Creating and sharing knowledge for telecommunications

Simple Ant Routing Algorithm (SARA): A routing protocol for mobile ad hoc networks


on 27-07-2012

... Fernando Ribeiro Correia, Escola Naval

July 27, 2012, Friday, 16h15m.

Abstract: A Mobile Ad-hoc Network has limited and scarce resources and thus routing protocols in such environment must be kept as simple as possible.

The Simple Ant Routing Algorithm (SARA) offers a low overhead solution, by optimizing the routing process. Three complementary strategies were used in our approach. During the route discovery, was used a new broadcast mechanism, called the Controlled Neighbor Broadcast (CNB), in which each node broadcasts a control message (Forward ANT - FANT) to its neighbors, but only one of them broadcast this message again. During the route maintenance phase, we further reduce the overhead, by only using data packets to refresh the paths of active sessions. Finally, the route repair phase is also enhanced, by using a deep search procedure called Deep Search Area (DSA), as a way of restricting the number of nodes used to recover a route. Thus, instead of discovering a new path from the source to the destination, it is tried the discovery of a new path between the two end-nodes of the broken link. A broadest search is only executed when the deeper one fails to succeed. This procedure allows to recover part of the original route and create a network of alternative routes around the area where was detected the broken link.

SARA was simulated and tuned to present a optimal performance. Was also compared it with the classical approach of AODV and other biological routing approaches. The results achieved show that SARA offers the smallest overhead of all the protocols under evaluation and presents an overhead reduction of almost 25% of the value achieved by the other proposals. SARA also presents the best goodput, specially for TCP traffic, but it needs more time to discover the routes.

Through the study performed, it was also developed two extensions, written as generic as possible, to be implemented in different routing protocols. The proposed extensions allow in a simple way identify traffic flow variations and differentiate between temporary and permanent broken links, through the analysis of the link behavior historic.

Room: 3.10, Mathematics
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Non-computability and financial markets


on 20-07-2012

... Daniel Graça, U Algarve / SQIG-Instituto de Telecomunicações

July 20, 2012, Friday, 16h15m.

In this talk we will explore the valuation problem: given an asset, how much is it worth? Although financial theory has provided solutions to this problem (which will be surveyed on the talk) in practice the “fair” value of an asset is hard to calculate. Some explanations to this hardness include speculative, non-rational behavior of markets, lack of data, or uncertainty about the future. We will show that, in addition to the previous factors, inherent non-computable behavior may also contribute to the difficulties found when trying to valuate an asset. More concretely, we will show using the models of Financial Theory, that even in rational markets with complete knowledge (present or future) of all data affecting the price of the asset, the valuation problem is not computable. More Information..