The design and analysis of routing protocols is an important issue in dynamic networks such as packet radio and ad-hoc wireless networks. Most conventional protocols exhibit their least desirable behavior for highly dynamic interconnection topologies. We propose a new methodology for routing and topology information maintenance in dynamic networks. The basic idea behind the protocol is to divide the graph into a number of overlapping clusters. A change in the network topology corresponds to a change in cluster membership. We present algorithms for creation of clusters, as well as algorithms to maintain them in the presence of various network events. Compared to existing and conventional routing protocols, the proposed cluster-based approach incurs lower overhead during topology updates and also has quicker reconvergence. The effectiveness of this approach also lies in the fact that existing routing protocols can be directly applied to the network -- replacing the nodes by clusters. 1 ...

We investigate the problem of providing a fair bandwidth allocation to each of n ows that share the outgoing link of a congested router. The buer at the outgoing link is a simple FIFO, shared by packets belonging to the n ows. We devise a simple packet dropping scheme, called CHOKe, that discriminates against the ows which submit more packets/sec than is allowed by their fair share. By doing this, the scheme aims to approximate the fair queueing policy. Since it is stateless and easy to implement, CHOKe controls unresponsive or misbehaving ows with a minimum overhead. 1 Introduction The Internet provides a connectionless, best eort, end-to-end packet service using the IP protocol. It depends on congestion avoidance mechanisms implemented in the transport layer protocols, like TCP, to provide good service under heavy load. However, a lot of TCP implementations do not include the congestion avoidance mechanism either deliberately or by accident. Moreover, there are a growi...

Event-driven sensor networks operate under an idle or light load and then suddenly become active in response to a detected or monitored event. The transport of event impulses is likely to lead to varying degrees of congestion in the network depending on the sensing application. It is during these periods of event impulses that the likelihood of congestion is greatest and the information in transit of most importance to users. To address this challenge we propose an energy efficient congestion control scheme for sensor networks called CODA (COngestion Detection and Avoidance) that comprises three mechanisms: (i) receiver-based congestion detection; (ii) open-loop hop-by-hop backpressure; and (iii) closed-loop multi-source regulation. We present the detailed design, implementation, and evaluation of CODA using simulation and experimentation. We define two important performance metrics (i.e., energy tax and fidelity penalty) to evaluate the impact of CODA on the performance of sensing applications. We discuss the performance benefits and practical engineering challenges of implementing CODA in an experimental sensor network testbed based on Berkeley motes using CSMA. Simulation results indicate that CODA significantly improves the performance of data dissemination applications such as directed diffusion by mitigating hotspots, and reducing the energy tax with low fidelity penalty on sensing applications. We also demonstrate that CODA is capable of responding to a number of congestion scenarios that we believe will be prevalent as the deployment of these networks accelerates.

In this paper, we consider the use of an application-layer performance measure --- the utility --- in the context of bandwidth allocation for an available bit rate service. Our bandwidth allocation scheme can be viewed as a generalization of traditional available bit rate service; our scheme is equivalent to bandwidth max-min allocation when the utility of all applications are equal. The goal of our allocation scheme is to provide good application-layer service to a wide diversity of applications sharing available bandwidth. We achieve this goal while also supporting changes in utility over time, tolerating some inaccuracy in utility function specification, and addressing the issue of circumvention through pricing. Keywords---Utility functions, available bit rate. I. INTRODUCTION A N important class of distributed applications are those that can adapt their resource usage based on feedback from the network. These applications are robust against variability in network performance an...

An ad hoc network consists of a number of mobile hosts who communicate with each other over a wireless channel without any centralized control. The basic problem is to obtain a distributed routing scheme so that under the network connectivity assumption any mobile host can transmit/receive data from any other host in the network. In this paper we propose a new routing algorithm for ad hoc networks. The proposed algorithm uses a more appropriate distance measure given by the expected delay along a path, instead of the number of hops used in most of the existing algorithms. This metric allows the algorithm to adapt to changes not only in the topology of the network, but also in the traffic intensity. The algorithm uses a novel technique for estimating the path delays without requiring the links to be bidirectional or the clocks at the nodes in the network to be synchronized. The proposed algorithm is able to perform both reliable and good routing with low communication overhead and compu...

In this paper, we address the problem of network survivability by presenting a unified approach where the wide-area circuit-switched teletraffic network and the underlying transmission facility network are considered simultaneously. We assume the backbone circuit-switched teletraffic network to be nonhierarchical with dynamic call routing capabilities. The transmission facility network is considered to be sparse (as is observed for emerging fiber optic networks) and is assumed to be two-arc connected. Our approach addresses the network survivability objective by considering two grade-of-service parameters: one for the traffic network under normal operating condition and the other for affected part of the network under a network failure. We present unified mathematical models and develop heuristic algorithms. We then present computational results to demonstrate the effectiveness of the unified approach. I. Introduction THE planning process for telecommunications networks can be catego...

The notion of lambda-Grids posits plentiful collections of computing and storage resources richly interconnected by dedicated dense wavelength division multiplexing (DWDM) optical paths. In lambda-Grids, the DWDM links form a network with plentiful bandwidth, pushing contention and sharing bottlenecks to the end systems (or their network links) and motivating the Group Transport Protocol (GTP). GTP features request-response data transfer model, ratebased explicit flow control, and more importantly, receiver-centric max-min fair rate allocation across multiple flows to support multipoint-to-point data movement. Our studies show that GTP performs as well as other UDP based aggressive transport protocols (e.g. RBUDP, SABUL) for single flows, and when converging flows (from multiple senders to one receiver) are introduced, GTP achieves both high throughput and much lower loss rates than others. This superior performance is due to new techniques in GTP for managing end system contention. 1.

An important requirement for pervasive computing systems is the ability to adapt at runtime to handle varying resources, user mobility, changing user needs, and system faults. In this paper we describe an approach in which dynamic adaptation is supported by the use of software architectural models to monitor an application and guide dynamic changes to it. The use of externalized models permits one to make reconfiguration decisions based on a global perspective of the running system, apply analytic models to determine correct repair strategies, and gauge the effectiveness of repair through continuous system monitoring. We illustrate the application of this idea to pervasive computing systems, focusing on the need to adapt based on performance-related criteria and models.

We argue that open networks designed using end-to-end arguments are particularly vulnerable to flooding, and that this vulnerability persists as hardware and operating systems technologies advance.

The end-to-end nature of Internet congestion control is an important factor in its scalability and robustness. However, end-to-end congestion control algorithms alone are incapable of preventing the congestion collapse and unfair bandwidth allocations created by applications which are unresponsive to network congestion. In this paper, we propose and investigate a new congestion avoidance mechanism called Network Border Patrol (NBP). NBP relies on the exchange of feedback between routers at the borders of a network in order to detect and restrict unresponsive traffic flows before they enter the network. The NBP mechanism is compliant with the Internet philosophy of pushing complexity toward the edges of the network whenever possible. Simulation results show that NBP effectively eliminates congestion collapse, and that, when combined with fair queueing, NBP achieves approximately maxmin fair bandwidth allocations for competing network flows. Keywords--- Internet, congestion control, con...