A CORBA-BASED REAL-TIME STREAM SERVICE FOR ATM NETWORKS

Abstract

Most of the CORBA-based distributed object computing environments are implemented over legacy network transports and distributed processing platforms such as TCP/IP and RPC (Remote Procedure Call). Their performance is unacceptable for critical real-time and performance-sensitive applications due to their high processing overheads, lack of features and mechanisms in supporting quality of service, and non-optimized presentation layer conversations. To overcome these shortcomings of CORBA-based environments in relation to supporting real-time distributed multimedia applications and to tackle object-oriented design with scheduling and quality of Service (QoS), we have proposed a CORBA-based Real Time Stream Service (RTSS). To bypass the CORBA overheads and to effectively utilize the resource reservation ability of the Asynchronous Transfer Mode (ATM) network, RTSS exchanges real-time data on a stream directly to and from the underneath transport stacks. This is a highly optimized path where there is little or no overhead. RTSS, on the other hand, exploits CORBA facility for less-time-critical-signalling such as connection management and stream control and thus making the application portable and interoperable. Hence, our approach is to separate signalling from real-time data transfer. RTSS offloads multimedia handling, scheduling and Quality of Service from the core of an application and provides Application Programming Interfaces (APIs) for the rapid development of applications that exchange continuous media in real-time. These APIs allow an application to specify a desired level of QoS during connection establishment. A connection is established only if available resources meet the QoS requirements. The QoS thus agreed is guaranteed throughout the lifetime of the connection when operating directly over ATM networks. RTSS also provides options for supporting legacy UDP and TCP for interoperability with existing TCP/IP applications. An admission control mechanism is also used in RTSS to safeguard applications from creating more connections and consuming more resources than the system can support without affecting existing services. In this thesis, the system and implementation of a prototype of RTSS are presented in detail. The benefits of RTSS for the development of real-time multimedia distributed applications are demonstrated through a simple video conference application running over an ATM network via ATM Adaptation Layer (AAL) and TCP/UDP stacks respectively. Performance measurements of RTSS for the videoconference application are also presented and discussed.