A note on functions associated with Gödel formulas

We give a characterization of functions associated with formulas of Gödel logic, following what has been done by McNaughton for Lukasiewicz logic.     

Efficient Wireless Network Simulations with Detailed Propagation Models

Accurate simulation of wireless networks requires realistic models of the channel propagation medium. The widely used free space model is computationally efficient but ignores many attenuation components which affect wireless signal propagation. This paper describes the impact of the accuracy of the wireless channel model on the accuracy of the results and on the execution time of large-scale network models. It then introduces means to reduce the runtime execution when deploying such detailed propagation models.     

Wireless Ad Hoc Multicast Routing with Mobility Prediction

An ad hoc wireless network is an infrastructureless network composed of mobile hosts. The primary concerns in ad hoc networks are bandwidth limitations and unpredictable topology changes. Thus, efficient utilization of routing packets and immediate recovery of route breaks are critical in routing and multicasting protocols. A multicast scheme, On-Demand Multicast Routing Protocol (ODMRP), has been recently proposed for mobile ad hoc networks. ODMRP is a reactive (on-demand) protocol that delivers packets to destination(s) on a mesh topology using scoped flooding of data. We can apply a number of enhancements to improve the performance of ODMRP. In this paper, we propose a mobility prediction scheme to help select stable routes and to perform rerouting in anticipation of topology changes. We also introduce techniques to improve transmission reliability and eliminate route acquisition latency. The impact of our improvements is evaluated via simulation.     

On-board satellite "split TCP" proxy

Several satellite systems currently in operation or under development claim to support broadband Internet applications. In these scenarios, transmission control protocol (TCP) plays a critical role. Unfortunately, when used with satellite links, TCP suffers from a number of well-known performance problems, especially for higher data rates and high altitude satellites with longer delays. In response to these difficulties, the satellite and Internet research communities have developed a large gamut of solutions ranging from architectural modifications to changes in the TCP protocol. Among these, one approach requiring minimal modifications involves splitting the TCP connection in two or more segments with one segment connecting terrestrial nodes across the satellite network. In this paper, we consider an evolution of this idea: placing a TCP proxy on board the satellite that further subdivides the end-to-end connection into separate TCP connections between ground and space. We focus upon the efficient use of buffer resources on board the satellite, while at the same time enhancing TCP performance. We evaluate two TCP protocol versions, TCP NewReno and TCP Westwood. We consider various geosynchronous earth orbit satellite scenarios, with and without the split proxy, and with different channel error conditions (random errors, shadowing, etc.). Using simulation, we show that an on-board proxy provides a number of distinct advantages and can enhance throughput up to threefold for both TCP New Reno and TCP Westwood, in some scenarios, with relatively modest on-board buffering requirements. The main contributions of this paper are: the on-board split proxy concept, the buffer management strategy, the use of a realistic "urban shadowing" model in the evaluation, and the extensive comparison of the recently announced TCP Westwood with the traditional TCP New Reno.     

An architecture for scalable, efficient, and fast fault-tolerant multicast provisioning

Providing fault tolerance to multicast connections is an important and challenging requirement of future networks. The existing techniques for fault-tolerant multicast can be grouped into on-demand and preplanned approaches. On-demand approaches can have long recovery latency. For faster recovery, preplanned approaches have been developed. However, in this type of approach the overhead cost is generally very high, especially when there is a large number of simultaneous groups in the network. In this paper first we provide an overview of the current multicast fault tolerance method . In add, on, we propose a novel architecture called Aggregated MPLS-Based Fault-Tolerant Multicast (AMFM) for scalable, efficient, and fast fault-tolerant multicast provisioning. AMFM falls in the category of preplanned approaches. Using the concept of aggregated multicast, AMFM facilitates fault tolerance in a very elegant way: it reduces the protection cost significantly; it is scalable to large numbers of groups; and it can also recover from failure in a very fast manner. This article describes the architecture of AMFM and provides a feasibility check from an implementation point of view. We also conduct experiments to evaluate the performance of AMFM and show it can provide fault tolerance in a scalable fashion.     

Congestion control in interconnected LANs

The reasons why congestion control is more difficult in interconnected local area networks (LANs) than in conventional packet nets are examined. The flow and congestion control mechanisms that can be used in an interconnected LAN environment are reviewed. The focus is on congestion control (that is, prevention of internal congestion); however some of the proposed schemes require the interaction of flow and congestion control. The schemes considered are dropping packets; input buffer limit, i.e. a limit on the number of input packets (i.e. packets from local hosts) that can be buffered in the packet switch; the use of choke packets, in which, whenever a bridge or router experiences congestion, it returns to the source a choke packet containing the header of the packet traveling in the congested direction and the source, on receiving the choke packet, declares the destination congested, and slows (or stops altogether, for a period of time) traffic to that destination; backpressure, which is the regulation of flow along a virtual connection; and congestion prevention, whereby a voice or video connection is accepted only if there is enough bandwidth (in a statistical sense) in the network to support it     

RATO-net: a random-access protocol for unidirectionalultra-high-speed optical fiber network

The local network medium is a pair of unidirectional fiber optic buses to which stations are connected via passive taps. For this configuration, a random-access protocol called RATO (random-access time-out) is presented. RATO provides random access, fairness, and bounded delay access to all stations, and is particularly suited for ultra-high-speed transmission when the performance of the popular Ethernet becomes unattractive. Simplicity and ease of hardware implementation of RATO under ultra-high-speed environment is emphasized because the only control requirements are the sensing of activity in the bus and a fixed time delay between consecutive transmissions from the same station. Results of simulation and performance comparisons of RATO with other schemes are given. In ultra-high-speed wide-area networks, RATO outperforms all these other schemes     

The probability that tweety is able to fly

In this note we examine the question of assigning a probabilistic valuation to a statement as “Tweety (a particular bird) is able to fly.” Namely, we suggest that a natural way to proceed is to rewrite it as “a (randomly chosen) bird with the same observable properties of Tweety is able to fly,” and consequently to assume that the probability of “Tweety is able to fly” is equal to the percentage of the past observed birds similar to Tweety that are able to fly. © 1994 John Wiley & Sons, Inc.     

A Scalable Overlay Multicast Architecture for Large-Scale Applications

In this paper, we propose a two-tier overlay multicast architecture (TOMA) to provide scalable and efficient multicast support for various group communication applications. In TOMA, multicast service overlay network (MSON) is advocated as the backbone service domain, while end users in access domains form a number of small clusters, in which an application-layer multicast protocol is used for the communication between the clustered end users. TOMA is able to provide efficient resource utilization with less control overhead, especially for large-scale applications. It also alleviates the state scalability problem and simplifies multicast tree construction and maintenance when there are large numbers of groups in the network. To help MSON providers efficiently plan backbone service overlay, we suggest several provisioning algorithms to locate proxies, select overlay links, and allocate link bandwidth. Extensive simulation studies demonstrate the promising performance of TOMA