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.

In this article we present a framework for the emerging Internet quality of service (QoS). All the important components of this framework --- integrated services, RSVP, differentiated services, multiprotocol label switching (MPLS), and constraintbased routing --- are covered. We describe what integrated services and differentiated services are, how they can be implemented, and the problems they have. We then describe why MPLS and constraint-based routing have been introduced into this framework, how they differ from and relate to each other, and where they fit into the differentiated services architecture. Two likely service architectures are presented, and the end-to-end service deliveries in these two architectures are illustrated. We also compare ATM networks to router networks with differentiated services and MPLS. Putting all these together, we give the readers a grasp of the big picture of the emerging Internet QoS. 12 IEEE Network . March/April 1999 9 and differenti...

Organizing massive amount of data on wireless communication networks in order to provide fast and low power access to users equipped with palmtops, is a new challenge to the data management and telecommunication communities. Solutions must take under consideration the physical restrictions of low network bandwidth and limited battery life of palmtops. This paper proposes algorithms for multiplexing clustering and nonclustering indexes along with data on wireless networks. The power consumption and the latency for obtaining the required data are considered as the two basic performance criteria for all algorithms. First, this paper describes two algorithms namely, (1, m) Indexing and Distributed Indexing, for multiplexing data and its clustering index. Second, an algorithm called Nonclustered Indexing is described for allocating static data and its corresponding nonclustered index. Then, the Nonclustered indexing algorithm is generalized to the case of multiple indexes. Finally, t...

For some time, the networking community has assumed that it is impossible to do IP routing lookups in software fast enough to support gigabit speeds. IP routing lookups must �nd the routing entry with the longest matching pre�x, a task that has been thought to require hardware support at lookup frequencies of millions per second. We present a forwarding table data structure designed for quick routing lookups. Forwarding tables are small enough to �t in the cache of a conventional general purpose processor. With the table in cache, a 200 MHz Pentium Pro or a 333 MHz Alpha 21164 can perform a few million lookups per second. This means that it is feasible to do a full routing lookup for each IPpacket at gigabit speeds without special hardware. The forwarding tables are very small, a large routing table with 40,000 routing entries can be compacted to a forwarding table of 150�160 Kbytes. A lookup typically requires less than 100 instructions on an Alpha, using eight memory references accessing a total of 14 bytes. 1

Compressed digital video is one of the most important traffic types in future integrated services networks. However, a network service that supports delay-sensitive video imposes many problems since compressed video sources are variable bit rate (VBR) with a high degree of burstiness. In this paper, we consider a network service that can provide deterministic guarantees on the minimum throughput and the maximum delay of VBR video traffic. A common belief is that due to the burstiness of VBR traffic, such a service will not be efficient and will necessarily result in low network utilization. We investigate the fundamental limits and tradeoffs in providing deterministic performance guarantees to video and use a set of 10 to 30 minute long MPEG-compressed video traces for evaluation. Contrary to conventional wisdom, we are able to show that, in many cases, a deterministic service can be provided to video traffic while maintaining a reasonable level of network utilization. We first conside...

Qo!3 requirements across networks, when the information available for ma:king routing decisions is inaccurate. This uncertainty about the actual stale of a network component arises naturally in a number of different environments, which are reviewed in the paper. The goal of the route selection process is then to identify a path that is most likely to satisfy the QoS re-quirements. For end-to-end delay guarantees, this problem is intractable. However, we show that by decomposing the end-to-end constraint into local delay constraints, efficient and tractable solutions can be established. ‘We first consider the simpler problem of decomposing the end-to-end

As Internet services become more popular and pervasive, a critical problem that arises is managing the performance of services under extreme overload. This paper presents a set of techniques for managing overload in complex, dynamic Internet services. These techniques are based on an adaptive admission control mechanism that attempts to bound the 90th-percentile response time of requests flowing through the service. This is accomplished by internally monitoring the performance of the service, which is decomposed into a set of event-driven stages connected with request queues. By controlling the rate at which each stage admits requests, the service can perform focused overload management, for example, by filtering only those requests that lead to resource bottlenecks. We present two extensions of this basic controller that provide class-based service differentiation as well as application-specific service degradation. We evaluate these mechanisms using a complex Webbased e-mail service that is subjected to a realistic user load, as well as a simpler Web server benchmark.

The development of multi-user networked virtual worlds has become a major area of interest in the computer and communications fields. However, there has been little effort to provide a coherent framework for understanding distributed virtual environments (VEs). In this paper we discuss VEs in the context of how communications, views, data, and processes are distributed while emphasizing those aspects critical to scaling environments. We find most of the systems described in this paper scale to accommodate a handful of users. We also discuss why systems which demand strong data consistency, causality, and reliable communications at the same time while supporting real-time interaction are not likely to scale very well. Furthermore, if the systems are to be geographically dispersed, then highspeed, multicast communication is required. . KEYWORDS: Virtual Reality, Distributed Interactive Simulation, Internet Protocol Multicast, Distributed Interactive Entertainment, Large-scale Virtual E...

Modern networked computing environments and applications often require---or can benefit from---the use of multiple communication substrates, transport mechanisms, and protocols, chosen according to where communication is directed, what is communicated, or when communication is performed. We propose techniques that allow multiple communication methods to be supported transparently in a single application, with either automatic or user-specified selection criteria guiding the methods used for each communication. We explain how communication link and remote service request mechanisms facilitate the specification and implementation of multimethod communication. These mechanisms have been implemented in the Nexus multithreaded runtime system, and we use this system to illustrate solutions to various problems that arise when implementing multimethod communication. We also illustrate the application of our techniques by describing a multimethod, multithreaded implementation of the Message Pas...

The nature of distributed multimedia applications is such that they require multipeer communication support mechanisms. The multimedia traffic needs to be delivered to end-systems, networks and end-users in a form that they can handle while satisfying the constraints imposed by the multimedia application. Quality of Service (QoS) mechanisms that can ensure full quality media playout at high-performance workstations, while at the same time providing appropriately filtered lower quality media for playout at other end-systems, are required. Existing multicast support mechanisms are deficient for this purpose, in a heterogeneous environment, because they work on a common denominator premise where the quality delivered depends on the least capable link or node involved in the multicast session. This paper proposes and analyses the use of filtering mechanisms as a means of supporting disparate receiver capabilities and QoS requirements. The paper describes the implementation of a number of f...