, and they provide useful insights for the feasibility of using software based audio/video delivery systems in general

Adapting H.323 terminals in a service-oriented collaboration system

The Global Multimedia Collaboration System is designed to bridge H.323, Session Initiation Protocol, Access Grid clients, and 2.SG/3G cellular phones in audio-visual collaborations. One of its key components is the H.323 gateway, which lets H.323 terminals interact with other clients, providing complete conferencing control services. This system is designed to help scientists and students who have access only to H.323 and SIP endpoints or cellular phones with scientific collaboration in the high-end Access Grid environment.

Investigating the performance of audio/video service architecture. II. Broker network

For pt.1 see ibid., p.120-127 (2005). Increasing network bandwidth and computing power provide new opportunities for videoconferencing systems over Internet. In addition to homes and small officies, even the cell phones have broadband Internet access in the near future. Therefore, we can imagine that the trend in the increasing usage of videoconferencing systems continues. This requires universally accessible and scalable videoconferencing systems that can deliver thousands of concurrent audio and video streams. However, developing videoconferencing systems over Internet is a challenging task, since audio and video distribution requires high bandwidth and low latency. Current videoconferencing systems such as IP-Multicast and H.323 can not fully address the problem of scalability and universal accessibility. We propose service oriented architecture for videoconferencing, GlobalMMCS, and use an event brokering middleware, NaradaBrokering, to deliver real-time audio and video streams to high number of users. The performance of the event brokering network is critical to the success of this videoconferencing system. In this paper, we evaluate the performance of NaradaBrokering broker network in distributed settings in the context of audio/video delivery. The results demonstrate that even small number of brokers can deliver audio/video streams to more than a thousand users with very good quality. They also provide guidelines for the deployment of GlobalMMCS in particular, and they provide useful insights for the feasibility of using software based audio/video delivery systems in general

Grid Service Architecture for Videoconferencing

In this paper we present a scalable, integrated and service-oriented collaboration system, namely Global Multimedia Collaboration System, based on the XGSP collaboration framework and NaradaBrokering messaging middleware. This system can provide videoconferencing services to heterogeneous endpoints such as H.323, SIP, Access Grid, RealPlayer as well as cellular phone. This paper discusses the design principle, system architecture and implementation in detail. The extensive performance measurement has been made to evaluate the scalability of the system.