a cross traffic estimator is proposed based on the loss ratio of the probe packets. This method aims to estimate the future networks' available bandwidth such as optical switching networks. In these networks, node's processing time other than tight link becomes the bottleneck. Most popular estimate techniques neglect it. In the scheme, probe traffic intensity and its drop ratio are collected and fitted using the 1 st order ordinary least squares (OLS) algorithm. OLS adopts probe traffic intensity as dependent variable and its drop ratio as independent variable. Then the intercept difference between fitted line and empirical line is just the cross traffic. Simulation shows that our scheme can obtain the bottleneck node cross traffic appropriately and outperforms the minimal backlogging algorithm which is also based M/G/1 model.