A connected hypercube with faulty links and/or nodes is called an injured hypercube. To enable any non-faulty node to communicate with any other non-faulty node in an injured hypcrcube, the information on component failures has to be made available to non-faulty nodes so as to route messages around the faulty components. We propose first a distributed adaptive fault-tolerant routing scheme for an injured hypercube in which each node is required to know only the condition of its own links. Despite its simplicity, this scheme is shown to be capable of routing messages successfully in an injured hypercube as long as the number of faulty components is less than n. Moreover, it is proved that this scheme routes messages via shortest paths with a rather high probability and the expected length of a resulting path is very close to that of a shortest path. Since the assumption that the number of faulty components is less than n in an n-dimensional hypercube might limit the usefulness of the above scheme, we also introduce a routing scheme based on depth-first search which works in the presence of an arbitrary number of faulty components. Due to the insufficient information on faulty components, however, the paths chosen by the above scheme may not always be the shortest. To guarantee all messages to be routed via shortest paths, we propose to equip every node with more information than that on its own links. The effects of this additional information on routing efficiency are analyzed, and the additional information to be kept at each node for the shortest path routing is determined. Several examples and remarks are also given to illustrate bur results. Index Terms: Injured and regular hypercubes, distributed adaptive fault-tolerant routing, dcpthfirst search, looping effects, network delay tables, failure information.

Abstract — In the Internet today, traffic engineering is performed assuming that the offered traffic is inelastic. In reality, end hosts adapt their sending rates to network congestion, and network operators adapt the routing to the measured traffic. This raises the question of whether the joint system of congestion control (transport layer) and routing (network layer) is stable and optimal. Using the established optimization model for TCP and that for traffic engineering as a basis, we find the joint system is stable and typically maximizes aggregate user utility, especially under more homogeneous link capacities. We prove that both stability and optimality of the joint system can be guaranteed for sufficiently elastic traffic simply by tuning the cost function used for traffic engineering. Then, we present a new algorithm that adapts on a faster timescale to changes in traffic distribution and is more robust to large traffic bursts. Uniting the network and transport layers in a multi-layer approach, this algorithm, Distributed Adaptive Traffic Engineering (DATE), jointly optimizes the goals of end users and network operators and reacts quickly to avoid bottlenecks. Simulations demonstrate that DATE converges quickly.

AN1 (formerly known as Autonet) is a local area network composedof crossbar switches interconnected by 100Mbit/second, full-duplex links. In this paper, we evaluate the performance impact of certain choices in the AN1 design. These include the use of FIFO input buffering in the crossbar switch, the deadlockavoidance mechanism, cut-through routing, back-pressure for flow control, and multi-path routing. AN1's performance goals were to provide low latency and high bandwidth in a lightly loaded network. In this it is successful. Under heavy load, the most serious impediment to good performance is the use of FIFO input buffers. The deadlock-avoidance technique has an adverse effect on the performance of some topologies, but it seems to be the best alternative, given the goals and constraints of the AN1 design. Cut-through switching performs well relative to store-and-forward switching, even under heavy load. Back-pressure deals adequately with congestion in a lightly-loaded network; under ...

Performance Issues in Mobile Wireless Networks. (August 1996) P. Krishna, B.S.(Hons.), Regional Engineering College, Rourkela, India; M.S., Texas A&M University Co--Chairs of Advisory Committee: Dr. Dhiraj K. Pradhan Dr. Nitin H. Vaidya The research presented in this dissertation deals with the following performance issues in mobile wireless networks: recovery, location management and routing. The mobile wireless environment poses challenging fault-tolerant data management problems due to the mobility of the users, limited bandwidth on the wireless link, and power restrictions on the mobile hosts. Thus, traditional fault-tolerance schemes cannot be directly applied to these systems. To this effect, extensions to existing traditional recovery schemes are presented which suit this environment. Analytical models are built to analyze the performance of these schemes to determine those environments where a particular recovery scheme is best suited. The trade-off parameters to evaluate the r...

Internet is widely known for lacking any kind of mechanism for the provisioning of Quality of Service guarantees. The Internet community concentrates its efforts on the Bandwidth Broker architecture towards this problem. This paper presents a design model of a multi-layer Bandwidth Broker architecture that introduces a Resource Control Layer, which is divided into two sub-layers. The upper one is responsible for the overall network administration, while the lower one performs per-flow policy-based admission control. The design models, the mechanisms, and algorithms adopted in this architecture will be delineated. KEYWORDS: BANDWIDTH BROKER, QUALITY OF SERVICE, INTEGRATED SERVICES, DIFFERENTIATED SERVICES, RESOURCE CONTROL POINT, RESOURCE CONTROL AGENT, APPLICATION MIDDLEWARE. DESIGN OF A MULTI-LAYER BANDWIDTH BROKER ARCHITECTURE 1.

This report is the author's Ph.D. dissertation which was completed under the ad-

Abstract—Traffic management is the adaptation of source rates and routing to efficiently utilize network resources. Traffic management today includes congestion control, routing and traffic engineering. In this paper, we perform a top-down redesign of traffic management using recent innovations in optimization theory. First, we propose a new objective function that captures the goals of both end users and network operators. Second, using various optimization decomposition techniques, we generate four distributed algorithms that divide traffic over multiple paths based on feedback from the network links. These distributed algorithms are provably stable and optimal. Third, combining the best features of these distributed algorithms, we construct TRUMP: a new traffic management protocol that is distributed, adaptive, robust, flexible and easy to manage. Packet-level simulations show TRUMP behaves well with realistic topologies, feedback delays, capacities, and traffic loads. Overall, we show that using optimization decomposition as a foundation, simulations as a building block, and engineering intuition as a guide can be a principled approach to protocol design. I.

The first six months of the project saw the employment of Matthew Barr and Chong-kwon Kim as research assistants. Although the grant period began in June, the commitment to sup-port the research arrived too late to employ students for the summer. Hence, both Barr and Kim began work in the fall. Each has been working on slightly different, but complementary, approaches to the support of heterogeneous traffic (;.e., voice, video, and data) on a single, integrated network. Barr has begun \examining techniques that trade communication bandwidth for decreased transmission delays. When the network is lightly used, these schemes attempt to use additional network resources to decrease communication delays. As the network utilization rises, the schemes degrade gracefully, still providing service but with minimal use of the network. Because the schemes use a combination of circuit and packet switching, they should respond to variations in the types and amounts of network traffic. Because Barr just began this work in September, there are few results to report thus far. As the work progresses, it will be discussed in more detail in future reports. Drawing on Reed's earlier work on integrated communication networks, Kim had already

Congestion in the network causes poor throughput and long delays for end users, and also leads to an inefficient usage of network resources. In the Internet today, end users run the Transmission Control Protocol (TCP) to adapt their sending

Traffic management refers to controlling how much traffic traverses each path in a network. On the Internet today, end hosts run congestion control to adapt sending rates, routers route traffic on shortest paths based on link weights, and operators tune link weights to direct traffic away from heavily-loaded links. This dissertation performs a top-down redesign of traffic management to support diverse application requirements, leveraging emerging technology trends in network virtualization and multipath routing. We begin by analyzing, then redesigning today’s traffic-management system. In the ’bottom-up ’ approach, we study the interaction of congestion control and traffic engineering using established optimization models. We find congestion control and traffic-engineering interact in a stable, though not always efficient manner. Efficiency can be improved by tuning the operator’s traffic-engineering function, but at the cost of robustness. In the ’top-down ’ approach, we propose a new objective function that captures