Existing works have approached the problem of reliable transport in ad-hoc networks by proposing mechanisms to improve TCP's performance over such networks. In this paper we show through detailed arguments and simulations that several of the design elements in TCP are fundamentally inappropriate for the unique characteristics of ad-hoc networks. Given that ad-hoc networks are typically stand-alone, we approach the problem of reliable transport from the perspective that it is justifiable to develop an entirely new transport protocol that is not a variant of TCP. Toward this end, we present a new reliable transport layer protocol for ad-hoc networks called ATP (ad-hoc transport protocol). We show through ns2 based simulations that ATP outperforms both default TCP and TCP-ELFN.

In this paper, we study the performance of the transmission control protocol (TCP) over mobile ad-hoc networks. We present a comprehensive set of simulation results and identify the key factors that impact TCP's performance over ad-hoc networks. We use a variety of parameters including link failure detection latency, route computation latency, packet level route unavailability index, and flow level route unavailability index to capture the impact of mobility. We relate the impact of mobility on the different parameters to TCP's performance by studying the throughput, loss-rate and retransmission timeout values at the TCP layer. We conclude from our results that existing approaches to improve TCP performance over mobile ad-hoc networks have identified and hence focused only on a subset of the affecting factors. In the process, we identify a comprehensive set of factors influencing TCP performance. Finally, using the insights gained through the performance evaluations, we propose a framework called Atra consisting of three simple and easily implementable mechanisms at the MAC and routing layers to improve TCP's performance over ad-hoc networks. We demonstrate that Atra improves on the throughput performance of a default protocol stack by 50%-100%.

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A noncontact experimental method for determining mass‐transfer boundary layer thicknesses in electrochemical systems has been examined. The technique is based on the premise that the relaxation in concentration overpotential after current interruption is an accurate measure of liquid‐phase mass‐transfer resistance. Experimental overpotential decay data were fitted to a theoretical surface concentration decay model. Boundary layer thicknesses were determined by matching the real time scale of the experimental data and the dimensionless time scale of the theoretical analysis. Overpotential relaxation experiments were performed at a vertical flat plate copper cathode with natural convection stirring. The effects of electrode height, current density, and electrolyte composition on mass‐transfer boundary layer thicknesses were examined and correlated. The results agree well with existing Sherwood‐Schmidt‐Grashof number correlations.