An ad-hoc network is the cooperative engagement of a collection of Mobile Hosts without the required intervention of any centralized Access Point. In this paper we present an innovative design for the operation of such ad-hoc networks. The basic idea of the design is to operate each Mobile Host as a specialized router, which periodically advertises its view of the interconnection topology with other Mobile Hosts within the network. This amounts to a new sort of routing protocol. We have investigated modifications to the basic Bellman-Ford routing mechanisms, as specified by RIP [5], to make it suitable for a dynamic and self-starting network mechanism as is required by users wishing to utilize ad hoc networks. Our modifications address some of the previous objections to the use of Bellman-Ford, related to the poor looping properties of such algorithms in the face of broken links and the resulting time dependent nature of the interconnection topology describing the links between the Mobile Hosts. Finally, we describe the ways in which the basic network-layer routing can be modified to provide MAC-layer support for ad-hoc networks.

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Highly dynamic Destination-Sequenced Distance-Vector routing (DSDV) for mobile computers

A nonintrusive appliance load monitor that determines the energy consumption of individual appliances turning on and off in an electric load, based on detailed analysis of the current and voltage of the total load, as measured at the interface to the power source is described. The theory and current practice of nonintrusive appliance load monitoring are discussed, including goals, applications, load models, appliance signatures, algorithms, prototypes field-test results, current research directions, and the advantages and disadvantages of this approach relative to intrusive monitoring. >

Nonintrusive appliance load monitoring

The large-scale behavior of routing In the Internet has gone virtually without any formal study, the exceptions being Chinoy's (1993) analysis of the dynamics of Internet routing information, and work, similar in spirit, by Labovitz, Malan, and Jahanian (see Proc. SIGCOMM'97, 1997). We report on an analysis of 40000 end-to-end route measurements conducted using repeated "traceroutes" between 37 Internet sites. We analyze the routing behavior for pathological conditions, routing stability, and routing symmetry. For pathologies, we characterize the prevalence of routing loops, erroneous routing, infrastructure failures, and temporary outages. We find that the likelihood of encountering a major routing pathology more than doubled between the end of 1994 and the end of 1995, rising from 1.5% to 3.3%. For routing stability, we define two separate types of stability, "prevalence", meaning the overall likelihood that a particular route is encountered, and "persistence", the likelihood that a route remains unchanged over a long period of time. We find that Internet paths are heavily dominated by a single prevalent route, but that the time periods over which routes persist show wide variation, ranging from seconds up to days. About two-thirds of the Internet paths had routes persisting for either days or weeks. For routing symmetry, we look at the likelihood that a path through the Internet visits at least one different city in the two directions. At the end of 1995, this was the case half the time, and at least one different autonomous system was visited 30% of the time.

/pdf/end-to-end-routing-behavior-in-the-internet-2zfv4dg7f1.pdf

End-to-end routing behavior in the Internet

One of the fundamental difficulties with trying to characterize the Internet''s behavior lies in its immense diversity. To date, efforts to characterize end-to-end Internet dynamics such as packet delay and loss have studied at most a handful of traffic traces and Internet paths, making it difficult to assess the generality of the findings. Yet solid assessments of Internet path properties are crucial for engineering transport protocols for high performance. In this work, we attempt to tackle this problem using a distributed framework we developed for conducting end-to-end measurements. In the first part, we report on an end-to-end routing study conducted using the framework, in which 37 sites participated, yielding about 40,000 routing measurements along 1,000 Internet paths. We characterize routing pathologies and failures, stability over time, and symmetry. In the second part of the study, we analyze 20,000 TCP bulk transfers measured using the same framework. We discuss: 1) errors introduced by the packet filters used to make the measurements; 2) dealing with unsynchronized and skewed clocks; 3) separating out TCP behavior from network behavior; 4) the surprisingly large variations between different TCP implementations; 5) pathological network behavior, such as out-of-order delivery, replication, and corruption; 6) a robust algorithm for estimating bottleneck bandwidth; and 7) the resulting characterizations of Internet packet loss and delay, including general assessments of queueing time scales and available bandwidth.

/pdf/measurements-and-analysis-of-end-to-end-internet-dynamics-2g9j633ch4.pdf

Measurements and analysis of end-to-end Internet dynamics

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

A cluster-based approach for routing in dynamic networks

An overview is provided in this paper of the routing procedures used in a number of operating networks, as well as in two commercial network architectures. The networks include TYMNET, ARPANET, and TRANSPAC. The network architectures discussed are the IBM SNA and the DEC DNA. The routing algorithms all tend to fall in the shortest path class. In the introductory sections, routing procedures in general are discussed, with specialization to shortest path algorithms. Two shortest path algorithms, one appropriate for centralized computation, the other for distributed computation, are described. These algorithms, in somewhat modified form, provide the basis for the algorithms actually used in the networks discussed.

Routing Techniques Used in Computer Communication Networks

Various algorithms have been proposed for determining the routing paths designed to minimize the average overall message time delay in message-switched networks. In this paper we describe the application of the gradient projection algorithm to this problem. This algorithm is a gradient-type search procedure designed to handle constrained optimization problems, into which category the routing problem falls. Calculations of the computational complexity of this algorithm indicate that it is particularly well-suited to networks with a limited number of commodities or source-destination pairs. The algorithm is applied to a representative group of distributed-type networks, of varying complexity. Execution times for this algorithm are compared with those obtained using the flow deviation routing algorithm. These agree roughly with the results of the computational requirement calculations; i.e., this algorithm generally requires less execution time for networks with a relatively small number of commodities than does the flow deviation method. (The actual running time depends significantly on the choice of the initial flows or routing paths, however.) For those networks in which all network nodes may be expected to communicate with all other nodes, however, the flow deviation method would be expected to be superior.

The Gradient Projection Algorithm for Multiple Routing in Message-Switched Networks

This work provides a framework for approaching the problem of fault detection in communication processes. Communication processes are modeled as finite state machines (FSMs), and the authors' model consists of two FSMs, one observing part of the behavior of the other. The authors prove that specific classes of faults are detectable, and give a procedure for constructing detectors, but the design of the minimum alphabet detector is NP-complete. An example applicable to the 802.2 protocol is provided. >

Simple finite-state fault detectors for communication networks

The problem of minimum cost identification of a finite state machine (FSM) using a trace of its event history is addressed. The motivation is fault identification in communication systems, although other applications are possible as well. The event history used for the identification is partially observed, i.e., it is known to be a member of a regular language. Any string which belongs in this regular language is a possible trace of the FSM's event history. Furthermore, the event history is assumed to be corrupted with deletions, additions, and changes of symbols. The FSM to be estimated is related to a known FSM by performing an unknown number of additions and changes of arcs. An identification algorithm based on a fast algorithm that can correct corrupted data strings generated by a known finite state machine is developed. Examples of the method are provided, including one based on the IEEE 802.2 logical link control protocol. >

Fault identification using a finite state machine model with unreliable partially observed data sequences

This paper provides a framework for approaching the problem of fault detection in large Communication Networks. Communication process are modeled as Discrete Event Systems (D.E.S.), so any fault will appear as a change of a D.E.S. Here we concentrate on the simplest case of Discrete Event systems, namely Finite State Machines (FSM).

M. Schwartz

Papers

Routing Techniques Used in Computer Communication Networks

The Gradient Projection Algorithm for Multiple Routing in Message-Switched Networks

Simple finite-state fault detectors for communication networks

Fault identification using a finite state machine model with unreliable partially observed data sequences

On the Design of Observers for Fault Detection in Communication Networks