We revisit the question of how much buffer an IP router should allocate for its Droptail FIFO link. For a long time, setting the buffer size to the bitrate-delay product has been regarded as reasonable. Recent studies of interaction between queueing at IP routers and TCP congestion control offered alternative guidelines. First, we explore and reconcile contradictions between the existing rules. Then, we argue that the problem of link buffer sizing needs a new formulation: design a buffer sizing algorithm that accommodates needs of all Internet applications without engaging IP routers in any additional signaling. Our solution keeps network queues short: set the buffer size to ¾Ä datagrams, where Ä is the number of input links. We also explain how end systems can utilize the network effectively despite such small buffering at routers.

The problem of determining the optimal buffer size for an Internet link has recently attracted the strong revived attention of networking scientists. While consonant in dissenting from the conventional wisdom to set the buffer size to the product of the link bitrate and round-trip propagation delay of served connections, the new studies often propose alternative guidelines that starkly contradict each other. In this paper, we review the problem of link buffer sizing from two simulation perspectives. First, we use the packet-level simulator ns-2, which is currently the predominant tool for evaluation of network designs, to explore the contradictions between the buffer sizing guidelines. We attribute the contradictions to differences in assumptions and goals of the earlier studies and present our own argument for using small constant buffer sizes. Second, we reflect on the suitability of ns-2 itself for studying the problem of link buffer sizing. We the identify ns-2 deficiencies that undermine the trustworthiness of results provided by this prevailing simulation tool. We also suggest directions and discuss challenges for designing a simulation methodology capable of providing undisputed answers on link buffer sizing.

In this article we outline a design of a high1 scalable network monitoring, visualloop capability. This capability allows network administrators to calibrate and fine-tune network and application parameters in real time according to observed traffic patterns. The goal of the NMVC system is to ensure adequate quality of service to network users, while maintaining high network resource utilization. The main components of our system are: a network probe and an endsystem probe which can probe gigabit/s links, software nework management agents that vide extensible multi-attribute event filtering for highly scalable data/event CO lection, efficient online event ordering algorithms that can help synthesize and display a consistent view of network health, status, and erformance and a View Choreographer that allows management applications anSadministrators to specify the mapping of network events to higher-level events and to visualization objects and updates.ization, and control (NMVC) system with a cy vanced algorithmic and human-in-theProommter networks (such as the Internet and the Gldbal InformationInfrastructure) have become critical for education, research, business, and most importantly military operations. Recent advances in network infrastructure technology (such as ATM and IPv6) have enabled the development of high-performance local area and wide area networks. Efficient management of these networks is essential. However, existing algorithmic methods for managing networks have not matured to the point where performance bottleneck and fault detection, isolation, correlation, and correction can be automated scalably [l]. Thus, it is crucial to build efficient and user-friendly network monitoring, visualization, and control (NMVC) systems.After studying several commercially available SNMP-and CMIP-based network monitoring and management systemsitools, we find that most are not suitable for the monitoring, control, and visualization of large high-speed ATM and other networks that are the target of this project. While these rools provide basic features like network discovery and management information base (MIB) browsing, they have many weaknesses. Most of these tools allow only status polling, which helps detect network failures. However, failure detection is a small component of today's network management. There are some tools that do both status and performance polling. However, they keep these two separate, and performance polling is done more often than status polling. This means that its takes longer to detect failures. Also, scalability is a major weakness of these tools. That is, they will not work or work well with large networks and with high-speed networks [2, 31. For example, most tools redundantly poll devices that are part of more than one network map. This generates excessive management traffic when administering large-scale MAN and WAN networks. For some of the tools, notably HP OpenView [4] and IBM NetViewi6000 [5], the architecture i s geared towards managing discrete entities with no knowledge of ...

Abstract-Packets in the Internet can experience large queueing delays during busy periods. Backbone routers are generally engineered to have large buffers, in which packets may wait as long as half a second (assuming FIFO service, longer otherwise). During congestion periods, these buffers may stay close to full, subjecting packets to long delays, even when the intrinsic latency of the path is relatively small. This paper studies the performance improvements that can be obtained for short-lived TCP flows by using more sophisticated packet schedulers, than are typical of Internet routers. The results show that the large buffers found in WAN routers contribute only marginally to improving router throughput, and the higher delays that come with large buffers makes them a dubious investment. The results also show that better packet scheduling algorithms can produce dramatic improvements in fairness. Using ns-2 simulations, we show that algorithms using multiple queues can significantly outperform RED and Blue, especially at smaller buffer sizes. Given a traffic mix of short-lived TCP flows with different round-trip times, longer round-trip time flows achieve ¢ ¤ £ ¦ ¥ of their fair-share using multiqueue schedulers, compared to § £ ¦ ¥ under RED and Blue. We observe a similar performance improvement for multi-hop paths. We also show that performance results can be reliably scaled across a wide range of parameter values, so long as the ratio of the buffer size to the link bandwidth-delay product is held invariant.

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This report describes an ATM Multipoint Connection Caching strategy (AMCC) to control the explosive growth of traffic within the network and at an endpoint in a large Distributed Interactive Simulation (DIS) application such as a battlefield simulation. For very large DIS applications with 100,000 entities, the current method of broadcasting information among entities will no longer be feasible due to computational and network bandwidth limitations. Our scheme divides the simulation space into grids and each grid square or a set of grid squares forms a multicast group. Entities join the groups within their perception range and thus, they