The Internet is rapidly changing from a set of wires and switches that carry packets into a sophisticated infrastructure that delivers a set of complex value-added services to end users. Services can range from bit transport all the way up to distributed value-added services like video teleconferencing, data mining, and distributed interactive simulations. Before such services can be supported in a general and dynamic manner we have to develop appropriate resource management mechanisms. These resource management mechanisms must make it possible to identify and allocate resources that meet service or application requirements, support both isolation and controlled dynamic sharing of resources across organizations sharing physical resources, and be customizable so services and applications can tailor resource usage to optimize their performance. The Darwin project is developing a set of customizable resource management mechanisms that support value-added services, In this paper we present these mechanisms, describe their implementation in a prototype system, and describe the results of a series of proof-of-concept experiments.

A critical issue in the design of fast packet-switch-based networks is the avoidance of data loss due to congestion. In the context of ATM networks, many link-level congestion control mechanisms for ABR traffic have been proposed and simulated, and a few have been implemented. This paper presents, for the first time, an experimental comparison of several such mechanisms. To drive this comparison, we have developed a set of benchmarks that provide a quantitative characterization of congestion control performance. We also describe a simple but novel technique, the "virtual port card", for implementing both non-native switch behavior and long link delays in ATM networks. This technique allows us to compare a wide range of mechanisms on a single flexible hardware platform. Our measurements show that while several of the ATM flow control mechanisms can eliminate cell loss, there are still several unresolved problems. First, for some traffic scenarios we see very poor application-level performance, especially in the presence of bursty traffic. Second, the performance is very sensitive to the flow control parameters and identifying an appropriate set of parameters is difficult since it depends heavily on the traffic conditions.

Commodityworkstations connected by commodity networks are increasingly viewed as an economically viable alternative to tightly coupled multiprocessors.In recent years, many scientific computing applications have been able to make effective use of various types of workstation clusters.The main difference between workstation clusters and the more traditional, tightly coupled distributedmemory systems is communication performance.In this paper we present a host-network interface architecture that supports efficient remote memory writes across standard ATM networks, bringing performance closer to that of special-purpose, tightly coupled systems for a large class of applications.We show that minimal hardware support is required on the adaptor, and that the required features are very similar to those already needed on adaptors for high-speed networks.We also describe an implementation of this architecture, and present measurements of communication performance indicating its effect on the breadth of applications that can use a general purpose network m an effective way.

Among the many benefits of ATM networking are the potential for connections with negotiated quality-of-service (QoS) guarantees and application-specific data management at network endpoints. We describe the architecture of a PCI bus host adapter for OC-3 and OC-12 ATM, focusing on challenges in the areas of buffer management and flow control, since these are vital to realizing the bandwidth and QoS potential of ATM endpoint hosts.

In all-to-all personalized communication (AAPC), every node of a parallel system sends a potentially unique packet to every other node. AAPC is an important primitive operation for modern parallel compilers, since it is used to redistribute data structures during parallel computations. As an extremely dense communication pattern, AAPC causes congestion in many types of networks and therefore executes very poorly on general purpose, asynchronous message passsing routers.

Network diagrams are a familiar graphic form that can express many different kinds of information. The problem of automating network-diagram layout has therefore received much attention. Previous research on network-diagram layout has focused on the problem of aesthetically optimal layout, using such criteria as the number of link crossings, the sum of all link lengths, and total diagram area. In this paper the authors propose a restatement of the network-diagram layout problem in which layout-aesthetic concerns are subordinated to perceptual-organization concerns. The authors present a notation for describing the visual organization of a network diagram. This notation is used in reformulating the layout task as a constrained-optimization problem in which constraints are derived from a visual-organization specification and optimality criteria are derived from layout-aesthetic considerations. Two new heuristic algorithms are presented for this version of the layout problem: one algorithm uses a rule-based strategy for computing a layout; the other is a massively parallel genetic algorithm. The authors demonstrate the capabilities of the two algorithms by testing them on a variety of network-diagram layout problems.>