This paper explores the issues involved in designing and developing network software architectures for large scale virtual environments. We present our ideas in the context of NPSNET-IV, the first 3D virtual environment that incorporates both the IEEE 1278 Distributed Interactive Simulation (DIS) application protocol and the IP Multicast network protocol for multi-player simulation over the Internet.

Present systems for streaming digital audio between devices connected by internet have been limited by a number of compromises. Because of restricted bandwidth and “best effort ” delivery, signal compression of one form or another is typical. Buffering of audio data which is needed to safeguard against delivery uncertainties can cause signal delays of seconds. Audio is in general an unforgiving test of networking, e.g., one data packet arriving too late and we hear it. Trade-offs of signal quality have been necessary to avoid this basic fact and until now, have vied against serious musical uses. Beginning in late 1998, audio applications specifically designed for next-generation networks were initiated that could meet the stringent requirements of professional-quality music streaming. A related experiment was begun to explore the use of audio as a network measurement tool. SoundWIRE (sound waves over the internet from real-time echoes) creates a sonar-like ping to display to the ear qualities of bidirectional connections. Recent experiments have achieved coast-to-coast sustained audio connections whose round trip times are within a factor of 2 of the speed of light. Full-duplex speech over these connections feels comfortable and in an IIR recirculating form that creates echoes like SoundWIRE, users can experience singing into a transcontinental echo chamber. Three simplifications to audio streaming are suggested in this paper: Compression has been eliminated to reduce delay and enhance signal-quality. TCP/IP is used in unidirectional flows for its delivery guarantees and thereby eliminating the need for application software to correct transmission errors. QoS puts bounds on latency and jitter affecting long-haul bidirectional flows. 1.

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1 Interaction Goals:

Recent traffic studies of high-resolution, high quality traffic measurements have revealed the phenomenon of long-range dependence in network traffic. The implication of the presence of long-range dependence in traffic is that actual network traffic exhibits more bursty behavior compared to traditional ”Poisson-like ” models. Traffic modeling and performance prediction in networks with long-range dependent flows is required for the design of efficient congestion control, routing and other network management algorithms. Here a non-Markovian phase process is used to model the traffic process. The phase process captures the macro-dynamic properties of the traffic. The traffic dynamics within each phase i.e., the traffic micro-dynamics, are then described by a random process with finite mean and variance. Network performance using this model has been evaluated in the form of delay vs load curves and cell loss ratio vs buffer size. By capturing the burstiness of the network traffic in the form of traffic macro-dynamics, the model developed here predicts ATM queue performance in network flows that may be inherently long-range dependent in nature. Extensive simulations based on traces of traffic collected from a wide area ATM network has been used to validate the developed