Study On Estimating Loss Rate Based On Network Tomography

Network tomography is a new type of network performance measurement technique, which overcomes some shortcomings of the traditional measurement methods and deduces network internal link performance parameters only through the edge measurement. The proposed of network tomography can solve the large-scale and isomerization network performance measurement better.This paper presents the technology of network performance measurement and network tomography technology firstly, mainly states the loss rate measurement technology, and then analyses and researches the technique of the unicast loss rate measurement. The unicast measurement technology uses simple and effective PMLE(Pseudo Maximum Likelihood Estimation) to calculate the loss rate. Due to defects of PMLE, namely the errors of loss rate will increase with the increasing depth of tree topology. For this problem, this paper reduces the depth of tree topology which is needed to be measured by introducing the DST(Divide Subtree) algorithm, and then calculates loss rate of each link by PMLE. The algorithm, which combines DST with PMLE, could lower the complexity and improve accuracy well. Meanwhile DST makes sure that the depth of sub-tree is maximum value and the number of new added active node is minimum value.Now existing unicast measurement technology is focused on the aspect of theory research, the unicast loss rate measurement system proposed makes unicast measurement technique applied in practice. In this measurement system, b2b(back-to-back)detection packets are sent to make measurement, but because original sending mechanism of detection packet is not flexible enough, sending rate can not change along with the change of measured network environment, a new sending mechanism with two time thresholds is explored. This mechanism can guarantee detection packets to be effective b2b detection packets. Meanwhile the composition of measuring system,the function of sending node and receiving node in the system are designed.Finally, this paper simulates the real network environment with the help of NS2 simulation software, and makes simulation test on the new sending mechanism with time threshold and on the statistical inference method combining DST dividing algorithm with PMLE. Through the analysis and comparison of the simulation results, the efficiency and rationality of the improved mechanism and the statistical inference algorithm after combination are verified.