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Metodologia para estimar o atraso em um sentido e experimentos na Internet

Antonio A. De A. RochaRosa M. M. LeãoEdmundo de Souza e Silva

Obtaining performance measures of a communication network such as delay distributions or packet loss probabilities is not an easy task. However, these measures are essential to build models in order to study, for instance, the efficacy of control mechanisms to increase the throughput of a connection or yet to study techniques aiming at compensating the poor quality of service offered by best-effort networks. Some measures such as the round trip time (RTT) can be easily obtained in most cases. On the other hand, other measures such as the one-way delay may be difficult to estimate. Without the use of special hardware, such as GPS equipment, it is necessary to employ techniques to compensate for the lack of synchronism between the clocks involved in the measurement. In this work we evaluate existing techniques to remove the clock skew and offset which are necessary to calculate the one-way delay. We also identify two problems that introduce errors in the calculation of this measure. A solution to overcome these problems is proposed and evaluated. The methodology to calculate the one-way delay was implemented in a tool that was used in a series of additional experiments to characterize the one-way delay distribution between two out of three points in the Internet: two in Brazil and another in the USA. These results are useful to choose the proper parameter values of a performance model that includes packet transmission delays.

http://www.lbd.dcc.ufmg.br:8080/colecoes/sbrc/2004/051.pdf

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