Abstract: A pa ssive ro und t rip time ( RT T) estimate alg ori thm called PRE ( passiv eRTT estima te) is proposed for the t raffic mo ni to r devices to estimate RT T of TCP connectio ns in the broadband netwo rk. PRE alg orithm can find o ut sending ro unds of the mo nitored TC P f low acco rding to the estimator of packag e ar riving interv al ( PAI) a nd estima tes RTT by measuring the leng th o f the sending round, which approximately equals to RTT. Ba se on PRE, pa ssive TC P measurement can be deployed in the t raf fic mo nito rs. Both simulation and practical ex periments validate that the a lg o ri thm can estimate RT T properly.

Key words: Transmisson control protocol, round trip time, passive measurement, parameter estimate